A phase vocoder without requiring phase unwrapping

In recent years, a number of algorithms for controlling parameters of an acoustic signal have been realized according as hardware technologies have been developed. A phase vocoder is one of the widely known methods for time scale modification (TSM) and pitch scale modification (PSM). The phase vocoder converts the length and the pitch of the acoustic signal by increasing or decreasing an instantaneous angular frequency. However, due to the phase unwrapping problem that occurs when the instantaneous angular frequency is estimated, the phase vocoder distorts the waveform of the modified signal. In order to alleviate this problem, we present a new algorithm for the phase vocoder. Our method does not encounter the phase unwrapping problem since we directly use the difference of phases between adjacent analysis frames to avoid estimating the instantaneous angular frequency. Moreover, our approach is effective even when the characteristics of the acoustic signal, e.g., a frequency and amplitude, change rapidly. © 2018 The Institute of Electrical Engineers of Japan.