ADD

Analog/Analog/Digital. A designation found on some compact discs, indicating that the program was recorded with an analog recorder, edited with an analog mixer, and transferred to the digital medium for playback.

AX Cooperator

A proprietary switching device, invented by Amy Krueger, designed to make rigorous double-blind tests easier to do.

AC

Alternating Current. The standard electrical power available from typical US power outlets. The current flow alternates direction, usually 60 times per second. AC can be affected by capacitance and inductance, depending on frequency, and is also affected by resistance. Also see 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.

ADD

Analog/Digital/Digital. A designation found on some compact discs, indicating that the program was recorded with an analog recorder, edited in the digital domain, and transferred to the digital medium for playback.

AES

The Audio Engineering Society. A professional audio society with members through out the professional, manufacturing, and educational community. They publish the JAES (Journal of the Audio Engineering Society).

AM

Amplitude Modulation. The encoding of a carrier wave by variation of its amplitude in accordance with an input signal. AM radio, while capable of being high-fidelity, is rarely configured that way.

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

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 subwoofer 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. Ambience is often synthetically added by the recording engineer if the recording environment was not reverberant enough to do the job naturally. Also see Sound field.

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 nondigital 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.

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 widescreen versions have a 1.77:1 (i6:9) 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 rapidly moving head and the slowly moving tape will vary, depending on 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 a 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. Also see 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/playback-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. Also see 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 win 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. Also see Dipole.

Bit

An abbreviation of "binary digit." A bit is a single digit in a binary number. Also see Byte.

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.

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. Also see 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.

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, decoder, and TV monitor are required to enjoy this format.

CD-1

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.

CRT

Cathode Ray Tube. The picture-producing part of a television set. Also see Directview 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 IV 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.

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.

Cardioidmicrophone

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 sifting 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. Also see 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 multichannel 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. Also see 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 modem television signal.

Classs-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 amplifiers 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.

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 listeners 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 wh

Combi player

An IV 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. Also see 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. Also see cx; 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 biamped system (if it is an active design). Also see 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 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.

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 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. VVhfle 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 11 weighted" as to audibility, because the ear is more sensitive to some frequencies than to others. Two common corrections for

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 program 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. Also see 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 amplifiers 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.

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. Also see 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 h 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. Also see 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 loudspeaker 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. Also see 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 D/A 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 D/A 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. Also see 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. Also see Reverberant field.

Direct-view TV

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. Also see 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 an 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 CD, although with nearly all music the subjective improvement is marginal.

Dolby Digital

The discrete 6-channel (OK, 5. 1: five, plus subwoofer) digital surround-sound system designed by Dolby and employing its AC-3 digital coding. While primarily a theater and video-sound format, the process is also workable for audio-only programs. Also see DTS Digital Sound; 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 SP, are wide-band systems for professional use. Dolby B offers about 10 dB of noise attenuation above 4 kHz. Dolby C works above I 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. Also see 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 IV discs) and the AC-3, Dolby Digital soundtrack.

Dolby Surround Sound

Four-channel ambience-extraction, derived-center-channel system used in theaters and home audio-video systems to provide three-dimensional effects. Also see Hafler circuit; Matrixing; Dolby Digital.

Dome driver

A common design for tweeter's 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.

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 rafter, which is partially compatible with standard VHS, ED Beta is not adaptable to the older Beta or SuperBeta systems. Also see 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 @,erv 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. Also see Planar-magnetic loudspeakers.

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.

FCC

Federal Communications Commission. The regulating body for radio and television transmission in the USA.

FM

Frequency Modulation. A radio-transmission technique that conveys data by encoding audio signals as variations in the frequency of the carrier signal.

Ferrofluid

Originally developed as a rotary seal, this substance is a magnetically attracted liquid that works well at cooling tweeter and midrange driver voice cofls This is because it stays suspended in the magnetic gaps between the coil and the heavy magnet assembly, conducting heat to the latter It also can affect speaker damping. In some tweeter designs, silicone grease will work better than Ferrofluid.

Fiber optics

A form of signal transmission that allows digital data to be transmitted as pulses of light, normally through special cable. The main advantage is a reduction of noise and distortion.

Flat response

In audio, a condition whereby a signal is not boosted or attenuated at specific frequencies over its operating range.

Flat-screen

Direct-view television picture tube with a flatter front surface picture tube (and usually shallower depth) than older (or cheaper) designs, allowing for a more undistorted picture, particularly when viewed from off to the side somewhat.

Flutter

A variation from exact speed, normally found in analog recording and play back devices. Called Nvhen the variations are slow, flutter is not a problem with digital record-playback systems, because their outputs are controlled by internal clock mechanisms. Also see Wow.

Flying erase head

An erase head built into a rotating VCR head drum. Most decks have the erase head mounted in a fixed position, limiting editing flexibility. The flying head makes it possible to do clean edits.

Frame

In video, one complete image on a TV screen that has been formed by progressive or interlaced scan lines. Also see Progressive scan; Interlaced scan.

Free field

The condition whereby a sound reaches the listener without having been reflected from any surface. Often misnamed the near field, although the latter exists at distances much closer to the sound source.

Frequency

A rate of vibration or signal oscillation. In audio, it normally involves the audible bandwidth. In video, it most typically involves the bandwidth of the sharpness component of the video signal, although the bandwidth of the color component of the signal is often of greater importance.

Frequency response

Sometimes called magnitude response, it is the measurement of the amplitude linearity of a component over a given frequency range. Frequency response is probably the most important aspect of audio system performance but there are different opinions about what is to be measured. A big problem with many recordings, even some contemporary ones, is that the microphones chosen to make them often have poor frequency response. The biggest problem with some of the studio-monitor speakers that are still being used to edit those recordings is their limited or ragged frequency response, particularly in the reverberant field. Using studio-located equalizers to compensate for those deficiencies results in recordings that are improperly equalized for playback on high-quality home speakers. Also see Direct field; Reverberant field.

Front-to-back (F/B) ratio

The F/B ratio relates to an antenna's sensitivity to signals from the front compared with its sensitivity to signals from the rear. In TV and FM radio reception, assuming the antenna is aimed property, a higher ratio will help prevent ghosts and muftipath distortion.

Gain

The amount of amplification developed by an amplifier, preamplifier, etc.

Ghosts

See Multipath distortion.

