(Use "Ctrl F" or "Apple F" to type in the word or acronym and "find" what you're looking for.)
AC-3 (audio coding 3) Dolby's digital audio data compression algorithm adopted for HDTV transmission and used in laserdiscs and
CDs for 5.1 multichannel home theater use. Competes with DTS Zeta Digital. The terms AC-1 and AC-2 are other versions
developed by Dolby for different applications.
acquisition time The time required for a sample-and-hold (S/H) circuit to capture an input analog value; specifically, the time for
the S/H output to approximately equal its input.
active equalizer A variable equalizer requiring power to operate. Available in many different configurations and designs. Favored
for low cost, small size, light weight, loading indifference, good isolation (high input and low output impedances), gain availability
(signal boosting possible), and line-driving ability. Disliked for increased noise performance, limited dynamic range, reduced reliability,
and RFI susceptibility; however, used everywhere.
adaptive delta modulation (ADM) A variation of delta modulation in which the step size may vary from sample to sample.
ADAT (Alesis digital audio tape) Digital tape recording system developed by Alesis, and since licensed to Fostex & Panasonic,
putting 8-tracks of 16-bit, 44.1kHz digital audio on S-VHS tape.
ADAT ODI (optical digital interface) See ADAT Optical.
ADAT Optical Alesis's proprietary multichannel optical (fiber optic) digital interface specification for their family of ADAT
modular digital multitrack recorders. This standard describes transmission of 8-channels of digital audio data through a single fiber
ADC (or A/D, analog-to-digital converter) The electronic component which converts the instantaneous value of an analog input
signal to a digital word (represented as a binary number) for digital signal processing. The ADC is the first link in the digital chain of
ADPCM (adaptive differential pulse code modulation) A very fast data compression algorithm based on the differences
occurring between two samples.
AES (Audio Engineering Society) Founded in 1949, the largest professional organization for electronic engineers and all others
actively involved in audio engineering. Primarily concerned with education and standardization.
AES-24 An AES standard for sound system control using a computer network to control audio equipment. Formerly called "SC-10"
(after the working group's subcommittee number), the title is Application protocol for controlling and monitoring audio systems
and is broken down into several parts, each issued separately. To date only Part 1: architecture is released; the remaining parts (at
least three) are in process.
AES/EBU interface The serial transmission format standardized for professional digital audio signals (AES3-1992 AES
Recommended Practice for Digital Audio Engineering - Serial Transmission Format for Two-Channel Linearly Represented
Digital Audio Data) A specification using time division multiplex for data, and balanced line drivers to transmit two channels of
digital audio data on a single twisted-pair cable using 3-pin (XLR) connectors. Issued as ANSI S4.40-1985 by the American
National Standards Institute. In addition, information documents are being prepared describing the transmission of AES3 formatted
data by unbalanced coaxial cable and by fiber optic cable.
algorithm A structured set of instructions and operations tailored to accomplish a signal processing task. For example, a fast Fourier
transform (FFT), or a finite impulse response (FIR) filter are common DSP algorithms.
aliasing The problem of unwanted frequencies created when sampling a signal of a frequency higher than half the sampling rate.
See: Nyquist frequency.
all-pass filter A filter that provides only phase shift or phase delay without appreciable changing the magnitude characteristic.
ampere Abbr. I, also A. 1. A unit of electric current in the International standard meter-kilogram-second (mks) system. It is the
steady current that when flowing in straight parallel wires of infinite length and negligible cross section, separated by a distance of
one meter in free space, produces a force between the wires of 2E-7 newtons per meter of length. 2. A unit in the International
System specified as one International coulomb per second and equal to 0.999835 ampere. [After Andr� Marie Amp�re.]
Amp�re, Andr� Marie (1775-1836) French physicist and mathematician who formulated Amp�re's law, a mathematical
description of the magnetic field produced by a current-carrying conductor.
amplitude 1. Greatness of size; magnitude. 2. Physics. The maximum absolute value of a periodically varying quantity. 3.
Mathematics. a. The maximum absolute value of a periodic curve measured along its vertical axis. b. The angle made with the
positive horizontal axis by the vector representation of a complex number. 4. Electronics. The maximum absolute value reached by
a voltage or current waveform.
analog A real world physical quantity or data characterized by being continuously variable (rather than making discrete jumps), and
can be as precise as the available measuring technique.
ANSI (American National Standards Institute) A private organization that develops and publishes standards for voluntary use in
anti-aliasing filter A low-pass filter used at the input of digital audio converters to attenuate frequencies above the half-sampling
frequency to prevent aliasing.
anti-imaging filter A low-pass filter used at the output of digital audio converters to attenuate frequencies above the half-sampling
frequency to eliminate image spectra present at multiples of the sampling frequency.
ASA (Acoustical Society of America) Founded in 1929, the oldest organization for scientist and professional acousticians and
others engaged in acoustical design, research and education.
ASCII (pronounced "ask-ee") (American Standard Code for Information Interchange) An ANSI standard data transmission
code consisting of seven information bits, used to code 128 letters, numbers, and special characters. Many systems now use an 8-bit
binary code, called ASCII-8, in which 256 symbols are represented (for example, IBM's "extended ASCII").
ASIC (application-specific integrated circuit) A large-scale integrated circuit whose function is determined by the final mask
layer for a particular application or group of applications; for example, an IC that does all the functions of a modem.
asymmetrical (non-reciprocal) response Term used to describe the comparative shapes of the boost/cut curves for variable
equalizers. The cut curves do not mirror the boost curves, but instead are quite narrow, intended to act as notch filters.
asynchronous A transmission process where the signal is transmitted without any fixed timing relationship between one word and
the next (and the timing relationship is recovered from the data stream).
ATM (asynchronous transfer mode) networking An extremely fast networking technology, already found on many disk editors
(Avid Sonic Solutions, Studio Audio, etc.) and predicted to infiltrate homes within the coming decade. ATM specifies the protocol
(i.e., the order and sequence) of the digital information on the network, but not the physical means of transmission (e.g., fiber optic,
twisted-pair, etc.). The protocol controls how the entire network is run and maintained.
atmospheric pressure Pressure caused by the weight of the atmosphere. At sea level it has a mean value of one atmosphere but
reduces with increasing altitude.
audio 1. Of or relating to humanly audible sound, i.e., audio is all the sounds that humans hear. 2. a. Of or relating to the
broadcasting or reception of sound. b. Of or relating to high-fidelity sound reproduction. [Audio traveling through air is vibrations, or
cycles of alternating pressure zones. Rarefaction follows each cycle of compression, which produces a wave.]
audio compression See: digital audio data compression
auditory filter Term used to describe the concept of critical bands. Analogous to a bandpass filter with a rounded top
("rounded-exponential" after Patterson and Moore, 1986). The filter is slightly asymmetric, being wider on the low-frequency side.
bandpass filter A filter that has a finite passband, neither of the cutoff frequencies being zero or infinite. The bandpass frequencies
are normally associated with frequencies that define the half power points, i.e. the -3 dB points.
band-limiting filters A >low-pass and a high-pass filter in series, acting together to restrict (limit) the overall bandwidth of a
bandwidth Abbr. BW The numerical difference between the upper and lower -3 dB points of a band of audio frequencies. Used to
figure the Q, or quality factor, for a filter.
bar A unit of pressure equal to one million dynes per square centimeter. (Yeah, I know you expected some wiseacre response, but
you ain't gonna get it!)
baud rate (pronounced "bawd"; after Baudot Code named for the French telegrapher Emile Baudot, 1845-1903) The transmitted
signaling speed, or keying rate of a modem. Often confused with bit rate. Bit rate and baud rat are NOT synonymous and shall
not be interchanged in usage. For example, one baud equals one half dot cycle per second in Morse code, one bit per second in a
train of binary signals, and one 3-bit value per second in a train of signals each of which can assume one of 8 different states, and so
on - all brought to you by the magic of advanced coding techniques that allow more than one bit per baud. Preferred usage is bit
rate, with baud used only when the details of a modem are specified.
BCD 1. (binary-coded decimal) Pertains to a number system where each decimal digit is separately represented by a 4-bit binary
code; for example, the decimal number 23 is represented as 0010 0011 (2 = 0010 and 3 = 0011, grouped together as shown), while in
straight binary notation, 23 is represented as 10111. 2. (binary-coded digit) A digit of any number system that is represented as a
fixed number of binary digits; from the previous example, the decimal digit 23 is represented as 10111.
bel Abbr. b, B Ten decibels. [After Alexander Graham Bell.]
Belchfire� Series Term coined by Crown International for their mythical power amplifier, the BF-6000SUX. Based on original
research into the first principles of teramagnostriction quasar-quadrature, the BF-6000SUX could have changed the design of all
future power amps, but it didn't. In spite of Crown's leap forward into the past of technical declination, the marketplace categorically
stated that it did not want 6,000 watts per channel in only one rack space - in spite of its six-foot depth and 206 lbs weight. The only
known use of a BF-6000SUX was to drive the experimental Electro-Voice Rearaxial Softspeaker, when Rane demoed their PI 14
Pseudoacoustic Infector using Jensen's JE-EP-ERs Multi-denomial Transpedance Informer for coupling - but many consider that
Bell, Alexander Graham (1847-1922) Scottish-born American inventor of the telephone. The first demonstration of electrical
transmission of speech by his apparatus took place in 1876. Bell also invented the audiometer, an early hearing aid, and improved the
bilinear transform A mathematical method used in the transformation of a continuous time (analog) function into an equivalent
discrete time (digital) function. Fundamentally important for the design of digital filters. A bilinear transform ensures that a stable
analog filter results in a stable digital filter, and it exactly preserves the frequency-domain characteristics, albeit with frequency
binary A condition in which there are two possible states; for example, the binary number system (base-2) using the digits 0 and 1.
bit Abbreviation for binary digit. The smallest amount of digital information. A bit can store or represent only two states, 0 and 1.
bit clock The synchronizing signal that indicates the rate of individual data bits over a digital audio interface.
bit error rate The number of bits processed before an erroneous bit is found (e.g., 10E13), or the frequency of erroneous bits (e.g.,
bit rate The rate or frequency at which bits appear in a bit stream. The bit rate of raw data from a CD, for example, is 4.3218
bit stream A binary signal without regard to grouping.
bit-mapped display A display in which each pixel's color and intensity data are stored in a separate memory location.
BNC (bayonet Neill Concelman, or baby N-connector, or bayonet connector) A bayonet-locking connector for slim coaxial
cables. What "BNC" truly stands for is still debated: 1) There is an "N-connector," similar to, but larger than the BNC-type, used for
fat coaxial cables; 2) Neill Concelman is credited with inventing this connector; 3) And, of course, it is a bayonet-style - so, take
boost/cut equalizer The most common graphic equalizer. Available with 10 to 31 bands on octave to 1/3-octave spacing. The flat
(0 dB) position locates all sliders at the center of the front panel. Comprised of bandpass filters, all controls start at their center 0 dB
position and boost (amplify or make larger) signals by raising the sliders, or cut (attenuate or make smaller) the signal by lowering
the sliders on a band-by-band basis. Commonly provide a center-detent feature identifying the 0 dB position. Proponents of boosting
in permanent sound systems argue that cut-only use requires adding make-up gain which runs the same risk of reducing system
headroom as boosting.
buffer In data transmission, a temporary storage location for information being sent or received.
burst error A large number of data bits lost on the medium because of excessive damage to or obstruction on the medium.
bus One or more electrical conductors used for transmitting signals or power from one or more sources to one or more destinations.
Often used to distinguish between a single computer system (connected together by a bus) and multi-computer systems connected
together by a network.
buss To kiss.
byte A group of eight bits (a word) operating together.
Cartesian coordinate system 1. A two-dimensional coordinate system in which the coordinates of a point in a plane are its
distances from two perpendicular lines that intersect at an origin, the distance from each line being measured along a straight line
parallel to the other. 2. A three-dimensional coordinate system in which the coordinates of a point in space are its distances from
each of three perpendicular lines that intersect at an origin. After the Latin form of Descartes, the mathematician who invented it.
CAV (constant angular velocity) A disc rotating at a constant number of revolutions per second. The LP is a CAV system at 33
1/3 rpm. Another example is the CAV laserdisc which plays two thirty minute sides.
CCIR (International Radio Consultative Committee) A branch of the International Telecommunications Union (ITU), a
specialized agency of the United Nations - thus the CCIR is a treaty organization related directly to the UN. The CCIR is concerned
with generating documents dealing with the preparation, transmission, and reception of all kinds of information using radio signals,
with the term "radio" being taken in the broadest sense, including television and telephony.
CD (compact disc) Trademark term for the Sony-Philips digital audio optical disc storage system. The system stores 75 minutes
(maximum) of digital audio and subcode information, or other non-audio data, on a 12-centimeter diameter optical disc. The disc is
made of plastic, with a top metallized layer, and is read by reflected laser light. Variations (such as the 3" disc) are reserved for
CD-I (compact disc interactive) System storing digital audio, video, text, and graphics information interactively, with user control
over content and presentation, on a 12-centimeter diameter optical disc.
CD+MIDI A System storing MIDI information in a disc's subcode area.
CD-PROM (compact disc programmable read-only memory) A write-once CD-ROM disc.
CD-R (compact disc-recordable) A compact disc that is recordable at least once.
CD-ROM (compact disc read-only memory) A method of storing digitally coded information, such as computer information or
database, on a 12-centimeter diameter optical disc.
CD-V (compact disc video) A system storing five minutes of analog video and digital audio plus twenty minutes of digital audio only
on a 12-centimeter diameter optical disc, and longer times on 20- or 30-centimeter diameter optical discs.
centi- Prefix for one hundredth (10E-2), abbreviated c.
charge Symbol q 1. Electricity. a. To cause formation of a net electric charge on or in (a conductor, for example). b. To energize
(a storage battery) by passing current through it in the direction opposite to discharge. 2. Physics. a. The intrinsic property of matter
responsible for all electric phenomena, in particular for the force of the electromagnetic interaction, occurring in two forms arbitrarily
designated negative and positive. b. A measure of this property. c. The net measure of this property possessed by a body or
contained in a bounded region of space.
checksum The sum of a group of data items used for error checking. If the checksum received equals the one sent, all is well.
Otherwise, the receiving equipment requests the data be sent again.
chromatic scale Music. A scale consisting of 12 semitones.
chrominance The color portion of the video signal - includes hue and saturation information but not brightness (see luminance).
CISC (complex instruction set computing) See: RISC
clock A timing device that generates the basic periodic signal used as a source of synchronizing signals in digital equipment.
CLV (constant linear velocity) A disc rotating at varying numbers of revolutions per second to maintain a constant relative velocity
between pickup and track across the disc radius. The CD is a CLV system rotating from 500 rpm (lead-in track) to 200 rpm
(lead-out track). Another example is the CLV laserdisc which plays two sixty minute sides.
coaxial cable A single copper conductor, surrounded with a heavy layer of insulation, covered by a thick surrounding copper shield
and jacket. A constant-impedance unbalanced transmission line.
