Gain normalization in a 4200 bps homomorphic vocoder

The authors describe a novel technique for coding the gains in a vector excitation homomorphic vocoder. In this system, the excitation signal, which is obtained by analysis-by-synthesis, consists of a part derived from a Gaussian codebook and a part derived from the past excitation. The authors show how the correlation between the two gain parameters of the excitation can be increased and how they can be jointly coded at a lower bit rate. This approach makes it possible to reduce the bit rate of the homomorphic vocoder from 4800 b/s to 4200 b/s with essentially no degradation in speech quality