High Efficiency AAC (HE-AAC) is a version of the MPEG-4 AAC audio coding standard that is especially developed to give a low bit rate after encoding. HE-AAC can encode 5.1 surround sound at a bit rate of only 128 kbps and consumer-grade stereo at 48 kbps or even at a bit rate of 32 kbps with still good quality.
HE AAC is a combination of the MPEG-4 AAC Low Complexity (LC) Object Type and Spectral Band Replication (SBR). This means that the high-frequency components of the signal are not encoded. These components are regenerated with the aid of a small amount of control data that is part of the AAC bitstream together with the encoded low-frequency part of the signal. HE-AAC is about 40% more efficient than MPEG-4 AAC LC.
HE-AAC is especially very usefull for streaming media, where capacity is still restricted, such as digital broadcasting, mobile multimedia and Internet services like Internet radio.