Codec (code-decode) A device for converting voice signals from analog to digital for use in digital transmission schemes, normally
telephone based, and then converting them back again. Most codecs employ proprietary coding algorithms for data compression,
common examples being Dolby's AC-2, ADPCM, and MPEG schemes.
combining response See: interpolating response
compander A contraction of compressor-expander. A term referring to dynamic range reduction and expansion performed by first
a compressor acting as an encoder, and second by an expander acting as the decoder. Normally used for noise reduction or
complex frequency variable An AC frequency in complex number form.
complex number Mathematics. Any number of the form a + bj, where a and b are real numbers and j is an imaginary number
whose square equals -1; and a represents the real part (e.g., the resistive effect of a filter, at zero phase angle) and b represents
the imaginary part (e.g., the reactive effect, at 90 phase angle).
composite video A video signal combining luminance, chrominance, and synchronization data on a single coax cable using RCA
connectors and color-coded yellow.
compression 1. An increase in density and pressure in a medium, such as air, caused by the passage of a sound wave. 2. The
region in which this occurs.
compression wave A wave propagated by means of the compression of a fluid, such as a sound wave in air.
compressor A signal processing device used to reduce the dynamic range of the signal passing through it. For instance, an input
dynamic range of 110 dB might pass through a compressor and exit with a new dynamic range of 70 dB. This clever bit of
skullduggery is normally done through the use of a VCA (voltage controlled amplifier), whose gain is a function of a control voltage
applied to it. Thus, the control voltage is made a function of the input signal's dynamic content. [Long answer: What "compression"
is and does has evolved significantly over the years. Originally compressors were used to reduce the dynamic range of the entire
signal; with modern advances in audio technology, compressors now are used more sparingly. First the classical case: The need for
compression arose the very first time anyone tried to record or broadcast audio: the signal exceeded the medium. For example, the
sound from a live orchestra easily equals 100 dB dynamic range. Yet early recording and broadcasting medium all suffered from
limited dynamic range. Typical examples: LP record 65 dB, cassette tape 60 dB (w/noise reduction), analog tape recorder 70 dB,
FM broadcast 60 dB, AM broadcast 50 dB. Thus "6 pounds of audio into a 4 pound bag" became the necessity that mothered the
invention of the compressor (sorry). Early compressors did not have a "threshold" knob, instead, the user set a center ("hinge") point
equivalent to the midpoint of the expected dynamic range of the incoming signal. Then a ratio was set which determined the amount
of dynamic range reduction. The earlier example of reducing 110 dB to 70 dB requires a ratio setting of 1.6:1 (110/70 = 1.6). The
key to understanding compressors is to always think in terms of increasing and decreasing level changes in dB about some
set-point. A compressor makes audio increases and decreases smaller. From our example, for every input increase of 1.6 dB
above the hinge point the output only increases 1 dB, and for every input decrease of 1.6 dB below the hinge point the output only
decreases 1 dB. If the input increases by x-dB, the output increases by y-dB, and if the input decreases by x-dB, the output
decreases by y-dB, where x/y equals the ratio setting. Simple - but not intuitive and not obvious. This concept of increasing above
the set-point and decreasing below the set-point is where this oft-heard phrase comes from: "compressors make the loud sounds
quieter and the quiet sounds louder." If the sound gets louder by 1.6 dB and the output only increases by 1 dB, then the loud
sound has been made quieter; and if the sound gets quieter by 1.6 dB and the output only decreases by 1 dB, then the quiet sound
has been made louder (it didn't decrease as much). Think about it - it's an important concept. With advances in all aspects of
recording, reproduction and broadcasting of audio, the usage of compressors changed from reducing the entire program to just
reducing selective portions of the program. Thus was born the threshold control. Now sound engineers set a threshold point such
that all audio below this point is unaffected, and all audio above this point is compressed by the amount determined by the ratio
control. Therefore the modern usage for compressors is to turn down (or reduce the dynamic range of) just the loudest signals.
Other applications have evolved where compressors are used in controlling the creation of sound. For example when used in
conjunction with microphones and musical instrument pick-ups, compressors help determine the final timbre by selectively
compressing specific frequencies and waveforms. Common examples are "fattening" drum sounds, increasing guitar sustain, vocal
"smoothing," and "bringing up" specific sounds out of the mix, etc.]
constant-Q equalizer (also constant-bandwidth) Term applied to graphic and rotary equalizers describing bandwidth behavior as
a function of boost/cut levels. Since Q and bandwidth are inverse sides of the same coin, the terms are fully interchangeable. The
bandwidth remains constant for all boost/cut levels. For constant-Q designs, the skirts vary directly proportional to boost/cut
amounts. Small boost/cut levels produce narrow skirts and large boost/cut levels produce wide skirts.
convolution A mathematical operation producing a function from a certain kind of summation or integral of two other functions. In
the time domain, one function may be the input signal, and the other the impulse response. The convolution than yields the result of
applying that input to a system with the given impulse response. In DSP, the convolution of a signal with FIR filter coefficients
results in the filtering of that signal.
correlation A mathematical operation that indicates the degree to which two signals are alike.
crest factor The term used to represent the ratio of the peak (crest) value to the RMS value of a waveform.
critical band Physiology of Hearing. A range of frequencies that is integrated (summed together) by the neural system, equivalent
to a bandpass filter (auditory filter) with approximately 10-20% bandwidth (approximately one-third octave wide). [Although the
latest research says critical bands are more like 1/6-octave above 500 Hz, and about 100 Hz wide below 500 Hz.] The ear can be
said to be a series of overlapping critical bands, each responding to a narrow range of frequencies. Introduced by Fletcher (1940) to
deal with the masking of a pure-tone by wideband noise.
current Symbol i, I Electricity. a. A flow of electric charge. b. The amount of electric charge flowing past a specified circuit point
per unit time, or the rate of flow of electrons. [As electrons flow in one direction, the spaces left behind, called holes, appear to flow
in the opposite direction. Thus, current can be visualized as electron flow (negative current flow), or in the opposite direction, hole
flow (positive current flow, sometimes called conventional current flow).]
current loop A data transmission scheme that looks for current flow rather than voltage levels. This systems recognizes no current
flow as a binary zero, and having current flow as a binary one. Favored for its low sensitivity to cable impedance. MIDI is an
example of a current loop interconnect system.
cut-only equalizer Term used to describe graphic equalizers designed only for attenuation. (Also referred to as notch equalizers, or
band-reject equalizers). The flat (0 dB) position locates all sliders at the top of the front panel. Comprised only of notch filters
(normally spaced at 1/3-octave intervals), all controls start at 0 dB and reduce the signal on a band-by-band basis. Proponents of
cut-only philosophy argue that boosting runs the risk of reducing system headroom.
cutoff frequency Filters. The frequency at which the signal falls off by 3 dB (the half power point) from its maximum value. Also
referred to as the -3 dB points, or the corner frequencies.
DA-88 Tascam's model number for their digital multitrack recorder using Sony-developed "Hi8" 8 mm video tape as the storage
medium. Becoming a generic term describing this family of recorders. See: DTRS
DAB (digital audio broadcast) NRSC (National Radio Systems Committee) term for the next generation of digital radio broadcast.
DAC (or D/A, digital-to-analog converter) The electronic component which converts digital words into analog signals that can
then be amplified and used to drive loudspeakers, etc. The DAC is the last link in the digital chain of signal processing
DAR (digital audio radio) EIA term for the next generation of digital radio broadcasting standards.
DASH (digital audio stationary head) A family of formats for ensuring compatibility among digital multitrack studio recorders
using stationary (as opposed to rotating) heads. The DASH standard, popularized by Sony and Studer, specifies 2 to 48 tracks, with
tape speeds from 12 to 76 cm/sec.
DAT (digital audio tape recorder ) 1. A digital audio recorder utilizing a magnetic tape cassette system with rotary heads similar
to that of a video recorder. 2. A little bit of something as in dis & dat.
data compression See: digital audio data compression
DAW (digital audio workstation) Any of several software/hardware systems using a computer as the basis for creating, editing,
storing, and playback of digital audio, using the computer's hard disk as the recording medium.
DB-25 connector A 25-pin D-shell connector standardized for RS-232 serial communications.
DB-9 connector A smaller 9-pin version of the connector used for RS-232 communications. First made popular by IBM in their
AT personal computer.
DCC (Digital Compact Cassette) Philips's digital version of the standard analog cassette tape system. A DCC recorder plays and
records both analog and digital cassettes.
DCE (Data Communications Equipment) Within the RS-232 standard, the equipment that provides the functions required to
establish, maintain, and terminate a connection, as well as the signal conversion, and coding required for communication between
data terminal equipment and data circuit - e.g., a modem or printer. See: DTE. The main difference between DCE and DTE is the
wiring of pins 2 and 3, thus the need for a null modem cable when tying two computers together.
decibel Abbr. dB A unit used to express relative difference in power, intensity, voltage or other, between two acoustic or electric
signals, equal to ten times (for power ratios - twenty times for all other ratios) the common logarithm of the ratio of the two levels.
Equal to one-tenth of a bel.
decimal digit Everyday normal base-10 numbers.
DED (pronounced "dead") (dark emitting diode) A variation of LED technology used exclusively by the CIA for clandestine
equipment. Also popular as power-off indicators.
de-emphasis See: pre-emphasis
de-esser A special type of audio signal compressor that operates only at high frequencies (>3 kHz), used to reduce the effect of
vocal sibilant sounds.
delta modulation A single-bit coding technique in which a constant step size digitizes the input waveform. Past knowledge of the
information permits encoding only the differences between consecutive values.
delta-sigma ADC See: delta-sigma modulation
delta-sigma modulation (also sigma-delta) An analog-to-digital conversion scheme rooted in a design originally proposed in 1946,
but not made practical until 1974 by James C. Candy. The name delta-sigma modulation was coined by Inose and Yasuda at the
University of Tokyo in 1962, but due to a misunderstanding the words were interchanged and taken to be sigma-delta. Both names
are still used for describing this modulator. Characterized by oversampling and digital filtering to achieve high performance at low
cost, a delta-sigma A/D thus consists of an analog modulator and a digital filter. The fundamental principle behind the modulator is
that of a single-bit A/D converter embedded in an analog negative feedback loop with high open loop gain. The modulator loop
oversamples and processes the analog input at a rate much higher than the bandwidth of interest (see: Sampling (Nyquist)
Theorem). The modulator's output provides 1-bit information at a very high rate and in a format that a digital filter can process to
extract higher resolution (such as 20-bits) at a lower rate.
Descartes, Ren� (1596-1650) French mathematician and philosopher. Considered the father of analytic geometry, he formulated
the Cartesian system of coordinates.
diatonic 1. Music. Of or using only the eight tones of a standard major or minor scale without chromatic deviations. 2. A cola
digital audio data compression Commonly shortened to "audio compression." Any of several algorithms designed to reduce the
number of bits (hence, bandwidth and storage requirements) required for accurate digital audio storage and transmission.
Characterized by being "lossless" or "lossy." The audio compression is "lossy" if actual data is lost due to the compression scheme,
and "lossless" if it is not. Well designed algorithms ensure "lost" information is inaudible - that's how you win the game.
digital audio The use of sampling and quantization techniques to store or transmit audio information in binary form. The use of
numbers (typically binary) to represent audio signals.
digital filter Any filter accomplished in the digital domain.
digital signal Any signal which is quantized (i.e., limited to a distinct set of values) into digital words at discrete points in time. The
accuracy of a digital value is dependent on the number of bits used to represent it.
digitization Any conversion of analog information into a digital form.
DIN Acronym for Deutsche Industrie Norm (Deutsches Institut fur Normung), the German standardization body.
disc The term used for any optical storage media. Originally popularized to refer to phonograph records. From Latin discus, the
term refers primarily to audio and video storage systems, such as compact discs, laser discs, etc., but the advent of CD-ROMs and
computer optical storage units blurs this distinction. Compare with disk
discreet Marked by, exercising, or showing prudence and wise self-restraint in speech and behavior. You may want to be discreet
when bussing someone.
discrete Constituting a separate thing; distinct, or a set of distinct things.
discrete Fourier transform (DFT) A DSP algorithm used to determine the Fourier coefficient corresponding to a set of
frequencies, normally linearly spaced. See: Fourier theorem.
disk The term used for any magnetic storage media such as computer diskettes or hard disks. From Greek diskos, the term refers
primarily to non-audio digital data storage, but the advent of hard disk digital audio recording systems fogs this up somewhat.
Compare with disc
dither The noise (analog or digital) added to a signal prior to quantization (or word length reduction) which reduces the distortion
and noise modulation resulting from the quantization process. Although there is a slight increase in the noise level, spectrally shaped
dither can minimize the apparent increase. The noise is less objectionable than the distortion, and allows low-level signals to be heard
DOS (pronounced "doss") (disk operating system) A software program controlling data in memory, disk storage, running programs
and I/O management.
downward expander See: expander
dropout An error condition in which bits are incorrect or lost from a digital medium. Also occurs with analog tape - audio or video.
DSD� (Dolby Stereo Digital) Dolby's name for its format for the digital soundtrack system for motion picture playback. Utilizes
their AC-3 system of digital compression. The signal is optically printed between the sprocket holes.
DSP (digital signal processing) A technology for signal processing that combines algorithms and fast number-crunching digital
hardware, and is capable of high-performance and flexibility.
DTE (Data Terminal Equipment) Within the RS-232 standard, the equipment comprising the data source, the receiver, or both -
e.g., personal computers or terminals. See: DCE. The main difference between DTE and DCE is the wiring of pins 2 and 3, thus the
need for a null modem cable when tying two computers together.
DTRST (digital tape recording system) Tascam's suggested term for describing their DA-88 type digital multitrack recorders.
DTS Coherent Acoustics� A competing digital soundtrack system for motion picture playback developed by Digital Theater
Systems Inc. (backed by Stephen Spielberg and Universal Studios). Its novelties are: 1) not requiring a special projector to read
digital code off the filmstrip like its competitors; 2) using only very moderate compression (3:1 verses Dolby's 11:1); and 3) offering
20-bit audio. The discrete digital full bandwidth six (6) channel sound is contained on a CD which is played synchronously with the
film. The synching time code is printed between the standard optical soundtrack and the picture.
DTS Zeta DigitalT Digital Theater Systems' audio compression scheme applied to laserdisc and CD technology for home theater
use. Competing format with Dolby's AC-3 algorithm.
ducker A dynamic processor that lowers (or "ducks") the level of one audio signal based upon the level of a second audio signal. A
typical application is paging: A ducker senses the presence of audio from a paging microphone and triggers a reduction in the output
level of the main audio signal for the duration of the page signal. It restores the original level once the page message is over.
duplex Pertaining to a simultaneous two-way independent transmission in both directions. Often referred to as "full duplex" which is
redundant. See also: half-duplex.
DVD (latest info says "DVD" no longer stands for anything! It used to mean "digital versatile disc" - and before that it meant
"digital video disc")(Also known as hdCD in Europe.) A new type of 12-centimeter (4.72") compact disc (same size as audio CDs
and CD-ROMs) that holds 10 times the information. Capable of holding full-length movies and a video game based on the movie, or
a movie and its soundtrack, or two versions of the same movie - all in sophisticated discrete digital audio surround sound. Originally,
two competing formats were proposed: One was the MultiMedia CD (MMCD), developed by Philips, Sony and 3M. The other was
the Super Density (SD) disc, from an alliance of 17 companies headed by Toshiba and Time Warner. MMCD was single-sided (but
two layers) holding up to 7.4 gigabytes, while SD proposed one- and two-sided varieties with (theoretically) as much as 18 gigabytes
of data. Both used the common MPEG-2 video encoding standard, but the audio compression formats differed - MMCD proposed
ISO/MPEG Layer II, while SD proposed Dolby AC-3. Both sides now have agreed to a single format. The composite agreement is
for a laminated single-sided, single-layer disc holding 4.7 gigabytes, and 133 minutes of MPEG-2 compressed video and audio. It is
backwards compatible, and expandable to two-layers holding 8.5 gigabytes. Ultimately two discs could be bounded together yielding
two-sides, each with two-layers, for a total of 17 gigabytes. There are three versions: DVD-Video (movies), DVD-Audio
(music-only) and DVD-ROM (games and computer use). The DVD-Audio standard is yet to be announced.
dynamic controllers (or dynamic processors) A class of signal processing devices used to alter an audio signal based solely upon
its frequency content and amplitude level, thus the term "dynamic" since the processing is completely program dependent. The two
most common dynamic effects are compressors and expanders, with limiters, noise gates (or just "gates"), duckers and levelers
being subsets of these. Another dynamic controller category includes exciters, or enhancers. And noise reduction units fall into a
final dynamic processor category.
dynamic range The ratio of the loudest (undistorted) signal to that of the quietest (discernible) signal in a unit or system as
expressed in decibels (dB). With reference to signal processing equipment, the maximum output signal is restricted by the size of the
power supplies, i.e., it cannot swing more voltage than is available. While the minimum output signal is determined by the noise floor
of the unit, i.e., it cannot put out a discernible signal smaller than the noise. Professional-grade analog signal processing equipment
can output maximum levels of +26 dBu, with the best noise floors being down around -94 dBu. This gives a maximum dynamic
range of 120 dB - pretty impressive numbers, which coincide nicely with the 120 dB dynamic range of normal human hearing (from
just audible to uncomfortably loud).
dyne A unit of force, equal to the force required to impart an acceleration of one centimeter per second per second to a mass of
one gram. Old usage for sound pressure.
