Editing Spectral band replication (section)

{{Short description|Low bitrate digital audio enhancement technique}}
[[File:Spectrogram of violin.png|thumb|Spectrogram of [[Media:Violin for spectrogram.ogg|this recording of a violin playing]]. Note the harmonics occurring at whole-number multiples of the fundamental frequency. SBR exploits this redundancy.]]
'''Spectral band replication''' ('''SBR''') is a technology to enhance audio or [[speech codec]]s, especially at low [[bit rate]]s and is based on harmonic redundancy in the frequency domain.

It can be combined with any [[Audio compression (data)|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.<ref>
{{Cite web
 |last        = Novak
 |first       = Clark
 |title       = Spectral Band Replication and aacPlus Coding - An Overview
 |url         = http://www.telos-systems.com/techtalk/aacplus/aacPlus_overview.pdf
 |access-date  = February 8, 2010
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20101130235115/http://telos-systems.com/techtalk/aacplus/aacPlus_overview.pdf
 |archive-date = November 30, 2010
 }}
</ref> Some guidance information for reconstruction of the high-frequency spectral envelope is transmitted as side information.

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.