Rate-Distortion Function for Speech Coding based on Perceptual Distort ion ~easuret

Abstract: In [I], we have proposed a perceptual distortion measure for speech coders using an auditory (cochlear) model. This measure evaluates the neural-firing crossentropy of the coded speech with respect to that of the original one. In this paper, the output space of the cochlear model is explored using this measure form so as to verify the existence of the pitch and the formant information. However, the prime objective of this article is to provide a ratedistortion analysis for speech coding. We evaluate a lower bound to the ratedistortion function based on this distortion measure and also compute the exact rate-distortion function using the Blahut algorithm. Four state-of-the-art speech coders with rates ranging from 4.8 kbps (CELP) to 32 kbps (ADPCM) are studied from the viewpoint of their performances with respect to the rate-distortion limits.