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. This original phase vocoder did not take into account the vertical coherence between adjacent frequency bins, and therefore, time stretching with this system did produce 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. This algorithm does not consider the problem to produce a coherent STFT, but it allows to find 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 the Laroche and Dolson proposed a rather simple 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 to preserve horizontal phase coherence for sound onsets (note onsets). A solution for this problem has been proposed by Roebel.
A software implementation of the phase vocoder based signal transformation that is using means similar to what has been described here above to achieve high quality signal transformation is for example Ircam's SuperVP.
Read more about this topic: Phase Vocoder
Famous quotes containing the word history:
“The second day of July 1776, will be the most memorable epoch in the history of America. I am apt to believe that it will be celebrated by succeeding generations as the great anniversary festival. It ought to be commemorated, as the day of deliverance, by solemn acts of devotion to God Almighty. It ought to be solemnized with pomp and parade, with shows, games, sports, guns, bells, bonfires and illuminations, from one end of this continent to the other, from this time forward forever more”
—John Adams (1735–1826)
“Every generation rewrites the past. In easy times history is more or less of an ornamental art, but in times of danger we are driven to the written record by a pressing need to find answers to the riddles of today.... In times of change and danger when there is a quicksand of fear under men’s reasoning, a sense of continuity with generations gone before can stretch like a lifeline across the scary present and get us past that idiot delusion of the exceptional Now that blocks good thinking.”
—John Dos Passos (1896–1970)
“Every library should try to be complete on something, if it were only the history of pinheads.”
—Oliver Wendell Holmes, Sr. (1809–1894)