EBU (European Broadcasting Union) A professional society that, among other things, helps establish standards.
EEPROM or E2PROM (electrically erasable programmable read-only memory) A version of read-only memory that can be
electrically erased and reprogrammed by the designer. Differentiated from standard EPROM (one "E") which requires ultraviolet
radiation for erasure.
EIA (Electronic Industries Association) Founded in 1924, The EIA is a private trade organization made up of manufacturers
which sets standards for voluntary use of its member companies (and all other electronic manufacturers), conducts educational
programs, and lobbies in Washington for its members' interests.
enhancers See: exciters
error correction A method using a coding system to correct data errors by use of redundant data within a data block. Often data is
interleaved for immunity to burst errors. Corrected data is identical to the original.
Ethernet A local area network (LAN) used for connecting computers, printers, workstations, terminals, etc., within short distances.
Ethernet operates over twisted-pair or coaxial cable at speeds up to 10 megabytes/sec (Mbps).
exciters (or enhancers) A term referring to any of the popular special-effect signal processing products used primarily in recording
and performing. All exciters work by adding harmonic distortion of some sort - but harmonic distortion found pleasing by most
listeners. Various means of generating and summing frequency-dependent and amplitude-dependent harmonics exist. Both even-
and odd-ordered harmonics find favorite applications. Psychoacoustics teaches that even-harmonics tend to make sounds soft, warm
and full, while odd-harmonics tend to make things metallic, hollow and bright. Lower-order harmonics control basic timbre, while
higher-order harmonics control the "edge" or "bite" of the sound. Used with discrimination, harmonic distortion changes the original
sound dramatically, more so than measured performance might predict.
expander A signal processing device used to increase the dynamic range of the signal passing through it. Expanders complement
compressors. For example, a compressed input dynamic range of 70 dB might pass through a expander and exit with a new
expanded dynamic range of 110 dB. [Long answer: Just like compression, what "expansion" is and does has evolved significantly
over the years. Originally expanders were used to give the reciprocal function of a compressor, i.e., it undid compression. Anytime
audio was recorded or broadcast it had to be compressed for optimum transfer. Then it required an expander at the other end to
restore the audio to its original dynamic range. Operating about the same "hinge" point and using the same ratio setting as the
compressor, an expander makes audio increases and decreases bigger. From this sense came the phrase that "expanders make
the quiet sounds louder and the loud sounds quieter." Using the same example from the compressor discussion: if the sound
increases by 1 dB but the output increases by 1.6 dB, then this quiet increase has been made louder; and if the sound gets smaller
by 1 dB but the output decreases by 1.6 dB, then the louder sound has been made quieter (it decreased more) - it's confusing, but
once understood, it is a valuable way of looking at it. Modern expanders usually operate only below a set threshold point (as
opposed to the center hinge point), i.e., they operate only on low-level audio. The term downward expander or downward
expansion evolved to describe this type of application. The most common use is noise reduction. For example, say, an expander's
threshold level is set to be just below the smallest vocal level being recorded, and the ratio control is set for 3:1. What happens is this:
when the vocals stop, the "decrease below the set-point" is the change from signal (vocals) to the noise floor (no vocals), i.e., there
has been a step decrease from the smallest signal level down to the noise floor. If that step change is, say, -10 dB, then the
expander's output will be -30 dB (because of the 3:1 ratio, a 10 dB decrease becomes a 30 dB decrease), thus resulting in a noise
reduction improvement of 20 dB.
extensible Of or relating to a programming language or a system that can be modified by changing or adding features. Capable of
being extended: AES-24 is an extensible protocol.
5.1 surround sound The digital audio multichannel format developed by the Motion Picture Experts Group (see: MPEG) for digital
soundtrack encoding for film, laserdiscs, videotapes, and HDTV broadcast. The designation "5.1" refers to the five discrete, full
bandwidth channels - left, right, & center fronts, plus left & right surrounds - and the ".1" usually refers to the limited bandwidth
subwoofer channel, but can also refer to a special effects/feature channel. Terminology used by both Dolby AC-3 Surround Digital
and DTS Zeta Digital (the home version of their theater Coherent Acoustics system).
FAQ (frequently asked question) Acronym commonly seen on bulletin boards, Internet Web sites, and corporate information
centers. By compiling FAQ lists (FAQs), organizations significantly reduce time spent repeatedly answering the same questions.
fax on demand One of the terms for the process of ordering fax documents from remote machines via telephone, using a
combination of voice processing and fax technologies. Also called fax-back.
fax-back See: fax on demand.
FDDI (fiber distributed data interface) An ANSI standard describing a 100 megabytes/sec (Mbps) fiber optic LAN; now also
specified for twisted-pair use.
femto- Prefix for one thousandth of one millionth (10E-15), abbreviated f.
FFT (fast Fourier transform) A DSP algorithm that is the computational equivalent to performing a specific number of discrete
Fourier transforms, but by taking advantage of computational symmetries and redundancies, significantly reduces the computational
fiber optics The technology of using glass fibers to convey light and modulated information. Short distances (typically less than 150
feet) use plastic fibers, while long distances must use glass fibers.
FIR (finite impulse-response) filter A commonly used type of digital filter. Digitized samples of the audio signal serve as inputs,
and each filtered output is computed from a weighted sum of a finite number of previous inputs. An FIR filter can be designed to
have completely linear phase (i.e., constant time delay, regardless of frequency). FIR filters designed for frequencies much lower
that the sample rate and/or with sharp transitions are computationally intensive, with large time delays. Popularly used for adaptive
FireWire (IEEE 1394) A joint Apple and TI implementation of the IEEE P1394 SerialBus Standard. It is a high-speed (200
Mbits/sec now, with 400 Mbits/s coming, and 1 Gbit/s on the horizon) serial bus for peripheral devices. It is intended to replace
Apple Desktop Bus (ADB) and SCSI (Microsoft has announced future Windows 95 support for IEEE 1394). FireWire supports
automatic configuration ("plug and play") and hot-plugging (changing peripheral devices while running). It is also isochronous,
meaning that a fixed slice of bandwidth can be dedicated to a particular peripheral - video, for instance. FireWire is on its way to
becoming the optimal digital interface for 21st-century applications. Fast, inexpensive and reliable for audio/video as well as
computer peripherals, IEEE 1394 carries all forms of digitized video and audio. A single FireWire interface can be used for all
entertainment-center interconnections, done in a daisy-chain fashion. New computer peripherals such as digital television, CD-ROM,
DVD, digital cameras (Sony's already announced) and home networks are the first users. See: USB for complementary low-speed
flanging Originally, "flanging" was achieved using two reel-to-reel tape recorders playing the same program, in synchronization, with
their outputs summed together. By alternately slowing down one machine, then the other, different phase cancellations occurred in
the summation process. The "slowing down" was done simply by pressing against the flanges of the tape reels, hence the original
term "reel flanging," soon shortened to just "flanging." Since the two identical signals would alternately add and subtract due to the
introduced phase (timing) difference, the audible effect was one of a sweeping comb filter. It was described as a "swishing" or
"tunneling" sound. Soon electronic means were devised to mimic true "reel flanging" by using delay lines and mixing techniques.
Adding a low-frequency oscillator to modulate the audio delay line's clock signal created a sweeping effect, much like a jet airplane
taking off. The best flangers used two delay lines. Compare with: phaser
floating point An encoding technique consisting of two parts: a mantissa representing a fractional value with magnitude less than
one, and an exponent providing the position of the decimal point. Floating point arithmetic allows the representation of very large or
very small numbers with fewer bits.
Fourier analysis Mathematics. The approximation of a function through the application of a Fourier series to periodic data.
Fourier, Baron Jean Baptiste Joseph (1768-1830) French mathematician and physicist who formulated a method for analyzing
periodic functions and studied the conduction of heat.
Fourier series Application of the Fourier theorem to a periodic function, resulting in sine and cosine terms which are harmonics of
the periodic frequency. [After Baron Jean Baptiste Joseph Fourier.]
Fourier theorem A mathematical theorem stating that any function may be resolved into sine and cosine terms with known
amplitudes and phases.
FPGA (field-programmable gate array) A programmable logic device which is more versatile (i.e., much larger) than traditional
programmable devices such as PALs and PLAs.
frequency 1. The property or condition of occurring at frequent intervals. 2. Mathematics. Physics. The number of times a
specified phenomenon occurs within a specified interval, as: a. The number of repetitions of a complete sequence of values of a
periodic function per unit variation of an independent variable. b. The number of complete cycles of a periodic process occurring per
unit time. c. The number of repetitions per unit time of a complete waveform, as of an electric current.
full duplex Redundant term. See: duplex
GAL� (generic array logic) Registered trademark of Lattice Semiconductor for their invention of EEPROM-based low-power
programmable logic devices.
gate See: noise gate
giga- A prefix signifying one billion (10E9), abbreviated G.
gigabyte A billion bytes.
GIGO (garbage in garbage out) Popular acronym used by programmers to indicate that incorrect information sent to a system
generally results in incorrect information received from it.
glass Popular jargon referring to glass fiber optic interconnection, or fiber optics in general.
GPIB (general purpose interface bus) See: IEEE-488.
granulation noise An audible distortion resulting from quantization error.
graphic equalizer A multi-band variable equalizer using slide controls as the amplitude adjustable elements. Named for the positions
of the sliders "graphing" the resulting frequency response of the equalizer. Only found on active designs. Center frequency and
bandwidth are fixed for each band.
gray code A sequence of binary values where only one bit is allowed to change between successive values. Generally "quieter"
(producing less audible interference) than straight binary coding for execution of commands in audio systems.
GUI (graphical user interface) A generic name for any computer interface that substitutes graphics (like buttons, arrows,
switches, sliders, etc.) for characters; usually operated by a mouse or trackball. First mass use was Apple's Macintosh� computers,
but is now dominated by Microsoft's Windows� programs.
gyrator filters Term used to describe a class of active filters using gyrator networks. Gyrator is the name given for RC networks
that mimic inductors. A gyrator is a form of artificial inductor where an RC filter synthesizes inductive characteristics. Used to
replace real inductors in filter design.
half-duplex Pertaining to a transmission over a circuit capable of transmitting in either direction, but only one direction at a time.
See also: duplex
harmonic series 1. Mathematics. A series whose terms are in harmonic progression, as 1 + 1/3 + 1/5 + 1/7 + . . . 2. Music. A
series of tones consisting of a fundamental tone and the overtones produced by it, and whose frequencies are consecutive integral
multiples of the frequency of the fundamental.
handshaking The initial exchange between two communications systems prior to and during transmission to ensure proper data
hard disk A sealed mass storage unit used for storing large amounts of digital data.
hard disk recording (HDR) See: DAW (digital audio workstation)
hardware The physical (mechanical, and electrical) devices that form a system.
hdCD (high density compact disc) See: DVD
HDCD (high definition compatible digital) Pacific Microsonics' trademark for their encode/decode scheme that allows up to 24
bit, 88.2 kHz digital audio mastering process, yet is compatible with normal 16 bit, 44.1 kHz CD and DAT formats. Claimed to sound
superior even when not decoded, and to be indistinguishable from the original if decoded.
HDTV (high definition television) The standard for digital television in North America, still being revised. When finished will
include a definition for picture quality at least that of a movie theater, or 35 mm slide, i.e., at least two million pixels (compared to
336,000 pixels for NTSC).
Helmholtz, Hermann Ludwig Ferdinand von (1821-1894) German physicist and physiologist who formulated the mathematical
law of the conservation of energy (1847) and invented an ophthalmoscope (1851) [An instrument for examining the interior
structures of the eye, especially the retina, consisting essentially of a mirror that reflects light into the eye and a central hole through
which the eye is examined. You aren't a real doctor without one!] Famous for his book, On the Sensations of Tone first published
hertz Abbr. Hz. A unit of frequency equal to one cycle per second. [After Heinrich Rudolf Hertz.]
Hertz, Heinrich Rudolf (1857-1894) German physicist who was the first to produce radio waves artificially.
hexadecimal A number system using the base-16, i.e., each number can be any of 16 values. Normally represented by the digits
0-9, plus the alpha characters A-F. Each hexadecimal digit can be represented by a four-bit binary number.
Hi8 See: DA-88
high-pass filter A filter having a passband extending from some finite cutoff frequency (not zero) up to infinite frequency. An
infrasonic filter is a high-pass filter.
HTML (hypertext markup language) The software language used on the Internet's World Wide Web (WWW). Used primarily
to create home pages containing hypertext.
HTTP (hypertext transfer protocol) The name for the protocol that moves documents around the Internet/Web. Used by the
various servers and browsers to communicate over the net.
hyperlink The protocol that allows connecting two Internet resources via a simple word or phrase; allowing the user a simply
point-and-click method to create the link.
hypertext Within WWW documents, the linking of words to other sections of text, pictures or sound is called hypertext. Hypertext
is created using the HTML software language. Also used frequently in Help files.
IC (integrated circuit) A solid state device with miniaturized discrete active components on a single semiconductor material.
IEC (International Electrotechnical Commission) A European organization (headquartered in Geneva, Switzerland) involved in
international standardization within the electrical and electronics fields. The U.S. National Committee for the IEC operates within
IEEE (Institute of Electrical and Electronic Engineers) The largest professional organization for electrical engineers. Primarily
concerned with education and standardization.
IEEE-488 also referred to as the general purpose interface bus (GPIB). Most common parallel format computer interface for
simultaneous control of up to 15 multiple peripherals.
IIR (infinite impulse-response) filter A commonly used type of digital filter. This recursive structure accepts as inputs digitized
samples of the audio signal, and then each output point is computed on the basis of a weighted sum of past output (feedback) terms,
as well as past input values. An IIR filter is more efficient than its FIR counterpart, but poses more challenging design issues. Its
strength is in not requiring as much DSP power as FIR, while its weakness is not having linear group delay and possible instabilities.
impedance The numerical measure of the "resistance" to current flow that a general electrical network has when excited with an
infrasonic Generating or using waves or vibrations with frequencies below that of audible sound. Compare with subsonic -
commonly used (erroneously) to mean infrasonic.
interpolating response Term adopted by Rane Corporation to describe the summing response of adjacent bands of variable
equalizers using buffered summing stages. If two adjacent bands, when summed together, produce a smooth response without a dip
in the center, they are said to interpolate between the fixed center frequencies, or combine well. [Historical note: Altec-Lansing
first described their buffered equalizer designs as combining and the terminology became commonplace. Describing how well
adjacent bands combine is good terminology. However, some variations of this term confuse people. The phrase "combining filter" is
a misnomer, since what is meant is not a filter at all, but rather whether adjacent bands are buffered before summing. The other side
of this misnomered coin finds the phrase "non-combining filter." Again, no filter is involved in what is meant. Dropping the word
"filter" helps, but not enough. Referring to an equalizer as "non-combining" is imprecise. All equalizers combine their filter outputs.
The issue is how much ripple results. For these reasons, Rane adopted the term "interpolating" as an alternative. Interpolating means
to insert between two points, which is what buffering adjacent bands accomplishes. By separating adjacent bands when summing,
the midpoints fill in smoothly without ripple.]
inverse square law Sound Pressure Level. Sound propagates in all directions to form a spherical field, thus sound energy is
inversely proportional to the square of the distance, i.e., doubling the distance quarters the sound energy (the inverse square law),
so SPL is attenuated 6dB for each doubling.
interleaving The process of rearranging data in time. Upon de-interleaving, errors in consecutive bits or words are distributed to a
wider area to guard against consecutive errors in the storage media.
I/O (input/output) Equipment or data used to communicate from a circuit or system to other circuits or systems, or the outside
ISDN (Integrated Services Digital Network) A high-capacity digital telecommunication network (mainly fiber optic) based on an
international telephone standard for digital transmission of audio, data and signaling - all in addition to standard voice telephone calls.
