Medium band waveform coding of speech signals based on short-time phase equalization
Masaaki Honda, Takehiro Moriya · The Journal of the Acoustical Society of America · 1985
A new speech coding method is presented utilizing perceptual redundancy for slow-varying, short-time phase characteristics. First, a speech signal model is introduced based on the all pole filter and all pass filter, which represent the power spectrum and the short-time phase of speech signals respectively. The phase equalization technique for canceling the short-time phase is then presented based on the time domain matched filtering method. Using this technique, the prediction residual of the speech signal is converted into a nearly zero-phase signal, or ideally into a pitch pulse sequence, which results in the temporal concentration of residual energies. The phase-equalized speech signal is efficiently encoded using variable-rate tree coding with temporal bit allocation. Experimental results show that quality of the phase equalized speech is almost indistinguishable from the original speech, and that the coded speech quality is equivalent to that of the 6.6 bit Log-PCM at a bit rate of 1 bit/sample. It is also confirmed that this system has the ability to make a speech quality change from natural to vocoder sounds by controlling the information bits for the main pulses and its residuals of the phase-equalized residual signal.