Improving the phase vocoder approach to pitch-shifting

A class of methods known as phase vocoders allows for implementing pitch shifting in the spectral domain. We extend the approach of shifting the isolated harmonics of the spectrum by introducing a new technique for separating the sinusoidal components. Keeping together the main lobe and the side lobes, which result from convolution of the harmonics with the spectrum of the analysis window in the Fourier transform, we minimize the leakage of energy and the related phase compensation problems. Furthermore, we integrate a robust enhancement to the update of the phase, based on tracking of the energy envelope. The formant structure of the signal is preserved by means of an all-pole speech production model. The proposed modifications lead to significant improvement of the quality of the pitch-shifted speech.