A pseudo glottal excitation model for the linear prediction vocoder with speech signals coded at 1.6 kbps

This paper presents a pseudo glottal excitation model for the type of linea r prediction vocoders with speech being coded at 1.6 kbps. While unvoiced s peech and silence intervals are processed with a stochastic codebook of 512 entries, a glottal codebook with 32 entries for voiced excitation is used to describe the glottal phase characteristics. Steps of formulating the pse udo glottal excitation for one pitch period consist of 1) applying a polyno mial model to simulate the low-frequency constituent of the residual, 2) in serting a magnitude-adjustable pulse sequence to characterize the main exci tation, and 3) introducing turbulent noise in series with the resulting exc itation. Procedures are described for codebook construction in addition to analysis and synthesis of the pseudo glottal excitation. Results in a mean opinion score (MOS) test show that the quality produced by the proposed cod er is almost as good as that by 4.8 kbps CELP coder for male utterances, bu t the quality for female utterances is yet somewhat inferior.