Bit rate reduction by automatic adaptation of quantizer step-size in DPCM systems

A Differential Pulse Code Modulation (DPCM) system with adaptative quantization is described. Theoretical considerations on the optimum parameters that determine the quantizer adaptation in order to minimize the quantizing noise are developed. The performances of a 32 kbit/sec computer simulation of such a system are shown and the particular type of output quantizing noise examined. Attention is devoted to subjective evaluation of the output quality, even in the presence of channel errors. It is concluded that the DPCM system, at a 32 kbit/sec rate is subjectively comparable with a 64 kbit/sec log-PCM system for the whole range of real telephone speech signals.