A2b
A2b music is an online music delivery company owned by AT&T. The service delivers music coded in a proprietary format based on MPEG-2 AAC. The format includes a copyright protection technology.


AAC (MPEG-2 Advanced Audio Coding)
AAC is the state of the art in MPEG natural audio coding. Including three different profiles, it delivers better sound quality at 96kbps than MPEG layer2 at 192kbps. It was previoulsy called MPEG-2 NBC (Non-Backward Compatible).


AC-3 (Audio Code 3)
AC-3 refers to a multichannel music compression technology that has been developed by Dolby Laboratories.
     Primary used only for cinema, it is now used in laserdisc and DVD. It is also known as Dolby Digital.


ADPCM (Adaptive Differential Pulse Code Modulation)
It is a compression technique which encodes the predictive residual instead of the original waveform signal so that the compression efficiency is improved by a predictive gain. Rather than transmitting PCM samples directly, the difference between the estimate of the next sample and the actual sample is transmitted. This difference is usually small and can thus be encoded in fewer bits than the sample itself.


Alias
Mirrored signal component resulting from sampling.


Analysis filterbank
Filterbank in the encoder that transforms a broadband PCM audio signal into a set of spectral coefficients.


Ancillary data
Part of the bitstream that might be used for transmission of ancillary data.


Arithmetic Coding
Perhaps the major drawback to each of the Huffman encoding techniques is their poor performance when processing texts where one symbol has a probability of occurrence approaching unity. Although the entropy associated with such symbols is extremely low, each symbol must still be encoded as a discrete value.
    Arithmetic coding removes this restriction by representing messages as intervals of the real numbers between 0 and 1. Initially, the range of values for coding a text is the entire interval [0, 1]. As encoding proceeds, this range narrows while the number of bits required to represent it expands. Frequently occurring characters reduce the range less than characters occurring infrequently, and thus add fewer bits to the length of an encoded message.


ATRAC (Adaptive Transform Acoustic Coding)
ATRAC is a lossy audio coding system based on psychoacoustic principles.It compresses compact disc audio to approximately 1/5 of the original data rate with virtually no loss in sound quality. It is the encoding scheme used in MiniDisc.


Audio buffer
A buffer in the system target decoder for storage of compressed audio data.