a2b music
A proprietary, secure music distribution system developed by AT&T. It uses AAC for compression.

AAC
Like MP3, Advanced Audio Coding is an audio encoding scheme specified by the MPEG-2 standard. Although it is part of MPEG-2 standard, it is not compatible with the MPEG Layer scheme or MP3. AAC was design by researchers from a number of companies and can be licensed from Dolby Laboratories. AAC encoding is more efficient than MP3, resulting in smaller file sizes for audio of similar quality. AAC can also provide many more audio channels than MP3, as well as a wider range of sampling rates for better sound quality than is possible with MP3. Although AAC by itself has not yet been widely used, it has been used as the basis for several proprietary secure formats, and it will be used in the audio portion of the MPEG-4 standard.

AD converters
Short for “analog/digital”; a device that converts an analog signal to a digital signal that represents equivalent information via sampling.

Adat
Digital 8-track audio recorder based on video tape by Alesis; the standard device in its class; diverse generations and models are available.

Adat Optical
Optical interface for parallel transmission of eight audio channels via fiber-optic cable. Now the established standard for digital multi-channel interfaces.

ADPCM
Adaptive delta pulse code modulation. An audio compression algorithm for digital audio based on describing level differences between adjacent samples.

ADSR
> Envelope

AES/EBU
Short for “Audio Engineering Society/European Broadcast Union”; this is the association’s standard transmission format for professional stereo digital audio signals. The format is similar to S/P-DIF. AES/EBU and S/P-DIF coax interfaces can communicate directly.

Aftertouch
A type of control data generated by pressing down on one or more keys on a synthesizer keyboard after they have reached and are resting on the keybed. > channel pressure, poly pressure.

AHRA
Audio Home Recording Act of 1992 allows comsumers to create copies of recordings for personal, non-commercial use.

AIFF
Audio interchange file format. A common Macintosh audio file format. It can be mono or stereo, at sampling rates up to 48kHz. AIFF files are QuickTime compatible.

Algorithm
A set of procedures designed to accomplish something. In the case of computer software, the procedures may appear to the user as a configuration of software components -- for example, an arrangement of operators in a Yamaha DX-series synthesizer -- or as an element (such as a reverb algorithm) that performs specific operations on the signal.

algorithmic composition:
A type of composition in which the large outlines of the piece, or the procedures to be used in generating it, are determined by the human composer while some of the details, such as notes or rhythms, are created by a computer program using algorithmic

aliasing
A type of distortion that occurs when digitally recording high frequencies with a low sample rate. A visual analogy can be found in video, when a car's wheels appear to slowly spin backwards while the car is quickly moving forward. Similarly when you try to record a frequency greater than one half of the sampling rate (Nyquist Frequency), instead of hearing a high pitch you may hear a low frequency rumble. An anti-aliasing filter can be used to remove high-frequencies before recording. However, once a sound has been recorded, aliasing distortion is impossible to remove without also removing other frequencies from the sound.

Amplitude
Amplitude is a term used to describe the amount of a signal. Amplitude is measured by determining the amount of  fluctuation in air pressure (of a sound), voltage (of an electrical signal), or numerical data (in a digital application). When the signal is in the audio range, amplitude is perceived as loudness.
In the audio sector, the term is often equated with "level " and "volume" processes.

Analog
Of, relating to, or being a mechanism in which data is represented by continuously variable physical quantities

Analog Audio
A continuously varying representation of sound waves. In most analog audio systems, a continuously varying voltage signal represents the sound wave.

Arpeggiator
A device that sequentially plays a pattern of notes over a range of the keyboard. The speed of the arpeggiation and pattern of notes are variable depending on the tempo and specified/pressed notes.

AT
Short for “Advanced Technology”, a computer bus system (see ISA).

ATRAC 3
Sony's Adaptive Transform Acoustic Coding 3 format is an improved version of the ATRAC encoding shceme used by MiniDisc Players. Sony said that ATRAC 3 will be SDMI compliant.

Attack
Start phase of a sonic event; the initial period of a typical envelope during which a sound's attribute (such as volume) increases from 0 (silence) to it's maximum amount. The length of the attack determines how "soft" or "harsh" a sound is.
For example, most drum or percussion sounds have a short amplitude attack time and thus have a sudden "harsh" start. A string sound usually has a long amplitude attack and thus has a "soft" start and eases in.

Attenuate
To reduce the level of a signal.

Attenuator
A potentiometer (pot) that is used to lower the amplitude of the signal passing through it. The amplitude can usually be set to any value between full (no attenuation) and zero (infinite attenuation). Pots can be either rotary or linear (sliders), and can be either hardware or "virtual sliders" on a computer screen.

Audio file
A file that actually contains digital audio data, as opposed to audio regions or audio segments.

Audio region
This simulated audio file holds the place for an actual audio file or portions thereof; it doesn’t contain audio data, only peripheral information such as the start and end point.

Audio segment
Same as audio region.

Aux
Short for auxiliary; in mixers, these circuits are usually identical to effects sends.