Voiced source extraction from an envelope of residual signals using LPC analysis

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This paper shows a new method to extract voiced source information to construct a high quality vocoder. As voiced source information, we can directly extract peak points and amplitudes of pitch pulses by estimating the envelope characteristic of the amplitudes of the time‐domain residual signals. Then we create the following algorithm adapting LPC analysis. First, the squared time‐domain residual signals are regarded as the “pseudo‐frequency‐domain power spectra.” Next, these signals are symmetrized and the inverse FFT is performed. Through these computations, the autocorrelation coefficients of the “pseudo‐frequency‐domain power spectra” are obtained. Then, LPC analysis is performed on these coefficients, and linear prediction coefficients ai are obtained. Next, the envelope signals of the magnitude spectra are computed by performing an FFT on the ai. Finally, the envelope characteristic of the time‐domain residual signals regarded as the power spectra is obtained. From these envelope signals, we can very easily extract exact peak points and amplitudes of pitch pulses during voiced segments. By using this method, a little change of pitch pulses during transition segments between voiced and unvoiced segments can be exactly extracted. We can synthesize a high quality voice using a PARCOR vocoder.