SBR (Spectral Band Replication) is a new audio coding bandwidth extension technology, which is standardized in ISO/IEC 14496-3:2001/Amd.1:2003 [ISO14496A].
It improves the performance of low bitrate audio and speech codecs by either increasing the audio bandwidth at a given bitrate or by improving coding efficiency at a given quality level. For example, SBR can be used in conjunction with MP3 (mp3PRO), AAC (HE-AAC), CELP, HVXC to achieve a quality at 64 kbps stereo (MP3, AAC) that compares to conventional stereo at a bitrate exceeding 100 kbps.
SBR can be used with mono and stereo as well as with multichannel audio.
HE-AAC profile is combining AAC LC profile and SBR technology. HE-AAC is widely for mobile multimedia services.
In accordance with the mathematical model used by SBR in most audio materials a very high correlation is observed between the lower frequencies and the higher frequencies of a spectrum. Therefore “smart” transposition allows the transmitted signals in higher frequencies to be restructured so as to avoid coding and transmitting them as spectral data. The subsequent SBR adjustment block improves the highest reconstructed frequency.
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