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Select the first letter of the word from the list below to jump to
appropriate section of the glossary.
Because of the large size this glossary it has been cut into sections as
follows:
- AC
Alternating Current. The standard electrical power available from US
power outlets. The current flow alternates direction, usually 60 times per
second. See also DC.- AC-3
See Dolby Digital- A/D
Analog to Digital. Refers to the conversion of analog sound or video to
digital during storage, manipulation, or recording.- AES
The Audio Engineering Society. A professional audio society with members
throughout the professional, manufacturing, and educational community.
They publish the JAES (Journal of the Audio Engineering Society). - AFM
Audio Frequency Modulated. - AM
Amplitude Modulation. A radio transmission technique that conveys data
by varying the strength of a high-frequency carrier signal. AM radio,
while capable of being high-fidelity, is rarely configured that way. - ATRAC
Adaptive Transform Acoustic Coding. The low-bit-rate data-reduction
encoding process used in the Sony-developed minidisk system. See also
Data reduction. - ATV
Advanced Television. The new digital-video spectrum assigned to handle
HDTV and standard-resolution formats. The space allocated for one HDTV
signal can also be used to handle several standard-resolution programs. - A/V Receiver
See Receiver. - Acoustic-Suspension Speaker
A sealed-box system that makes use of the air behind a woofer to control
cone movement. Originally conceived by Harry Olson many decades ago, this
woofer system design was refined and put into use by Edgar Villchur,
making it the foundation of his company, Acoustic Research, in the 1950s
and '60s. See also
Infinite Baffle. - Active Crossover
A powered electronic network that divides up the frequency constituents
of an audio signal (bass, midrange, and treble) before it is amplified and
sent to the various drivers in a speaker system. While active crossovers
are often contained within sub-woofer enclosures along with the bass
driver(s), those that work with multiway systems may also be outboard
mounted. - Ambience
As a general audio term, ambience is the background-sound quality of a
listening room, surround processor, and/or recording. The ambience of a
recording is what gives it space and a sense of realism. It is the sound
of the "hall" or recording studio itself. The recording engineer often
synthetically adds ambience if the recording environment was not
reverberant enough to do the job naturally. See also
Sound Field. - Ambience Extraction
The use of left-minus-right dematrixing and signal rerouting and
(sometimes) delaying techniques to send hall ambience or reverberation
already present on a stereophonic audio or video recording to surround
speakers to simulate a concert-hall effect. See also
Matrixing; Dolby
Surround Sound. - Ambience Synthesis
The routing of delayed, processor-modified or processor-created ambience
signals, in addition to those already on a recording (even one that is
monophonic), to surround speakers to simulate a concert-hall effect.
See also DSP.- Ambisonic Recording
A surround-sound recording technique practiced by Nimbus, Hyperion, and
a few other companies. See also
Calrec Soundfield Microphone. - Amp
Ampere. A measurement of electrical current. This term is also sometimes
used as an abbreviation for amplifier.- Amplifier
A device (sometimes called an "amp") for boosting the amplitude of a
given electrical signal; ideally, without affecting its quality. - Analog Signal
The exact electrical or mechanical replica of any particular audio or
video input to a system. Any signal originally produced by non-digital
recording equipment, even though the finished item may be a digital audio
disc or a digitally compressed video signal. Note that no matter what the
recording medium, the sound or picture we ultimately experience is analog.
We live in a subjectively analog world.- Analog Videodisc
See LV. - Anamorphic
In video and film, a wide-screen process of recording images so that
each frame is horizontally compressed ("squeezed") on a videodisc or strip
of film. During playback via a theater projector (by means of a special
lens), from a disc player (done electronically), or within a TV set (also
done electronically), the image is reciprocally expanded to restore its
shape to normal. Anamorphic expansion can best be accomplished in the
video realm if the playback monitor is a wide-screen model. The best-known
anamorphic film process is CinemaScope, which applies an approximate 2:1
compression-2: 1 expansion. - Anechoic
Without echo. An anechoic situation exists when acoustic signals
produced by a source are not reflected back to it or anywhere else. Room
reverberation does not exist under anechoic conditions. Most recordings
are not recorded anechoically, because the sonic signature of the
environment is a part of what the engineer will want to record. Note that
because the ground is reflective, a true anechoic condition would only
exist fairly high up off the ground and outdoors. A skydiver experiences
anechoic conditions. See also
Ambience. - Antenna
A device for receiving radio-frequency (RF) signals from a source and
making them strong enough to be handled by a tuner, television set,
satellite receiver, etc. - Articulation
As commonly used to describe recordings, articulation refers to the
clarity and inner detail of the assorted instruments of a recorded
ensemble. Regarding hardware, it refers to the ability to delineate the
material on recordings.- Aspect Ratio
The width-to-height ratio of a television screen, letterboxed image on
that screen, or motion-picture theater screen. Typical TV sets have a
1.33:1(4:3) ratio, while wide-screen versions have a 1.77:1 (16:9) ratio.
