Speech coding system

摘要

In a speech coding system with an encoder and a decoder cooperating with said encoder, the speech encoder comprises a pre-processor and an ADPCM encoder with a quantizer and step-size adaptation means, while the speech decoder comprises an ADPCM decoder with similar step-size adaptation means as in the ADPCM encoder and with a decoder, and a post-processor. The quantizer is provided with storage means containing values for a correction factor alpha(c(n)) of the step-size DELTA(n), said correction factor being dependent on the quantizer output signal c(n). The step-size adaptation occurs in accordance with the relation: 1 $\Delta \left(n+1\right)=\Delta \left(n\right)·A·\{\begin{array}{cc}\mathrm{alpha}\left(c\left(n\right)\right)& \mathrm{if}itit\mathrm{alpha}\left(c\left(n\right)\right)<1\\ \mathrm{alpha}\left(c\left(n\right)\right)+b& \mathrm{if}itit\Delta itit\left(n\right)·A·c_{\max }<{\mathrm{\Delta <}}_{}\end{array}$