An enhanced AAC audio format from Dolby Laboratories that delivers near CD-quality sound in as little as 32 Kbps. aacPlus extends Low Complexity AAC (AAC LC). Also known as "High Efficiency AAC" (HE-AAC), aacPlus was originally developed by Stockholm-based Coding Technologies, which Dolby acquired in 2007. See AAC
HE-AAC version 1 - AAC+
HE-AAC version 2 - Enhanced AAC+ (eAAC+)
HE-AAC v1 (AAC+) uses Coding Technologies' Spectral Band Replication (SBR) to cut the sampling rate in half. SBR then encodes the missing high frequencies at 1.5 Kbps and stores them in the auxiliary data fields. The decoder restores the high frequencies from the SBR data. See mp3PRO
HE-AAC v2 (eAAC+) uses Parametric Stereo (PS), which combines the left and right channels into a monaural signal. PS encodes the differences between channels as parametric data at 3 Kbps, which is used to decode the monaural stream back into stereo.