Modern motion-picture ratios run the gamut from 1.66:1 to 2.76:1, and
these will often be the ratios used when images are letterboxed to a
conventional-ratio TV screen.- Attenuate
To reduce in amplitude- Audiophile
A person who has an enduring interest in audio.- Azimuth
In audio, the angle between the magnetic gap of a tape head and the
direction of travel of the tape, ideally 90 degrees. In video (VCR) use,
it involves the angle at which a tape-head gap intersects the scan
movement. This angle between the direction of the nature of the signals
and the positioning of the various video and hi-fi audio heads.
- Bandwidth
A Range of frequencies. With audio recordings,bandwidth refers to the
sound system's or recording's ability to capture the frequency-response
range of the ensemble and soloists. With regard to a home playback system,
it refers to the "audible" bandwidth the system should be able to
reproduce, usually from 20 or 30 Hz up to 15 or 20 kHz. See also
Frequency.- Bass
The low-frequency range of the audible spectrum, running from 20 Hz (or
a bit lower) up to anywhere from 200 to 500 Hz, a total of four octaves or
more.- Bass Reflex
A speaker-box design that makes use of a port or drone cone that,
according to parameters outlined by Thiele and Small more than twenty
years ago, allows the rear radiation of a woofer cone to reinforce the
output of the front, extending and smoothing low-range response. At
frequencies below the reinforcement range, there will be a sharp cutoff as
the port signal goes back out of phase with the front.- Betamax
Also called Beta; this is the original home video recorder pioneered by
Sony in 1975. More advanced versions are SuperBeta and ED Beta. (The
latter is not record/play-back-compatible with SuperBeta or any of the
earlier versions.) While some Beta recorders are still available, the JVC-promoted
VHS system has become the dominant format for everyday home video
recording. See also ED Beta;
VHS.- Biamping
Using separate amplifiers to power the crossover-separated drivers in a
speaker system. When a powered subwoofer is added to a system, the latter
automatically becomes biamped, with the satellites separately amplified
from the subwoofer. With the right speakers, biamping can boost the output
capabilities of a sound system considerably.- Bias
An inaudible, high-frequency signal combined with an audio signal
recorded on analog tape to magnetize it properly and reduce distortion.
The factors that determine a particular bias level and frequency are the
tape-head gap, the tape formulation, and the recording speed. Ordinarily,
increasing the bias level will lower distortion at the expense of a bit
more noise and reduced high-frequency response. Reducing the bias level
will lower the noise floor and flatten out the high end a bit, but at the
expense of higher distortion. This tradeoff does not exist with digital
tape recorders.- Bipole Loudspeaker
A speaker system with drivers facing front and rear that are wired in
phase. Because of this, their signals do not generate out-of-phase
cancellation effects, and side radiation is not radically attenuated.
Bipoles should be placed away from the front wall so that their
rear-facing signals can be properly reflected. See also
Dipole.- Bit
An abbreviation of "binary digit:' A bit is a single digit in a binary
number. See also Byte.- Bitstream Processing
This form of digital processing is used in most of the new compact-disc
and laservideo players and involves sampling at extremely high rates (also
called single bit, MASH, pulse-width modulation, pulse-density modulation,
etc.). While bitstream processing reduces low-level distortion, its main
advantage is cost savings for the manufacturer-and hopefully you.- Blend
When used in reference to audio recordings or playback systems, blend
relates to the smooth interaction of assorted instruments or singers
within a recorded ensemble.- Boston Audio Society
The oldest national audio hobby society in the United States, with
membership from around the country and world; they publish an influential
journal.- Boundary Effects
The wave cancellation and reinforcement effects that exist when audio
signals interact with a room, its furnishings, and even the speaker
cabinet itself. In a recording studio, boundary effects will color the
sound that is received by the microphones. Sometimes this enhances the
sound; sometimes it does not. See also
Comb Filtering.- Bright
A subjective term to describe a recording that has a lot of audible
high-frequency energy.- Byte
A byte is the number of bits necessary to encode one character of
information in any given computer system, including digital video and
audio systems.
