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

Chapter 7

P. Dutilleux, G. De Poli and U. Zölzer

In this chapter we discuss several time domain algorithms which are a combination of smaller processing blocks like amplitude/phase modulators, filters and delay lines. These effects mainly influence the pitch and the time duration of the audio signal. We will discuss two approaches for time stretching of audio signals. They are based on an analysis stage, where the input signal is divided into segments (blocks) of fixed or variable length, and a synthesis stage where the blocks of the analysis stage are recombined by an overlap and add procedure. These time stretching techniques perform time scaling without modifying the pitch of the signal. The further section focuses on pitch shifting, and introduces three techniques: block processing based on time stretching and resampling, delay line modulation and pitch-synchronous block processing. The last section on time shuffling and granulation presents a more creative use of time-segment processing. Short segments of the input signal are freely assembled and time placed in the output signal. The wide choice of strategies for segment organization implies a sound composition attitude from the user.

Contents

• Introduction
• Variable Speed Replay
• Time Stretching
  • Historical Methods - Phonogene
  • Synchronous Overlap and Add (SOLA)
  • Pitch-synchronous Overlap and Add (PSOLA)
• Pitch Shifting
  • Historical Methods - Harmonizer
  • Pitch shifting by time stretching and resampling
  • Pitch Shifting by Delay Line Modulation
  • Pitch Shifting by PSOLA and Formant Preservation
• Time Shuffling and Granulation
  • Time Shuffling
  • Granulation
• Conclusion
• Sound and Music
• Bibliography

Keywords: Time Stretching, Time Scaling, Pitch Shifting, Frequency Scaling, SOLA, PSOLA, Shuffling, Granulation

Contents