Spectral Band Replication
From Hydrogenaudio Knowledgebase
Spectral Band Replication (SBR) is a parametrical coding method developed by CodingTechnologies to enhance audio quality at low bitrates.
Guessing the nontransmitted higher frequency range of a compressed audio file by using some helper bits (transmited with the stream) in addition to the transmitted base band. SBR allows a restoration (not reconstruction) of the upper frequency range without lots of bits. It is used by MP3Pro, HE AAC and Digital Radio Mondiale.