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- CAV
Constant Angular Velocity. CAV discs rotate at the same speed throughout
their playing time. A feature of "standard-play" laser videodiscs, CAV
allows sharp and steady freeze-frame and slow- and fast-motion video (but
not audio) playback with standard laser-video players. A major
disadvantage of CAV videodiscs is their short playback time. Compare
CLV.- CD
Compact Disc.- CD+G
Compact Disc, plus Graphics. This format stores still images, graphics,
and textual material in addition to audio. A special player and decoder
are required to enjoy this format.- CD-I
Compact Disc, Interactive. This format stores video, graphics, text, and
audio, with the user in control of the way this material is displayed. A
special player/decoder and TV monitor are required to enjoy this format.- CEDIA
Custom Electronic Design and Installation Association. A national dealer
organization that requires its members to have at least two years
experience and be licensed and insured. While not exactly a degree in home
audio-video, CEDIA certification at least means that a dealer has some
basic knowledge about audio and video. However, I have seen installations
by CEDIA members that were much less effective than they could have been,
probably because the customer was more interested in visual aesthetics
than performance.- CLV
Constant Linear Velocity. CLV discs rotate at different speeds during
their playback time, running fast at the beginning and slowing down as
they play along. "Extended play" videodiscs, CDs, and DVDs are all made in
this format. The primary advantage of CLV discs is their extended playback
time, because full use is made of the available linear space on the disc.
The main disadvantage of CLV analog laser videodiscs is their inability to
display sharp and steady freeze-frame and slow- and fast-motion video with
conventional laser-video players. Compare
CAV.- CRT
Cathode Ray Tube. The picture-producing part of a television set. See
also Direct-view television set; Projection television set; LCD.- CX
An audio noise reduction process developed by Columbia for use in LP
records and FM radio. Not particularly successful at first, it was later
successfully used with LV discs.- Cables
The shielded copper or fiber-optic interconnecting wires used to connect
audio or video components, although unshielded speaker wire is sometimes
included in this category.- Calrec Soundfield Microphone
A specialized, four-capsule, four-channel, coincident-pickup microphone
that was specifically designed for Ambisonic recording. The Calrec unit is
also a superb stereo microphone and has the additional advantage of being
remotely adjustable for pickup pattern, making it easier for a recording
technician to adjust for best frequency response and sound-stage imaging.- Capacitance
In active or passive AC circuits, a form of frequency-dependent
resistance produced by a capacitor. A capacitor will block DC and will,
depending on its design (its capacitance), let higher frequencies pass
through at differing levels of attenuation, with very high frequencies
often not affected at all.- Capstan
A rotating, usually metal, shaft in a tape recorder which, in
conjunction with the rubberized pinch roller, pulls the tape across the
heads. A dual-capstan recorder has capstans at each end of the head block
for more uniform tape movement.- Cardioid Microphone
A microphone designed for picking up sounds mainly from the front and
sides, with little sensitivity to sounds toward the rear. The pickup
pattern is heart-shaped-thus the name. Cardioid pickup patterns tend to be
frequency dependent, making it necessary to carefully place and aim them
for good balance. Design variants include the hyper-cardioid and super-cardioid,
which have less sensitivity to the side and somewhat more sensitivity to
the rear.- Cartridge
In a phonograph, the device that converts the mechanical output of the
stylus to an electrical signal for the preamplifier.- Cassette
A self-contained tape storage and playback device,
designed to be used with an audio or videocassette tape recorder.- Center Channel
In A/V systems, this is the so-called "dialogue channel" that is located
between the left and right main speakers. However, in most video
applications, it does much more than reproduce dialogue. In audio-only
recordings-which are given Dolby encoding-this channel can add central
focus, particularly when you are sitting away from the central axis. While
