The Art of Sound Reproduction The Art of Sound Reproduction John Watkinson Focal Press An imprint of Butterworth-Heinemann Ltd 225 Wildwood Avenue, Woburn, MA 01801-2041 Linacre House, Jordan Hill, Oxford OX2 8DP A member of the Reed Elsevier plc group OXFORD JOHANNESBURG BOSTON MELBOURNE NEW DELHI SINGAPORE First published 1998 John Watkinson 1998 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloguing in Publication Data A catalogue record for this book is available from the Library of Congress ISBN 0 240 51512 9 Typeset by Laser Words, Madras, India Printed and bound in Great Britain Contents Preface xiii Chapter 1 Introduction 1 1.1 A short history 1 1.2 Types of reproduction 8 1.3 Sound systems 12 1.4 Portable consumer equipment 14 1.5 Fixed consumer equipment 14 1.6 High-end hi-fi 16 1.7 Public address 16 1.8 Multitrack recording 18 1.9 Sound radio 18 1.10 Film and television sound 20 References 20 Chapter 2 Audio basics 21 2.1 Periodic and aperiodic signals 21 2.2 Frequency response and linearity 21 2.3 The sine wave 24 2.4 Root mean square measurements 26 2.5 The deciBel 28 2.6 Audio level metering 32 2.7 Vectors 34 2.8 Phase angle and power factor 35 2.9 Audio cabling 36 2.10 Moving masses 39 2.11 Introduction to digital processes 42 2.12 Logic elements 43 2.13 Storage elements 45 2.14 Binary adding 47 2.15 Gain control by multiplication 47 2.16 Transforms 50 2.17 The Fourier transform 54 2.18 The discrete cosine transform (DCT) 63 vi Contents 2.19 The wavelet transform 65 2.20 Magnetism 65 2.21 Electromagnetic compatibility (EMC) 70 2.22 Electrical safety 71 References 72 Chapter 3 Sound and psychoacoustics 74 3.1 What is sound? 74 3.2 The ear 75 3.3 The cochlea 77 3.4 Level and loudness 78 3.5 Frequency discrimination 80 3.6 Critical bands 81 3.7 Beats 84 3.8 Music and the ear 85 3.9 The sensation of pitch 88 3.10 The physics of sound 90 3.11 The speed of sound 91 3.12 Wavelength 93 3.13 The Doppler effect 94 3.14 The wave number, k 94 3.15 How sound is radiated 95 3.16 Proximity effect 97 3.17 Intensity and power 98 3.18 The inverse square law 99 3.19 Wave acoustics 99 3.20 Radiation into smaller solid angles 102 3.21 Refraction 106 3.22 Reflection, transmission and absorption 107 3.23 Reverberation 109 References 110 Chapter 4 Sources of sound 111 4.1 Producing sounds 111 4.2 Vibrating bars 111 4.3 Vibrating panels 113 4.4 Vibrating strings 114 4.5 Vibrating diaphragms 116 4.6 Using airflow 116 4.7 Resonators 118 4.8 The organ 120 4.9 Wind instrument principles 122 4.10 Wind instruments 124 4.11 Brass instruments 125 4.12 Stringed instruments 126 4.13 The pianoforte 128 4.14 Percussion instruments 128 4.15 Electrical and electronic instruments 129 Contents vii 4.16 The human voice 130 4.17 Non-musical sound sources 134 4.18 The sound of a piston engine 134 4.19 Vehicle noise 136 4.20 Aircraft noise 136 4.21 Helicopter noise 137 References 138 Chapter 5 Microphones 139 5.1 Introduction 139 5.2 Microphone principles 139 5.3 Microphone limitations 146 5.4 Microphone mechanisms 148 5.5 Electrodynamic microphones 150 5.6 Electrostatic microphones 151 5.7 Phantom power 153 5.8 Stands and suspensions 154 5.9 Wind noise 157 5.10 Radio microphones 157 References 158 Chapter 6 Loudspeakers and headphones 159 6.1 Loudspeaker concepts 159 6.2 Loudspeaker mechanisms 163 6.3 Directivity 165 6.4 The moving coil speaker 168 6.5 Magnets 170 6.6 Coils 173 6.7 Cones 174 6.8 Low-frequency reproduction 176 6.9 Crossover networks 179 6.10 Enclosures 180 6.11 Electrostatic loudspeakers 180 6.12 Power amplifiers 184 6.13 Speaker cables 187 6.14 Active loudspeakers 189 6.15 Headphones 191 References 193 Chapter 7 Stereophony 194 7.1 History of stereophony 194 7.2 Directionality in hearing 194 7.3 Hearing in reverberant conditions 198 7.4 The stereophonic illusion 202 7.5 Stereo microphones 204 7.6 Headphone stereo 207 7.7 Alternative microphone techniques 208 viii Contents 7.8 M-S stereo 209 7.9 Mono compatibility 211 7.10 Stereo metering 211 7.11 Surround sound 213 7.12 Microphone criteria for stereo 216 7.13 Loudspeaker criteria for stereo 216 References 217 Chapter 8 Digital