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Audio Effects: Theory, Implementation and Application PDF

362 Pages·2014·4.22 MB·English
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Engineering – Electrical R e i s s • M c P h Audio Effects e THEORY, IMPLEMENTATION r Audio Effects s AND APPLICATION o n “ … a fascinating new book on audio processing algorithms. It starts from basics of digital audio engineering and signal processing, and then contin- ues to explain in detail the most important audio effects algorithms. I very T h e o r y, I m p l e m e n t a t i o n much like the chapter on delay-line effects, which gives a great overview of all the well-known methods, such as slapback and ping-pong delay effects, and flanging and chorus algorithms. This book not only explains the basic a n d A p p l i c a t i o n idea and applications of each method, but also briefly shows the mathemat- ics in the background of all techniques.” —Vesa Välimäki, Aalto University, Esbo, Finland A “This book strikes a great balance between theory and get-your-hands-dirty u applications. … The strong orientation to families of effects found in every recording studio means that readers of this book can look forward to making d a full set of useful, relevant, real-world effects.” i —Alex U. Case, University of Massachusetts Lowell, USA o Audio Effects: Theory, Implementation and Application explores digital audio effects relevant to audio signal processing and music informatics. It supplies fundamental background information on digital E signal processing, focusing on audio-specific aspects that constitute the f building block on which audio effects are developed. The text integrates theory and practice, relating technical implementation to musical implica- f tions. It can be used to gain an understanding of the operation of existing e audio effects or to create new ones. In addition to delivering detailed c coverage of common (and unusual) audio effects, the book discusses current digital audio standards, most notably VST and AudioUnit. Source t code is provided in C/C++ and implemented as audio effect plug-ins with accompanying sound samples. Each section of the book includes study s questions, anecdotes from the history of music technology, and examples that offer valuable real-world insight, making this an ideal resource for researchers and for students moving directly into industry. Joshua D. Reiss K15885 ISBN: 978-1-4665-6028-4 Andrew P. McPherson 90000 9 781466 560284 Audio Effects Theory, Implementation and Application Joshua D. Reiss Queen Mary University of London, United Kingdom Andrew P. McPherson Queen Mary University of London, United Kingdom Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2015 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20140911 International Standard Book Number-13: 978-1-4665-6029-1 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmit- ted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Contents Preface ......................................................................................................................ix About the Authors ..............................................................................................xiii 1. Introduction and Fundamentals ..................................................................1 Understanding Sound and Digital Audio ....................................................1 Working with Decibels ...............................................................................4 Level Measurements ...................................................................................5 Representing and Understanding Digital Signals ......................................6 Representing Complex Numbers .............................................................6 Frequency and Time– Frequency Representations .................................8 Aliasing ......................................................................................................10 Modifying and Processing Digital Signals ................................................12 The Z Transform and Filter Representation ..........................................13 Digital Filter Example ...............................................................................16 Nonlinear and Time- Varying Effects .....................................................17 2. Delay Line Effects ........................................................................................21 Delay ................................................................................................................21 Theory .........................................................................................................21 Other Delay Types ....................................................................................23 Implementation .........................................................................................25 Applications ...............................................................................................29 Vibrato Simulation .........................................................................................30 Theory .........................................................................................................31 Implementation .........................................................................................32 Applications ...............................................................................................38 Flanging ..........................................................................................................38 Theory .........................................................................................................40 Common Parameters ................................................................................45 Implementation .........................................................................................47 Applications ...............................................................................................50 Chorus .............................................................................................................51 Theory .........................................................................................................51 Common Parameters ................................................................................54 Summary: Flanger and Chorus Compared ...............................................56 3. Filter Design ..................................................................................................59 Filter Construction and Transformation ....................................................61 Simple Prototype Low- Pass Filter ...........................................................61 High- Order Prototype Low- Pass Filter ..................................................62 iii iv Contents Changing the Gain at the Cutoff Frequency .........................................64 Shifting the Cutoff Frequency .................................................................65 Creating a Shelving Filter ........................................................................66 Inverting the Magnitude Response ........................................................67 Simple Low- Pass to Band-Pass Transformation ...................................67 Popular IIR Filter Design ..............................................................................69 Low Pass .....................................................................................................70 High Pass ....................................................................................................71 Low Shelf ....................................................................................................74 High Shelf ...................................................................................................75 Gain at Bandwidth ....................................................................................77 Band-Pass Filters .......................................................................................77 Band-Stop Filters .......................................................................................78 Peaking and Notch Filters .......................................................................80 The Allpass Filter ...........................................................................................81 Applications of Filter Fundamentals...........................................................84 Exponential Moving Average Filter .......................................................84 Loudspeaker Crossovers ..........................................................................85 4. Filter Effects ...................................................................................................89 Equalization ....................................................................................................89 Theory .........................................................................................................89 Implementation .......................................................................................100 Applications .............................................................................................104 Wah- Wah .......................................................................................................105 Theory .......................................................................................................105 Implementation .......................................................................................109 Phaser ............................................................................................................112 Theory .......................................................................................................112 Implementation .......................................................................................114 5. Amplitude Modulation ..............................................................................125 Tremolo ..........................................................................................................125 Theory .......................................................................................................125 Implementation .......................................................................................127 Ring Modulation ..........................................................................................131 Theory .......................................................................................................131 Implementation .......................................................................................136 Applications .............................................................................................138 6. Dynamics Processing .................................................................................141 Dynamic Range Compression ...................................................................141 Theory .......................................................................................................141 Implementation .......................................................................................150 Contents v Application ...............................................................................................158 Summary ..................................................................................................160 Noise Gates and Expanders .......................................................................160 Theory and Implementation ..................................................................160 Applications .............................................................................................163 7. Overdrive, Distortion, and Fuzz ..............................................................167 Theory............................................................................................................167 Characteristic Curve ...............................................................................167 Hard and Soft Clipping ..........................................................................169 Input Gain ................................................................................................170 Symmetry and Rectification ..................................................................171 Harmonic Distortion ..............................................................................173 Intermodulation Distortion ...................................................................177 Analog Emulation ...................................................................................179 Implementation ............................................................................................180 Basic Implementation .............................................................................180 Aliasing and Oversampling ..................................................................180 Filtering ....................................................................................................181 Common Parameters ..............................................................................182 Tube Sound Distortion ...........................................................................182 Code Example ..........................................................................................183 Applications ..................................................................................................185 Expressivity and Spectral Content .......................................................185 Sustain ......................................................................................................185 Comparison with Compression ............................................................185 8. The Phase Vocoder .....................................................................................189 Phase Vocoder Theory ................................................................................189 Overview ..................................................................................................189 Windowing ..............................................................................................192 Analysis: Fast Fourier Transform .........................................................194 Interpreting Frequency Domain Data .................................................194 Synthesis: Inverse Fast Fourier Transform ..........................................196 Filterbank Analysis Variant ...................................................................198 Oscillator Bank Reconstruction Variant ..............................................199 Phase Vocoder Effects .................................................................................199 Robotization .............................................................................................200 Whisperization ........................................................................................204 Time Scaling ............................................................................................206 Pitch Shifting ...........................................................................................207 Phase Vocoder Artifacts .........................................................................210 vi Contents 9. Spatial Audio ...............................................................................................213 Theory............................................................................................................213 Panorama..................................................................................................213 Precedence................................................................................................216 Vector Base Amplitude Panning ...........................................................219 Ambisonics ..............................................................................................220 Wave Field Synthesis ..............................................................................225 The Head- Related Transfer Function ...................................................228 Implementation ............................................................................................232 Joint Panorama and Precedence ...........................................................232 Ambisonics and Its Relationship to VBAP ..........................................233 Implementation of WFS .........................................................................234 HRTF Calculation ...................................................................................234 Applications ..................................................................................................235 Transparent Amplification .....................................................................235 Surround Sound ......................................................................................235 Sound Reproduction Using HRTFs ......................................................236 10. The Doppler Effect .....................................................................................239 A Familiar Example .....................................................................................239 Derivation of the Doppler Effect ................................................................241 Simple Derivation of the Basic Doppler Effect ....................................241 General Derivation of the Doppler Effect ............................................242 Simplifications and Approximations ...................................................244 Implementation ............................................................................................245 Time- Varying Delay Line Reads ...........................................................245 Applications ..................................................................................................250 11. Reverberation ..............................................................................................253 Theory............................................................................................................253 Sabine and Norris– Eyring Equations ..................................................255 Direct and Reverberant Sound Fields ..................................................257 Implementation ............................................................................................259 Algorithmic Reverb ................................................................................259 Generating Reverberation with the Image Source Method ..............262 Convolutional Reverb .............................................................................267 Other Approaches ...................................................................................270 Applications ..................................................................................................270 Why Use Reverb? ....................................................................................270 Stereo Reverb ...........................................................................................272 Gated Reverb ............................................................................................272 Reverse Reverb ........................................................................................272 Common Parameters ..............................................................................273 Contents vii 12. Audio Production........................................................................................277 The Mixing Console ....................................................................................278 The Channel Section ...............................................................................278 The Master Section ..................................................................................281 Metering and Monitoring ......................................................................281 Basic Mixing Console .............................................................................282 Signal Flow and Routing ............................................................................282 Inserts for Processors, Auxiliary Sends for Effects ............................283 Subgroup and Grouping ........................................................................285 Digital versus Analog .................................................................................287 Latency ......................................................................................................287 Digital User Interface Design ................................................................288 Sound Quality .........................................................................................288 Do You Need to Decide? ........................................................................289 Software Mixers ...........................................................................................290 Digital Audio Workstations ...................................................................290 Common Functionality of Computer- Based DAWs ...........................291 MIDI and Sequencers .............................................................................292 Audio Effect Ordering.................................................................................293 Noise Gates ..............................................................................................293 Compressors and Noise Gates ..............................................................293 Compression and EQ ..............................................................................295 Reverb and Flanger .................................................................................296 Reverb and Vibrato .................................................................................296 Delay Line Effects ...................................................................................296 Distortion .................................................................................................297 Order Summary ......................................................................................298 Combinations of Audio Effects ..................................................................298 Parallel Effects and Parallel Compression ...........................................298 Sidechaining ............................................................................................299 Combining LFOs with Other Effects ...................................................303 Discussion .....................................................................................................304 13. Building Audio Effect Plug- Ins ...............................................................307 Plug- In Basics ................................................................................................307 Programming Language ........................................................................307 Plug- In Properties ...................................................................................308 The JUCE Framework .............................................................................308 Theory of Operation ....................................................................................308 Callback Function ...................................................................................309 Managing Parameters ............................................................................309 Initialization and Cleanup .....................................................................310 Preserving State .......................................................................................311 viii Contents Example: Building a Delay Effect in JUCE ...............................................312 Required Software ..................................................................................312 Creating a New Plug- In in JUCE ..........................................................312 Opening Example Plug- Ins ....................................................................315 File Overview ..........................................................................................315 PluginProcessor.h....................................................................................316 PluginProcessor.cpp ...............................................................................319 PluginEditor.h ..........................................................................................327 PluginEditor.cpp .....................................................................................329 Summary ..................................................................................................334 Advanced Topics ..........................................................................................335 Efficiency Considerations ......................................................................335 Thread Safety ...........................................................................................336 Conclusion ....................................................................................................338 References ...........................................................................................................339

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