Spectral entropy and coefficient rate for speech coding

Variable rate speech coding is well-suited for network and wireless communications and is necessary to maintain good speech quality and intelligibility at ever-lower rates. In 1960 Campbell used a version of the asymptotic equipartition property (AEP) to derive a relationship between the entropy of the source power spectral density and the minimum coefficient rate required to encode the source. We analyze Campbell´s coefficient rate expression and investigate its properties for autoregressive (AR) processes and for speech. We compare the coefficient rate to the familiar entropy rate power, and to the AIC model order criterion of Akaike (1971), and consider these quantities as rate indicators for dynamically varying the rate of speech coders