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A-4 : See Voice of the Theater.
A-7 : See Voice of the Theater.
A-chain : The part of the motion picture reproduction system in a theater that contains the sound transducer (such as an optical analog track reader or digital sound format decoder), preamp, noise reduction and matrix decoding, where applicable. The A-chain equipment decodes the sound in preparation for the B-chain and loudspeakers.
A-DAM : Akai Digital Audio Multitrack. A format developed by Akai in 1987 for recording twelve tracks of digital audio data on a standard Video-8 cassette and which allows the synchronization of multiple decks for 24- or 36-track recording. The tape runs at four times the normal Video-8 speed and gives about 15 minutes sof’ recording time at 44.1kHz.
A-roll : Film footage used to introduce or provide backup material for a live video broadcast.
A-track : The primary dialog track cut by the picture editor. The B-track and subsequent tracks would be used for overdubs.
A-type : See Dolby noise reduction.
A-weighting : An equalization curve first applied to sound level meters in an attempt to make their measurements correspond better to the perceived loudness of sounds, decreasing the sensitivity of the meter to frequencies below 1kHz. An important note is that the bottom octave (32Hz) is attenuated by almost 40dB; the second octave (63Hz) by 26dB, and the third octave (125Hz) by 16dB. See B-weighting, C-weighting, equal loudness curves, SPL.
A.I.R. : Always In Record. The practice in a recording session to record virtually everything on the off-chance that something which was not formally recorded as a take will be useful.
A/B : A comparison between two recordings of the same material; pre- and post-equalization, or pre- and post-effects, or any other comparison between two similar audio devices.
A/D : See analog-to-digital converter.
A440 : See concert pitch.
AAC : Advanced Audio Coding. A flexible streaming format that supports multichannel audio including subwoofer and embedded data channels, using a variety of sample rates up to 96kHz. AAC is being developed as a successor to MPEG-2.
Aachen Head : A binaural microphone developed by Head Acoustics.
AAF : Advanced Authoring Format. A cross platform interchange format used in the creation, editing, and distribution of media content in an all-digital environment.
AB recording : In the US, this means recording with a spaced pair. In Europe, this means recording with a coincident pair.
AB-reel : Term for a 23-minute or 2,050’ maximum reel of film specially made for theater screening. The AB-reel may originally have been made from two 1,000’ edit reels; "Projection reel 1AB" would have been originally been reel #1 and reel #2 during editing and mixing. (In the event that the total footage of the first three editing/mixing reels added up to less than 2,050’, there may be a projection reel "1ABC," but this is rare.) It is becoming more commonplace to edit films in AB reel format as the magnetic film units are gradually replaced with DAWs. AB-reels are also known as "big reels" or "2,000-foot reels." AB-reels are not the same as A/B-rolls, in which the camera negative is checker boarded into two strands, allowing for simple optical effects such as fades and dissolves to be made when making original-negative prints (see EK Negative) called interpositives. This latter process is not limited to two (A, B) rolls, but can involve as many rolls of film as desired, e.g., a camera negative cut in four strands would have a "D-roll."
ABS : ABSolute time. Timecode which is the actual running/recording time in HH:MM:SS, where 00:00:00 is the head of the tape. For example, DATs use ABS timecode. See also feet/frames.
absorption coefficient : The ability of a material to absorb, rather than reflect, sound waves. A higher absorption coefficient means better acoustical damping. See bass trap, boundary effect, standing wave, Sabins.
AC : Alternating current. The current flows in both directions.
AC bias : See bias.
AC coupling : Coupling between electronic circuits that passes only time-varying signals (i.e., alternating current), not direct current.
AC-1 : A form of ADPCM(Adaptive Delta (Differential) Pulse Code Modulation). It was first used in 1985 for digital radio (sound-only) applications and since adopted for other DBS (direct broadcast satellite) services, including soundtrack-with-video, satellite communication networks, and digital cable radio systems. AC-1 has a data rate between 220 kbps and 325 kbps.
AC-2 : A transform encoding/ decoding scheme for audio compression developed by Dolby labs which uses 256-band transform coding at a data rate of 128 kbps or 192 kbps on two channels. Used in the Dolby Fax System and also DP5xx encoding.
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