Adaptive Quantization in Differential PCM Coders
P. Cummiskey, James L. Flanagan · The Journal of the Acoustical Society of America · 1973
A differential PCM coder is described in which the quantizer is automatically adapted to the error variance. The transmitted bit stream is examined by digital logic which in turn adjusts the quantizer step size to reduce slope overload and granular distortion. For a given bit rate, increased quality over PCM and DPCM coding results. The receiver incorporates adaptation logic identical to that of the transmitter, and reconstructs a signal estimate similar to that made by the transmitter. Digital hardware implementation of the coder is described, and transmission performance at rates of 18, 24, and 32 kilobits/sec is demonstrated.