Advanced audio codec - AAC - is an audio coder/decoder standardized by the ISO/IEC Moving Picture Experts Group (MPEG) committee in 1997 as an improved but non-backward-compatible alternative to MP3. Like MP3, AAC is intended for high-quality audio (like music) and expert listeners have found some AAC-encoded audio to be indistinguishable from the original audio at bit rates around 128 kbps, compared with 192 kbps for MP3.

Advanced audio codec plus is a version of the AAC coder that is used to provide enhanced audio quality at high frequencies. The AACPlus system uses spectral band replication to improve the audio quality when possible. The AACPlus system has multiple streams of audio information which are composed of a base stream that can be combined with another stream to adjust (improve) the characteristics of the high-frequency audio signal components.

HE ACC is a version of the MPEG AAC system with spectral band replication (SBR) added to improve audio quality and/or lower the necessary data transmission rate.

ACC LD is a version of the MPEG AAC system that is designed to provide good audio quality while providing and maximum signal processing delay that does not exceed 20 msec.