Multi-prototype waveform coding using frame-by-frame analysis-by-synthesis

A new mechanism for using analysis-by-synthesis techniques in low rate waveform interpolation based coders is introduced. The algorithm, implemented as part of a multi-prototype waveform coder, exploits the high quality speech produced by interpolating unquantised speech-domain prototype waveforms. In the new scheme, a frame of prototype waveforms is quantised using two sets of codebook searches, one representing the slowly evolving prototype shape and the other the rapid, noisy components. The scheme offers performance advantages over the previous open-loop multi-prototype waveform coder, particularly when perceptual weighting is incorporated in the search. Reductions in search complexity and the use of the scheme for quantisation at higher rates are also considered. This results in a generalised analysis-by-synthesis waveform interpolation architecture with closed-loop optimisation of all prototype waveform properties