A cost-effective alternative to satellite links.
ISO (International Standards Organization or International Organization for Standardization) Founded in 1947 and consisting
of members from over 90 countries, the ISO promotes the development of international standards and related activities to facilitate
the exchange of goods and services worldwide. The U.S. member body is ANSI. [Interesting tidbit: according to ISO internet info,
"ISO" is not an acronym! It is a derived Greek word, from isos, equal. For example, isobar, equal pressure, or isometric, equal
length. Take a small jump from "equal" to "standard" and you have the name of the organization. It offers the further advantage of
being valid in all the official languages of the organization (English, French & Russian), whereas if it were to be an acronym it would
not work for French and Russian.]
isochronous ("iso" equal + "chronous" time) A term meaning time sensitive; isochronous transmission is time sensitive
transmission. For example, voice and video require isochronous transmission since audio/video synchronization is mandated.
JavaT The trademarked name for a powerful new object-oriented programming language developed by Sun Microsystems. Java
allows high-speed fully interactive Web pages to be developed for the Internet or any type of platform. National Semiconductor
hosts the first commercial Java Web site.
jitter A tendency towards lack of synchronization caused by electrical changes. Technically the unexpected (and unwanted) phase
shift of digital pulses over a transmission medium. A discrepancy between when a digital edge transition is supposed to occur and
when it actually does occur - think of it as nervous digital, or maybe a digital analogy to wow and flutter.
jitter timing error Short-term deviations of the transitions of a digital signal from their ideal positions in time.
justify To shift a numeral so that the most significant digit, or the least significant digit, is placed at a specific position in a row.
kHz (kilohertz) One thousand (1,000) cycles per second.
kilo- Abbreviated k (always lower-case). A prefix signifying one thousand (10E3).
Kilo- Abbreviated K (always upper-case). A prefix used in computer work to signify multiples of 1024 (i.e., 2E10). Meant to
distinguish base-2 (binary) from base-10 (decimal) magnitudes. For example, a "16K" memory is actually 16,384 bits (i.e., 16 times
1024, or 2E14).
LAN (local area network) A combination of at least two computers and peripherals on a common wiring scheme, which allows
two-way communication of data between any devices on the network.
Laplace, Marquis Pierre Simon de (1749-1827) French mathematician and astronomer who formulated the theory of probability.
laser (light amplification by stimulated emission of radiation) A device which generates coherent, monochromatic light waves.
All CD players contain a semiconductor laser in their optical pickup.
LCD (liquid crystal display) A display of numerical or graphical information made of material whose reflectance or transmittance
changes when an electric field is applied. An LCD requires ambient light or back-lighting for viewing.
LED (light emitting diode) A self-lighting semiconductor display of numerical or graphical information based on the light emitting
characteristics of a solid-state device that emits incoherent (i.e., random direction) light when conducting a forward current.
leveler A dynamic processor that maintains (or "levels") the amount of one audio signal based upon the level of a second audio
signal. Normally, the second signal is from an ambient noise sensing microphone. For example, a restaurant is a typical application
where it is desired to maintain paging and background music a specified loudness above the ambient noise. The leveler monitors the
background noise, dynamically increasing and decreasing the main audio signal as necessary to maintain a constant loudness
differential between the two. Also called SPL controller.
lift/dip Popular European term meaning boost/cut.
limiter A compressor with a fixed ratio of 10:1 or greater. The dynamic action effectively prevents the audio signal from becoming
any larger than the threshold setting. For example, if the threshold is set for, say, +16 dBu and the input signal increases by 10 dB
to +26 dB, the output only increases by 1 dB to +17 dBu, essentially remaining constant. Used primarily for preventing equipment,
media, and transmitter overloads. A limiter is to a compressor what a noise gate is to an expander.
linear PCM A pulse code modulation system in which the signal is converted directly to a PCM word without companding, or other
lossy See: digital audio data compression
loud Having offensively bright colors: a loud necktie.
loudness The SPL of a standard sound which appears to be as loud as the unknown. Loudness level is measured in phons and
equals the equivalent SPL in dB of the standard. [For example, a sound judged as loud as a 40 dB-SPL 1 kHz tone has a loudness
level of 40 phons. Also, it takes 10 phons (an increase of 10 dB-SPL) to be judged twice as loud.]
low-pass filter A filter having a passband extending from DC (zero Hz) to some finite cutoff frequency (not infinite). A filter with a
characteristic that allows all frequencies below a specified rolloff frequency to pass and attenuate all frequencies above.
Anti-aliasing and anti-imaging filters are low-pass filters.
LSB (least significant bit) The bit within a digital word that represents the smallest possible coded value; hence, the LSB is a
measure of precision.
luminance That part of the video signal which carries the information on how bright the TV signal is to be.
MADI (multichannel audio digital interface) An AES recommended practice document Digital Audio Engineering - Serial
Multichannel Audio Digital Interface (MADI) AES-10-1991 (ANSI S4.43-1991) specifying and controlling the requirements for
digital interconnection between multitrack recorders and mixing consoles. The standard provides for 56 simultaneous digital audio
channels which are conveyed point-to-point on a single coaxial cable fitted with BNC connectors along with a separate
synchronization signal. Fiber optic implementation is specified in document AES-10id-1995, entitled AES information document for
digital audio engineering - Engineering guidelines for the multichannel audio digital interface (MADI) AES 10. Basically,
the technique takes the standard AES/EBU interface and multiplexes 56 of these into one sample period rather than the original two.
magnitude 1. Mathematics. a. A number assigned to a quantity so that it may be compared with other quantities. b. A property that
can be quantitatively described, such as the volume of a sphere, the length of a vector, or the value of a voltage or current
MD (MiniDisc) Trademark term for the Sony digital audio recordable optical storage system utilizing data compression to reduce
MDM (modular digital multitrack) Generic term used to describe any of the families of digital audio multitrack recorders. The
most common examples being the Alesis ADAT series and the Tascam DTRS (DA-88) series.
mega- 1. A prefix signifying one million (10E6). abbreviated M. 2. A prefix used in computer work to signify multiples of 1,048,576
(i.e., 2E20). Meant to distinguish base-2 (binary) from base-10 (decimal) magnitudes. For example, a "16M" memory is actually
16,777,216 bits (i.e., 16 times 1,024,576, or 2E24). Also (unfortunately) abbreviated M.
megabyte A million bytes.
megaflops See: MFLOPS
MFLOPS (pronounced "mega-flops") (million floating point operations per second) A measure of computing power.
micro- Prefix for one millionth (10E-6), abbreviated �.
microbar 1. A unit of pressure equal to one millionth of a bar. 2. A really small place to have a beer.
microcontroller See: microprocessor
microprocessor An integrated circuit that performs a variety of operations in accordance with a list of instructions. The core of a
microcomputer or personal computer, a one chip computer.
MIDI (musical instrument digital interface) Industry standard bus and protocol for interconnection and control of musical
instruments. First launched in 1983, now generalized and expanded to include signal processing and lighting control.
milli- Prefix for one thousandth (10E-3), abbreviated m.
minimum-phase filters Electrical circuits From an electrical engineering viewpoint, the precise definition of a minimum-phase
function is a detailed mathematical concept involving positive real transfer functions, i.e., transfer functions with all zeros restricted
to the left half s-plane (complex frequency plane using the Laplace transform operator s). This guarantees unconditional stability in
the circuit. For example, all equalizer designs based on 2nd-order bandpass or band-reject networks have minimum-phase
MIPS (million instructions processed per second) A measure of computing power.
MLS (maximum-length sequences) A time-domain-based analyzer using a mathematically designed test signal optimized for
sound analysis. The test signal (a maximum-length sequence) is electronically generated and characterized by having a flat
energy-vs-frequency curve over a wide frequency range. Sounding similar to white noise, it is actually periodic, with a long repetition
rate. Similar in principle to impulse response testing - think of the maximum-length sequence test signal as a series of randomly
distributed positive- and negative-going impulses. See: MLSSA
MLSSA (pronounced "Melissa") (maximum-length sequences system analyzer) Trademarked name for the first MLS
measurement instrument designed by DRA Laboratories (Sarasota, FL). Maximum-length-sequences methods were used for room
impulse response measurement by M.R. Schroeder in 1979 (based on work dating back to the mid-60's); however, it was not until
1987 that the use of MLS became commercially available. The first MLS instrument was developed and made practical by Douglas
Rife, who described the principles in his landmark paper (co-authored by John Vanderkooy, University of Waterloo)
"Transfer-Function Measurement with Maximum-Length Sequences" (J. Audio Eng. Soc., vol. 37, no. 6, June 1989), and followed
up with new applications described in "Modulation Transfer Function Measurement with Maximum-Length Sequences" (J. Audio
Eng. Soc., vol. 40, no. 10, October 1992). Further information available directly from DRA Laboratories: Fax (941) 925-0964.
MMCD (multimedia compact disc) See: DVD
modem (modulator-demodulator) A peripheral device used to convert digital signals ("1s" and "0s") into analog signals (tones) and
vice-versa, necessary for communication using standard telephone lines.
mojo 1. A charm or amulet thought to have magic powers. 2. Slang: power, luck, etc., as of magical or supernatural origin. 3. Abbr.
Mother Jones magazine, or reference to their Internet news network: The Mojo Wire.
MOR (magneto-optical recording) An erasable optical disc system using magnetic media and laser reading/writing.
MPEG (Moving Picture Experts Group) A working group within SMPTE who set, among other things, specifications for
compression schemes for audio and video transmission. A term commonly used to make reference to their image-compression
scheme (MPEG-2) for full motion video.
MS-DOS� (Microsoft� disk operating system) Microsoft's registered trademark for their PC operating system.
MSB (most significant bit) The bit within a digital word that represents the biggest possible single-bit coded value.
multi-denomial transpedance informer Term coined by Jensen Transformers for their mythical product, the JE-EP-ERs, first
introduced in 1987, which almost changed the whole audio transformer industry. The Jensen JE-EP-ERs pioneered the use of triple
electonomic shielding and intrinsic eddy-breeding, until outlawed by Congress in 1988. Voluntarily discontinued when their stock of
zeta-metal ran out, preventing any further use of interstage transpedance informance. Considered by many to be the only necessary
accessory when coupling a Rane PI 14 Pseudoacoustic Infector to a Crown Belchfire� BF-6000SUX amplifier for playback using
an Electro-Voice Rearaxial Softspeaker.
multimedia Generally refers to personal computers capable of multiple forms of communication methods. These constitute a
minimum combination of stereo audio, video, text, and graphics, plus the more complex system includes fax and telephony provisions.
multiplex To interleave two or more signals into a single output; a process of selecting one of a number of inputs and switching its
information to the output.
music vs. noise "The sensation of a musical tone is due to a rapid periodic motion of the sonorous body; the sensation of a noise to
non-periodic motion." from On the Sensation of Tone (1862) Hermann Helmholtz.
nano- A prefix for one billionth (10E-9), abbreviated n.
narrow-band filter Term popularized by equalizer pioneer C.P. Boner to describe his patented (tapped toroidal inductor) passive
notch filters. Boner's filters were very high Q (around 200) and extremely narrow (5 Hz at the -3 dB points). Boner used 100-150 of
these sections in series to reduce feedback modes. Today's usage extends this terminology to include all filters narrower than
1/3-octave. This includes parametrics, notch filter sets, and certain cut-only variable equalizer designs.
network Generally used to mean a multi-computer system (as opposed to a single computer bus-type system) where multiple
access is allowed from more than one computer at a time. Characterized by full two-way (duplex) communications between all
equipment and computers on the network.
nibble A group of four bits or half a byte (8-bits).
noise floor Normally the lowest threshold of useful signal level (although sometimes audible signals below the noise floor may be
noise gate An expander with a fixed "infinite" downward expansion ratio. Used extensively for controlling unwanted noise, such as
preventing "open" microphones and "hot" instrument pick-ups from introducing extraneous sounds into the system. When the
incoming audio signal drops below the user set-point (the threshold point) the expander prevents any further output by reducing the
gain "zero." The actual gain reduction is typically on the order of -80 dB, thus once audio falls below the threshold, effectively the
output level becomes the residual noise of the gate. Common terminology refers to the gate "opening" and "closing." Another popular
application uses noise gates to enhance musical instrument sounds, especially percussion instruments. Judicious setting of a noise
gate's attack (turn-on) and release (turn-off) times adds "punch," or "tightens" the percussive sound, making it more pronounced. A
noise gate is to an expander as a limiter is to a compressor.
noise reduction See: expander
noise shaping A technique used in oversampling low-bit converters and other quantizers to shift (shape) the frequency range of
quantizing error (noise and distortion). The output of a quantizer is fed back through a filter, and summed with its input signal. Dither
is sometimes used in the process. Oversampling A/D converters shift much of it out of the audio range completely. In this case, the
in-band noise is decreased, which allows low-bit converters (such as delta-sigma) to equal or out-perform high-bit converters (those
greater than 16 bits). When oversampling is not involved, the noise still appears to decrease by 12 dB or more because it is
redistributed into less audible frequency areas. The benefits of this kind of noise shaping are usually reversed by further digital
nonvolatile Refers to a memory device which does not lose its data when power is removed from the system.
NSP (native signal processing) Intel-designed method of using a powerful microprocessor (like their Pentium CPU) for signal
processing functions normally done by separate DSP chips.
null modem cable Special wiring of an RS-232 cable such that a computer can talk to another computer without a modem (thus
"null" modem). As a minimum a null modem cable reverses pins 2 and 3 on a standard RS-232 cable - but other pins may also need
changing and shorting together.
Nyquist frequency The highest frequency that may be accurately sampled. The Nyquist frequency is one-half the sampling
frequency. For example, the theoretical Nyquist frequency of a CD system is 22.05 kHz.
object-oriented or object-based programming A software technique in which a system program is expressed completely in
terms of predefined things (objects), consisting of a set of variables and operations which can be performed on them, and the
connections between objects.
octal A number system using the base-8, i.e., each digit can be any of 8 values, represented by the digits 0-7. Each octal digit can
also be represented by a three-bit binary number (since 2E3 =8).
octave 1. Audio. The interval between any two frequencies having a ratio of 2 to 1. 2. Music a. The interval of eight diatonic
degrees between two tones, one of which has twice as many vibrations per second as the other. b. A tone that is eight full tones
above or below another given tone. c. An organ stop that produces tones an octave above those usually produced by the keys
ohm Abbr. R, (Greek upper-case omega). A unit of electrical resistance equal to that of a conductor in which a current of one
ampere is produced by a potential of one volt across its terminals. [After Georg Simon Ohm.]
Ohm, Georg Simon (1789-1854) German physicist noted for his contributions to mathematics, acoustics, and the measurement of
one-bit data converter Loose reference to any of the various data conversion schemes (e.g., delta-sigma, adaptive delta
modulation, etc.) that use only one binary bit (i.e., levels 1 and 0) in the conversion and storage process.
one-third octave 1. Term referring to frequencies spaced every one-third of an octave apart. One-third of an octave represents a
frequency 1.26-times above a reference, or 0.794-times below the same reference. The math goes like this: 1/3-octave = 2E1/3 =
1.260; and the reciprocal, 1/1.260 = 0.794. Therefore, for example, a frequency 1/3-octave above a 1 kHz reference equals 1.26
kHz (which is rounded-off to the ANSI-ISO preferred frequency of "1.25 kHz" for equalizers and analyzers), while a frequency
1/3-octave below 1 kHz equals 794 Hz (labeled "800 Hz"). Mathematically it is significant to note that, to a very close degree, 2E1/3
equals 10E1/10 (1.2599 vs. 1.2589). This bit of natural niceness allows the same frequency divisions to be used to divide and mark
an octave into one-thirds and a decade into one-tenths. 2. Term used to express the bandwidth of equalizers and other filters that
are 1/3-octave wide at their -3 dB (half-power) points. 3. Approximates the smallest region (bandwidth) humans reliably detect
change. See: critical bands. Compare with: third-octave
op amp (operational amplifier) An analog integrated circuit device characterized as having two opposite polarity inputs and one
output, used as the basic building block in analog signal processing.
optocoupler Any device that functions as an electrical-to-optical or optical-to-electrical transducer.
ordinate Mathematics. The plane Cartesian coordinate representing the distance from a specified point to the x-axis, measured
parallel to the y-axis.
