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.