Conditional vector quantization for speech coding

In many speech-coding-related problems, there is available information and lost information that must be recovered. When there is significant correlation between the available and the lost information source, coding with side information (CSI) can be used to benefit from the mutual information between the two sources. In this paper, we consider CSI as a special VQ problem which will be referred to as conditional vector quantization (CVQ). A fast two-step divide-and-conquer solution is proposed. CVQ is then used in two applications: the recovery of highband (4-8 kHz) spectral envelopes for speech spectrum expansion and the recovery of lost narrowband spectral envelopes for voice over IP. Comparisons with alternative approaches like estimation and simple VQ-based schemes show that CVQ provides significant distortion reductions at very low bit rates. Subjective evaluations indicate that CVQ provides noticeable perceptual improvements over the alternative approaches.