A low-band spectrum envelope modeling for high quality pitch modification

A low-band spectrum envelope reconstruction method was tested to see if it could improve the sound quality of speech modified by the PSOLA (pitch synchronous overlap add) method. In the conventional TD (time domain)-PSOLA method, the spectrum envelope extracted using a Hanning window with a two-pitch-period length had no reliable information in the band of frequencies lower than original F₀. This problem causes the sound degradation of the F₀ modified speech. In the proposed method, the low-band spectrum envelope was properly modified according to the F₀ modification rate. The amplitude of the F₀ harmonic components in the low-band was reproduced based on the spectral tilt of the spectrum envelope. Subjective listening test results suggest this proposed method yields better sound quality than the conventional TD-PSOLA method when the downward modification rate exceeds 0.4 octave.