LPC Speech Coding Based on Variable-Length Segment Quantization

This paper presents a low bit rate LPC coder based on variable-length segment quantization. In this segment vocoder, the speech spectral parameter sequence is represented as the concatenation of variable-length spectral segments generated by linearly time-warping fixed-length code segments. Both the sequence of code segments and the segment lengths are efficiently determined using a dynamic programming procedure. This procedure minimizes the spectral distance measure between the original and the coded spectral sequence in a given interval. An iterative algorithm is also developed for designing fixed-length code segments for the training spectral sequence. This iterative algorithm consists of updating segment boundaries of the training spectral sequence using an a priori codebook, and updating the codebook using these segment sequences. Convergence of this algorithm is discussed theoretically and experimentally. In experiments, the performance of variable-length segment quantization for voice coding is compared to that of fixed-length segment quantization and vector quantization.