Book on DAFX - Digital Audio Effects Edited by Udo Zölzer ISBN: 0-471-49078-4 John Wiley & Sons, 2002

Chapter 8

D. Arfib, F. Keiler and U. Zölzer

This chapter describes the use of time-frequency representations of signals in order to produce transformations of sounds. A very interesting (and intuitive) way of modifying a sound is to make a two-dimensional representation of it, modify this representation in some or other way and reconstruct a new signal from this representation. Consequently a digital audio effect based on time-frequency representations requires three steps: an analysis (sound to representation), a transformation (of the representation) and a resynthesis (getting back to a sound). We introduce the fundamental techniques for time-frequency processing, demonstrate several implementation schemes and illustrate the variety of effects possible in the two-dimensional time-frequency domain.

Contents

• Introduction
• Phase Vocoder Basics
  • Filter bank summation model
  • Block-by-block analysis/synthesis model
• Phase Vocoder Implementations
  • Filter Bank Approach
  • Direct FFT/IFFT Approach
  • FFT Analysis/Sum of Sinusoids Approach
  • Gaboret Approach
  • Phase Unwrapping and Instantaneous Frequency
• Phase Vocoder Effects
  • Time-frequency Filtering
  • Dispersion
  • Time Stretching
  • Pitch Shifting
  • Stable/Transient Components Separation
  • Mutation between Two Sounds
  • Robotization
  • Whisperization
  • Denoising
• Conclusion
• Bibliography

Keywords: Time-frequency Processing, Signal Representations, Transforms, Fourier Transforms, Phase Vocoder

Contents