Golden ear

A term describing audio buffs who have the (real or imagined) ability to hear subtle differences in recorded sound.

Gray-scale linearity

In video, an indication of how accurately a VCR, disc player, or TV set handles subtle variations of gray-from lighter shades down to near black.

Ground

The zero-voltage reference used to signify a negative connection.

Group delay

The frequency-dependent variation in signal delivery time from an audio component. In loudspeaker systems, this can result from crossover anomalies or differences in listening distances. Many speaker manufacturers 'lime align' the drivers to compensate for group-delay problems, but these solutions only work if the listener is locked into a specific location and the system is auditioned from very close up. At normal listening distances, the group delay from any decent loudspeaker system is inaudible.

HDTV

High-Definition Television.

Hafler circuit

An ambience-recovery circuit designed by David Hafler in the 1960s. The L-minus-R matrix principle that is its basis is similar to what is employed in the Dolby Surround version, but without the need for extra amplifiers.

Hard matte

See Matting.

Harmonic distortion

The most common form of audio distortion, it shows up as additional unwanted signals at multiples of the original frequency. Thus, a 1-kHz tone may have second order harmonic distortion at 2 kHz, third-order at 3 kHz, etc. These can continue upward to beyond the seventh or eighth order. The percentage total of all these measurements is called total harmonic distortion (THD) and is commonly used in audio test reports. However, different components generate different ratios of odd and even orders, making some sound better than others - even though their THD measurements may be the same.

Heads

The parts of an audio or video tape recorder that lay down or pick up the magnetic signal on the tape.

Hi-fi video

The videotape medium that makes use of specially encoded signals to carry the audio part of the video program. The Beta version uses the video heads on the rotating tape drum. The VHS system has separate audio heads-also on the tape drum-in addition to the video heads. Newer formats employ digital audio.

High-pass filter

Within an audio crossover network, the electronic or passive circuitry that allows the high frequencies to go to a speaker system or amplifier. Also see Low-pass filter.

Home-theater system

An audio-video system that is high enough in quality to simulate a theatrical experience in the home. While most video components, especially television sets, may be inadequate to spectrum, reducing distortion and the sometimes abrupt an 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 CD, although with nearly all music the subjective improvement is marginal.

Horizontal resolution

In video, one of the more common specifications listed by manufacturers. It is the ability of a component (television, VCR, disc player) to resolve detail sideways across a television screen. Many NTSC television monitors have horizontal-resolution capabilities well beyond any source material they might have to reproduce, making the one-upmanship battle of resolution specifications more of an advertisers too] than something significant. This measurement can be calculated either from a component's video frequency response or by means of a resolution chart on a monitor.

Hz

Hertz, or cycles per second (cps), or pitch. The name comes from Heinrich Hertz, a German physicist.

IC

Integrated Circuit. A miniature electrical circuit.

IDTV

Improved-Definition Television. IDTV sets employ digital line, which allows NTSC-spec interlaced scan lines to simulate a more artifact-free progressive scan. Also see Interlaced scan; Progressive scan.

IEC

International Electrotechnical Commission.

IEEE

Institute of Electrical and Electronic Engineers.

IHF

Institute of High Fidelity.

IPS

Inches per second.

ISO

International Standards Organization.

Imaging

The ability of a component (usually a loudspeaker pair) or recording to form a realistic sound stage with precise instrumental and/or vocal localization. In fact, imaging is often more dependent upon recording techniques than speaker-system design. A few speaker systems, when reproducing certain recordings, perform imaging feats that even live music cannot duplicate.

Imaging Science Foundation (ISF)

An organization founded by Joe Kane to promote the correct alignment of existing TV picture systems and improve the quality of future systems.

Impedance

In a DC (direct current) circuit, the same thing as resistance. In an AC (alternating current) circuit, impedance is the complex interaction of inductive and capacitive forces-in addition to resistance. In such a circuit, impedance is dependent upon frequency. Also see Resistance; Input impedance; Output impedance.

Indexing

With audio (DCC and MiniDisc) and video recorders, this is the ability to electrically mark a point on a tape or disc for later access. Some CD, LV, and DVD players also have an indexing playback function, but it will only work with discs that are specially encoded with indexing points.

Infinite baffle

If the front of a loudspeaker driver is acoustically isolated from its back, it is said to be operating in an infinite baffle. Practical limitations result in enclosures behind drivers that still isolate the rear from the front. Also see Dipole; Acoustic-suspension speakers; Electrostatic speakers; Planar-magnetic speakers.

Infrared

A part of the electromagnetic spectrum that is just below the frequency range of visible light. Most remote controls work with infrared light.

Infrasonic filter

A type of high-pass filter that attenuates frequencies below the audible range reducing the work that woofers and amplifiers must do when reproducing signals that contain very low-frequency, but audible, sounds or even subsonic energy. Useful with LP-record playback to limit annoying record-player and cutting-lathe rumble and the studio or hall noise present on some CD recordings, particularly those made in churches and older halls.

Input impedance

The "load" actually seen by a source connected to an input. In audio, the input impedance should be considerably larger than the connected component's output impedance to avoid signal losses and frequency-response irregularities. In video, the input and output impedances should nearly match.

Integrated amplifier

Sometimes called a control amplifier, this is a receiver minus a tuner or, if you like, a power amplifier plus a preamplifier. Some integrated amplifiers are very elaborate and contain AV switching and even surround-sound processing.

Interlaced scan

The process of imaging a television picture by having the numerous scan lines that form the picture laid down at two intervals, with each positioned adjacent to the other. Done correctly, it allows for a sharper picture at any given transmission bandwidth. Also see Progressive scan.

Intermodulation distortion (IMD)

Electronically similar to mechanical Doppler distortion in that it results from a higher-frequency signal distorting as it rides on one of lower frequency. Unlike Doppler distortion, the one-dimensional nature of IMD within an electronic component can make it quite audible. Also see Doppler distortion.

Jog/shuttle dial

A control dial found on some VCRs and laser-video players that allows the user to more easily execute forward and reverse picture searches.

Kbps (sometimes kbis)

Kilobits per second.

KHz

Kilohertz, or thousands of cycles per second. Also see Hz.

Kell factor

A psychovisual phenomenon that determines how much the eye can resolve on a TV screen.

