Sub-band coding: Difference between revisions

Revision as of 22:27, 24 July 2019

Revision as of 13:53, 27 July 2019

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{{no footnotes|date = October 2011}}

[[File:SubBandCoding.svg|thumb|500px|SubbandSub-band coding and decoding signal flow diagram]]

In [[signal processing]], '''subbandsub-band coding''' ('''SBC''') is any form of [[transform coding]] that breaks a signal into a number of different [[frequency band]]s, typically by using a [[fast Fourier transform]], and encodes each one independently. This decomposition is often the first step in data compression for audio and video signals.

SBC is the core technique used in many popular [[lossy audio compression]] algorithms including [[MP3]].

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First, a digital filter bank divides the input signal spectrum into some number (e.g., 32) of subbands. The psychoacoustic model looks at the energy in each of these subbands, as well as in the original signal, and computes masking thresholds using psychoacoustic information. Each of the subband samples is quantized and encoded so as to keep the quantization noise below the dynamically computed masking threshold. The final step is to format all these quantized samples into groups of data called frames, to facilitate eventual playback by a decoder.

Decoding is much easier than encoding, since no psychoacoustic model is involved. The frames are unpacked, subband samples are decoded, and a frequency-time mapping reconstructs an output audio signal.

==Applications==

Beginning in the late 1980s, a standardization body, the [[Moving Picture Experts Group]] (MPEG), developed standards for coding of both audio and video. Subband coding resides at the heart of the popular MP3 format (more properly known as [[MPEG-1 Audio Layer III]]), for example.

SubbandSub-band coding is used in the [[G.722]] codec which uses subbandsub-band adaptive differential pulse code modulation (SB-[[ADPCM]]) within a bit rate of 64 kbit/s. In the SB-ADPCM technique, the frequency band is split into two subbandssub-bands (higher and lower) and the signals in each subbandsub-band are encoded using ADPCM.

==References==

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==External links==

* [https://web.archive.org/web/20070613152917/http://www.otolith.com/otolith/olt/sbc.html SubbandSub-Band Coding Tutorial]

{{Compression Methods}}