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Glossary of Technical Terms

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TermDefinitionDemo
A-weighting See Frequency Weighting
A/B test A form of listening test in which two sounds are compared with each other in a rapid A/B fashion. Ideally, the listeners would not know the identity of the two products being compared. See Double-Blind Listening Test.
A/D Converter A device that accepts an analog signal at its input, and outputs a digital version of the signal.
A/V Audio/Video
A/V receiver Combines the following functions in one device: audio- and video-signal switcher; surround sound decoder; multichannel amplifier; preamplifier, including tone controls and other effects; and radio tuner.
Absorption In acoustical absorption, sound energy is converted into heat. See: Resistive Absorbers, Diaphragmatic Absorbers, Resonant Absorbers, Absorption Coefficient, Sabine.
Absorption Coefficient The proportion of incident sound that is absorbed by a surface. Usually this is expressed as a number between 0 and 1, or a percentage. In most materials, the amount af absorption changes with the angle of incidence. The specification is normally a 'random incidence' measurement.
AC see Alternating Current
AC Line Conditioner or Protector A device inserted between the wall outlet and your equipment to isolate it from voltage spikes and unwanted high frequency signals that may be picked up by the power lines. High quality audio equipment may already have some of this kind of isolation built in. See also: AC Voltage Stabilizer
AC Voltage Stabilizer A device inserted between the wall outlet and your equipment to maintain a constant voltage level. Used in buildings and neighborhoods where line voltage fluctuates widely because of heavy variable loads.
AC-3 The first descriptor for what is now called Dolby Digital.
Acoustic Suspension A closed box loudspeaker enclosure in which the compliance (spring) of the air inside the box is a substantial portion of the total compliance of the system, including the mechanical suspension of the woofer. See: Suspension, Compliance
Acoustical Interference When two or more sounds arriving from different directions combine at a point in space, e.g. at an ear or microphone, those components which are in step with each other (in phase) will add (constructive interference) and those that are out-of-phase will subtract, or cancel each other (destructive interference). See: In Phase, Out-of-Phase, Comb Filter.
Acoustics The physical science dealing with how sound is produced, propagated, manipulated and perceived. See also: Room Acoustics
Active Crossover An analog or digital device performing high-pass, low-pass and bandpass functions ahead of power amplifiers driving the transducers in a loudspeaker.
Active Loudspeaker A loudspeaker which has a built-in power amplifier for at least one driver, usually the woofer or subwoofer. It may also have amplifiers for mid and high frequency drivers. See: Powered Tower
Active Matrix Decoder See: Matrix Encode/Decode
AES/EBU The two-channel digital audio communication process that was standardized by the Audio Engineering Society (AES) and the European Broadcasting Union (EBU).
Aftermarket The sale of components for installation after the customer has purchased the original item. For example, aftermarket car audio equipment can embellish or replace the originally supplied system.
Algorithm A step-by-step procedure for solving a problem or accomplishing a task, usually by using a microprocessor or DSP (see below). In digital audio, algorithms are often used for sound processing, data compression and surround sound en-/decoding.
Alternate Channel Selectivity A measure of the ability of a radio tuner to reject information from a radio station close to the frequency of the one being listened to.
Alternating Current An electric current that moves in both directions, cycling at a regular rate, as in 60 Hz home power, or at a variable rate as in an electrical music signal being supplied to a speaker. Also used to describe the accompanying alternating voltages, cycling between positive and negative.
AM see Amplitude Modulation
AM Rejection A specification describing to how well a radio tuner can ignore changes in the amplitude of an FM signal, such as those caused by propagation effects and interference.
Ambience In audio this refers to the reflected and reverberant sound characteristics of an acoustic space. All rooms can be acoustically 'live' or 'dead'. Large rooms can be flattering to musical performances (concert hall) or hostile (gymnasium).
Ammeter A device used to measure current flow in amperes.
Amperage The magnitude of an electrical current as expressed in amperes.
Ampere Unit of measurement for the electric current flowing through a circuit. Abbreviated: amp.
Ampere-hour A measure of the quantity of electricity delivered by a battery determined by multiplying the integrated current in amperes by the duration of the current flow in hours.
Ampere-hour capacity Rating for a battery describing current in amperes that can be drawn over a period of time in hours before the discharge limit is exceeded.
Amplification An increase in signal level.
Amplifier A device that increases the magnitude of the voltage, current or power in an electronic system. In audio systems, preamplifiers and surround processors amplify voltages. Power amplifiers amplify both voltage and current, therefore providing more power output in order to drive loudspeakers.