LCD

Liquid Crystal Display. Instead of cathode ray tube (CRT) displays or CRT projection tubes, some television sets employ the LCD, which is cooler running, lighter in weight, and smaller in size. Some very small sets have direct-view displays. A few others are front-projection models that focus light through several LCD panels, with the resultant image projected to an external screen. Also see CRT; Direct-view television set; Projection television set.

LED

Light Emitting Diode. Often used as an indicator on A/V components.

LEDE

Live-End-Dead-End room. A room designed to attenuate speaker reflections from adjacent walls, while highlighting the more delayed, scattered reflections from the far end, behind the listeners. This keeps the recorded signals from being strongly modified by the front of the listening room and allows the longer delays from the rear to place room-generated ambience where it belongs. An LEDE room will be heavily padded at the speaker end and lined with diffusing panels at the other end. The absorptive characteristics of this room may result in recordings that are overly bright when played back on wide-dispersion speaker systems located in typical, somewhat more reflective, home-listening rooms.

LP

Long Play. In VCR parlance, the middle recording and playback speed available on some units. In audio, the short term for the analog, long-play, 331/3-rpm, vinyl disc.

LSB

Least Significant Bit.

LV

LaserVideo. This is the earliest laser-read videodisc system; sometimes Galled the analog videodisc.

Late reflections

In room acoustics, the sounds that arrive at the listening position after being reflected from multiple room surfaces. They are the aural clues to the size of the listening space. In DSP, they are the electrically delayed signals that a home or studio processor creates to simulate larger room spaces.

Learning remote

A remote control that is designed to learn commands from a variety of other (dedicated) controls, simplifying user control of multiple components.

Letterboxing

Video reproduction of a film that places the entire, uncropped picture on the TV screen-eliminating the pan-and-scan problems that result when a wide format is cropped to fit a 4:3-ratio (or even, in the case of extremely wide originals, a 16:9-ratio) screen. While often helpful in capturing all the action on the screen, the smaller size of the individuals within the picture (even when the TV monitor is a fairly big one) and the loss of detail involved in not using all the vertical scan lines may be counterproductive. Also see Matting; Pan and scan.

Line doubling

See IDTV.

Line level

Low-voltage output signals available at the shielded (RCA, XLR) connections of pre-amplifiers, CD players, tape recorders, etc., designed to interface with the line-level inputs of amplifiers, subwoofers, tape inputs, etc. Also see Speaker level.

Line-source loudspeaker

A line source is a tall, vertically oriented, narrow driver or line of drivers. because of this design, the "driver' will behave like a very large source over the vertical dimension and like a smaller one over the horizontal dimension. When very taH, the resultant erratic vertical dispersion and phase cancellations will affect performance in both the direct and reverberant fields.

Linear audio track

The monophonic analog sound track that runs down one side of a videotape. Far inferior in sound quality to what can be obtained with hi-fi videotape, this is what you will hear if you plug your VCR (even a hi-fi model) directly into the RF input of a TV set.

Linear stereo tracks

These are the non-hi-fi stereo tracks that are available on some prerecorded videotapes. They usually employ Dolby Noise Reduction to improve the S/N ratio that is sacrificed when going from a mono linear audio design to stereo, but they are still far inferior to the stereo tracks that are standard on any hi-fi,-audio-equipped video recorder. This feature has fallen into disuse but may be found on some used models.

Liquid-cooled speaker

See Ferrofluid.

Liquid-cooled tube

These are found on CRT-type projection television sets and involve a liquid solution hermetically sealed between the projection tubes and the lens assembly. The coolant prolongs the life of the tubes and keeps heat expansion from distorting the picture.

Listening distance

In home audio, the subjective distance of the listener from the performers on a recording. The distance can be somewhat altered by careful use of the volume control, but the recorded sense of space around the instruments and the depth of the sound stage that result from good minimalist microphone techniques win also play a large part in determining it.

Loudness compensation

A circuit available on many preamplifier's, integrated amplifiers, and receivers that attempts to compensate for the loss in low-frequency hearing sensitivity at lower volume control settings. While simplified switched versions usually are crudely effective at best and certainly less workable than simple bass tone controls, some of the more sophisticated, continuous-control versions may work well-although still no better than the bass controls.

Low-pass filter

Within an audio crossover network, the electronic or passive circuitry that allows the low frequencies to go to a speaker system or amplifier. Also see High-pass filter.

Mbps (sometimes mp/s)

Megabits per second.

MD

See MiniDisc.

MOL

Maximum Output Level.

MOSFET

Metal-Oxide-Semiconductor-Field-Effect Transistor. A special, high-peak-current output transistor used in some power amplifiers.

MPEG

Motion pictures Experts Group. A group that meets under the auspices of the International Standards Organization in order to generate standards for digital-video and video-audio data compression/reduction.

MSB

Most Significant Bit. The first bit in a binary number. In 16-bit digital-audio play-back systems, it contributes 32,000 times more to the output signal than the 16th (least significant) bit. Thus, errors in MSB circuitry occurring at very low levels can cause audible distortion and nonlinearities.

MTS

Multichannel TV Sound. The standard stereophonic audio reception and noise-reduction process used in all true stereo television receivers not using satellite or digital decoders.

Macrovision

A jamming signal encoded into most prerecorded videotapes that makes it difficult to do tape-to-tape copies.

Masking

Under ordinary conditions, the process by which the threshold of hearing of one sound is raised by the presence of another. In both digital video and digital audio, a technique that allows a system to delete superfluous (inaudible or invisible) artifacts from a data stream by means of data reduction or data compression, enabling the system to transmit or store wide-bandwidth information within a much smaller bandwidth. Four notable uses of masking involve Dolby AC-3 Digital Surround Sound, MPEG video, DCC cassettes, and the MiniDisc. Also see Data reduction.

Matrixing

In audio, the electrical mixing of two or more channels of sound down to one or more new ones. The latter can later be "dematrixed" back to the original number. With two-channel stereo, this will involve both left-plus-right (derived center) and left-minus-right (extracted ambience) processing. Dematrixing can also be applied to two-channel stereophonic signals that were not consciously matrixed from multiple originals, with variable results. While used in FM-signal transmissions and processes to receive stereo audio signals, its most notable use is in surround-sound processors. Also see Dolby Surround; Hafler circuit; Extraction processors.

Matting

The application of a mask to a film or video program to remove information from the top and/or bottom of a picture. Used extensively in both theater presentations and video letterboxing. A hard matte is applied to the camera during the filming or videotaping process and, like anamorphic manipulation, delivers a true wide-screen image. A soft matte is a postproduction process that is done digitally when a film is transferred to videodisc or by means of projection gates in a theater.

