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.