Soft-decision decoding of binary block codes in CELP speech coding

It is shown that the residual codebook in CELP speech coders can be replaced with a spherical code derived from an error-correcting code with low encoding complexity. Fast soft-decision decoding algorithm for binary block codes is modified to search the closest code vector in the spherical code. The quantization is done adaptively in the spectral domain in order to concentrate the quantization power on the most important components according to the LPC-parameters.