PITCH SYNCHRONOUS INNOVATION CODE EXCITED LINEAR PREDICTION (PSI-CELP)

This paper proposes a new speech coding method pitch synchronous innov ation code excited linear predictor (PSI-CELP). This method is based o n CELP but adds pitch synchronous innovation. This results in even ran dom codevectors being adaptively converted to have pitch periodicity f or voiced frames. This scheme can improve the synthesized speech quali ty of voiced frames in the low bit-rate CELP without increasing either computational complexity or bit rate. In addition to pitch synchronou s innovation, this paper also proposes four other methods in which the quality of synthesized speech is effectively improved or the computat ional complexity is reduced for low bit-rate CELP: (1) the perceptual weighting filter is an MA-type and uses nonquantized LPC parameters; ( 2) the fixed codebook is prepared as part of the adaptive codebook for nonperiodic frames; (3) the random codebook consists of two-channel c onjugate sub-codebooks; and (4) codebook searches are made using delay ed decision. In a speech coding system with pitch synchronization of r andom codevectors, improvements in ratio SNR, segmental SNR, and opini on equivalent Q value are respectively 1.6 dB, 1.0 dB, and 0.5 dB. The se basic methods were adopted in the standard codec for Japanese half- rate digital mobile telephone service.