Microphone

An electroacoustic device that turns the acoustic signals that come in contact with it into electrical signals for recording. Its behavior is just the opposite of that of a loudspeaker.

Midbass

The part of the bass frequency range between roughly 100 and 300 Hz.

Midrange

The middle range of the audible spectrum, running anywhere from 300 to 500 Hz on up to 3 or 4 kHz, a total of four octaves or more. The speaker component that handles this area is called the midrange driver,

MiniDisc (MD)

Sony's new data-reduced, small-disc, digital format.

Mixing console

The piece of equipment that recording engineers use to edit the material they recorded or are in the process of recording.

Monaural

See Monophonic.

Monitor: audio

With regard to recording, this refers to the listening the recording engineer does while "recording" and editing a program (usually music). With regard to audio playback, it refers to the speaker systems used in the monitoring and mixing room, which may be commercial models but can also be models designed for consumer use that are often better than the commercial models.

Monitor: video

Refers to TV sets without a tuner, which thereby require connection to a video source of some kind to produce a picture. However, many monitors designed for home use have both monitoring connections and a tuner.

Monophonic

A recording or sound system that has only one channel, usually with au the sound (in most cases, music) coming from just one speaker system.

Moving-coil cartridge

A phonograph cartridge that makes use of a moving coil attached to the internal end of the stylus assembly to excite a magnetic field in a fixed-magnet structure, producing an electrical output for amplification. Rarely available these days, except as highend audio items, and electroacoustically no better than the moving-magnet design.

Moving-magnet cartridge

A phonograph cartridge that makes use of a moving magnet attached to its stylus assembly to excite a magnetic field in a fixed-coil structure, producing an electrical output for amplification.

Multipath distortion

In FM radio transmissions, this effect occurs when a signal, because of being reflected from some surface (building, hill, etc.), arrives slightly later than the signals arriving directly from the transmitter. Because of the nature of FM-stereo matri)dng, it can cause audible problems if the antenna and/or tuner is not well designed. In video, the effect causes ghost images.

NAB

The National Association of Broadcasters.

NR

Noise Reduction.

Near field

Technically, the region where the particle velocity is mostly out of phase with the sound pressure-meaning that it can be very close to the listener at higher frequencies. Popularly-and incorrectly-it is often considered to be any point where the direct sound is significantly louder than the reflected sound.

Negative feedback

In all amplifiers, a part of the output signal that is fed back and added to the input signal out of phase, somewhat reducing the gain, limiting distortion, and imparting stability. Negative feedback, when used properly, can also improve frequency response. At higher frequencies, the feedback may not be fast enough, and the result will be increased transient intermodulation distortion. Under most conditions, this will not be audible. Feedback may be used "locally," in sections of an amplifier, or 11 generally," to control the response of the whole unit. Also see TIM.

Noise floor

The noise generated by an audio device in the absence of any input signal.

Noise reduction: audio

A blanket term to describe a variety of background-noise-suppressing systems (Dolby, dbx, CX, etc.), which are employed in audio and video sound systems. Even hi-fi video recorders have proprietary audio noise-reduction circuitry. Most digitalaudio systems do not require it.

Noise reduction: video

On some VCRs and laser-video players, digital noise reduction Is used to improve picture quality, especially as it relates to video grain and snow in dark areas.

Noise shaping

Digital recording techniques that take advantage of the ears reduced sensitivity at high frequencies.

Notch Filter

In video systems, this removes a small part of the TV signal where color information is most concentrated, reducing unwanted artifacts from less-than-perfect signals. Also see Comb filter.

Objective testing

The proper use of instrumentation or rigorously managed listening comparisons, rather than casual or uncontrolled techniques, to evaluate audio or video equipment. Also see Subjective testing.

Octave

A pitch interval or frequency ratio of two to one. Thus, a jump from 50 Hz to 1 00 Hz is one octave, as is a jump from 5,000 Hz to I 0,000 Hz (5 kHz to 1 0 kHz). In listening to musical programs, the interaction of ear and brain makes it difficult to resolve minor frequency-response anomalies narrower than about a third of an octave.

Off-axis

Any listening, viewing, measuring, or recording position that is not directly in front of the forward axis of a TV set, loudspeaker, or microphone.

Ohm

A basic unit of electrical resistance. Also see Resistance; Impedance; Reactance.

Omni-directional microphone

A microphone that picks up wide-bandwidth sound equally well from all directions. A variant is the subcardioid, which has somewhat less sensitivity in one direction.

On-axis

Any listening, viewing, measuring, or recording position that is directly in front of a TV set, loudspeaker, or microphone.

Open-reel recorder

A tape recorder that holds its tape in individual reels rather than cassettes. Reels vary in diameter from 5 to 10 inches.

Output impedance

The impedance seen by an electrical load attached to the output terminals of an audio or video device. For practical purposes, the output impedance of any audio amplifying equipment should be low in comparison to what it is connected to. It should not only be low at low frequencies, where it will affect bass damping, but should also be low at higher frequencies to insure a flat frequency response. In video systems, output and input impedances should closely match.

Oversampling

In most digital playback equipment, the sampling frequency is increased two, four, or, in the case of bitstream devices, even hundreds of times. However, the new samples are artificially included between the originals and will not actually affect the 16 bit information. What this digital filtering technique does is reduce the need for steep analog filters to remove ultrasonic hash, saving the manufacturer and hopefully the purchaser money. Although nearly all modem CD players use this technique in one form or another, there is no evidence that oversampling markedly improves playback sound.

PAC

Perceptual Audio Encoder. A 5.1 -channel surround-sound system developed by Bell Laboratories, and designed originally to compete in the broadcast realm with Europe's Musicam and Dolby's AC-3 systems.

PASC

Precision Adaptive Sub-Band Coding. The low-bit-rate, digital data-reduction coding process used in the Philips-developed DCC tape-recording system. Also see Data reduction.

PCM

Pulse Code Modulation. The standard playback or recording system employed by the CD and most professional-grade digital recorders, including DAT. In contrast to digital data-reduction systems, PCM recording systems allow 100 percent of the material recorded to be played back.

PIP

Picture in Picture. A TV set that can place a smaller picture derived from a different signal within the larger main picture. In most sets, this requires the addition of another tuner, usually from a VCR.

