New techniques for multi-prototype waveform coding at 2.84 kb/s

The paper describes new techniques for prototype waveform (PW) coding at coding rates as low as 2.84 kb/s. The algorithm produces good communications quality speech with significant improvements over previously reported PW coding schemes. In multi-prototype waveform (MPW) coding, prototypes are extracted at 2.5 ms intervals. No distinction is necessary between voiced and unvoiced speech since the normalised LP residual prototypes are coded as a combination of a noise vector and smoothly evolving pitch pulse. At low bit rates it is unnecessary to explicitly code the underlying pulse shape-the relative magnitude of the rapidly evolving noise vectors is sufficient to describe the level of periodicity in each prototype. Prototypes are quantised using either an open or closed-loop scheme with similar results. Quantised prototypes are interpolated by continuous phase interpolation of Fourier coefficients in the discrete frequency domain.