Spectral Band Replication
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 was developed by coding technologies, and is useful for medium and high quality coding (although the latter is arguable) at low and medium data rates. It is used by MP3Pro, HE AAC and digital radio mondiale.