P-mount cartridge

A plug-in phono cartridge originally designed by Technics but now used by a number of other companies. Its main advantage is ease of alignment.

PWM

Pulse Width Modulation. See Bitstream processing.

Pan and Scan

A method of transferring wide-screen films to smaller-ratio TV screens, whereby the full image is not shown at all times. For example, an original Wide-screen shot might show two people talking to each other; in a pan-and-scan version, each person might be shown individually, with the camera moving (panning) between them as they speak. Also see Letterboxing.

Pan potting

The individual level controls for each channel in a multitrack recording mixer are called pan pots. Pan potting is used to adjust each of those tracks for acceptable balance.

Passive crossover

A nonpowered electrical network that divides the frequency constituents of an audio signal (bass, midrange, and treble) after it has been amplified and then routes them to the various drivers in a speaker system. In most situations, it is enclosed within the same box as the speaker drivers.

Passive radiator

Also called drone cone. A nonpowered bass driver. Passive-radiator drivers are often employed and behave as independent bass speakers below the resonance of the active drivers. Also see Bass reflex.

Perceptual coding

See Masking.

Phantom-center channel

The image that is formed between two front-center speakers when they combine their identical outputs. Such an image cannot usually be property formed unless the listener is sifting in the "sweet spot." Also see Dolby Surround; Matrixing.

Phase distortion

Also called phase shift and sometimes group delay, it results when one part of the frequency spectrum is delayed more than another. Phase shifts can cause test waveforms viewed on an oscilloscope to distort but must be fairly extreme if they are to be audible when listening to music under normal home-playback conditions, at least with loudspeakers.

Pinch roller

See Capstan.

Pink noise

Random noise (hiss) that has equal energy in each octave.

Pinna

The projected, curved parts of the outer ear that contour the frequency response and phase characteristics of the sounds going to the inner ear, allowing the brain to determine from which direction they emanate.

Planar-magnetic loudspeaker

A flat, panel-type speaker that radiates sound from both front and back. This design looks similar to some electrostatic designs but uses a widely dispersed variant of the magnet-and-coil system found in typical dynamic models. Because of this, there is less electrical load on the amplifier, and thus these speakers are less likely to cause erratic amplifier behavior.

Polar response

A plot of output amplitude of a single frequency vs. the angle off-axis. In other words, the variation in radiated or received energy with the angle relative to the axis of the radiator or receiver. The measurement can be used with either speakers or microphones. Also see Radiation pattern.

Power response

In loudspeakers, the integrated output in au directions. In most rooms, the overall level of the power response swamps the tonal effects of the direct signal. Also see Room response.

Preamplifier

Strictly speaking, the stage of an audio circuit that amplifies the very small output of a phonograph cartridge, allowing it to be successfully further amplified by a power amplifier. The term is often applied to the entire control section of a receiver, integrated amplifier, or stand-alone "preamplifier." Some stand-alone preamps also contain surround-sound processing circuitry and A/V switching.

Precedence effect

When identical sounds come from two different speaker systems, if the distance is great enough, the ear tends to attribute all the sound to the near one. This phenomenon is one reason that the surround-channel sound in a DPL system is delayed relative to the main channels. Similar to the Franssen effect, where percussive bass signals have their localization determined by the position of higher-frequency drivers in a speaker system. Also known as the Haas effect. Also see Direct field; Power response.

Pre-emphasis

A deliberate change in the frequency response of a recording system for the purpose of reducing distortion or improving the signal-to-noise ratio.

Pro Logic

The proprietary system of center-channel steering licensed by Dolby Corporation. Its function is to "steer" center-channel information to a center speaker in Dolby encoded audio programs. On nonencoded material, the steering may still offer an improvement over standard two-front-channel playback. Also see Phantom-center channel.

Progressive scan

The process of imaging a picture by having the numerous scan lines that form it laid down continuously, eliminating artifacts that result from interlacing. Commonly used in computer monitors and high-definition television sets. Also see Interlaced scan.

Projection television set

A TV that employs either three CRT tubes or an LCD arrangement to project an image on a special screen. The most common are rear-projection models, which use lenses and mirrors within a large box to project the image to the inside of a translucent screen, the outside of which faces the viewer. Less common are front-projection models, which mount the projector across the room from a conventional screen.

Psychoacoustics

The study of the relationship between human hearing perception and stimulus; in other words, the study of how we hear.

Punch

A strictly subjective term that refers to the ability of a recording to deliver dynamic snap and impact.

Push-pull woofer system

A bass loudspeaker that makes use of two woofer drivers mounted in the same cabinet but facing in opposite directions. Wired out of phase from each other, this mounting technique allows the two to move in and out together, reducing even-order distortion products. The system is used in both ftffl-range systems and subwoofers.

Q

In loudspeakers, a measure of directionality. At low frequencies, the Q will always be low. At higher frequencies, it gets larger, depending on the size of the drivers involved. Thus, Q is a measurement of frequency-dependent radiation pattern and polar characteristics. Q is also a measurement of the slope of any peaks in loudspeaker, equalizer, or microphone frequency-response curves.

Quadraphonic sound

The term used to describe any of several surround-sound systems developed in the 1970s. These days, the term surround sound is more popular.

Quantization

In a digital-audio signal, the number of possible values available to represent various levels of amplitude.

RCA plug

The standard audio line level and video-connecting plug found on amateur-grade equipment in the USA.

RF

Radio Frequency. A signal used to transmit audio and video information through the air or through cable. While virtually all receiver-equipped TV sets and VCRs can receive RF signals, all VCRs and some laser-video players can also transmit them through a cable to a TV set. The latter function results in picture and sound that is inferior to what is possible with direct video and audio hookups.

RFI

Radio Frequency Interference.

RGB input

Red/Green/Blue input. The separate-color professional-grade interface that some TV monitors employ to receive data-grade video. The result is a picture much improved over that delivered by regular direct-video or even S-Video inputs.

RIAA

Recording Industry Association of America. This group develops standards for recordings in this country. The RIAA "curve" is a record/playback compensation curve applied to LP records that allows them to have flat response with minimum distortion.

RMS

Root Mean Square. A common measurement of average power output in audio amplifiers.

RPM

Revolutions per minute.

RTA

See Real-time analyzer.

