The Phase Vocoder – Part I


Richard Dudas, Cort Lippe


The phase vocoder is a tool used to perform time-stretching and pitch-shifting on recorded sounds. Its name derives from the early “vocoders” (contraction from “voice encoders”), which used a set of bandpass filters in parallel over many frequency bands, to crudely analyze and reconstruct speech. Unlike the classic vocoder, the phase vocoder is instead based on a Short-Term Fourier Transform (STFT) – a Fourier Transform performed sequentially on short segments of a longer sound – and in practical use has little to do with the hardware vocoders of the 1960s and 1970s. The phase vocoder can, however, be considered a type of vocoder because the Fourier Transform returns a set of amplitude values for a set of frequency bands spaced evenly across the sound’s spectrum, similar to the older vocoder’s set of bandpass filters. Of course the phase vocoder, as its name suggests, not only takes into account the amplitude of these frequency bands, but also the phase of each band.

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Where this article has been cited:

• Ferreira, José Luís, “Une approche de l’électronique ‘live’: Une étude de stratégies”Revue Francophone Informatique Musicale, No. 1, Association Française d’Informatique Musicale, Maison dea Sciences de l’Homme, Paris, France, 2011

• Porres, Alexandre T., “Dissemination Of Computer Music Theory Outside Academia”Proceedings of the International Computer Music Conference (ICMC), New York, USA, 2010

• Massarelli, Carlo, e-Zampognë: Analisi delle zampogne italiane e sviluppo di uno strumento musicale elettronico che ne recupera le caratteristiche, Masters Thesis, Politecnico di Torino, Corso di Laurea in Ingegneria del Cinema e dei Mezzi di Comunicazione, Torino, Italy, 2009