Variable bit rate MBELP speech coding via V/UV distribution dependent spectral quantization

A variable bit rate multiband excited linear predictive speech coder is proposed in this paper. Speech signals are compressed at different bit rates ranging from 0.88 kbps to 2.6 kbps according to the mode of operation and the optimum V/UV transition frequency. An average bit rate of 1.24 kbps is achieved. The proposed speech coder improves the speech quality by splitting the non-stationary speech segments for analysis. The V/UV distribution of a short-time speech spectrum is represented efficiently by using a closed-loop minimised V/UV transition frequency. Depending on the V/UV transition frequency, the spectrum envelope is quantized at variable bit rates through embedded differential predictive scalar and vector quantizations of the LSP parameters. The proposed spectral quantization scheme results in a spectral distortion comparable to a fixed 24-bit 2-dimensional differential scalar quantization scheme.