Random noise

Any kind of hiss-like noise produced by special noise generators. Similar noise can also be heard when a TV or radio tuner is tuned to a channel that has no station transmitting. Also see Pink noise; White noise.

Real-time analyzer(RTA)

A device for measuring the amplitude of specific signals in the audio bandwidth. An RTA presents a continual readout of the signal amplitude in evenly divided spectral bands, with either music or test signals as a source. Also see Frequency response.

Real-time counter

On VCRs, DCC decks, and MiniDisc recorders, a device that measures play and record time in actual seconds, minutes, and hours instead of arbitrary numbers.

Receiver

In audio, a component combining a tuner, preamplifier, and amplifier into one chassis. Most modem audio receivers also contain AN switching abilities and surround-sound circuitry. In video, any component that can receive antenna or Gable video signals.

Resistance

Commonly, the non-frequency-dependent resistance of current flow within an electrical circuit. Also see Impedance.

Resonance

The tendency for a mechanical or electrical system to vibrate at specific frequencies. The most common problems with resonances in modern audio hardware involve loudspeaker systems and microphones.

Reverberant field

A technical term that defines the sound field that exists when the reflected sound in a listening or monitoring room predominates over the direct sound from the source (be it a loudspeaker or performers). Obviously, it is strongly effected by room layout, reflectivity, and size. Also see Direct field.

Reverberant sound (reverb)

The amount of ambience and hall reflections captured during the recording process. Reverb ran be recorded naturally, but many engineers add it synthetically to compensate for deficiencies in the recording environment.

Reverberation

The multiple sound reflections that result when sound is produced in an enclosed space. Also see Ambience; Early reflections; Late reflections.

Ribbon speaker

A design that uses a long, very thin narrow metal conductor suspended in a magnetic field. Ribbons are usually employed as tweeter's or tweeter-midranges, because their design does not allow for good performance in the bass range. Ribbons usually have good horizontal and limited vertical dispersion. Also see Line-source loudspeaker.

Rolloff

Commonly, a gradual reduction of audio output above and below specific frequencies. Usually applied to loudspeaker or microphone performance, it can also be used to describe the sound of recordings at their frequency extremes.

Room response

The power response of a loudspeaker as measured in a given room. The measurement includes both the direct signal and the reflections from the room boundaries, minus the sound absorbed by the furnishings. Also see Power response.

Rumble

The low-frequency mechanical noise that appears on some recordings, which can be caused by any number of things, including mechanical or stage noise at the recording source. In the old days, rumble was also caused by LP turntables feeding through to the speakers or from the sound made by the cuffing lathe that made the record master.

SAP

Second Audio Program. In video systems, the SAP channel can be used to provide an alternate soundtrack-especially helpful when there is a need to broadcast dialogue in a language different from what is being delivered by the main channels.

S-VHS

See Super-VHS.

S-connector

The video hookup employed by S-VHS, ED Beta, and some laser-video players to keep the Y (luminance) and C (chrominance) signals separate. This hookup is commonly called a Y/C connection. Also see Super-VHS

SLP

In VCR parlance, Super Loncy Play, the slowest play and record speed. Sometimes called EP, or Extended Play.

SMPTE

Society of Motion Picture and Television Engineers.

SIN ratio

See Signal-to-noise ratio.

SP

In VCR parlance, Standard Play, the fastest play and record speed.

SPL

Sound-Pressure Level. Also see dB.

Sampling rate

In digital systems, the rate in Hz at which the circuitry determines the signal amplitude. For CDs, this is 44.1 kHz; for RDAT recorders, it ran be either 48, 44.1, or 32 kHz.

Saturation

A magnetic-recording term used to describe a condition whereby recording tape or tape heads are carrying all the signals that they can handle. Any additional input results in no additional storage or recording output levels.

Scan-velocity modulation

A feature on some TV sets that adjusts the rate of horizontal movement of the electron beam as it scans the picture. This results in a sharper picture.

Sensitivity

A standardized speaker measurement that determines how loud a system will sound under controlled conditions. The standard procedure agreed upon by the industry is output, in dB at I meter with 2.83 volts applied, which will amount to I waft at 8 ohms (2 wafts at 4 ohms). While sensitivity has little bearing on overall sound quality, it will be a factor in determining the required amplifier power.

Shadow mask

On a direct-view television picture tube, this is the perforated screen that is bonded behind the front glass surface, which limits color distortion (or blooming) and also improves contrast. Also see CRT.

Signal-to-noise ratio (SIN ratio)

Often arbitrarily assigned, the SIN ratio should be the difference, in dB, between the noise floor of a playback component or sound recording and the loudest level it can achieve with inaudible distortion. The measurement is sometimes weighted as to audibility, because the ear is more sensitive to some frequencies than others. The most generous scale is dBA (A-weighted). In any case, the larger the SIN number, the better. Also see dB; Noise floor.

Slew rate

See TIM.

Slope

In audio, the rate of change that a frequency-response curve displays, normally stated in dB per octave. Among other things, slope can relate to crossover-point attenuation rates, woofer low-end rolloff rates, or equalizer control functions.

Software

Another term for audio or video recordings.

Solid state

Electronic circuits whose active elements are transistors and integrated circuits, rather than tubes.

.Sound field

In audio-video circles, this term relates to the "totality" of the sound presented by the sound-system-recording combination. In audio-only recordings it will involve the direct sound of the players, the sense of envelopment, the reverberation and ambience of the studio or hall-and even the interaction of the recording with the playback system and its environment. In A performance, it will involve how well the sound of the system interacts with the material on the TV screen. While the quality of the source material is critical, the sound field will be greatly influenced by the quality of the playback system, its arrangement within the listening-viewing room, and whether it incorporates surround-sound hardware.

Sound power

The amount of energy radiated by an audio source, measured in joules per second, or watts. Its most common use is with loudspeakers, where power response is measured by how sound power varies with frequency.

Sound stage

In audio or video sound, this often vaguely defined term refers mostly to the lefteight spread of the sound between the speakers in a playback system. It can also be used to define a sense of front-to-back depth. While the sound system layout can be critical, recording quality is also of great importance in influencing the sound stage.

Source

The signal that is played through an audio or video system. It may be something received over an antenna or cable system or be from an installed component like a VCR, videodisc player, CD player, or audiocassette deck.

