AAC (Advanced Audio Coding) is an audio compression scheme first standardized within MPEG in 1997. AAC was designed to provide high quality audio at lower bit-rates than previous MPEG audio compression formats. AAC was further refined through the MPEG-4 standardization process and has subsequently been enhanced with bandwidth extension technology yielding High Efficiency AAC (HE AAC), and with the addition of parametric stereo, resulting in High Efficiency AAC version 2 (HE AAC v2).

The "AAC Family" is set of backwards-compatible audio coding technologies: MPEG-4 AAC LC decoders can playback MPEG-2 AAC LC bit-streams, MPEG-4 HE AAC decoders can playback both MPEG-4 and MPEG-2 AAC LC bit-streams, etc. In this way the AAC family can support a wide variety of applications ranging from extremely low bit-rates required for music delivery over cellular phone networks, to “transparent” quality (indistinguishable from the original source material) for the most discriminating listeners.

A copy of the MPEG-4 Audio standard, which incorporates the AAC formats, can be purchased from the ISO online store (search for “14496-3”).