UC Santa Barbara

As speech-coding standards have improved over the years, so complexity has increased, and less emphasis been placed on low encoding/decoding delay. We present a low-complexity, low-delay speech codec based on tree-coding with sample-by-sample adaptive long- and short-code generators that incorporates pre- and post-filtering for perceptual weighting and multimode speech classification with comfort noise generation (CNG). The pre-/post-weighting filters adapt based on the code generator parameters available at both the encoder and decoder rather than the usual method that uses the input speech. The coding of the multiple speech modes and comfort noise generation is accomplished using the code generator adaptation algorithms, again, rather than using the input speech. Codec complexity comparisons are presented and operational rate distortion curves for several standardized speech codecs and the new codec are given. Finally, codec performance is shown in relation to theoretical rate distortion bounds.