The Phase Vocoder: A Tutorial

TLDR: This article attempts to explain the operation of the phase vocoder in terms accessible to musicians, relying heavily on the familiar concepts of sine waves, filters, and additive synthesis, and employing a minimum of mathematics.

Abstract: For composers interested in the modification of natural sounds, the phase vocoder is a digital signal processing technique of potentially great significance. By itself, the phase vocoder can perform very high fidelity time-scale modification or pitch transposition of a wide variety of sounds. In conjunction with a standard software synthesis program, the phase vocoder can provide the composer with arbitrary control of individual harmonics. But use of the phase vocoder to date has been limited primarily to experts in digital signal processing. Consequently, its musical potential has remained largely untapped. In this article, I attempt to explain the operation of the phase vocoder in terms accessible to musicians. I rely heavily on the familiar concepts of sine waves, filters, and additive synthesis, and I employ a minimum of mathematics. My hope is that this tutorial will lay the groundwork for widespread use of the phase vocoder, both as a tool for sound analysis and modification, and as a catalyst for continued musical exploration.