Low-bit-rate speech coding using a two-dimensional transform of residual signals and waveform interpolation

Proposes two efficient excitation coding schemes that use a pitch synchronous two-dimensional Fourier transform of linear prediction residual signals. One quantizes and transmits part of the 2D transform coefficients. Transmission of only low transition frequency coefficients results in less perceivable quantization distortion with fewer quantization bits. The other coding scheme is prototype waveform interpolation (PWI) coding using smoothed prototype waveforms. A frequency domain prototype waveform smoothing technique improves the perceptual speech quality of conventional PWI coding. A simulation result of a 1900 bps proposed vocoder is presented. The authors also present a multiband excitation approach for the proposed PWI coding scheme to further improve quality