Techniques for improving subjective quality of PSI-CELP and its evaluation results

This paper describes techniques for evaluating and improving subjective quality of PSI-CELP speech coding. In low bit-rate speech coding, it is impossible to design good coders based on only objective evaluation measures such as SNR, SNRseg, and cepstral distances: subjective evaluation is essential. The PSI-CELP codec for mobile communications has been designed to be optimal under the following conditions: error free, burst error, low level power, and background noise. A perceptual weighting filter and a postfilter improve the subjective quality. The relationships between subjective and objective evaluation measures have been investigated to obtain error-robust coders. The subjective quality of the resulting half-rate PSI-CELP codec is better than that of the Japanese full-rate codec.