Speech coding: Difference between revisions

Revision as of 11:41, 30 June 2007

Revision as of 07:55, 20 July 2007

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The [[A-law algorithm]] and the [[Mu-law algorithm]] are used in nearly all land-line long distance telephone communications. They can be seen as a kind of speech encoding, requiring only 8 bits per sample but giving effectively 12 bits of resolution.

The most common speech coding scheme is [[Code- Excited Linear PredictivePrediction]] ([[CELP]]) coding, which is used for example in the [[GSM]] standard. In CELP, the modelling is divided in two stages, a [[linear prediction|linear predictive]] stage that models the spectral envelope and code-book based model of the residual of the linear predictive model.

In addition to the actual speech coding of the signal, it is often necessary to use [[channel coding]] for transmission, to avoid losses due to transmission errors. Usually, speech coding and channel coding methods have to be chosen in pairs, with the more important bits in the speech data stream protected by more robust channel coding, in order to get the best overall coding results.