Variable rate vector quantization of the speech spectral envelope

Effective rate variation during active speech is a necessary component of sophisticated variable rate speech compression schemes. Here, we use open-loop estimates of spectral shape to roughly determine signal bandwidth and bit allocations for variable rate encoding of spectral parameters. We analyze the application of the relative entropy functional to sets of line-spectrum pairs (LSPs) and transform-based generalized spectral distributions of Gibson et al. (1993). We present experimental results demonstrating that the relative entropy of these quantities can be used to good advantage in developing variable rate vector quantization schemes for the spectral envelope of speech signals