CODEUR CELP À COMPLEXITÉ RÉDUITE

Abstract
CELP coder enables speech coding with good quality at bit rates as low as 4 kps. Several methods have been developed to lessen the computation task. We present a new multistage method that preserves the qualities of the CELP coder with reduced complexity. The basic idea is to find a subset S₁ of candidate codewords by approximating the synthetic signal energy. This approximation is obtained by restricting the frequency range and sub-sampling. A full exact search is done on this subset. The procedure can be iterated. Typically, for an initial codebook of 1024 words and a single stage of sub-sampling by a factor equal to q₁ = 5, the size of the subset S₁ is 70 and the calculation gain is 9. This performance can be improved up to a calculation gain of 13 by introducing several stages of sub-sampling q₁ = 5 and q₂ = 2.