HE-AAC

High Efficiency AAC aka HE-AAC aka aacPlus

aacPlus is a lossy data compression scheme for audio streams. It is based on MPEG-4, and combines three techniques: Advanced Audio Coding (AAC), Spectral Band Replication (SBR), and parametric stereo (PS).

aacPlus was standardized by the MPEG as part of the MPEG-4 Part 3 specification, under the High Efficiency AAC (HE-AAC) name.

For details on the MPEG-4 Part 3 specification, see wikipedia:MPEG-4_Part_3.

The codec can operate at very low bitrates and is good for Internet radio streaming. A 48 kilobit-per-second stream is considered to have higher quality than 128 kbit/s MP3.

In HE-AAC, Spectral Band Replication (SBR) technology has been applied to AAC, and was incorporated into the standard to form High Efficiency AAC v1 (HE-AAC v1), (sometimes known as aacPlus v1).

Another recent introduction to AAC is Parametric Stereo ( aacPlus v2 or Enhanced aacPlus ). These technologies significantly improve the performance of AAC at lower bitrates, and are used, for example, in Digital Radio Mondiale .

Support

HE-AAC is supported in the free FAAD2 decoding library, and hence in many free players, and in Winamp and foobar2000.

See also

• .m4a file extension (the "mpeg4-audio" extenstion popularized by Apple iTunes)

External links

• Tuner2.com list of Internet radio stations using aacPlus
• aacPlus explained
• Open Source AAC codec FAAC (encoder) and FAAD2 (decoder)