Variable-Rate Finite-State Vector Quantization
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A finite-State vector quantizer is a finite-state machine that can be viewed as a collection of memoryless full-searched vector quantizers, where each input vector is encoded using a vector quantizer associated with the current encoder state; the current state and codeword selected determine the next encoder state . In , the state codebooks are unstructured. In addition, it is assumed that all the state codebooks have the same cardinality leading to a fixed-rate system. In this paper, we present two variable-rate variations of the system in . In the first system we let the state codebook sizes be different for different states. In the second system along with the flexibility of having different codebook sizes for different states, we use pruned tree-structured vector quantizers  as the state quantizers. For encoding samples speech data, both of these schemes perform significantly better than the scheme in . The second system gives the best performance of all. Performance improvements of up to 4.25 dB at the rate of 5/8 bits per sample are obtained.