Time-scale and pitch-scale modification by the phase vocoder without occurring the phase unwrapping problem

A phase vocoder is one of the well-known methods for time-scale and pitch-scale modification. This method performs time-scale and pitch-scale modification by increasing or decreasing an estimated instantaneous angular frequency. However, due to the phase unwrapping problem, which is a well-known problem in the phase vocoder, the phase vocoder distorts the waveform of modified signal. The phase unwrapping problem occurs when the phase vocoder estimates the instantaneous angular frequency. In this paper, we propose a phase vocoder without occurring the phase unwrapping problem. The proposed method uses the difference of phases between adjacent analysis frames directly for the phase modification. Because this method does not use the estimated instantaneous angular frequency, the phase unwrapping problem can be avoided. We verified the effectiveness of the proposed method by simulations of time-scale and pitch-scale modification.