Patent ID: 6996523

Claim:
A frequency domain interpolative CODEC system for low bit rate coding of speech, comprising: a linear prediction (LP) front end adapted to process an input signal providing LP parameters which are quantized and encoded over predetermined intervals and used to compute a LP residual signal; an open loop pitch estimator adapted to process said LP residual signal, a pitch quantizer, and a pitch interpolator and provide a pitch contour within the predetermined intervals; and a signal processor responsive to said LP residual signal and the pitch contour and adapted to perform the following steps: extract a prototype waveform (PW) from the LP residual and the open loop pitch contour for a number of equal sub-intervals within the predetermined intervals; normalize the PW by said PW's gain; represent a variable dimension PW in a magnitude domain without further decomposition of said PW into complex components in a mean plus deviations form in multiple bands; compute a voicing measure, said voicing measure characterizing a degree of voicing of said input speech signal and is derived from several input parameters that are correlated to degrees of periodicity of the signal over the predetermined intervals; provide for a voicing classification for the predetermined intervals based on the computed voicing measure; and quantize the PW multi-band mean plus deviations for all speech frames in a magnitude domain using a hierarchical quantization method that employs fixed dimension vector quantizers (VQ) with parameters based on the voicing classification.