Evolution of Variable Rate Speech Coders

A method for design of multi-mode variable rate speech coders is described. Based on a standard fixed rate CELP speech coder, a large number of coder modes are "bom" by modifying the bit allocations to the coder parameters. Then, an evolution process starts, where only modes with good performance survive to be included in the final multi-mode coder. To measure the perfor mance of the modes, a cost criterion is developed. This criterion rewards high segmental SNR and penalizes high rate to favor efficient coders.