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Recent developments in vector quantization as applied to speech compression have allowed significant reductions in the bit rate of LPC vocoders. A 2400 bps LPC vocoder is being modified to operate at 800 bps while retaining acceptable intelligibility and naturalness in quality. The design of such a speech compression system is discussed and a demonstration tape played.

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Vector and scalar quantization techniques for LPC filter coefficients are compared. Geometric comparisons are made in the coefficient space and spectral distortion comparisons are made along a number of distortion measure scales. Spectral and statistical characteristics of the quantization errors for both techniques are also examined in detail. Correlations to listening comparisons of output synthesis speech will be presented. Taped examples will also be played.