A SOUND RECOGNITION PROCESS comprises training a sound recognition system to a shape Hidden Markov Model (HMM) from a shape codebook of shape codewords, and to a separate gain HMM from a gain codebook of gain codewords. An unknown token is assigned to the sound category associated with the shape HMM and gain HMM with the greatest probability product. Shape and gain codewords replacements for incoming Linear Predictive Coded (LPC) vectors are selected by choosing the codeword with minimum distortion between the codeword and a combination of the vector and some of the preceding codewords, exponentially weighted by time.