Nuggehally S. Jayant

Signal compression based on models of human perception

The notion of perceptual coding, which is based on the concept of distortion masking by the signal being compressed, is developed. Progress in this field as a result of advances in classical coding theory, modeling of human perception, and digital signal processing, is described. It is proposed that fundamental limits in the science can be expressed by the semiquantitative concepts of perceptual entropy and the perceptual distortion-rate function, and current compression technology is examined in that framework. Problems and future research directions are summarized. >

Coding speech at low bit rates: Advanced algorithms and hardware for voice telecommunications are paring hit rates by at least a factor of four, without losing intelligibility

Digital coding techniques are described that promise to enhance the applicability of voice communications and storage. The techniques allow more speech to be represented with a given number of binary digits, without losing natural voice quality. The advanced coding techniques just becoming available yield natural-sounding telephone speech at digital transmission rates of 16, 8, and eventually 4 Kb/s as well as the standard 64 and 32 Kb/s rates. The author discusses quantification of voice quality, the implementation of algorithms for digital coding using chips, algorithms for prediction and bit allocation, human sound perception, and hybrid coding approaches.

Multiple delta modulation of a speech signal

A speech signal was passed through a cascade of identical delta modulators. Signal degradation (as a function of the number of delta modulations I) was initially more rapid when the delta modulation was adaptive (ADM) than if it was linear (LDM). However, the rate of degradation was nearly constant in LDM, while for ADM it decreased monotonically with I (as in PCM); and at I=6, the ADM still maintained a significant SNR advantage.

Characteristics of a delta modulator

Additional results from a previously described computer simulation of an adaptive delta modulator are presented and interpreted, and their relevance to a proposed upper bound on delta-modulator performance is indicated.