OSD (on-screen display) chip An integrated circuit providing all necessary functions for adding text to television or video monitor
OTPROM (one-time programmable read-only memory) A redundant term, incorrectly used to mean PROM - a PROM, by
definition, is a one-time device.
oversampling A technique where each sample from the converter is sampled more than once, i.e., oversampled. This
multiplication of samples permits digital filtering of the signal, thus reducing the need for sharp analog filters to control aliasing.
PA-232 An RS-232-based variant of the PA-422 AES standard.
PA-422 A pro audio implementation of Electronics Industries Association EIA-422 interconnection standard, defined and adopted
by the Audio Engineering Society as AES Recommended practice for sound-reinforcement systems - Communications interface
(PA-422) AES 15-1991 (ANSI S4.49-1991).
PAL� (programmable array logic) Original registered trademark of Monolithic Memories Inc. (now owned by Advanced Micro
Devices, Inc.) for their fuse-link once-programmable logic parts which have a programmable AND array, but a predefined OR
array. See also: PLA, PLD & FPGA.
PAQRAT A trademark of the Rane Corporation for their device that converts AES/EBU stereo 18-24 bit digital audio two track
data into 16-bit compatible four tracks for recording and playback on modular digital multitrack tape machines such as Alesis ADAT
and Tascam DTRS (DA-88) models.
paragraphic See: parametric equalizer
parallel interface The printer port in the PC world. A parallel port conforming to the quasi-standard called the Centronics Parallel
Standard (there is no EIA standard). Originally a 36-pin connector, now more often a D-25 type connector. A parallel (as opposed
to serial) interface transfers all bits in a word simultaneously. See also: serial interface.
parametric equalizer A multi-band variable equalizer offering control of all the "parameters" of the internal bandpass filter
sections. These parameters being amplitude, center frequency and bandwidth. This allows the user not only to control the
amplitude of each band, but also to shift the center frequency and to widen or narrow the affected area. Available with rotary and
slide controls. Subcategories of parametric equalizers exist which allow control of center frequency but not bandwidth. For rotary
control units the most used term is quasi-parametric. For units with slide controls the popular term is paragraphic. The frequency
control may be continuously variable or switch selectable in steps. Cut-only parametric equalizers (with adjustable bandwidth or not)
are called notch equalizers, or band-reject equalizers.
parity A redundant error detection method in which the total number of binary 1's (or 0's) is always made even or odd by appending
one or more bits.
pascal Abbr. Pa A unit of pressure equal to one newton per square meter. [After Blaise Pascal.]
Pascal, Blaise (1623-1662) French philosopher and mathematician. Among his achievements are the invention of an adding
machine and the development of the modern theory of probability.
passive equalizer A variable equalizer requiring no power to operate. Consisting only of passive components (inductors, capacitors
and resistors) passive equalizers have no AC line cord. Favored for their low noise performance (no active components to generate
noise), high dynamic range (no active power supplies to limit voltage swing), extremely good reliability (passive components rarely
break), and lack of RFI interference (no semiconductors to detect radio frequencies). Disliked for their cost (inductors are
expensive), size (and bulky), weight (and heavy), hum susceptibility (and need careful shielding), and signal loss characteristic
(passive equalizers always reduce the signal). Also inductors saturate easily with large low frequency signals, causing distortion.
Rarely seen today, but historically they were used primarily for notching in permanent sound systems.
PC (personal computer) Original term coined by IBM to describe their first personal computers; now used to mean all
IBM-compatible personal computers, or any personal computer.
PC-Card See: PCMCIA
PC-DOS� (personal computer disk operating system) IBM's trademarked acronym for their PC operating system. If PC-DOS
runs on an IBM compatible, it is then called MS-DOS.
PCI (peripheral component interconnect) Intel-designed high performance CPU interconnect strategy for "glueless" I/O
subsystems. A 32- or 64-bit local-bus specification, characterized by being self-configuring, open, high-bandwidth and
processor-independent - allowing for modular hardware design.
PCM (pulse code modulation) A conversion method in which digital words in a bit stream represent samples of analog
information. The basis of most digital audio systems.
PCMCIA (Personal Computer Memory Card International Association) The association and first name given to the
standardized credit-card size packages (a.k.a. smart cards) for memory and I/O (modems, LAN cards, etc.) for computers, laptops,
palmtops, etc. Nicknamed PC-Card, which is now the preferred term.
PDA (personal digital assistant) A small palmtop-like computer designed for specific tasks such as a pocket calculator. Other
examples include personal electronic diaries, memo takers, communicators, web browsers, dictionary-translators, etc. Apple's
Newton is a PDA. IBM refers to theirs as personal communicators.
peaking response Term used to describe a bandpass shape when applied to program equalization.
period Abbr. T, t 1. The period of a periodic function is the smallest time interval over which the function repeats itself. [For
example, the period of a sine wave is the amount of time, T, it takes for the waveform to pass through 360 degrees. Also, it is the
reciprocal of the frequency itself: i.e., T = 1/f.] 2. Mathematics. a. The least interval in the range of the independent variable of a
periodic function of a real variable in which all possible values of the dependent variable are assumed. b. A group of digits separated
by commas in a written number. c. The number of digits that repeat in a repeating decimal. For example, 1/7 = 0.142857142857...
has a six-digit period.
peripheral Equipment physically independent of, but which may interface to a computer or a controller.
phase lock loop A circuit for synchronizing a variable local oscillator with the phase of a transmitted signal. The circuit acts as a
phase detector by comparing the frequency of a known oscillator with an incoming signal and then feeds back the output of the
detector to keep the oscillator in phase with the incoming frequency. Commonly used for bit-synchronization.
phaser Also called a "phase shifter," this is an electronic device creating an effect similar to flanging, but not as pronounced. Based
on phase shift (frequency dependent), rather than true signal delay (frequency independent), the phaser is much easier and
cheaper to construct. Using a relatively simple narrow notch filter (all-pass filters also were used) and sweeping it up and down
through some frequency range, then summing this output with the original input, creates the desired effect. Narrow notch filters are
characterized by having sudden and rather extreme phase shifts just before and just after the deep notch. This generates the needed
phase shifts for the ever-changing magnitude cancellations.
phase shift The fraction of a complete cycle elapsed as measured from a specified reference point and expressed as an angle. out
of phase. In an un-synchronized or un-correlated way. See: polarity
phase delay A phase-shifted sine wave appears displaced in time from the input waveform. This displacement is called phase
phasor 1. A complex number expressing the magnitude and phase of a time-varying quantity. It is math shorthand for complex
numbers. Unless otherwise specified, it is used only within the context of steady-state alternating linear systems. [Example: 1.5 /27�
is a phasor representing a vector with a magnitude of 1.5 and a phase angle of 27 degrees.] 2. For some unknown reason, used a lot
by Star Fleet personnel.
phon A unit of apparent loudness, equal in number to the intensity in decibels of a 1,000 Hz tone judged to be as loud as the sound
pi Symbol (Greek lower-case pi) 1. Mathematics. A transcendental number, approximately 3.14159, represented by the symbol ,
that expresses the ratio of the circumference to the diameter of a circle and appears as a constant in many mathematical
expressions. 2. Filters. Equal to 180 degrees or integral multiples thereof.
pico- Prefix for one trillionth (10E-12), abbreviated p.
pink noise Pink noise is a random noise source characterized by a flat amplitude response per octave band of frequency (or any
constant percentage bandwidth), i.e., it has equal energy, or constant power, per octave. Pink noise is created by passing white
noise through a filter having a 3 dB/octave roll-off rate. See white noise discussion for details. Due to this roll-off, pink noise sounds
less bright and richer in low frequencies than white noise. Since pink noise has the same energy in each 1/3-octave band, it is the
preferred sound source for many acoustical measurements due to the critical band concept of human hearing.
pixel (picture element) The smallest element on a display surface, like a video screen, that can be assigned independent
PLA (programmable logic array) A programmable logic device in which both the AND & OR arrays are programmable.
PLD (programmable logic device) The generic name for an integrated circuit offering a vast array of logic function building
blocks that the circuit designer defines (programs) to interconnect for specific applications.
polarity A signal's electromechanical potential with respect to a reference potential. For example, if a loudspeaker cone moves
forward when a positive voltage is applied between its red and black terminals, then it is said to have a positive polarity. A
microphone has positive polarity if a positive pressure on its diaphragm results in a positive output voltage. [Usage Note: polarity
vs. phase shift: polarity refers to a signal's reference NOT to its phase shift. Being 180� out-of-phase and having inverse
polarity are DIFFERENT things. We wrongly say something is out-of-phase when we mean it is inverted. One takes time; the
other does not.]
PowerPC A super powerful RISC processor PC jointly developed by IBM, Apple and Motorola, designed to run any PC operating
system (MS-DOS, UNIX, Windows, OS/2, Mac OS. etc.). Featured in Apple's line of "PowerMac" computers.
pre-emphasis A high-frequency boost used during recording, followed by de-emphasis during playback, designed to improve
PROM (programmable read-only memory) A memory device whose contents can be electrically programmed (once) by the
proportional-Q equalizer (also variable-Q) Term applied to graphic and rotary equalizers describing bandwidth behavior as a
function of boost/cut levels. The term "proportional-Q" is preferred as being more accurate and less ambiguous than "variable-Q." If
nothing else, "variable-Q" suggests the unit allows the user to vary (set) the Q, when no such controls exist. The bandwidth varies
inversely proportional to boost (or cut) amounts, being very wide for small boost/cut levels and becoming very narrow for large
boost/cut levels. The skirts, however, remain constant for all boost/cut levels.
protocol A specific set of rules, procedures or conventions relating to format and timing of data transmission between two devices.
A standard procedure that two data devices must accept and use to be able to understand each other.
pseudoacoustic infector Term coined by Rane Corporation for their mythical product, the PI 14, first introduced in 1988, which
almost caught the attention of the music industry. An acoustic stimulator designed to add a little bit of this and a little bit of that to
recordings to give them a sense of now previously unobtainable. Rane's PI 14 introduced a unique here-to-there (and-back-again)
pan control. Transformer operation required the Jensen JE-EP-ERs when coupling directly into a Crown Belchfire� BF-6000SUX
for playback through an Electro-Voice Rearaxial Softspeaker. Today, PI 14s are considered quite scarce and highly collectable.
psychoacoustics The scientific study of the perception of sound.
PWM (pulse width modulation) A conversion method in which the widths of pulses in a pulse train represent the analog
q (lower-case) Physics. The symbol for charge.
Q (upper-case) Quality factor. Filters. The selectivity factor, defined to be the ratio of the center frequency f divided by the
quad flat pack The most commonly used package in surface mount technology to achieve a high lead count in a small area. Leads
are brought out on all four sides of a thin square package.
quantization error Error resulting from quantizing an analog waveform to a discrete level. In general the longer the word length,
the less the error.
quantization The process of converting, or digitizing, the almost infinitely variable amplitude of an analog waveform to one of a
finite series of discrete levels. Performed by the A/D converter.
quasi-parametric See: parametric equalizer
radian Mathematics. A unit of angular measure equal to the angle subtended at the center of a circle by an arc equal in length to
the radius of the circle, approximately 57�17'44.6 Filters. Frequency is measured in radians/second. One cycle (360�) equals 2 pi
RAM (random access memory) A memory device in which data may be read out and new data written into any address or
RaneWare™ A trademark of Rane Corporation used to identify Rane software products - not something to keep you dry.
RAQ (rarely asked questions) The really important questions that should be asked, but never are. The answers to RAQs are kept
hidden within government and corporate walls.
rarefaction 1. A decrease in density and pressure in a medium, such as air, caused by the passage of a sound wave. 2. The region
in which this occurs.
R-DAT or DAT (rotary head digital audio tape recorder ) A digital audio recorder utilizing a magnetic tape cassette system
similar to that of a video recorder.
real-time operation What is perceived to be instantaneous to a user (or more technically, processing which completes in a specific
rearaxial softspeaker Term coined by Electro-Voice for their mythical loudspeaker, the SP13.5TRBXWK. Claimed by many to be
the speaker that couldn't be made, it might have changed all future loudspeaker design, but it didn't. Characterized by being
undirectional, the designer's claimed it produced silken highs and woolen lows. The only loudspeaker known to incorporate both
"presence" and "absence" controls. Based on a ridiculously simple principle that still cannot be explained, the SP13.5TRBXWK was
only heard once, during the Rane demo of their PI 14 Pseudeoacoustic Infector, coupled by a Jensen JE-EP-ERs Multi-denomial
Transpedance Informer to a Crown Belchfire BF-6000SUX amplifier. No one survived.
reconstruction filter A low-pass filter used at the output of digital audio processors (following the DAC) to remove (or at least
greatly attenuate) any aliasing products (image spectra present at multiples of the sampling frequency) produced by the use of
real-world (non-brickwall ) input filters.
recursive A data structure that is defined in terms of itself. For example, in mathematics, an expression, such as a polynomial, each
term of which is determined by application of a formula to preceding terms. Pertaining to a process that is defined or generated in
terms of itself, i.e., its immediate past history.
RISC (reduced instruction set computer) A computer design that achieves high performance by doing the most common
computer operations very quickly, utilizing a high speed processing technology that uses a far simpler set of operating commands.
Primarily found in workstations and PowerPCs. The alternative to CISC (complex instruction set computing), the original way of
RJ (Registered Jacks) As in red RJ-12 modular telephone jacks used by Rane Corporation for external power supply connection.
ROM (read-only memory) A memory from which data, after initial storage, may only be read out, but new data cannot be written
in. The normal audio CD is an example of a read-only system.
root mean square Abbr. rms, RMS Mathematics. The square root of the average of the squares of a group of numbers. A useful
and more meaningful way of averaging a group of numbers.
rotary equalizer A multi-band variable equalizer using rotary controls as the amplitude adjustable elements. Both active and passive
designs exist with rotary controls. Center frequency and bandwidth are fixed for each band.
RS (Recommended Standard) As in RS-232 serial interface standard, et al.
RS-232 The standard serial interface (EIA/TIA-232-E) used on most personal computers. A format widely supported for
bidirectional data transfer at low to moderate rates. The most common interface method used to connect personal computers with
peripheral hardware and instruments. Use is restricted to one peripheral at a time and short distances. The standard originally called
for DB-25 connectors, but now allows the smaller DB-9 version.
RS-422 The standard adopted in 1978 by the Electronics Industry Association as EIA-422-A, Electrical characteristics of
balanced voltage digital interface circuits. A universal balanced line twisted-pair standard for all long distance (~1000 m, or
~3300 ft) computer interconnections, daisy-chain style.
RS-485 The standard describing the electrical characteristics of a balanced interface used as a bus for master/slave operation.
Allows up to 32 users to bridge onto the line (as opposed to RS-422's need to daisy-chain the interconnections).
RS-490 The standard adopted in 1981 by the EIA entitled Standard Test Methods of Measurement for Audio Amplifiers. The
power amp testing standard for consumer products.
RW 232T (also RaneWare) A trademark of Rane Corporation used to identify Rane's RS-232-based variant of the PA-422 AES
sample rate conversion The process of converting one sample rate to another, e.g. 44.1 kHz to 48 kHz. Necessary for the
communication and synchronization of dissimilar digital audio devices, e.g., digital tape machines to CD mastering machines.
sample-and-hold (S/H) A circuit which captures and holds an analog signal for a finite period of time. The input S/H proceeds the
A/D converter, allowing time for conversion. The output S/H follows the D/A converter, smoothing glitches.
Sampling (Nyquist)Theorem A theorem stating that a bandlimited continuous waveform may be represented by a series of
discrete samples if the sampling frequency is at least twice the highest frequency contained in the waveform.
sampling frequency or sampling rate The frequency or rate at which an analog signal is sampled or converted into digital data.
