Speech coding using waveform matching based on LPC residual phase equalization

A speech analysis-synthesis method based on linear predictive coding (LPC) residual phase equalization is presented for low-bit- rate natural sounding speech coding. In this method, the phase-equalized LPC residual signal is represented as the output of the quasi-periodic impulsive excitation to an all-zero filter, which captures harmonic deviation in the residual spectrum which has not been compensated for by LPC inverse filtering of the input speech signal. The impulsive excitation is specified by the instantaneous pitch excitation instant and amplitude. A procedure is presented to determine the excitation parameters and the all-zero filter using a waveform matching criterion. The coder performance is studied objectively and subjectively with a focus on the potential of the excitation model to produce high-quality speech. A speech coder designed for bit rates lower than 4.8 kb/s is discussed.