A NOVEL VARIABLE RATE LPC QUANTIZER FOR HIGH PERFORMANCE SPEECH CODER

A highly efficient algorithm termed adaptive forward-backward vector quantization (APBVQ) is de- veloped for variable bit rate quantization of linear pre- dictive coding (LPC) coefficients and integrat.ed with the FS1016 Federal Standard Code Excited Linear Pre- dictive (CELP) coder. This results in a high perfor- mance low bit rate speech coder called as AFBVQ- CELP which brings in two-fold bit rate reduction by backward LPC indexing and by forward LPC VQ. In AFBVQ, a previously decoded and temporally close speech signal is re-segmented into overlapping blocks. As the LPC coefficients calculated from one of those synthetic blocks are spectrally close to the cur- rent unquantized LPC coefficients, the backward LPC indexing is used to encode the current speech block; otherwise, the forward linear prediction is practised with the split vector quantization supported by a very efficient codebook initialization termed Mixture Gaus- sian Clustering (MGC) (l).