Expressed in Hertz (cycles per second). For example, compact disc sampling rate is 44,100 samples per second or 44.1 kHz,
however in pro audio other rates exist: common examples being 32kHz, 48kHz, and 50kHz. [Historical note re 44.1kHz vs.
44.056kHz: Since the first commercial digital audio recorders used a standard helical scan video recorder for storage,
there had to be a fixed relationship between sampling frequency and horizontal video frequency, so these frequencies
could be derived from the same master clock by frequency division. For the NTSC 525-line TV system, a sampling frequency
of 44,055.94 Hz was selected, whereas for the PAL 625-line system, a frequency of 44,100 Hz was chosen. The 0.1%
difference shows up as an imperceptible pitch shift.]
sampling The process of representing the amplitude of a signal at a particular point in time.
SAR (successive approximation register) A type of analog-to-digital converter using a digital-to-analog converter to determine the
output word successively, bit by bit.
SCMS (pronounced "scums") (serial copy management system) The copy protection scheme applied to consumer digital
recording equipment - it does not apply to professional machines. This standard allows unlimited analog-to-digital copies, but only one
digital-to-digital copy. This is done by two control bits (the C and L bits) contained within the digital audio data.
SCSI port (pronounced "scuzzy") (small computer system interface) A standard 8-bit parallel interface used to connect up to
seven peripherals, such as connecting a CD-ROM player or document scanner to a microcomputer.
SD (super density compact disc) See: DVD
SDDST (Sony Dynamic Digital Sound) Sony's competing format for the digital soundtrack system for motion picture playback.
The signal is optically printed outside the sprocket holes, along both sides of the print. Sony recently developed a single camera
system that records all three digital formats (DSD, DTS & SDDS) on a single inventory print, thus setting the stage for long term
coexistence of all formats.
SDIF (Sony digital interface format) Sony's professional digital audio interface utilizing two BNC-type connectors, one for each
audio channel, and a separate BNC-type connector for word synchronization, common to both channels. All interconnection is done
using unbalanced 75 ohm coaxial cable of the exact same length (to preserve synchronization), and is not intended for long distances.
semitone Music. An interval equal to a half tone in the standard diatonic scale. Also called half step, half tone.
serial interface A connection which allows transmission of only one bit at a time. An example in the PC world is a RS-232 port,
primarily used for modems and mice. A serial interface transmits each bit in a word in sequence over one communication link. See
also: parallel interface.
shelving response Term used to describe a flat (or shelf) end-band shape when applied to program equalization. Also known as
bass and treble tone control responses.
sibilant Linguistics. adj. Of, characterized by, or producing a hissing sound like that of (s) or (sh): the sibilant consonants; a
sibilant bird call. A sibilant speech sound, such as English (s), (sh), (z), or (zh).
sigma-delta See: delta-sigma modulation
sine Abbr. sin Mathematics. 1. The ordinate of the endpoint of an arc of a unit circle centered at the origin of a Cartesian
coordinate system, the arc being of length x and measured counterclockwise from the point (1, 0) if x is positive or clockwise if x is
negative. 2. In a right triangle, the ratio of the length of the side opposite an acute angle to the length of the hypotenuse.
sine curve Mathematics. The graph of the equation y = sin x. Also called sinusoid.
sine wave Physics. A waveform with deviation that can be graphically expressed as the sine curve.
sinusoid Mathematics. See: sine curve
smoothing filter See: anti-imaging filter
SMPTE (pronounced "simty") (Society of Motion Picture and Television Engineers) A professional engineering society that,
among other activities, helps establish standards, including a time code standard used for synchronization.
S/N ratio (signal-to-noise ratio) The ratio of signal level (or power) to noise level (or power), normally expressed in decibels.
sone A subjective unit of loudness, as perceived by a person with normal hearing, equal to the loudness of a pure tone having a
frequency of 1,000 hertz at 40 decibels sound pressure level.
sonorous 1. Having or producing sound. 2. Having or producing a full, deep, or rich sound.
sound 1.a. Vibrations transmitted through an elastic material or a solid, liquid, or gas, with frequencies in the approximate range of
20 to 20,000 hertz, capable of being detected by human ears. Sound (in air) at a particular point is a rapid variation in the air pressure
around a steady-state value (atmospheric pressure) - that is, sound is a disturbance in the surrounding medium. b. Transmitted
vibrations of any frequency. c. The sensation stimulated in the ears by such vibrations in the air or other medium. d. Such sensations
considered as a group. 2. Auditory material that is recorded, as for a movie. 3. Meaningless noise. 4. Music. A distinctive style, as
of an orchestra or a singer.
sound off To express one's views vigorously: He was always sounding off about his boss.
sound pressure The RMS value of the rapid variation in air pressure, measured in pascals, microbars, or dynes - all used
interchangeable, but pascals is now the preferred term.
sound pressure level or SPL The RMS sound pressure expressed in dB re 20 microPa (the lowest threshold of hearing for 1 kHz.
[As points of reference, 0 dB-SPL equals the threshold of hearing, while 140 dB-SPL equals irreparable hearing damage.] See:
inverse square law
SPARS (Society of Professional Audio Recording Services) Founded in 1979, a professional trade organization that unites the
manufacturers of audio recording equipment and providers of services, with the users. Their goal is worldwide promotion of
communication, education and service among all those who make and use recording equipment.
S/PDIF (Sony/Philips digital interface format, also seen w/o slash as SPDIF) A consumer version of the AES/EBU digital audio
interconnection standard based on coaxial cable and RCA connectors.
SPL controller See: leveler
SPL See: sound pressure level
subcode Non-audio digital data encoded on a CD that contains definable information such as track number, times, copy inhibit,
subsonic Having a speed less than that of sound in a designated medium. [Use infrasonic if referring to frequencies below human
subtend 1. Mathematics. To be opposite to and delimit: The side of a triangle subtends the opposite angle. 2. To underlie so as
to enclose or surround: flowers subtended by leafy bracts.
supersonic Having, caused by, or relating to a speed greater than the speed of sound in a given medium, especially air. [Use
ultrasonic if referring to frequencies above human hearing range.]
symmetrical (reciprocal) response Term used to describe the comparative shapes of the boost/cut curves for variable equalizers.
The cut curve exactly mirrors the boost curve.
synchronous A transmission process where the bit rate of the signal is fixed and synchronized to a master clock.
T-1 A digital transmission scheme utilizing two twisted-pair capable of handling a minimum of 24 voice channels. Used for
connecting networks across remote distances.
TCP/IP (transmission control protocol/internet protocol) A set of protocols developed by the Department of Defense in the '70s
to link dissimilar computers across many kinds of networks and LANs. Popular with Ethernet users.
TDIF (Teac digital interface format) Tascam's (Teac) 8-channel digital audio interface to their DA-88 digital multitrack recorder,
using unbalanced signal transmission and a DB-25 type connector.
TDS (time-delay spectrometry) A sound measurement theory and technique developed in 1967 by Richard C. Heyser at the Jet
Propulsion Laboratories of the California Institute of Technology.
TEF (time-energy-frequency) The term adopted to describe the entire spectrum of TDS measurements, including energy-time
curves. Popularized by Richard Heyser through his participation in Synergetic Audio Concepts seminars. Made practical in 1979 by
the Techron division of Crown International - Cal Tech's first TDS licensee, and introduced as the TEF System 10.
third-octave Term referring to frequencies spaced every three octaves apart. For example, the third-octave above 1 kHz is 8 kHz.
Commonly misused to mean one-third octave. While it can be argued that "third" can also mean one of three equal parts, and as
such might be used to correctly describe one part of an octave spit into three equal parts, it is potentially too confusing. The
preferred term is one-third octave.
THX� Lucasfilm, Ltd. term meaning several things: 1) Their audio playback design and certification program for commercial
cinema theaters; 2) Their audio playback specification for home cinema systems; 3) Approved audio/video playback equipment
meeting their standards of quality and performance; and 4) Laserdiscs and VHS tapes mastered by them to meet their quality and
performance standards. The term comes from two sources: George Lucas's first film THX-1138, and a somewhat tongue-in-cheek
reference to Tomlinson Holman's eXperiment, after their original technical director, patentee and creative force behind all the
TIA (Telecommunications Industry Association) Created in 1988 by a merger of the US Telecommunications Suppliers
Association (USTSA) and the EIA's Information and Telecommunications Technologies Group (EIA/ITG). This organization works
with the EIA in developing technical standards and collecting market data for the telecommunication industry.
timbre (pronounced "tambur") 1. The quality of a sound that distinguishes it from other sounds of the same pitch and volume. 2.
Music. The distinctive tone of an instrument or a singing voice.
time 1.a. A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to
the future. b. An interval separating two points on this continuum. c. A number, as of years, days, or minutes, representing such an
interval. d. A similar number representing a specific point on this continuum, reckoned in hours and minutes. 2. Music. a. The
characteristic beat of musical rhythm: three-quarter time. b. The rate of speed at which a piece of music is played; the tempo.
["Time is what keeps everything from happening all at once." unknown source]
tone 1. Music. a. A sound of distinct pitch, quality, and duration; a note. b. The interval of a major second in the diatonic scale; a
whole step. c. A recitational melody in a Gregorian chant. 2.a. The quality or character of sound. b. The characteristic quality or
timbre of a particular instrument or voice.
TOSLINK (Toshiba link) A popular consumer equipment fiber optic interface based upon the S/PDIF protocol, using an
implementation first developed by Toshiba.
transcendental number Mathematics. a. Not capable of being determined by any combination of a finite number of equations with
rational integral coefficients. b. Not expressible as an integer or as the root or quotient of integers. Used of numbers, especially
nonrepeating infinite decimals.
transversal equalizer A multi-band variable equalizer using a tapped audio delay line as the frequency selective element, as
opposed to bandpass filters built from inductors (real or synthetic) and capacitors. The term "transversal filter" does not mean "digital
filter." It is the entire family of filter functions done by means of a tapped delay line. There exists a class of digital filters realized as
transversal filters, using a shift register rather than an analog delay line, with the inputs being numbers rather than analog functions.
truncate To eliminate without round-off some low-order bits, often after performing an arithmetic computation.
TTL (transistor transistor logic) The workhorse digital logic integrated circuit family introduced as a standard product line in 1964.
twisted-pair Standard two conductor copper cable, with insulation extruded over each conductor and twisted together. Usually
operated as a balanced line connection. May be shielded or not.
two-bit Costing or worth 25 cents: a two-bit cigar.
UART (universal asynchronous receiver-transmitter) The device that performs the bidirectional parallel-to-serial data
conversions necessary for the serial transmission of data into and out of a computer.
ULSI (ultra-large-scale integration) A logic device containing a million or more gates.
ultrasonic Of or relating to acoustic frequencies above the range audible to the human ear, or above approximately 20,000 hertz.
Compare with supersonic.
UPS (uninterruptible power supply) A back-up power supply (commonly used with computers) that automatically continues to
supply power when the main AC source fails.
URL (uniform resource locator) A Web address. A consistent method for specifying Internet resources in a way that all Web
browsers understand. For example, "http://www.erinet.com/chulbert/" is the URL for Craig Hulbert Incorporated'ss home page on
the web. The "http" part tells the Web browser what protocol to use, and the remainder of the URL, " www.erinet.com/chulbert/," is
the Internet address.
USB (universal serial bus) A new low-speed (12 Mbits/sec) serial bus that acts like a special purpose local area network.
Proposed by a consortium of Compaq, Digital, IBM, Intel, Microsoft, NEC and Northern Telecom in March of 1995, the intended
purpose is to replace the typical cable ghetto found on most PCs. A USB equipped machine would have only three ports: USB,
monitor, and LAN. The USB port would support 63 devices, and eliminate the need for all specialized parallel, serial, graphics,
modem, sound/game or mouse ports. USB is completely "plug and play," i.e., it detects and configures all devices automatically, and
allows "hot swapping" of devices. See: FireWire for complementary high-speed system.
UV (ultraviolet) Electromagnetic radiation at frequencies higher than visible light yet lower than those of x-rays. Commonly used to
erase EPROMs and in wireless and fiber optic data transmission.
vaporware Refers to either hardware or software that exist only in the minds of the marketeers.
variable-Q equalizer See: proportional-Q equalizer
vector Mathematics. A quantity, such as velocity, completely specified by a magnitude and a direction.
virus A self-replicating program released into a computer system for mischievous reasons. Once triggered by some preprogrammed
event (often time or date related), the results vary from humorous or annoying messages, to the destruction of data or whole
operating systems. Bad bad.
VLSI (very-large-scale integration) Refers to the number of logic gates in an integrated circuit. By today's standards, a VLSI
device could contain up to one million gates.
volatile Refers to a memory device which loses any data it contains when power is removed from the device. Examples would
include static and dynamic RAMs.
volt Abbr. E, also V. The International System unit of electric potential and electromotive force, equal to the difference of electric
potential between two points on a conducting wire carrying a constant current of one ampere when the power dissipated between
the points is one watt. [After Count Alessandro Volta.]
Volta, Count Alessandro (1745-1827) Italian physicist who invented the battery (1800). The volt is named in his honor.
VRML (virtual reality modeling language) A developing standard for describing interactive 3D scenes delivered across the
internet. In short, VRML adds 3D data to the Web. Heavily supported by Silicon Graphics (SGI) workstations, competing with Sun's
Java loaded workstations.
W3 An abbreviation for World Wide Web.
wavelength Symbol (Greek lower-case lambda) The distance between one peak or crest of a sine wave and the next
corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency.
white noise Analogous to white light containing equal amounts of all visible frequencies, white noise contains equal amounts of all
audible frequencies (technically the bandwidth of noise is infinite, but for audio purposes it is limited to just the audio frequencies).
From an energy standpoint white noise has constant power per hertz (also referred to as unit bandwidth), i.e., at every frequency
there is the same amount of power (while pink noise, for instance, has constant power per octave band of frequency). A plot of
white noise power vs. frequency is flat if the measuring device uses the same width filter for all measurements. This is known as a
fixed bandwidth filter. For instance, a fixed bandwidth of 5 Hz is common, i.e., the test equipment measures the amplitude at each
frequency using a filter that is 5 Hz wide. It is 5 Hz wide when measuring 50 Hz or 2 kHz or 9.4 kHz, etc. A plot of white noise
power vs. frequency change is not flat if the measuring device uses a variable width filter. This is known as a fixed percentage
bandwidth filter. A common example of which is 1/3-octave wide, which equals a bandwidth of 23%. This means that for every
frequency measured the bandwidth of the measuring filter changes to 23% of that new center frequency. For example the
measuring bandwidth at 100 Hz is 23 Hz wide, then changes to 230 Hz wide when measuring 1 kHz, and so on. Therefore the plot
of noise power vs. frequency is not flat, but shows a 3 dB rise in amplitude per octave of frequency change. Due to this rising
frequency characteristic, white noise sounds very bright and lacking in low frequencies. [Here's the technical details: noise power is
actually its power density spectrum - a measure of how the noise power contributed by individual frequency components is
distributed over the frequency spectrum. It should be measured in watts/Hz; however it isn't. The accepted practice in noise theory
is to use amplitude-squared as the unit of power (purists justify this by assuming a one-ohm resistor load). For electrical signals this
gives units of volts-squared/Hz, or more commonly expressed as volts/root-Hertz. Note that the denominator gets bigger by the
square root of the increase in frequency. Therefore, for an octave increase (doubling) of frequency, the denominator increases
by the square root of two, which equals 1.414, or 3 dB. In order for the energy to remain constant (as it must if it is to remain white
noise) there has to be an offsetting increase in amplitude (the numerator term) of 3 dB to exactly cancel the 3 dB increase in the
denominator term. Thus the upward 3 dB/octave sloping characteristic of white noise amplitude when measured in constant
percentage increments like 1/3-octave.]
