An Improved Weighting Function for Low-rate CELP Speech Coding
Chul Hong Kwon · Journal of Electrical Engineering and Information Science · 1997
Below 4.8 kbits/s, code-excited linear predictive(CELP) coders in general suffer from two kinds of perceptually important degradation. One is noise between adjacent harmonics of output speech, that is, inter-harmonic noise, which results in roughness in voiced sound. The other is poor reproduction of speech signal at high frequencies, that is, high frequency mismatch. Several approaches have been introduced to remedy these degradations. These approaches, however, are known to be inadequate for the perceptually weighted mean-squared error criterion typically used in the conventional CELP coder. In order to get the quality as best as possible particularly at a low rate, we propose in this paper an improved weighting function which utilizes the spectral weighting methodology and also takes into account the periodic character in voiced sound. The proposed weighting function can adapt to variation of pitch by itself without any pitch estimation in voiced sound and is also applicable to all speech segments without any voiced/unvoiced discrimination algorithm. Simulation results show that the performance of the CELP coder with the proposed weighting function is better than that of the conventional CELP coder.