in the Pro Logic version it is derived" from the identical left and right
signals, with Dolby Digital and DTS Digital Surround, the center channel
is a discrete source. See also
Dolby Digital; Dolby Pro
Logic; DTS;
Sweet spot.- Channel
In audio, a distinct path for a signal that is being recorded or played
back. Standard stereo has two channels. Pro Logic-decoded audio still has
two, but they carry two additional "matrixed" channels. Dolby Digital and
DTS audio have five full-range channels and a subwoofer channel. In video,
a signal transmitted at a particular frequency.- Channel Block
A feature on some television sets that allows parents to make it
impossible for children to watch undesirable programs.- Channel Separation
In audio, a measurement of the amount of leakage between the various
channels in a multi-channel installation, specified in dB. While a higher
number is better, anything greater than 20 dB (a ratio of 100:1) will be
adequate for full stereo separation. See also
Cross-Talk.- Chroma-Differential Gain
In video, a measure of how color saturation varies with scene
brightness.- Chroma-Differential Phase
In video, a measure of how color hue varies with scene brightness.- Chroma Level
In video, a measure of color saturation.- Chroma Phase
In video, a measure of color hue, usually adjustable with the tint
control on a TV set.- Chrominance
The color component of a modern television signal.- Class-A Amplifier
A design in which the output devices of the amplifier conduct current
all of the time. These amps have very low distortion but also tend to run
hot and normally have fairly low maximum power outputs.- Class-AB Amplifier
Much more common-and cheaper-than the Class-A type, the output devices
of this amp design are set to conduct current only part of the time. While
exhibiting more measurable distortion than the Class-A design, the
Class-AB amplifier's distortion will still be inaudible, and the amp will
run cooler, produce more power, and cost far less.- Clipping
In audio, the result of an analog signal's being overdriven to the
extent that its peak levels cannot be accommodated, and therefore are
"clipped" off from the audible signal. Typical in smaller amplifiers, it
is the most audible of common electronic distortions.- Closed-Loop Drive
A tape-recorder drive system in which the tape is pulled by dual
capstans on either side of the heads. The result is a very uniform tension
and less wow, flutter, and scrape-induced distortion- Coincident-Microphone
Recording
A technique whereby two directional microphones (one for each channel)
are located very close to each other and aimed at specific sections of the
ensemble to be recorded. This is said to keep timing differences as well
as phase and comb-filtering effects to a minimum. Also called Intensity
stereo.- Coloration
In audio, a subjective term to describe levels of audible distortion.- Color Noise
The irregular, grainy characteristic that appears in large color areas
on all video pictures. The level of noise will vary, depending on the
quality of the TV set, the quality of the playback device, and the quality
of the source material.- Color Temperature
A measure of the relative warmth or coolness of a television picture;
most often stated in degrees Kelvin. Warm pictures display a reddish cast;
cool pictures, bluish. While NTSC specifications call for a certain
standard, individual viewers (and manufacturers) often have ideas of their
own regarding what looks right.- Comb Filter: Video
A circuit that separates chrominance and luminance signals in a
television set or laser-video player to control interference. In many
sets, it is digitally implemented. It is superior to the simple "notch"
filters found in older and cheaper sets.- Comb Filtering: Audio
The result of two audio signals interacting in such a way that their
combined outputs cause the frequency response to become more irregular and
choppy appearing-like the teeth of a comb. This can happen when the
outputs of two speaker systems (or even speaker drivers with overlapping
outputs within the same system) reach the listener's ears at slightly
different times. The effect is rarely detrimental unless the alternating
peaks and dips are widely spaced. Wall reflections combining with the main
signals also cause comb-filtering effects, although the result here is
usually an enhanced sense of spaciousness. Indeed, at higher frequencies,
comb-filtering effects are usually not unpleasant if the speaker systems
are wide-dispersion models and listening is done in the reverberant field.
