This paper proposes a new speech coding method called PSI-CELP (Pitch Synchronous Innovation CELP). This method is based on CELP, but adds pitch synchronous innovation, which means that even random codevectors are adaptively converted to have pitch periodicity for voiced frames. In addition, this paper also proposes four other methods: (a) an FIR-type perceptual weighting filter using unquantized LPC parameters, (b) a fixed codebook that is prepared as part of the adaptive codebook for nonperiodic frames, (c) a random codebook which consists of two conjugate sub-codebooks, and (d) codebook searches using delayed decision. Due to these methods, SNR and subjective quality are significantly improved. These basic methods were adopted in the standard CODEC for Japanese half-rate digital mobile telephone service.
Bibliographic reference. Miki, Satoshi / Mano, Kazunori / Ohmuro, Hitoshi / Moriya, Takehiro (1993): "Pitch synchronous innovation CELP (PSI-CELP)", In EUROSPEECH'93, 261-264.