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Main Group 60: Phase Vocoder Analysis/Synthesis
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Sub Id  Contents

        The MIT Media Lab Phase Vocoder
01      Testfiles for pvanal 
    1   4 partials, 1 sec
    2   4 partials, .2 sec
        Testing Procedure
        A Sample Session at the Terminal    
        From Phase to Frequency
22      Ktimpnt Variations 
    1   LINE pointer, 1:1 ratio, santur1.pv1
    1B  LINSEG pointer, variable ratios, speech1.pv1  
    1C  LINE pointer, 1:250 ratio, snap.pv1
    2   EXPON, 1:1 & 1:2 ratio, santur1.pv1
    3   LFO pointer, 1:1.25 ratio, santur1.pv1
23      Kfmod Variations 
    1   EXPON transposition, santur1.pv1
    2   LINSEG transposition, speech1.pv1
  
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Overview

The phase vocoder analyzes and resynthesizes audio signals. The
underlying analysis-synthesis model assumes in this case that the
signal is well represented by a sum of sinusoids. Wind, brass,
string, speech and a number of percussive sounds are well
represented by the phase vocoding technique. Some other
percussive sounds like clicks, or certain signal-to-noise sound
combinations are not well represented as a sum of sinusoids.
(Dolson 1987)

Analysis
The program pvanal performs an analysis of a soundfile and writes
the result to an analysis file. The analysis basically consists
of an FFT, where framesize of the window (a number of consecutive
audio samples) and window overlap factor are optional CL
arguments. The analysis file will be at least twice as big as the
soundfile and contains alternating magnitude and frequency
values. This data can be interpreted as sequence of short time
Fourier transforms (per frame) or as the time-varying response of
a bank of narrow bandpass filters (per channel). 

Modification
Software can modify frequency and/or amplitude data over the
whole or a partial range of analyzed data. Moore gives a thorough
exposition of programs to implement these possibilities. (Moore
1990: pp.227-263)
  
Synthesis
The synthesis is done by Csound's unit generator PVOC. The
original sound can be resynthesized with high fidelity. More
commonly time and/or frequency modifications are performed during
resynthesis. In this case, the PVOC unit will interpolate between
given 'stable' points.

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Suggested Reading

Dolson, Mark 1989.
"Fourier-Transform-Based Timbral Manipulations."
in Mathews, M.V. and J.R. Pierce, eds.1989. 
Current Directions in Computer Music Research. 
MIT press, pp. 105-112.

Dolson, Mark 1987. 
"The Phase Vocoder: A Tutorial."
Computer Music Journal 10(4):14-27.

Dudley, Homer 1939.
"The Vocoder." Bell Labs. Rec. 18:122-126.
Reprinted in IEEE Transactions on Acoustics, Speech and Signal
Processing ASSP-29(3):347-351.

Flanagan, J.L. and R.M. Golden 1966.
"Phase Vocoder."     
Bell System Technical Journal 45:1493-1509.
Reprinted in IEEE Transactions on Acoustics, Speech and Signal
Processing ASSP-29(3):388-404.

Gordon, J.W., and John Strawn 1985.
"An Introduction To The Phase Vocoder."
in J. Strawn, ed. 1985. 
Digital Audio Signal Processing: An Anthology. 
A-R Editions, pp. 221-270.

Grey J.M. 1977.
"Multidimensional Perceptual Scaling of Musical Timbres."
Journal of the Acoustical Society of America 61(5):1270-1277.

Grey, J.M., and J.A. Moorer 1977.
"Perceptual Evaluations of Synthesized Musical Instrument Tones."
Journal of the Acoustical Society of America 
62(2):454-462.

Grey, J.M., and J.W. Gordon 1978.
"Perceptual Effects of Spectral Modification on Musical Timbres."

Journal of the Acoustical Society of America 
63(5):1493-1500.

Griffin, D.W., and J.S. Lim 1984.
"Signal Estimation from Modified Short-Time Fourier Transform."
IEEE Transactions on Acoustics, Speech and Signal Processing
ASSP-32(2):236-243.

Moore, F.R. 1990.
"The Phase Vocoder."
in Elements of Computer Music.
Prentice-Hall, pp. 227-263.

Moorer, J.A. 1978.
"The Use of The Phase Vocoder in Computer Music Applications."
Journal of the Audio Engineering Society 26(1/2):42-45.

Portnoff, M.R. 1976.
"Implementation of the Digital Phase Vocoder Using the Fast
Fourier Transform."  
IEEE Transactions on Acoustics, Speech and Signal Processing
ASSP-24:243-248.

Portnoff, M.R. 1980.
"Time-Frequency Representation of Digital Signals and Systems
Based on Short-Time Fourier Analysis."  
IEEE Transactions on Acoustics, Speech and Signal Processing
ASSP-28(1):55-69.


Portnoff, M.R. 1981a.
"Short-Time Fourier Analysis of Sampled Speech."  
IEEE Transactions on Acoustics, Speech and Signal Processing
ASSP-29(3):364-373.

Portnoff, M.R. 1981b.
"Time-Scale Modification of Speech Based on Short-Time Fourier
Analysis."  
IEEE Transactions on Acoustics, Speech and Signal Processing
ASSP-29(3):374-390.

Press, William H. et al. 1988.
"Fast Fourier Transform." in Numerical Recipes in C: The Art of
Scientific Computing. 
Cambridge: Cambridge University Press, pp. 496-536.

Wishart, T. 1990.
"The Phase Vocoder."  Composers' Desktop Project Csound for Atari
Manual. York, England: CDP.

