- Phase vocoder
A phase vocoder is a type of
vocoder which can scale both thefrequency andtime domain s of audio signals by using phase information. The computeralgorithm allowsfrequency-domain modifications to a digital sound file (typically time expansion/compression and pitch shifting).At the heart of the phase vocoder is the
STFT (short-time Fourier transform), typically coded usingfast Fourier transform s. The STFT converts atime domain representation of sound into atime-frequency representation (the "analysis" phase), allowing modifications to the amplitudes or phases of specific frequency components of the sound, before resynthesis of thefrequency domain representation into the time domain by the inverse STFT. The time scale of the resynthesis does not have to be the same as the time scale of the analysis, allowing for high-quality time-scale modification of the original sound file.Since the boundaries between each window need to be in phase, this method results in an audible "phase smearing" effect, especially on transients. (Similar to phase
dispersion .)Fact|date=April 2008 Many other methods have been developed that mix aspects of the phase vocoder with other methods, to produce similar effects while maintaining phase coherence at transients.Fact|date=April 2008See also
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Audio timescale-pitch modification External links
* [http://www.panix.com/~jens/pvoc-dolson.par The Phase Vocoder: A Tutorial] - A good description of the phase vocoder
* [http://www.ee.columbia.edu/~dpwe/papers/LaroD99-pvoc.pdf New Phase-Vocoder Techniques for Pitch-Shifting, Harmonizing and Other Exotic Effects]
* [http://www.ircam.fr/equipes/analyse-synthese/roebel/paper/dafx2003.pdf A new Approach to Transient Processing in the Phase Vocoder]
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