audio signals 219 8.1 Introduction to digital audio 219 8.2 Binary 221 8.3 Conversion 224 8.4 Sampling and aliasing 224 8.5 Choice of sampling rate 228 8.6 Sampling clock jitter 228 8.7 Aperture effect 230 8.8 Quantizing 232 8.9 Quantizing error 234 8.10 Introduction to dither 238 8.11 Requantizing and digital dither 241 8.12 Dither techniques 244 8.12.1 Rectangular pdf dither 244 8.12.2 Triangular pdf dither 246 8.12.3 Gaussian pdf dither 247 8.13 Basic digital-to-analog conversion 247 8.14 Basic analog-to-digital conversion 255 8.15 Alternative converters 260 8.16 Oversampling 263 8.17 Oversampling without noise shaping 269 8.18 Noise shaping 270 8.19 Noise-shaping ADCs 274 8.20 A one-bit DAC 277 8.21 One-bit noise-shaping ADCs 279 8.22 Two’s complement coding 281 8.23 Level in digital audio 283 8.24 The AES/EBU interface 285 References 299 Chapter 9 Analog audio recording 301 9.1 Introduction to analog recording 301 9.2 Tape recording 302 9.3 Magnetic tape 305 9.4 Heads 307 9.5 Biased recording 310 9.6 Cross-field bias 313 9.7 Pre-emphasis and equalization 314 9.8 Sources of noise 316 9.9 Head alignment 318 Contents ix 9.10 Capstan motors 320 9.11 Servo-controlled capstans 321 9.12 Brushless motors 323 9.13 Reel motors 325 9.14 Tension servos 326 9.15 The analog multitrack recorder 327 9.16 The Compact Cassette 329 9.17 Additional quality criteria in stereo 330 9.18 Analog noise reduction 332 9.19 Audio in analog VTRs 335 9.20 The vinyl disk 336 9.21 Vinyl disk players 338 References 343 Chapter 10 Digital recording 344 10.1 Introduction 344 10.2 Time compression 348 10.3 Replay synchronization 351 10.4 Practical digital recorders 351 10.5 Channel coding 357 10.6 Group codes 359 10.7 Error correction and concealment 361 10.8 Introduction to the Reed Solomon codes 364 10.9 Modulo-n arithmetic 367 10.10 The Galois field 368 10.11 R S calculations 370 10.12 Correction by erasure 374 10.13 Introduction to DAT 377 10.14 Half-inch and 8 mm rotary formats 384 10.15 Digital audio disk systems 386 10.16 Audio in digital VTRs 391 Appendix 10.1 Calculation of Reed Solomon generator polynomials 395 References 396 Chapter 11 Optical disks in digital audio 397 11.1 Types of optical disk 397 11.2 CD and MD contrasted 400 11.3 CD and MD disk construction 401 11.4 Rejecting surface contamination 402 11.5 Playing optical disks 404 11.6 Focus and tracking system 407 11.7 Typical pickups 412 11.8 CD readout 413 11.9 How optical disks are made 418 11.10 How recordable MiniDiscs are made 422 11.11 Channel code of CD and MD 423 11.12 Error-correction strategy 432 x Contents 11.13 Track layout of MD 436 11.14 Player structure 437 11.15 Sony mastering disk 447 References 447 Chapter 12 Audio editing 448 12.1 Introduction 448 12.2 Tape-cut editing 449 12.3 Editing on recording media 453 12.4 The structure of an editor 454 12.5 Timecode 455 12.6 Locating the edit point 455 12.7 Non-linear editing 458 12.8 Editing in DAT 460 12.9 Editing in open-reel digital recorders 461 References 463 Chapter 13 Audio signal processing 464 13.1 Introduction 464 13.2 Level control 465 13.3 Grouping 471 13.4 Automation 473 13.5 Dynamics 475 13.6 Equalization 479 13.7 Multitrack consoles 482 13.8 Console buses 486 13.9 The inline strip 487 13.10 Fader flip 489 13.11 Console operating modes 491 13.12 Solo 492 13.13 Ancillary functions 493 13.14 Stereo mixers 494 13.15 Effects 495 13.16 Introduction to audio compression 497 13.17 Non-uniform coding 501 13.18 Floating-point coding 503 13.19 Predictive coding 505 13.20 Sub-band coding 507 13.21 Transform coding 511 13.22 A simple sub-band coder 513 13.23 Compression formats 514 13.24 ISO MPEG compression 515 13.25 Compression artifacts 517 References 517 Chapter 14 Sound quality considerations 519 14.1 Introduction 519 14.2 Objective testing 521 Contents xi 14.3 Subjective testing 528 14.4 Digital audio quality 533 14.5 Digital audio interface quality 539 References 541 Index 543 This Page Intentionally Left Blank Preface Sound reproduction has always been a challenging area in which to work owing to the large number of engineering and artistic disciplines it embraces.