Audio codec

From Wikipedia, the free encyclopedia

An audio codec is a computer program that compresses/decompresses digital audio data according to a given audio file format or streaming audio format. Most codecs are implemented as libraries which interface to one or more multimedia players, such as XMMS, Winamp or Windows Media Player.

In some contexts, the term "audio codec" can refer to a hardware implementation or sound card. When used in this manner, the phrase audio codec refers to the device encoding an analog audio signal to a digital audio signal, or decoding an analog audio signal from a digital audio signal. Thus, in such a context, the term is actually referring to a combined audio AD/DA converter. One example is Intel Corporation's AC'97 standard, which is comprised of a digital controller paired with an analog unit.

The use of digital samples to represent audio data is subject to some fundamental limitations regardless of the codec. The bandwidth is limited by the Nyquist Sampling Theorem so that the highest audio frequency that can be reconstructed from the digital data is half the sample frequency. The dynamic range is limited by quantization noise which is half the weight of the least significant bit of each sample. A perfect linear codec (which is considered lossless) will suffer these types of signal degradation but nothing else. Codecs which are considered lossy will suffer the same fundamental types of signal degradation plus some additional lost signal which varies from codec to codec.