Preface

DAFX is a synonym for digital audio effects. It is also the name for a European research project for co-operation and scientific transfer, namely EU-COST-G6 “Digital Audio Effects” (1997–2001). It was initiated by Daniel Arfib (CNRS, Marseille). In the past couple of years we have had four EU-sponsored international workshops/conferences on DAFX, namely, in Barcelona (DAFX-98), Trondheim (DAFX-99), Verona (DAFX-00) and Limerick (DAFX-01). A variety of DAFX topics have been presented by international participants at these conferences. The papers can be found on the corresponding web sites.

This book not only reflects these conferences and workshops, it is intended as a profound collection and presentation of the main fields of digital audio effects. The contents and structure of the book were prepared by a special book work group and discussed in several workshops over the past years sponsored by the EU-COST-G6 project. However, the single chapters are the individual work of the respective authors.

Chapter 1 gives an introduction to digital signal processing and shows software implementations with the MATLAB® programming tool. Chapter 2 discusses digital filters for shaping the audio spectrum and focuses on the main building blocks for this application. Chapter 3 introduces basic structures for delays and delay-based audio effects. In Chapter 4 modulators and demodulators are introduced and their applications to digital audio effects are demonstrated. The topic of nonlinear processing is the focus of Chapter 5. First, we discuss fundamentals of dynamics processing such as limiters, compressors/expanders and noise gates, and then we introduce the basics of nonlinear processors for valve simulation, distortion, harmonic generators and exciters. Chapter 6 covers the wide field of spatial effects starting with basic effects, 3D for headphones and loudspeakers, reverberation and spatial enhancements. Chapter 7 deals with time-segment processing and introduces techniques for variable speed replay, time stretching, pitch shifting, shuffling and granulation. In Chapter 8 we extend the time-domain processing of Chapters 2–7. We introduce the fundamental techniques for time-frequency processing, demonstrate several implementation schemes and illustrate the variety of effects possible in the 2D time-frequency domain. Chapter 9 covers the field of source-filter processing, where the audio signal is modeled as a source signal and a filter. We introduce three techniques for source-filter separation and show source-filter transformations leading to audio effects such as cross-synthesis, formant changing, spectral interpolation and pitch shifting with formant preservation. The end of this chapter covers feature extraction techniques. Chapter 10 deals with spectral processing, where the audio signal is represented by spectral models such as sinusoids plus a residual signal. Techniques for analysis, higher-level feature analysis and synthesis are introduced, and a variety of new audio effects based on these spectral models are discussed. Effect applications range from pitch transposition, vibrato, spectral shape shift and gender change to harmonizer and morphing effects. Chapter 11 deals with fundamental principles of time and frequency warping techniques for deforming the time and/or the frequency axis. Applications of these techniques are presented for pitch-shifting inharmonic sounds, the inharmonizer, extraction of excitation signals, morphing and classical effects. Chapter 12 deals with the control of effect processors ranging from general control techniques to control based on sound features and gestural interfaces. Finally, Chapter 13 illustrates new challenges of bitstream signal representations, shows the fundamental basics and introduces filtering concepts for bitstream signal processing. MATLAB implementations in several chapters of the book illustrate software implementations of DAFX algorithms. The MATLAB files can be found on the web site http://www.dafx.de.

I hope the reader will enjoy the presentation of the basic principles of DAFX in this book and will be motivated to explore DAFX with the help of our software implementations. The creativity of a DAFX designer can only grow or emerge if intuition and experimentation are combined with profound knowledge of physical and musical fundamentals. The implementation of DAFX in software needs some knowledge of digital signal processing and this is where this book may serve as a source of ideas and implementation details.

I would like to thank the authors for their contributions to the chapters and also the EU-Cost-G6 delegates from all over Europe for their contributions during several meetings, especially Nicola Bernadini, Javier Casajús, Markus Erne, Mikael Fernström, Eric Feremans, Emmanuel Favreau, Alois Melka, Jøran Rudi and Jan Tro. The book cover is based on a mapping of a time-frequency representation of a musical piece onto the globe by Jøran Rudi. Thanks to Catja Schümann for her assistance in preparing drawings and LATEX formatting, Christopher Duxbury for proof-reading and Vincent Verfaille for comments and cleaning up the code lines of Chapters 8 to 10. I also express my gratitude to my staff members Udo Ahlvers, Manfred Chrobak, Florian Keiler, Harald Schorr and Jörg Zeller for providing assistance during the course of writing this book. Finally, I would like to thank Birgit Gruber, Ann-Marie Halligan, Laura Kempster, Susan Dunsmore and Zoë Pinnock from John Wiley & Sons, Ltd for their patience and assistance.

My special thanks are directed to my wife Elke and our daughter Franziska.

Hamburg, March 2002

Udo Zölzer