During recording, the comb-filtering effects of widely spaced microphones
can be measurably similar to what is reproduced by speakers, but the
result may be subjectively more disturbing. Microphone comb filtering is
similar to what is sometimes intentionally applied electrically to a
monophonic signal to create a pseudo-stereo effect. See also
Diffraction.- Combi Player
An LV or DVD player that can play a variety of audio and video
recordings.- Component Input/Output
High-grade video connection found on some data-grade and high-end
monitors and line doublers. These allow suitable input sources to deliver
even better video performance than an S-Video hookup. See also
RGB Input- Compression
In radio transmissions, the process of making the louder passages a bit
quieter (and sometimes, making the quiet ones a bit louder) in order to
reduce background noise and increase the effective range of the station.
In tape recording, compression is used to mask background noise during the
recording process. During playback, a mirror image expansion of the signal
will result in the original dynamics being reproduced-minus the background
noise. See also Dolby;
DBX.- Crossover Network
The circuit that routes the proper electrical signals (highs, midrange,
bass) to the various drivers in a loudspeaker system (if it is a passive
design) and to the various amplifiers in a bitmapped system (if it is an
active design). See also
Active Crossover;
Passive Crossover.- Cross-Talk
In audio, the leakage of a signal from one channel of a system to
another. A system with low cross-talk will have good separation between
channels. In a stereo audio program, a separation of 20 dB (100:1) should
be adequate, although in some professional applications a level of up to
60 dB may be required. In video recorders and disc players, the leakage of
a signal from one track to an adjacent track.- Current
The flow of electricity through a conductor. See also
AC;
DC.- Curve
In audio, the representation of frequency over a given range, in
relation to a fixed standard of amplitude.
- D/A
Digital to Analog. Refers to conversion of digital material back to
analog during the playback process.- DAC
Digital-to-Analog Converter. The circuit that changes binary digital
data back to an equivalent analog form so that it can be handled by
conventional amplifiers, speakers, or TV monitors.- DAT
Digital Audio Tape. DAT recorders, which use a magnetically coded PCM
system rather than an optically read one like the compact disc, are
divided into two types: RDAT, which has its tape heads attached to a
rotating drum to keep linear tape speeds low (the heads are similar to but
smaller than those used on video recorders), and SDAT, which uses
stationary heads and requires great quantities of tape running at high
speed.- dB
One-tenth of a Bel. Named in part after Alexander Graham Bell (hence the
capital B) and used in both audio and video applications, the number of
Bels is the common logarithm of the ratio of two powers. If two powers
differ by 1 Bel, the greater one will be 10 times the other. A 100-watt
amplifier is 1 Bel, or 10 dB, higher in output than a 10-watt unit.
Decibels are ratios, not fixed quantities. While used to describe both
video and audio phenomenon, the more common popular use involves the
latter. For example, it is said that an individual can usually hear volume
changes in the neighborhood of 1 dB, depending on the bandwidth of the
manipulated signal. When measuring audio signal-to-noise ratios, the
difference between the quietest and loudest sounds is stated in dB. With
some kinds of equipment, such as microphones, analog tape recorders, or LP
playback systems, the measurement is "weighted" as to audibility, because
the ear is more sensitive to some frequencies than to others. Two common
corrections for hearing characteristics are the A-weighted and the
somewhat more rigorous C-weighted scales, indicated as dBA or dBC,
respectively. See also
Signal-to-noise ratio.- DBS
Direct-Broadcast Satellite.- dbx noise reduction
A system making use of complementary compression and expansion
techniques to reduce background noise in analog tape and MTS video
systems. It was also used for a limited time in some LP recordings and FM
radio transmissions.- DC
Direct Current. Electrical energy that flows in one direction only. DC
is blocked by capacitance, restrained by resistance, and unaffected by