WOM (write-only-memory) Term coined by Signetics in 1972 for their 25000 Series 9046XN Random Access
Write-Only-Memory integrated circuits. Based on SEX (Signetics EXtra secret) processes, these devices employ both enhancement
and depletion mode P-Channel, N-Channel, and NEU-Channel MOS transistors (devices which simultaneously, randomly, or not at
all, enhance or deplete regardless of gate polarity). The world's supply of WOMs was quickly consumed by newly designed airline
baggage-handling equipment, where they are still used today to store the exact real-time location of each bag. WOM production was
suddenly discontinued when it was discovered that the only copy of the mask code had been accidentally filed into a WOM location.
word An ordered set of bits that is the normal unit in which information may be stored, transmitted, or operated upon within a given
computer - commonly 16 or 32 bits.
word clock The synchronizing signal that indicates the sampling frequency or rate of sample words over a digital audio interface.
word length The number of bits in a word.
World Wide Web (WWW and/or W3) A way to present resources and information over the Internet, or according to its inventor
CERN (European Laboratory for Particle Physics), "The World Wide Web (W3) is the universe of network-accessible information,
an embodiment of human knowledge."
WOROM (write-once read-only memory) Systems in which data may be written once, but not erased and rewritten. Usually
refers to CD-ROM technology that can be recorded once only.
write To record data on a medium.
WWW (World Wide Web) See: World Wide Web.
X The electronic symbol for reactance - the imaginary part (don't worry about it) of impedance.
Xilinx� (pronounced zi-links; after xi the 14th letter of the Greek alphabet) Leading manufacturer of field-programmable logic
XLR� Registered trademark of ITT-Cannon. The original model number series for Cannon's 3-pin circular connectors - invented by
them - now an industry generic term.
XOR Acronym for exclusive OR, a type of logic gate where a logic 1 output is based upon A or B inputs being present - but not
Y The electronic symbol for admittance - the inverse of impedance.
Y-connector A three-wire circuit that is star connected. Also spelled wye-connector.
Y/N Software program "yes/no" response prompt. A "Y" or "N" keystroke is expected.
yield The number of devices that work as planned, specified as a percentage of the total number actually fabricated. Normally used
to quantify a run of integrated circuits.
Yt Chemical symbol for yttrium - my absolute favorite element, next to ytterbium.
YUV video The coding process used in CD-I in which the luminance signal (Y) is recorded at full bandwidth on each line and
chroma values (U and V) are recorded at half bandwidth on alternate lines.
Z The electronic symbol for impedance.
Z-transform A mathematical method used to relate coefficients of a digital filter to its frequency response, and to evaluate stability
of the filter. It is equivalent to the Laplace transform of sampled data and is the building block of digital filters.
zap To eradicate all or part of a program or database, sometimes by lightning, sometimes intentionally.
Zyzyyzyski, Zyzeikkel The last name listed in the 1994 Everett and Vicinity, WA telephone directory - really.
ACCUAPI (AccuSoft) AccuSoft Application Program Interface. See API.
Additive Primary Colors (imaging) Red, Green, Blue, which are the 3 colors used to create all other colors when direct, or
transmitted, light is used (as in a video monitor). They are called additive primaries, because when these three colors are
superimposed they produce white.
Anti-Aliasing (imaging) A method of filling in data which has been missed due to under-sampling. In imaging this usually takes on
the process of removing jagged edges by interpolating values in-between pixels of contrast. These methods are most often used to
remove or reduce the stair-stepping artifact found in digital high contrast images.
AOI (image processing) Area Of Interest. An area of interest is a rectangle within an image defined as two points within the
image. Thus, an AOI can be written as (x1,y1)-(x2,y2). Because of its definition all AOI are parallel with the image's axes. See also
API (software) Application Programmer's Interface. The set of routines that make up a library or toolkit. Some times called a
Aspect Ratio (imaging) The proportion of an image's size given in terms of the horizontal length verses the vertical height. An
aspect ratio of 4:3 indicates that the image is 4/3 times as wide as it is high.
Bezier Curve (graphics) A curve created from endpoints and two or more control points that serve as positions for the shape of
the curve. Originated by P. Bezier (~1962) for the use in car body descriptions.
Bit Block Transfer A raster operation that moves a block of bits representing some portion of an image or scene from one location
in the frame buffer to another. Usually written as "bit blt"
Bin (image processing) See histogram.
Bit Block Transfer (Windows) An optimized movement of a large block of computer memory from one location to another. Used
for moving images or sub-images to and from areas of computer memory.
Bit Blt Pronounced "bit blit". See BIT BLock Transfer.
Bitmap (imaging) An image is called a bit map if it contains a value for each of its pixels. This is the opposite of vector images
where a small set of values can generate an object.
Bit Plane (imaging) A hypothetical 2-D plane containing a single bit of memory for each pixel in a image. If each 8-bit pixel is
thought of as a stack of 8 coins, and an image as many rows and columns of these stacked coins then the 3rd bit plane would be the
plane consisting of the 3rd coin from each stack.
Bounding Rectangle (geometry) The smallest rectangle that fits around a given object. In imaging the rectangle is usually
rotationally restricted to be parallel to both image axes.
.BMP (file format extension) Format originator: Microsoft Corporation 16011 NE 36th Way, Box 97917/Redmond, WA
Call-back Function (software) A call-back function is a function that is passed to another function as a parameter. The function
receiving the call-back function can then call this function. This is used to change the behavior of a given routine without knowing
beforehand what it will be expected to do.
Cartesian Coordinates (imaging) The usually 2 dimensional equally spaced grid iron that uniquely assigns every point in the plane,
(one and only one), coordinate pair; (x,y). In imaging each point is usually referred to as a pixel and the x and y values take on
integer values. Most images use the top-left as the (0,0), or origin. See also coordinates.
Chroma-key (image processing) An image blending function which replaces pixels of a specified hue range with pixels from a
second image. This is often referred to the weatherman effect because most weather forecasters use a solid blue or green
background to make it look as if they are standing in front of a huge weather map. It is important to remember that it is the hue that
is used in the blending function and not the intensity or saturation.
C.I.E (color imaging) Commission Internationale de l'Eclairage. (International Commission of Illumination). A standards
organization which provides specifications for the description of device independent color.
Clipboard (Windows) The clipboard is a windows data structure used to exchanged data between applications. It is a common
area where applications and place data and others can access it. These operations are usually referred to as Cut (place data in) and
Paste (take data out).
Closing (image processing) See morphology.
CMY & CMYK Cyan, Magenta, Yellow, (K)black. Computer monitors are additive, but color printers are subtractive. Instead of
combining light from monitor phosphors, printers coat paper with colored pigment which remove specific colors from the illumination
light. CMY is the subtractive color model that corresponds to the additive RGB model. Cyan, magenta, and yellow are the color
complements of red, green, and blue. Due to the difficulties of manufacturing pigments that will produce black when mixed together,
a separate black ink is often used and is referred to as K ('B' is already used for blue).
Color Map (imaging) See Look-Up-Table.
Color Model (imaging) See color space.
Color Space (imaging) A mathematical coordinate system (space) for assigning numerical values to colors. There are many ways
to define such spaces, each with its own benefits and problems. See CMY & CMYK, IHS, HSL, HSV, Lab (L*a*b*), RGB,
Compression (imaging) An image processing method of saving valuable disk and memory space by reducing the amount of space
required to save a digital image. The graphics data is rewritten so that it is represented by a smaller set of data. Not to be confused
with encoding. See also lossless and lossy compression.
Compression Ratio (imaging) The ratio of a file's uncompressed size over its compressed size.
Concave (geometry) A 2 dimensional blob, such as a ROI, on which at least one tangent can be drawn which touches the blob at
two different locations and there is a point on the tangent between the two contacts which does not touch the blob. In simpler words,
if a rubber band could be snugly wrapped around a concave blob there would be places where the rubber band lifts off and therefor
does not touch the blob. Concave is the opposite of convex.
Convex (geometry) A 2 dimensional blob, such as a ROI, on which every tangent that can be drawn touches the blob at a
continuous stretch of the blob's surface with no gaps. In simpler words, if a rubber band could be snugly wrapped around a convex
blob there would be no places where the rubber band lifts off and is not touching the blob. Convex is the opposite of concave.
Convolution (image processing) An image processing operation which can be used to spatially filter an image. A convolution is
defined by a kernel which is a, usually small, matrix of fixed numbers. The size of the kernel, the numbers within it, and a single
normalizer value define the operation that will be applied to the image. The kernel is applied to the image by placing the kernel over
the image to be convolved and sliding it around so that it is centered over every pixel in the original image. At each placement the
numbers (pixel values) from the original image are multiplied by the kernel number which is currently aligned above it. The sum of all
these products is tabulated and divided by the kernel's normalizer. This result is placed into the new image at the position of the
kernels center. The kernel is then translated to the next pixel position and the process repeats until all image pixels have been
processed. As an example a 3x3 kernel holding all '1's with a normalizer of 9 performs a neighborhood averaging operation. Each
pixel in the new image is the average of its 9 neighbors from the original. coordinates A pair of numbers which represent a specific
location in a two-dimensional plane such as an image or on a map. See also absolute, device, Cartesian, polar, relative, screen, and
Crop (imaging) An image processing method of removing the region near the edge of the image, but keeping a central area.
.DCX (file format extension) Format originator: Intel
DDB (Windows) Device Dependent Bitmap. A Window image specification which depends on the capabilities of a specific
graphics display controller. Since a DDB is matched to the current graphics controller, it is fast and easy to display since large
blocks of its memory need only be copied to the controller. See also DIB.
Decompression (imaging) When an image or other digital data set is compressed and stored, it is not usable until it is
decompressed into it original form.
Device Coordinates (imaging) The coordinates of the coordinate system that describe the physical units by which the computer
screen is defined.
Device Dependent (software) Software that was written to work on a specific set of hardware platforms. Since these routines
make use of physical device attributes, that may not exist or that may behave differently on other devices, they will most often not
work on other devices. See device independent and DIB.
Device Driver (software) A set of low-level software routines which work with and control a specific hardware device. The
names and functions are often standardized across many similar devices. This allows higher level software to use the hardware as a
generic device. This frees the higher level software from dealing with the particulars of the specific devices and allows device to be
Device Independent (software) Software or data structures that have been designed specifically to work with or on a wide set of
hardware platforms. See device dependent and DIB.
DIB (Windows) Device Independent Bitmap is a Windows defined image format specification. It is called device independent
because of its straightforward, common-denominator, format. It has all the information that a basic digital image needs and is laid out
in a simple specification that is easy to get at. Its simplicity makes it an ideal format for holding images that need to be shared by
several programs. See also DDB, and the book Programming Windows by Charles Petzold, begin with page 611.
Dilation (image processing) See morphology.
Dithering (imaging) The method of using neighborhoods of actual display pixels to represent one image intensity or color. This
method allows low intensity resolution display devices to simulate higher resolution images. For example, a binary laser printer can
use block patterns to display gray-scale images. See also Half-tone.
DLL (Microsoft Windows) Dynamic Linked Library. A compiled and linked collection of computer functions that are not directly
bound to an executable the way regular libraries are. These libraries are linked at run-time by Windows. Since Windows is in charge
of managing (loading, linking, and removing) the DLLs, they are available to all executables currently running. Thus, each executable
can link to a commonly shared DLL saving memory by avoiding redundant functions from co-existing. DLLs also allow a new level
of modularity by providing a means to modify and update executables without re-linking. All that need be done is copy a new version
of the DLL to the correct disk directory.
DPI (printing) Dots Per Inch. Usually refers to the number of printer dots that can be printed in one inch. Higher value printers will
print sharper images.
Edge (image processing) In an image an edge is a region of contrast or color change. Edges are often useful in machine vision
since optical edges often mark the boundary of physical objects.
Edge detection (image processing) A method of isolating and locating an optical edge in a given digital image.
Edge map (image processing) An edge map is the output of an image processing filter that transforms an image into one where
intensity represents a change in the contrast (optical edge) of the original.
(Eight) 8 Bit Image (digital imaging) An image where each pixel has 8 bits of information in it. An 8-bit pixel can take on one of
256 possible values. There are two common types of 8-bit images: gray scale and indexed color. In gray-scale images each pixel
takes on one of 256 shades of gray and the shades are linearly distributed from 0 (black) to 256 (white). An 8-bit gray-scale image
doesn't require a palette but may have one anyway. An indexed color image is always a palette image. Each pixel is used as an
index into the palette. Thus these images can have up to 256 different colors in them at one time. This includes hues as well as
shades. Indexed 8-bit images are good for low color resolution images that will not need to be processed later on. They are 3x's
smaller than full-color RGB images, but because the pixel values are not linear many image processing algorithms cannot work with
them. They must be promoted to 24 bit first.
8g (AccuSoft term) This indicates 8 bit gray scale. Used to distinguish between 8 bit indexed color (8i) and 8 bit gray-scale. An 8g
DIB image is one in which each pixel in the bitmap is unchanged by its palette when displayed. That is, each palette entry is the
same as its index.
8i (AccuSoft term) This indicates 8 bit indexed color. Used to distinguish between 8 bit gray scale (8g) and 8 bit indexed color. An
8 bit indexed color DIB is one in which each 8 bit pixel value in the bitmap is used as an index to the palette. The palette in turn
dictates with which RGB color the pixel is to be displayed. These images are compact ways of storing color images but are difficult
to process because the bytes which make up the pixel can no longer be ordered with any certainty.
Encoding The manner in which data is stored when uncompressed (binary, ASCII, etc.), how it's packed (e.g. 4-bit pixels may be
packed at a rate of two pixels per byte), and the unique set of symbols used to represent the range of data items. .EPS (file format
extension)Encapsulated Postscript. Format originator: Adobe Systems, Inc.: 1585 Charleston Road Mountain View, CA 94039
Equalize (image processing) An image processing algorithm which redistributes the frequency of image pixel values so that any
given continuous range of values is equally represented. An equalized image has the same number of pixels in the range from 10-20
as it does from 200-210. However, since digital images have quantized intensity values, the range totals are rarely identical but
Erosion (image processing) See morphology.
File Format (software) A specification for holding computer data in a disk file. The format dictates what information is present in
the file and how it is organized within it.
Filter (image processing) An image processing filter is a transform which removes a specified quantity from an image. For
instance a spatial filter removes either high, medium or low spatial frequencies from an image.
(Four) 4 Bit Image (digital imaging) An image file format which allows for 4-bits per pixel. Such an image can contain up to 16
(24) different colors or levels of gray within it at one time.
Frame (imaging) A single picture, usually taken from a collection of images such as in a movie or video stream.
Frame Buffer (imaging hardware) A computer peripheral which is dedicated to storing and sometimes manipulating digital
Frame Processes (image processing) A class of image processing algorithms which operate on a single image at a time.
FX (imaging) See special effects.
Gain & Level (imaging) Gain and level are image processing terms which roughly correspond to the brightness and contrast
control on a television. The gain is the "contrast", and the level is the " brightness" . By changing the level the entire range of pixel
values are linearly shifted brighter or darker. Gain on the other hand linearly stretches or shrinks the intensity range, thus altering the
Gamma Correction (imaging) A non-linear function that is used to correct the inherent non-linearities of cameras and monitors.
The intensity of the luminescent phosphor on the raster display when struck by an electron beam is non-linear. Gamma correction is
an adjustment to pixel intensity values that make up for this inherent non-linearity.
Geometric Transform (image processing) A class of image processing transforms which alter the location of pixels. This class
includes rotates and warps.
.GIF (file format extension) Graphics Interchange File Format. Format originator: CompuServe Inc. 500 Arlington Center
Blvd./Columbus, OH 43220. Uses the LZW compression created by Unisys, which requires special licensing. It is the same as the
LZW compression used in the TIFF file format, except that the bytes are reversed and the string table is upside-down. All GIF files
have a palette. Some GIF files can be interlaced in that the raster lines can appear as every 4 lines, then every 8 lines, then every
other line. This is due to GIF files usually being received from a modem.
GUI Graphical User Interface. A computer-user interface which uses graphical objects and a mouse for user interaction. Microsoft
Windows is one such GUI. Each program that runs under Windows follows similar conventions.
Graphics Library (software) A collection of software routines which work on digital images. Such collections usually contain
routines for drawing various graphical objects such as lines, circles, and rectangles.
Gray Level (imaging) A shade of gray assigned to a pixel. The shades are usually positive integer values taken from the
gray-scale. In an 8-bit image a gray level can have a value from 0 to 255.
