Stephen D. Voran

Abstract: We describe a 2-channel multiple-description speech coder based on the ITU-T Recommendation G.711 PCM speech coder. The new coder operates in the PCM code domain in order to exploit the companding gain of PCM. It applies a pair of 2-dimensional structured vector quantizers to each pair of PCM codes, thus exploiting the correlation between adjacent speech samples. If both quantizer outputs are received, they are combined to generate an approximation to the original pair of PCM codes. If only one quantizer output is received, a coarser approximation is still possible. When using 6 bits/sample/channel (for a total data rate of 96 kbps) the coder provides an equivalent PCM speech quality of 7.3 bits/sample when both channels are working and 6.4 bits/sample when one channel is working.

Keywords: fading; quantization; speech coding; decoding; Internet telephony; Phase change materials; propagation loss; Communication channels; pulse modulation; speech enhancement

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