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.

When needed, it also reconstructs or adaptively mixes in noise-like information in selected frequency bands in order to faithfully replicate signals that originally contained no or fewer tonal components.

The SBR idea is based on the principle that the psychoacoustic part of the human brain tends to analyse higher frequencies with less accuracy; thus harmonic phenomena associated with the spectral band replication process needs only be accurate in a perceptual sense and not technically or mathematically exact.

[2] Lars Liljeryd, Kristofer Kjörling, and Martin Dietz received the IEEE Masaru Ibuka Consumer Electronics Award in 2013 for their work developing and marketing HE-AAC.

Opus's CELT part performs spectral folding on the MDCT bin level, making it a far less advanced but lower-delay technique compared to SBR.

Spectrogram of this recording of a violin playing . Note the harmonics occurring at whole-number multiples of the fundamental frequency. SBR exploits this redundancy.