AACplus (also commonly referred to as AAC+) is a trade name (used by Coding Technologies) for the HE-AAC V1 compression format. HE-AAC stands for High Efficiency Advanced Audio Encoding and is an enhanced version of the AAC format (more accurately known as AAC-LC (Low Complexity AAC)). This lossy codec was implemented in to the MPEG-4 Audio standard in 2003.
Software media programs like iTunes (version 9 and higher) and Winamp (pro version) support the encoding and decoding of AACplus. While other software like VLC media player and foobar2000 can only playback HE-AAC encoded audio files.
The AACplus algorithm (used by streaming music services like Pandora Radio), employs a technology called Spectral Band Replication (SBR) to enhance audio reproduction while maximizing compression efficiency. This system actually replicates missing higher frequencies by transposing lower frequencies -- these are stored at 1.5 Kbps. Incidentally SBR is also used in the MP3Pro format.
The audio format file extensions associated with AACplus are:
- .m4a
- .MP4
- .,M4b
- .m4V
As well as several software media players supporting AACplus, online music services like Pandora Radio and other Internet radio services also use this format due to its low bandwidth requirements (for speech broadcasts in particular) -- as low as 32 Kbps being acceptable.