inductance. - DCC
See Digital
Compact Cassette.- DDD
Digital/Digital/Digital. A designation found on some CDs, indicating
that the pro-gram was recorded and edited digitally, before being
transferred to the final digital format.- DPL
See Dolby Pro Logic- DSP
Digital Signal Processing. Used in both audio and video. In audio
playback systems, it is most often used with surround-sound synthesizers
to simulate hall, club, or studio ambience. However, it is also used in
equalizers and filters, and versions of it are also employed to enhance
material produced by Dolby Surround decoders. In video, DSP is used in
everything from comb filters to MPEG data compression to line-doubling
circuits-with the goal of enhancing picture quality.- DTS
Digital Theater Systems. A discrete, 5.1-channel format designed
originally for motion-picture use. It is the main competitor of Dolby
Digital. See also Dolby
Digital.- DVD
Digital Video (or Versatile) Disc. The CD-sized, digital laser-video
format that is replacing the old analog laser-video system and may replace
the CD as an advanced surround-sound audio-only format.- DVT
Digital Video Tape.- Damping: electrical
Also called "damping factor," a measurement of a power amplifier's
ability to control the motion of a speaker diaphragm after the signal
drops to zero. Directly related to the amplifier's output impedance.- Damping:mechanical
The mechanical resistance that is applied to a speaker diaphragm to keep
it from resonating after the input signal drops to zero. Also applicable
to a phonograph stylus.- D'Appolito speaker
configuration
In this arrangement, three speaker drivers are stacked vertically, with
the tweeter sandwiched between two woofer and/or midrange units. This
controls vertical dispersion and crossover lobbing for less ceiling and
floor bounce, and it often improves focus and clarity. Most
THX speakers follow a variant of this design. - Data reduction
In digital video and audio transmission or storage systems, a process
that eliminates nonvisible or nonaudible aspects of pictures or sound that
are not ordinarily perceived because of "masking," allowing a much higher
storage density. Data reduction-sometimes called lossy compression-is not
the same as data compression. The latter allows the compressed information
to be restored to its original status; the former permanently eliminates
material that cannot be detected by eye or ear. See also
Compression; Masking;
PCM.- De-emphasis
A form of equalization used in both analog FM tuners and CD players to
reduce noise and distortion in program material that has received
pre-emphasis.- Delay Line
An electrical circuit designed to delay the output of a given input
signal a fixed amount, usually for the purpose of adding a synthesized
ambience to the program. This is done in the studio to add artificial
reverb to a program and can also be done at home with a surround-sound
processor. Dolby Surround also adds delay to help separate the
surround-channel sound from that of the main channels.- Dematrixing
See Matrixing.- Depth
In the context of sound reproduction, depth refers mostly to the ability
of a recording or sound system to project a sense of front-to-back
distance within an ensemble or the sound stage. It may also refer to a
sense of depth within the recording environment itself, especially with
Dolby-encoded material. See also Envelopment.- Derived center channel
See Dolby Surround;
Matrixing.- Diffraction
The deflection of a sound wave by an obstacle in its path. Its
wavelength must be short in relation to the size of the obstacle if the
effect is to be significant. With loud-speaker playback situations,
diffraction effects often manifest themselves as comb-filtering or phase
anomalies, most of which are inaudible at normal listening distances.- Diffuse sounding
An undesirable quality in a recording or improperly positioned speakers
that results in an unrealistically spread-out sound, particularly with
centered, solo instruments. See also
Phasiness.- Digital Compact Cassette
Philips's not particularly successful, data-reduced, digital-tape
format. Audibly equal in quality to the CD, but less convenient to work
with.- Digital output
On all DAT decks, as well as some DCC decks and CD, LV, and DVD players,
this is the coaxial or fiber-optic output that can pass digital signals to
outboard DIA converters or surround processors or other digital recorders.
