A high-qulaity speech coding method (SPMEX) at 4.8 kb/s is proposed. The SPMEX selects a suitable excitation signal, based on the decision from acoustic features of speech signal in a frame. Improved pitch interpolation multi-pulse (PMPC) excitation is selected for vowel-like speech. In PMPC, multi-pulse during only one pitch period is calculated in the frame. Further, gain and phase adjusting coefficients are calculated for each of the other pitch periods in the same frame, in order to produce high-quality synthetic speech. Multi-pulse excitation (MPC) is selected for stop and transition-like speech. Stochastic codebook (SC) excitation is selected for Meat ion-like speech. Subjective evaluation results show that 4.8 kb/s SPMEX reconstructs high-quality synthetic speech, which is equivalent to 48 kb/s /n-law PCM.
Bibliographic reference. Ozawa, Kazunori (1989): "A 4.8 kb/s high-quality speech coding using various types of excitation signals", In EUROSPEECH-1989, 1306-1309.