Editing Phase vocoder (section)

== History ==
The phase vocoder was introduced in 1966 by Flanagan as an algorithm that would preserve horizontal coherence between the phases of bins that represent sinusoidal components.<ref>{{cite journal|doi=10.1002/j.1538-7305.1966.tb01706.x|author=Flanagan J.L. and Golden, R. M.|title=Phase vocoder|journal=Bell System Technical Journal|volume=45|issue=9|pages=1493–1509|year=1966}}</ref> This original phase vocoder did not take into account the vertical coherence between adjacent frequency bins, and therefore, time stretching with this system produced sound signals that were missing clarity.

The optimal reconstruction of the sound signal from STFT after amplitude modifications has been proposed by Griffin and Lim in 1984.<ref>{{cite journal|doi=10.1109/TASSP.1984.1164317|author=Griffin D. and Lim J.|title=Signal Estimation from Modified Short-Time Fourier Transform|journal=IEEE Transactions on Acoustics, Speech, and Signal Processing|volume=32|issue=2|pages= 236–243|year=1984|citeseerx=10.1.1.306.7858}}</ref> This algorithm does not consider the problem of producing a coherent STFT, but it does allow finding the sound signal that has an STFT that is as close as possible to the modified STFT even if the modified STFT is not coherent (does not represent any signal).

The problem of the vertical coherence remained a major issue for the quality of time scaling operations until 1999 when Laroche and Dolson<ref>{{Cite journal
 | author = J. Laroche and M. Dolson
 | title = Improved Phase Vocoder Time-Scale Modification of Audio
 | journal = [[IEEE Transactions on Speech and Audio Processing]]
 | volume = 7
 | issue = 3
 | pages = 323–332
 | year = 1999
 | url = http://www.cmap.polytechnique.fr/~bacry/MVA/getpapers.php?file=phase_vocoder.pdf&type=pdf
| doi = 10.1109/89.759041
 | url-access = subscription
 }}</ref> proposed a means to preserve phase consistency across spectral bins. The proposition of Laroche and Dolson has to be seen as a turning point in phase vocoder history. It has been shown that by means of ensuring vertical phase consistency  very high quality time scaling transformations can be obtained.

The algorithm proposed by Laroche did not allow preservation of vertical phase coherence for sound onsets (note onsets). A solution for this problem has been proposed by Roebel.<ref>Roebel A., "A new approach to transient processing in the phase vocoder", DAFx, 2003. [http://www.ircam.fr/equipes/analyse-synthese/roebel/paper/dafx2003.pdf pdf] {{webarchive|url=https://web.archive.org/web/20040617224423/http://www.ircam.fr/equipes/analyse-synthese/roebel/paper/dafx2003.pdf |date=2004-06-17 }}</ref>

An example of software implementation of phase vocoder based signal transformation using means similar to those described here to achieve high quality signal transformation is [[Ircam]]'s SuperVP.<ref>"[http://anasynth.ircam.fr/home/english/software/supervp SuperVP]", ''Ircam.fr''.</ref>{{verification needed|date=July 2011}}