While it may be useful as a way to transfer digital data to another
recording device for dubbing purposes or to an AC-3 decoder, connecting a
digital output to an outboard converter to improve" ordinary playback
sound quality beyond what a typical (even cheap) unit's built-in DIA
converter can deliver is pointless and may actually reduce sound quality.- Dipole
With regard to loudspeakers, the sound-radiating pattern produced by all
flat-panel designs and some surround speakers, including all THX-certified
models. The sound is radiated equally from the front and rear, with the
two wave fronts out of phase with each other and with the energy radiated
to the sides attenuated because of cancellation effects. See also
Bipole loudspeaker. With regard to microphones, another name for the
figure-eight design that picks up sound front and rear, with the two
signals recorded out of phase with each other and with little energy
picked up from the sides. With regard to antennas, a type that receives
signals mainly from two opposite directions, with little sensitivity to
the sides. Most wire-lead antennas sold with receivers and tuners are
dipole types.- Direct field
The listening position in a room where the direct sound from a speaker,
set of speakers, or live performer(s) is louder than the sound reflected
from nearby boundaries. Normally, you would have to be very close to the
sound source for this to occur at all audible frequencies. See also
Reverberant field.- Direct-view television
set
A TV that employs a single picture tube that projects the image upon the
inner surface of its flared end. The end of the tube is specially treated,
faces the viewer, is rectangular in shape, and ranges in diagonal size
from a few inches on up to 40 inches.- Dispersion
The ability of a loudspeaker to radiate sound over a given angle. In a
microphone, it is the ability of that device to receive sound over a given
angle. See also Radiation pattern; Polar response.- Distortion
Any changes made to an original, "clean" audio or video signal, either
at the recording end or at the playback end.- Distribution amplifier
A powered video splitter that divides an incoming video RF signal for
several pieces of equipment (TVs, VCRs) while at the same time amplifying
it enough to compensate for losses incurred during the process.- Dither
A very low-level amount of random noise that, when added during
the digital recording process, decorrelates quantization error by
spreading the quantization noise across the audio spectrum, reducing
distortion and the sometimes abrupt and unrealistic silence that occurs
when PCM digital-audio signals drop to very low levels. Dither allows
engineers to record at levels below the least significant bit and the
apparent noise floor of the recording system, allowing for better very
low-level ambience pickup and a higher subjective dynamic range. Dither
can be audible, but it is possible to shape its spectrum so that it is
less intrusive. This is a feature of the "Sony Super Bit Mapping"
recording process, for example, and a number of other recording companies
have similar "20-bit" designs. Done well, these really can give us true
19-or 20-bit performance from the 16-bit PCM system employed with the GD,
although with nearly all music the subjective improvement is marginal.
The 5.1 digital surround-sound system designed by Dolby and employing
its AC-3 digital coding. See Also
DTS; Dolby Surround
Sound- Dolby HX Pro
A special circuit in analog tape recorders that uses the recorded
signal's high frequencies to simulate high-frequency bias. This feature
automatically lowers the recorder-generated bias to reduce distortion and
improve headroom at high frequencies. Unlike Dolby B, C, or S, this system
is not complementary and does not require special decoding during playback- Dolby noise reduction
A noise-attenuating system that makes use of complementary compression
and expansion techniques over specific frequency bands to reduce
background noise in analog tape systems. Dolby A and SR are wide-band
systems for professional use. Dolby B offers about 10 dB of noise
attenuation above 4 kHz. Dolby C works above 1 kHz and increases the
attenuation to about 20 dB. Dolby S gives about 24 dB of noise reduction.- Dolby Pro Logic
Sometimes abbreviated DPL, an enhanced version of Dolby Surround Sound
that employs analog or digital "steering" circuitry to enhance surround
effects and also provide a signal for a center-channel speaker. See
also Steering.- Dolby SR-D
Identifies 35-mm film releases that incorporate both a standard 4:2:4
Dolby matrix soundtrack (in analog form, as compared with the PCM digital
version used with some LV discs) and the AC-3, Dolby Digital soundtrack.
