A Low Bit Rate Scalable CWI Coder based on Wavelet Transform

This paper presents a scalable characteristic waveform interpolation (CWI) speech coder based on wavelet transform (WT) at low bit rate ranging from 1.8 kbit/s to 3.6 kbit/s. The characteristic waveform surface is decomposed into a series of reduced time resolution surfaces using B-spline biorthogonal linear phase filter banks. The common coding parameters form the basic layer at 1.8 kbit/s that can produce an acceptable speech quality. The different wavelet decomposition surfaces form different enhancement layers and improve the speech quality successively with efficient quantization. Subjective listening test showed that this scalable WT-CWI coder performs well at low bit rate.