Embedded WI coding between 2.0 and 4.8 kbit/s

This paper describes an embedded speech coder based on waveform interpolation (WI) techniques. Since the quantization of line spectral frequency (LSF) parameters is fairly orthogonal to the quantization of excitation information, designing an embedded system with WI is much easier than that of other approaches. By using a hierarchical bit-allocation of excitation signals that consist of a slowly evolving waveform (SEW) and a rapidly evolving waveform (REW), the proposed system works well at the bit-rate of 2.0, 2.4, 3.0, 4.0 and 4.8 kbit/s. Listening tests indicate that the performance of the new system is comparable to an optimized fixed-rate WI coder, and the quality degrades gracefully as the bit-rate decreases.

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