Multiple-description PCM speech coding by complementary asymmetric vector quantizers

We describe new 2-channel multiple-description speech coders based on the ITU-T recommendation G.711 PCM speech coder. The new coders operate in the PCM code domain in order to exploit the companding gain of PCM. They apply pairs of complementary asymmetric 2D vector quantizers to each pair of PCM codes, thus exploiting the correlation between adjacent speech samples. If both quantizer outputs are received (two channels working), they are combined to generate an approximation to the original pair of PCM codes. If only one quantizer output is received (one channel failed, one channel working), a coarser approximation is still possible. The vector quantizers use rectangular cells, and the aspect ratio of the cells controls the speech-quality trade-off between the two-channel and one-channel cases.