William C. Adams

Quantizing Characteristics for Signals Having Laplacian Amplitude Probability Density Function

The optimum (minimum mean-squared-error criterion) and optimum uniform quantizer characteristics for signals characterized by the Laplacian amplitude probability density function are given in tabular form. These results correct and extend previously published results.

Entropy Measurements for Three Adaptive Source Encoders

The entropy of the output of three adaptive source encoders, AΔM, APCM, and ADPCM, is measured for speech inputs at low sampling rates. It is attempted to correlate the source encoder output entropies, normalized to the channel bit rate, with the results of informal listening tests. It was hypothesized that the channel bit rate utilization factor would predict subjective ranking of the source encoders. The results of measurements do not support this hypothesis; an intuitive explanation is offered.

Linear Delta Modulation Quantizing Noise Characteristics

A formula for signal-to-quantizing noise ratio (SNR) in delta modulation systems is obtained by modifying an existing result for DPCM systems. Computer simulation is used to examine the behavior of the terms in the modified SNR formula.