Four-Channel ambience-extraction, derived-center-channel system used in
the theaters and home audio-video systems to provide three-dimensional
effects. See Also
Hafler circuit; Matrixing;
Dolby Digital- Dome driver
A common design for tweeters and occasionally midranges that uses a
hemispherical radiating surface instead of a conventional cone. Its
advantages are low mass, rigid structure, high power handling, and wide
dispersion, given the voice-coil size.- Doppler distortion
The frequency shift caused when a high-frequency signal is being
reproduced by the same speaker driver that is also reproducing a signal at
a lower frequency. Doppler (sometimes called FM) distortion may be audible
with certain test tones but is rarely heard with musical material.- Driver
An individual speaker element in a loudspeaker system. - Drone cone
See Passive radiator.- Dropout
In audio or video tape recording, the result of a coating defect or a
dirt deposit on the tape. This creates a momentary discontinuity in the
played-back signal. These effects are more audible or visible at lower
tape speeds.- Dry sounding
In a recording, this refers to a lack of hall reverberation and
ambience. Under some conditions, and with some kinds of music, this may
not be bad. Under most conditions, especially when large-scale ensembles
are performing, it is not a desirable quality. See also
Ambience; Reverberation.- Dubbing
Copying a recording from one audio or video recorder to another.- Dynamic range
The relationship between the loudest and quietest parts of a live- or
recorded-music program. The technical definition is the total harmonic
distortion, plus 60 dB, when a device reproduces a 1 -kHz signal recorded
at -60 dB below maximum. (Example: THD + N of -25 dB plus 60 dB = a
dynamic range of 85 dB.)-
-
- ED Beta
The professional-grade Beta format produced by Sony that is similar in
concept to S-VHS but somewhat higher in quality. Unlike the latter, which
is partially compatible with standard VHS, ED Beta is not adaptable to the
older Beta or SuperBeta systems. See also
Betamax;
VHS.- EIA
Electronic Industries Association.- EP
In VCR parlance, Extended Play. Sometimes called SLP (Super Long Play).- EPL
External Processor Loop. Essentially a relabeled tape loop within a
preamplifier, integrated amplifier, or audio receiver. Its function is to
allow the easy installation of outboard-mounted signal processors.- Early reflections
With regard to room acoustics, the reflections that arrive within a few
milliseconds of the original sound. Depending on the direction from which
they are coming, they can either add spaciousness to the sound or muddy
the detail. With regard to DSP, they are the electrically delayed signals
that a processor creates to simulate smaller concert halls (or the
reflections close to an ensemble in a larger hall).- Echo
These are reverberation artifacts so spread out in time (especially the
initial reflection) that the reflected signal is perceived as a distinct
sound. A distinct echo is usually not desirable, unless a recording was
made in a reverberant space, such as a very large church.- Efficiency
The ability of an audio device to turn mechanical energy to
electrical (microphones, phonograph cartridges) or vice versa
(loudspeakers, amplifiers). For example, the more efficient a loudspeaker
is, the louder it will play with a given input. A typical
acoustic-suspension speaker may be anywhere from 0.5% to 2% efficient;
some horn speaker systems surpass 20%. The leftover energy is dissipated
as heat. Under most conditions, efficiency has little to do with sound
quality, but with speakers, high efficiency allows one to use a
lower-powered amplifier.- Electrostatic speaker
A design that uses the attractive and repulsive forces of electrostatic
charges between fixed surfaces and a lightweight, typically large, movable
diaphragm. The prime advantage of this design is the uniform distribution
of force on the moving mass. Its main drawbacks are poor dispersion at
high frequencies, limited movement (output), and the lack of an enclosure.
The latter two restrict deep-bass output. See also
Planar-magnetic loudspeakers.- Envelopment
In the context of sound reproduction, envelopment mainly refers to the
ability of a recording or audio-video system to impart a sense of space,
depth, and ambience to the sound. With regard to playback system hardware,
the term deals with the ability to recreate, or possibly synthesize, that
same sense of space. In most cases, a system will do this better if a
surround-sound feature is employed.- Equalizer
There are many types of equalizers, but most use discrete controls to
vary rather narrow sections of the response range of a sound system to
reduce speaker, room, or recording anomalies. Tone controls are wide-band
equalizers, as are low-bass "subwoofers." Equalizers are also used in
recording studios to deal with the same problems as home units.- Expander
In home audio, a device that increases the dynamic range of an incoming
signal by making the loud passages louder and the quiet ones quieter.
Rarely required with modern digital program material, expanders can make
older recordings and video soundtracks that were compressed to accommodate
analog-playback-medium limitations more realistic sounding. Some expansion
circuits, like Dolby B, C, and S, as well as the dbx system still used in
MTS video sound systems, are designed to work with signals that were
previously compressed in a specific manner.- Extraction processors
These are surround-sound devices for home use that "extract" a
left-minus-right component from the sound of a recording and send it to
specially placed effects speakers for additional ambience and
reverberation. The technique works best with material that has been
encoded with the necessary matrixed signals (such as Dolby), but it also
works well with standard recordings that have a substantial amount of
noncoherent reverberation on them. The extraction processor routes a lot
of that reverb to the ambience speakers. See also
Synthesizing processors;
Surround sound; Dolby Surround Sound;
Hafler circuit; Matrixing.
Revised:
October 27, 2007.
All trademarks or product names mentioned herein are the property of their
respective owners.
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