Speaker level

The moderate-voltage outputs of an amplifier or amplifier section of a receiver or integrated amplifier. While these are mainly designed to power loudspeaker systems, some subwoofers have speaker-level inputs to their built-in active or passive crossover networks. Also see Line level.

Square wave

A waveform consisting of a fundamental and all the odd-numbered harmonies it produces. Because it consists of energy to at least the 20th harmonic, it can be used for frequency-response evaluation with electronic components. Any amplifier that can reproduce an exact 1 kHz fundamental square wave cleanly will be clean to -10 kHz.

Standing waves

These are irregularities (quite audible and unwanted in the bass range) that result when sounds reflected back and forth between the walls of a room interact with each other and with the direct sounds from the speaker systems that produced them to form alternate reinforcements (peaks) and nulls. The effect is dependent upon the size and shape of the room and the listening position and, to a smaller degree, on the positioning of the speakers. Standing waves can be detrimental to sound reproduction at lower frequencies in small and/or badly proportioned rooms, where their effects are often extreme.

Starsight

A proprietary subscription-activated menu system built into some TV sets and VCRs to aid in program selection and recording.

Steering

Most notably used in Dolby Pro Logic systems, the electronic manipulation of recorded audio signals from two-channel sources allowing encoded center-channel material that would ordinarily only be vaguely imaged to be positively routed to a center speaker and surround material to be similarly routed to the surround speakers. The goal of steering up front is to simulate three discrete-channel sources, with surround steering normally simulating a broad sense of space around the viewer.

Stereo

From the Greek for "solid." In audio, it ordinarily refers to a recorded program that uses two speakers in front to recreate the left-right sound-stage image of a live performance. If done right, stereophonic reproduction ran also lend a certain degree of depth to the sound. Surround- and ambient-effect sound systems, making use of more than the standard two "front" speakers, are also an advanced form of stereo. The latest incarnation for home audio-video is Dolby AC-3.

Stylus

The external moving part of a phonograph cartridge. Usually, it will included a jeweled tip (nearly always a diamond) and a cantilever or shank connecting the tip to the magnets or coils within the cartridge body.

Subjective testing

Judging audio or video gear by listening or viewing without using any measurement instruments. While some people can be quite sensitive to differences in audio or video quality, many are misled either by environmental factors or personal predispositions. Also see Objective testing.

Subsonic filter

See Infrasonic filter.

Subwoofer

An electronic or mechanical device that extends the deep-bass response of an audio system. The most common are add-on, large, conventional woofers, which must be carefully aligned to work property. Electronic-type "subwoofers" are actually equalizers that are dedicated to standard woofer systems and electrically boost the low-bass range to achieve smooth, flat low-bass response. Many add-on subwoofers incorporate electronic equalizers to flatten out the bottom of their ranges. Also see Equalizer; Woofer.

Suckout

Bass-range reflections from nearby floor or wall boundaries that partially null the primary signal coming from the speaker itself. The suckout phenomenon differs from standing waves or higher-frequency reflections in that relocating the listening position or padding the walls is not a cure. Suckout involves only the bass, particularly the midbass (although it can also cause interactions in the low bass between two widely spaced woofer systems), and requires very careful speaker placement to correct. Also see Standing waves.

SuperVHS

Also called S-VHS; the high-band, sharper-picture upgrade to standard VHS.

Supertweeter

A tweeter designed to reproduce the very highest frequencies above the 2-15 kHz range normally handled well by a good standard tweeter. Supertweeters are usually found in four- or five-way systems and are sometimes placed on the back of a cabinet, facing the wall behind the system. Note that a decent conventional tweeter should be capable of doing everything important that a supertweeter should do, because the highest frequency most people can hear distinctly (particularly if they are past the teen years) is about 15 kHz, and most music and film sound does not have significant energy past 12 to 13 kHz. The only way a supertweeter would offer an advantage would be if its radiating-surface diameter was very small-say one-half inch or less. This would result in improved dispersion above 10 kHz, compared with that of a typical 1-inch dome tweeter. Some supertweeters are said to have strong response to well above 20 kHz, but CDs, videodiscs, and videotapes do not reproduce that range, and nobody can hear up that h

Surround sound

The matrixed, synthesized or discrete rear, side, or center-channel outputs that are integrated with the main channels of a stereophonic audio or audio-video system to enhance realism and ambiance. Most modem versions have separate amplification for those channels. Also see Dolby Surround; Ambisonic; Hafler circuit; Dolby Digital; DTS; Center Channel; DSP; Extraction processors; Synthesizing processors.

Surround speakers

The usually small speakers that are placed toward the sides or toward the rear in a surround-sound playback system and handle the decoded, extracted, or synthesized ambience signals. Some manufacturers refer to them as "rear-channel' speakers, a misnomer.

Sweet spot

The so-called "best" listening (or viewing) position for enjoying an audio (or audiovideo) system. Usually, it is centered between the main speakers and about as far from their connecting axis as they are from each other. Sweet-spot listening is mandatory for good imaging with systems that employ only two speakers up front. Also see Center channel.

Synthesizing processors

These are surround-sound devices for home use, such as those produced by @'aiiiaha, Onkyo, and Levcon, that add their own preprogrammed hall ambience and reverberation to the sound of a recording. This "overlay" of ambience can greatly benefit soine recordings, particularly those that are fairly dry sounding. However, the effect can muddy the sound of recordings that have a fairly large amount of reverberation to begin with. Recording engineers often employ synthesizing devices to add ambience to the recordings themselves. Also see Ambience; Surround sound; Extraction processors.

THD

See Harmonic distortion. (Total Harmonic Distortion)

THX

A Lucas Film Corporation performance certification program for A/V software and hardware, particularly dealing with Dolby Pro Logic and Dolby Digital behavior but also involving TV monitor and laser-video picture and sound quality. Also see Dolby Pro Logic; Dolby Digital.

Tapeloop

On most preamplifiers, integrated amplifiers, and receivers, the switch-operated hookup that allows a tape deck to be property integrated into the system. A tape loop will have an input for tape playback and an output for tape recording. Also see EPL; Tape monitor.

Tape monitor

The switch that inserts a tape loop into a circuit. With some recorders, this allows you to do an A/B comparison between the source material and the recording as it is being made.

Timbre

The quality given to a sound, particularly a musical sound, by its overtones. In audio, a popular term describing the basic tonal quality of a sound system, particularly the speakers.

