New Phase-Vocoder Techniques are Real-Time Pitch Shifting, Chorusing, Harmonizing, and Other Exotic Audio Modifications
Jean Pierre LAROCHE, Mark Dolson · Journal of the Audio Engineering Society · 1999
The phase vocoder is a well-established tool for time-scaling and pitch shifting speech and audio signals. Its theory is now well understood and improvements have been proposed to reduce artifacts commonly encountered when time expanding signals by large factors. In the literature the phase vocoder has been described primarily as a tool for time scaling rather than pitch shifting, the latter usually being achieved by a combination of time scaling and sampling-rate conversion. The authors focus mainly on pitch-scale modifications of speech and audio signals and discuss the drawbacks of the standard time-scaling and resampling technique. Two alternative techniques are presented which reduce the complexity and computational cost significantly while offering dramatically extended capabilities. In particular, the new techniques, which operate solely in the frequency domain, enable chorusing, harmonizing, and nonstandard frequency modifications such as partial stretching (nonlinear frequency saling), frequency inversions, and so on.