Perceptual Weighting in LSP-Based Multi-Description Coding for Real-Time Low-Bit-Rate Voice Over IP

Abstract

This paper focuses on improving an LSP-based multi-description coding (MDC) scheme for concealing losses when real-time CELP-coded speech data is sent over IP networks. In that scheme, LSP vectors are interleaved because they are highly correlated and can be reconstructed by interpolations when packets are delayed or lost. However, excitation vectors are random in nature and must be replicated in order to conceal losses. To avoid increasing the bit rate of the encoded speech, the excitation vectors are generated from longer subframes. This leads to lower quality of the decoded speech because noise from outside formant regions is over-emphasized, and more excitation information is extracted there. To improve quality, we propose in this paper to modify the perceptual-weighting filter (PWF) in the coder in order to adjust the allocation of noise inside and outside formant regions. We further study a method that selects the PWF in such a way that maintains high quality of the LSP-based MDC across different voice streams and loss scenarios. Experimental results on FS-1016 CELP (4800 bps), ITU G.723.1 ACELP (5300 bps), and ITU G.723.1 MP-MLQ (6300 bps) demonstrate noticeable improvements in decoding quality