The Phase Vocoder – Part II


Richard Dudas, Cort Lippe


In our last article about the phase vocoder we saw how to create a basic phase vocoder for time-stretching. While it is by no means a simple MSP patch, it is a useful one. In addition to time-stretching, the phase vocoder has been used for transposition and “freeze” effects, which we will be discussing in this article. Furthermore, in the last part, we designed two phase vocoder patches — one which works with polar coordinates (amplitude and phase values), and one which works with cartesian (x, y) coordinates. Whereas the former is easier to understand (and simpler to patch together), the latter is more efficient, since it avoids using trigonometric math functions (specifically the arctan function), which are computationally expensive. We will take our existing phase vocoder patch as a starting point, and show our modifications to both the polar and cartesian versions.

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