Spectral band replication

Spectral band replication (SBR) is a technology to enhance audio or speech codecs, especially at low bit rates and is based on harmonic redundancy in the frequency domain.

It can be combined with any audio compression codec: the codec itself transmits the lower and midfrequencies of the spectrum, while SBR replicates higher frequency content by transposing up harmonics from the lower and midfrequencies at the decoder. Some guidance information for reconstruction of the high-frequency spectral envelope is transmitted as side information.