Suboptimal search procedures for selecting the innovation sequences in stochastic coders

A suboptimal searching procedure of innovation sequence for code excited linear predictive (CELP) coding algorithms is described. A three-step search algorithm has been investigated. The first step consists of a MPLPC (multipulse linear predictive coding) algorithm. From a codebook containing 1024 Gaussian central-clipped sequences a reduced set of about 40 innovation sequences is selected using the multipulse sequence computed in the first step. The final innovation sequence is determined by performing the full search algorithm with the reduced set of sequences. Informal subjective listening tests were made with speech coded using the three-step algorithm.