4 kbps improved pitch prediction CELP speech coding with 20 ms frame

This paper proposes a new pitch prediction method for 4 kbps CELP (code excited LPC) speech coding. In the conventional CELP speech coding, synthetic speech quality deteriorates rapidly at 4 kbps, especially for female and children´s speech with short pitch period. The important reason is that when the pitch period is shorter than the subframe length, simple repetition of the past excitation signal based on the estimated lag, not the true pitch prediction, is usually used in the adaptive codebook operation. The proposed pitch prediction method can carry out the true pitch prediction by utilizing the current subframe excitation codevector signal, when the pitch prediction parameters are determined. For further improvement, a split weighting method and a low-complexity harmonic and spectral perceptually-weighting method have also been developed. The informal listening test result shows that the 4 kbps coder with 20 msec subframe, utilizing all of the proposed improvements, achieves 0.2 MOS higher results than the coder without them