Gray Scale (imaging) A range of gray levels. Zero is usually black and higher numbers indicate brighter pixels.
Group III Fax (imaging compression) A CCITT standard for transmission of facsimile data. It can compress black and white
images using a combination of differential, run length and Huffman coding.
Half-tone (imaging) The reproduction of a continuous-tone image on a device which does not directly support continuous output.
This is done by displaying or printing pattern of small dots which from a distance can simulate the desired output color or intensity.
These methods are used extensively in magazines and newspapers.
Handle (software) A handle is used to reference a data object. A handle is a type of pointer but it usually contains, internally, much
more information about the referenced object.
Histogram (imaging) A tabulation of pixel value populations usually displayed as a bar chart where the x-axis represents all the
possible pixel values and the y-axis is the total image count of each given pixel value. That is, a histogram counts how many pixels in
the image have a given intensity value or range of values. Each histogram intensity value or range of values is called a bin. Each bin
contains a positive number which represents the number of pixels in the image that fall within the bin's range. A typical 8-bit
gray-scale histogram contains 256 bins. Each bin has a range of a single intensity values. Thus, bin 0 contains the number of pixels in
the image that have a gray-scale value of 0 or black. Likewise, bin 255 contains the number of white (255) pixels. When the
collection of bins are sorted (0-255) and charted, the graph displays the intensity distributions of all the images pixels.
HSL (color imaging) Hue Saturation, and Lightness. A method of describing any color as a triplet of real values. The hue
represents the color or wavelength of the color. It is sometimes called tone and is what most people think of as color. The hue is
taken from the standard color wheel and is thus calibrated in degrees about the wheel. Saturation is the depth of the color. It states
how gray the color is. It is a real valued parameter from 0.0 to 1.0 with 0.0 indicating full gray and 1.0 representing pure hue. The
lightness is how black or white a color is. It also ranges from 0.0 to 1.0 but with 0.0 representing black and 1.0 white. A lightness of
0.5 is pure hue.
HSV (color imaging) Hue, Saturation, and Value.
Huffman Coding (image compression) A method of encoding symbols that varies the length of the code in proportion to its
information content. Groups of pixels which appear frequently in a image are coded with fewer bits than those of lower occurrence.
IHS(color imaging) Intensity, Hue, and Saturation
Indexed Color Image (imaging) An image where each pixel value is used as an index to a palette for interpretation before it can
be displayed. Such images must, therefore, contain a palette which has been initialized specifically for a given image. The pixel
values are usually 8-bit and the palette 24-bit (8-red, 8-green, and 8-blue). See also eight-bit image.
Image Format (image storage) Refers to the specification under which an image has been saved to disk or in which it resides in
computer memory. There are many commonly used digital image formats in use. Some of the most used are TIFF, DIB, GIF, and
JPEG. The image format specification dictates what image information is present and how it is organized in memory. Many formats
support various sub-formats or 'flavors'.
Image Format Library Replaced by ImageGear. It was able to read and write all of the major and many of the minor image
formats. It also contained a full image display and handling package. See also image format.
Image Processing The general term "image processing" refers to a computer discipline wherein digital images are the main data
object. This type of processing can be broken down into several sub-categories, including: compression, image enhancement, image
filtering, image distortion, image display and coloring, and image editing. See also Machine Vision
Invert Intensity (image processing) An image processing operation where each pixel, one at a time, is subtracted from the
maximum pixel value allowed. This produced a photographic negative of the original.
For an 8-bit image the inverse function is: invert( pix) = 255-pix; For an 8-bit RGB image the function is: invert( Rpix) = 255-Rpix;
invert(Gpix) = 255-Gpix; invert(Bpix) = 255-Bpix;
Jaggies(imaging) A term used to describe the visual appearance of lines and shapes in raster pictures that results from drawing
them using a grid of insufficient spatial resolution.
JPEG (image compression) Joint Photographic Experts Group. A collaborative specification by the CCITT and the ISO for image
compression. JPEG is usually a lossy compression.
.JPG (file format extension) Format originator: Joint Photographics Experts Group
Kernel (image processing) A small matrix of pixels, usually no bigger that 9x9, that is used as an operator during an image
convolution. The kernel is set prior to the convolution in a fashion that will emphasize a particular feature of the image. Kernels are
often used as spatial filters, each one tuned to a specific spatial frequency that the convolution is intended to highlight. See also
Lempel Ziff Welch (data compression) A dictionary based image compression method with lossless performance which results in
fair compression ratios. Must files can be compressed around 2:1.
Level (imaging) See gain & level.
Library (software) A collection of software functions that can be called upon by a higher level program. Most libraries are
collections of similar routines such as those used for graphical or image processing. See also DLL.
Look-Up-Table (computer hardware) A look-up-table or LUT is a continuous block of computer memory that is initialized in
such a fashion that it can be used to compute the values of a function of one variable. The LUT is set up so that the functions
variable is used as an address or offset into the memory block. The value that resides at this memory location becomes the functions
output. Because the LUT values need only be initialized once, LUTs are very useful for image processing because of their inherent
high speed. LUT[pixel_value] = f( pixel_value ) LUTs come in various widths, usually in units of bits. An nxm bit LUT has 2n
addresses or 256 stored values. Each value is 2m bits wide. If the second dimension is left off it can be assumed to be equal to the
first. In gray-scale image processing LUTs are commonly 8x8, and the bit widths are usually assumed. A linear LUT, sometimes
called a NOP LUT or pass through, is a LUT that has been initialized to output the same values as the input.
NOP_LUT[pixel_value ] = pixel_value. See also Palette.
Lossless (image compression) A method of image compression where there is no loss in quality when the image is
uncompressed. The uncompressed image is mathematically identical to its original. Lossless compression is usually lower in
compression ratio than lossy compression.
Lossy (image compression) A method of image compression where some image quality is sacrificed in exchange for higher
compression ratios. The amount of quality degradation depends on the compression algorithm used and a user selected quality
LUT (computer) Look-Up-Table. See Look-Up-Table
LUT Transform (image processing) A LUT transform is an image processing method that takes an image and passes each pixel,
one at a time, through a pre-set LUT. Thus, each new pixel is a function of one and only one pixel from the original image and is
arranged in the same location. Any image processing algorithm that transforms a single pixel into another single pixel, both from the
same location, can be performed quickly using a LUT. Square_root_LUT[ pixel_value ] = sqrt( pixel_value ) See Look-Up Table
LZW (data compression) Lempel Ziff Welch . See Lempel Ziff Welch
Machine Vision A sub-discipline of artificial intelligence which uses video cameras or scanners to obtain information about a given
environment. Machine vision processes extract information from digital images about objects in the image. This is the opposite of
computer graphics which takes various data describing objects in and produces an output image. Machine vision takes an image in
and outputs some level of description about the objects in it, (i.e. color, size, brightness). See also Image Processing
Matrix Operation (image processing) See neighborhood process.
Median Filter (image processing) An image spatial filtering operation based on an input pixel and its 8 neighbors. The resulting
value is the median (5th from the sorted values). A median filter is often used to reduce spike or speckling noise from a gray-scale
image. It has the advantage over convolution smoothing in that it better preserves edges.
Morphing (image processing) An imaging process where one image is gradually transformed into a second image, where both
images previously exist. The result is a sequence of in-between images which when played sequentially, as in a film loop show, give
the appearance of the starting image being transformed to the second image. Morphing is made up of a collection of image
processing algorithms. The two major groups are: warps and blends. Not to be confused with morphology.
Morphology (image processing) A neighborhood image processing algorithm similar to image convolution except that Boolean
logic is applied instead of arithmetic. There are two types of morphology, binary and gray-scale. Both have similar operation but are
carried out differently because of the data width. The four major operations are; erosion, dilation, opening, and closing. Erode - a
filter which tends to make bright objects smaller. Dilation - a filter which tends to make bright objects larger. Opening - an erosion
followed by a dilation. Closing - a dilation followed by an erosion. Not to be confused with morphing.
MPEG(image compression) Motion Pictures Experts Group. An ISO specification of the compression of digital-broadcast quality
full-motion video with its sound track.
Neighborhood Process (image processing) A class of image processing routines which works on neighborhoods of pixels at a
time. Each pixel in the new image is computed as a function of the neighborhood of the pixel from the original pixel. The
neighborhood ID is defined by a kernel which is set once for each image to be processed. See also point process.
One (1) bit image (digital imaging) An image comprised of pixels that contain only a single bit of information. Each pixel is either
on or off. Normally, "on" is white and "off" is black.
Opening (image processing) See morphology.
Overlay (imaging) An image or sub-image that can be placed over a given image. The pixels from the original image are not
altered but the overlay can be viewed as if they had been. Usually used to place temporary text and annotation marks such as
arrows on a image.
Packed Bits (imaging) A binary image is usually stored in computer memory 8 pixels per byte. When this is the case each byte is
referred to as being filled with packed bits This saves space but makes reading and writing any individual pixel somewhat harder
since most computers cannot directly access memory in chunks smaller than a byte.
Palette (digital imaging) A digital images palette is a collection of 3 look-up-tables or "LUT"s which are used to define a given
pixels display color. One LUT for red, one for green and one for blue. The number of entries in the LUTs depends on the width in
bits of the image's pixels.
A palette image is one which requires its palette in order to be displayed in a fashion which makes sense to the viewer. This is often
the case of color 8-bit images. Without a palette describing what color each pixel is to be displayed with, such an image would most
likely be displayed as randomly selected noise.
A gray-scale palette is one where each of the 3 LUTs are linear. That is, the output is whatever is input to them. Since each color
component (R, G, B) will be an equal value, any pixels input to them will be displayed in a varying shade of gray.
See also Look-Up-Table
Pattern recognition (imaging) A sub-discipline of machine vision where images are searched for specific patterns. Optical
character recognition or "OCR" is one type of pattern recognition, where images are searched for the letters of the alphabet.
.PCX (file format extension)
Format originator: ZSoft Corp.
450 Franklin Road Suite 100
Marietta, GA 30067
Pixel (imaging) Short for the mostly obsolete term PIcture (X) ELement. This is the most fundamental element of a digital image.
A digital image is made up of rows and columns of points of light. Each indivisible point of light is called a pixel. Each pixel in an
image is addressed by its column (x) and its row (y) usually written as the coordinate pair (x,y). An 8-bit pixel can take on one of
256 values. A 24-bit pixel has 3, 8-bit components for each of the primary colors, red, green, and blue.
Point Process (image processing) A class of image processing transforms where every pixel is taken, one at a time, from a
provided image and mathematically transformed into a new value with no input from any other pixel in them image. A point process
is a degenerative neighborhood process where the kernel is a matrix of pixels which is 1x1 or in other words a single pixel.
Polar Coordinates (imaging) An alternative to the usual Cartesian method of addressing image pixels. Polar coordinates use the
coordinate pair, angle and radius from an origin instead of column and row.
Posterize (imaging) A special effect that decreases the number of colors or gray-scales in an image. The default image pixel
contains 256 levels of gray or 256 levels of red, green, and blue. Using this effect reduces these numbers.
Pseudocolor (image processing) A method of assigning color to ranges of a gray-scale image's pixel values. Most often used to
highlight subtle contrast gradients or for visually quantifying pixel values. The applied color usually has no correspondence to the
original, physical imaged scene. The colors are used only as a guide or highlight.
Raster (imaging) A term which for historical reasons is used to describe a single row of a digital image. Thus a raster image is one
that is made up of rows of pixels. This is opposed to vector images, where an image is made up of a list of polygon nodes. A raster
is sometimes called a scan-line.
Relative coordinates refer to position, as identified as the distance from a local origin.
Render (imaging) The process of displaying an image. The final and actual displayed image is said to have been rendered.
Resolution (imaging) There are two types of resolution in digital images; spatial and intensity. Spatial resolution is the number of
pixels per unit of length along the x and y axis. Intensity resolution is the number of quantized levels that a pixel can have.
RGB (imaging) Red, Green, Blue. A triplet of numeric values which are used to describe a color.
RGBQUAD Red, Green, Blue, Quad. A set of four numbers used to describe a color. The forth number is always set to zero. By
using this strange and seemingly wasteful color value an efficient color LUT or palette can be created. It is more efficient to use
such a LUT because most computers find multiplying by 4 easier then by 3, as would be the case in an RGB triplet.
ROI (AccuSoft image processing) Region Of Interest. A region of interest or ROI is a specification and date structure which
allows for the definition of arbitrarily shaped regions within a given image, often called sub-images. A ROI can be thought of as a
place holder which remembers a location within an image. ROIs can be one of several types, each defined in a manor which makes
sense for its type. At any one time a ROI is either a rectangle (also called an AOI), square, circle, or a segment list. A rectangle is
defined by any two points in the image. From these two points one and only one rectangle can be drawn. A square is defines by a
single point and a single length. A circle by its center and radius. A segment list is an arbitrary list of triplets (x,y,xlen); a single point
and a length to the right.
Every point in an image is either inside or outside of a given ROI.
Most image processing functions in this package work only within a given ROI. The ROI can encompass the entire image.
See also AOI.
Scan line (imaging) See Raster.
Screen Coordinates (imaging) Screen coordinates are those of the actual graphics display controller. The origin is almost always
at the upper left hand corner of the display.
See also Coordinates.
Segment (imaging) A contiguous section of a raster line. Defined in physical coordinates by the triplet of its left most point and
length (x, y, length).
Shear (image processing) A skew is image distortion which most often occurs when a scanner is sampling am image and the
image slides to either side before the scan is complete. This has the effect of transforming squares into rhombuses.
Special Effects (image processing) Any image processing transform which is applied mostly for its artistic value.
Stretch Intensity (image processing) An image processing method which takes a given image and assures that the intensity
distribution fills the entire range of possible values. An 8-bit image that has stretched will always have at least one pixel with a value
of zero and one of 255. The term comes from the before and after histogram of the given image. A stretch operation will linearly
stretch a histogram so that is ranges from the minimum pixel value to the maximum pixel value.
.TGA (file format extension)
Format originator: Truevision, Inc.
7340 Shadeland Station
Indianapolis, IN 46255
TIFF (file format) Tagged Image File Format. See Complete Format Reference for more information.
.TIF (file format extension)
Format originator: Aldus Corp and Microsoft Corp
411 First Ave South 16011 NE 36th Way
Seattle, WA 98104 Redmond, WA 98073
Thumbnail (imaging) A small copy of an image. Usually used to display many images on the screen at once.
Transform (image processing) An algorithm which takes an image, alters it, and outputs a new image. Sometimes written as
See also Point transform, Neighborhood transform, and Geometric.
Triplet (digital imaging) Three numbers which when used together represent a single quantity or location such as RGB or (x,y,z).
Twenty-Four (24)- bit image (digital imaging) A 24-bit image contains pixels which are made up of RGB triplets.
Video Stream (video) A sequence of still images that are transmitted and displayed in synchronous order given the appearance of
Warp (image processing) A geometric image processing routine which distorts an image by spatially compressing and stretching
.WMF (file format extension)
Format originator: Microsoft Corp
16011 NE 36th Way
Redmond, WA 98073
World Coordinates The real valued coordinates that make sense for the object, treating it as if it really exists. Thus, the world
coordinates of a house on a map would be in miles or longitude and latitude. This is the opposite of screen, device or model
.WPG (file format extension) Format originator: Word Perfect Corp
(x,y) A mathematical method for referring to a pixel from a digital image. Since most digital images are maintained as a Cartesian
matrix of pixels, each pixel has a unique address which can be described as an x or horizontal displacement from the origin and a y
or vertical displacement from the origin. See also coordinates.
Xform Short-hand for transform.
YIQ (color imaging) (Y)luminance, (I), (Q). YIQ is the color model used for U.S. commercial television. It was designed to be
backwards compatible with the old black and white television sets. "Y" or luminance is a weighted average of the red, green, and
blue which give more weight to red and green than to blue. The I and Q contain the color components. Together they are called the
(Z) A mathematical method for referring to a pixel's intensity from a digital image. Thus an image can be written as: I(x,y)=z
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