Amplitude The magnitude of an electrical signal (voltage, current or power), sound (sound pressure or intensity), or movement of a mechanical device such as a loudspeaker diaphragm.
Amplitude Modulation A method of radio broadcasting in which the radio carrier frequency is amplitude modulated by the audio signal. Typically limited in bandwidth, and susceptible to interference and static. However, it propagates well over long distances and around hills and buildings. Abbreviated AM.
Analog An electrical signal in which the voltage (or current) waveform has the same form as the original acoustical sound waves. See also Digital
Analog-to-digital converter See A/D converter.
Anamorphic A film or video format in which a widescreen image has been "squeezed" horizontally (either with lenses or by digital manipulation) to fit a standard 4:3 aspect ratio. Correct picture geometry is restored on playback by "unsqueezing" the image into its original aspect ratio. Anamorphic DVDs are sometimes marked "Enhanced for widescreen TVs." See: Widescreen, Aspect Ratio.
Anechoic Without echoes, reflections or reverberation.
Anechoic Chamber A room without echoes or reflections that is used for precise acoustical measurements, not contaminated by normal room acoustical factors, including noise. It is the ultimate 'dead' room. See Reverberation.
Anode The electrically positive terminal of a battery, or the plate of a vacuum tube.
Aperture Ratio In digital display devices, this is a measure indicating the percentage of the available area that is used for active pixels. Some displays have obvious inactive 'frames' around individual pixels, leading to the description 'screen-door' effect when viewing such a display from insufficient distance.
Aquaplas A water based compound high in particulates which is used to adjust the mass of, and to add damping to, a variety of loudspeaker diaphragm materials.
Articulation / Articulation Index Having to do with the intelligibility of speech. This is measured using listeners who try to identify randomly presented 'nonsense' words and phrases. The Articulation Index is the percentage of correct identifications. Used mainly in large venues.
Artifact In video, the degradation of picture details when a video decoding system cannot keep up with frame-by-frame changes. Video compression systems (codecs) rely on the common reality that only portions of a picture change from frame to frame. If a lot of the picture is changing (as in panning across a crowd of people) decoders may not be able to keep up, and the result is that portions of the picture may momentarily revert to large blocks of color. Other artifacts can be seen in jagged edges, 'staircasing' of guitar strings, etc. Fortunately, most are brief.
Artificial Reverberation Synthesized reflected sounds intended to add to a recording the acoustical impression of being in a specific size and kind of room, such as a concert hall, stadium, club, etc. Inexpensive versions tend to be very artificial sounding. The best versions are hardly distinguishable from the real thing, and in fact are used in numerous concert performing spaces to improve on less-than-perfect natural acoustics. Also, the electronic reverberation added to close-miked recordings.
Aspect Ratio The width-to-height ratio of a visual image. Standard NTSC television sets have an aspect ratio of 4:3 (4 units wide by 3 units high). Widescreen television sets have an aspect ratio of 16:9. Many films are produced with even wider ratios. Pictures with aspect ratios different from the display will show dark bars at the top and bottom, or at the sides. See: Widescreen, NTSC.
ATRAC Acoustic Transformation Adaptive Coding. A perceptual encoding system used in the Sony MiniDisc format. See: Perceptual Coding
Attack In music, the onset of a sound or note.
Attenuation A reduction in signal or sound level.
Audio Frequency Range The range of human hearing commonly accepted as 20 to 20,000 Hertz (cycles per second).
Audio Interconnect Cable A shielded wire used to link the audio signal output of one device to the input of another audio device.
Audio Oscillator A test instrument that produces single frequency tones for measuring the performance of audio devices.
Audio Signal An audio frequency signal in electronic form or after conversion to sound.
Audiometer A device for testing various aspects of hearing performance, beginning with the hearing threshold, the smallest sound that one can hear at various stantardized frequencies.
Audiophile Anyone interested in the reproduction of sound.
Auto Convergence An automated feature for aligning the red, green and blue guns of a CRT projector or rear-projection television. See: Convergence
Auto Turn-on A signal sensing circuit designed to turn an audio component on when it receives a music signal.
Axial Modes The acoustical resonances in rooms that occur between opposing parallel surfaces: walls, or floor and ceiling. See Room Resonances.
Azimuth In tape recorders, the angle made by the magnetic gap in the record/play heads and the direction of tape motion. The playback azimuth must equal the record azimuth or there will be a loss of high frequencies on playback.


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