A low-band spectrum envelope reconstruction method for PSOLA-based F ₀ modification

A low-band spectrum envelope reconstruction method was tested to see if it could improve the sound quality of F₀ modified speech with the PSOLA (Pitch Synchronous Overlap Add) method. In the conventional PSOLA method, the extracted spectrum envelope using a Hanning window with two-pitch-period length had no reliable information in the band of frequencies lower than the original F₀. This problem causes sound degradation of the F₀ modified speech when the F₀ is shifted downward. 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 were reproduced based on the spectral tilt of the spectrum envelope. Subjective listening tests suggest the proposed method yields improved sound quality than the conventional TD-PSOLA method when the downward modification rate exceeds 0.4 octave.