Book on Edited by
Udo Zölzer |

**Chapter
8**

Time-frequency
Processing |

*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