Three-way speaker

A loudspeaker system that uses separate drivers for the high frequencies, midrange, and bass. Certain designs may have more than three speaker drivers, but because some are paired together to handle the same frequencies, they will still be three-way designs. Also see Two-way speaker.

Time-base corrector

A circuit found in all analog IV players (advanced versions employ digital circuitry) and some VCRs that electrically corrects for small mechanical speed errors.

Time sniffing

Setting a VCR to record a program for later viewing.

Tonality

A subjective term that refers to the clarity and accuracy of the sound of an instrument or group of instruments. It can also refer to those qualities in vocal reproduction.

Tone arm

The mechanism on an LP record player that holds the cartridge in proper position over the record.

Tone burst

A momentary sine-wave signal that is used to test the transient response of an audio component. While a tone burst can theoretically measure the tendency of a component, particularly a loudspeaker, to continue to oscillate after the input signal is cut off, a proper frequency-response sweep will do the same thing, because these resonances will show up as peaks or dips in the sweep curve. Also see Frequency response; Transient response.

Tone control

The control on a preamplifier, integrated amplifier, or receiver that boosts or cuts certain segments of the audible bandwidth. Bass and treble controls are the most common versions, but some units have midrange controls also. Also see Equalizer.

Tracking

The ability of a CD player, IV player, VCR, or LP phonograph stylus to follow the mechanical or electrical pattern on a tape or disc.

Tracking control

On a videotape recorder, the control that adjusts the "head-switching" network contained within the deck's electronic circuitry. Many modem decks have automatic tracking controls, an excellent idea.

Transient response

The ability of an audio component to quickly respond to the signal being fed to R. Transient response is more critical in mechanical components like speakers, phono cartridges, and microphones. Also see Tone burst.

Transparency

In audiophile circles, the ability of a sound system or recording to achieve a realistic sense of imaging, space, and clarity. Most commonly used to describe the capabilities of speaker systems.

Transponder

Used in video satellites to receive program material from ground-station uplinks and then retransmit it to properly aimed dish receivers back on the ground.

Transport

The mechanical part of an LP turntable, audio tape deck, CD player, IV player, or VCR that moves the disc or tape so that the signal can be reproduced.

Treble

The high-frequency range of the audible spectrum, running from 3 or 4 kHz on up to 15 or 20 kHz (less than three octaves).

Tuner

The component that receives the RF signals (radio, video, satellite) from an antenna or cable system. Audio tuners are sometimes stand-alone units but are usually configured as part of an audio or audio-video receiver. Video tuners are usually included as part of a TV set or VCR. A satellite receiver is a tuner designed to receive either analog or digital satellite-transmitted signals that are received by a dish antenna.

Tweak

To adjust an audio or video component so that it works at its very best. Also, a slang term for an audio extremist who dwells on the more mythical aspects of audio in preference to more rational beliefs that are substantiated by objective testing procedures.

Tweeter

The individual speaker unit (driver) designed to handle the treble range. Also see Treble.

Two-way speaker

A speaker system that uses separate drivers for the high and low frequencies; the midrange frequencies are split between them. Two-way systems usually suffer from midrange dispersion problems, because the woofer, which must be robust enough to do decent work down low, is usually not small enough in diameter. Some two-way systems employ a nonpowered passive radiator to augment the deep bass. Also see Three-way speaker; Passive radiator.

Universal remote control

A remote control that has been preprogrammed by its maker to operate a variety of components.

VBI

See Vertical blanking interval.

VCR

Videocassette recorder. Also see Video recorder.

VCR Plus

A time-shift control system installed in some VCRs to simplify recording. Also available in handset-type controllers for older video recorders.

VHS

Video Home System. The now-dominant home-video tape-recording system developed by JVC as competition to the Sony-designed Beta format.

Vertical blanking interval

The horizontal black bar visible on a TV picture when the vertical-hold control is adjusted so that the picture "rolls" off center. The VBI consists of 21 lines and, because each line arrives at two 1/6o-second intervals, totals 42 of the 525 lines available with the NTSC system. The VBI allows a video-picture scan line to return to the starting point at the next picture frame (the first nine lines contain the signal pulses that synchronize picture transmission) and also is useful for carrying specially encoded data to multiple recipients in the video distribution chain.

Vertical resolution

The ability of a television component (VCR, laser-video player, or TV set) to resolve detail vertically on a television screen. Usually stated in lines of detail from screen top to screen bottom, vertical-resolution limits of consumer-grade television sets are set by the FCC.

Video enhancer

A circuit designed to boost picture detail. Sometimes useful in dubbing material from one VCR to another.

Video recorder

A tape recorder designed to record and play back video and audio signals received via cable or antenna. VCRs can also copy material from another recorder or laservideo player. Hi-fi versions produce higher-quality audio performance than standard models.

Video Guide

A proprietary subscription-activated menu system designed to aid in television program selection and recording. Also see StarSight.

Videophile

A person who has an enduring interest in video, particularly and home theater.

Voice coil

The wire coil surrounded by the magnet assembly in a moving-coil, dynamic loudspeaker. The coil is attached to a diaphragm (which may be a cone, dome, or some kind of hybrid air mover) of the driver and causes it to move when excited by a signal from an amplifier. Most voice coils are made from copper wire, although a few are made of aluminum wire.

W/ch

Watts per channel.

Watt

A unit of power. Amplifiers do not deliver wafts (they deliver voltage), nor do speakers create them. When presented to a specific load (speaker impedance), current flows and the power dissipated is rated in wafts. Wattage produced may be calculated by multiplying voltage times current or by squaring the voltage and dividing it by the impedance.

White noise

Similar to pink noise, except that white noise contains equal energy at each frequency point. Also see Pink noise.

Woofer

The individual speaker unit (driver) designed to handle the bass range. Some speaker enclosures contain multiple woofer drivers to increase bass power.

Wow

The speed variation of a mechanical playback device such as an LP record player or analog tape recorder. Short-term speed variations are sometimes called flutter. Digital recording and playback devices do not produce wow, because their outputs are controlled (and slightly delayed) by an internal dock mechanism. Wow created by warped LP records is called warp wow

XS Stereo Sound

A proprietary stereophonic video system designed by Thomson electronics for budget-grade TV sets. This is not a true Stereo system like the dbx version used in MTS; instead it uses small amounts of negative cross-feed to simulate stereo. Also see dbx; MTS.

YC connector

See S-connector.