Audio Metering Measurements, Standards and Practice This page intentionally left blank Audio Metering Measurements, Standards and Practice Eddy B. Brixen AMSTERDAM l BOSTON l HEIDELBERG l LONDON l NEW YORK l OXFORD PARIS l SAN DIEGO l SAN FRANCISCO l SINGAPORE l SYDNEY l TOKYO Focal Press is an Imprint of Elsevier Focal Press is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK 30 Corporate Drive, Suite 400, Burlington, MA 01803, USA First published 2011 Copyright Ó 2011 Eddy B. Brixen. Published by Elsevier Inc. All Rights Reserved. The right of Eddy B. Brixen to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangement with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Control Number: 2010938289 ISBN: 978-0-240-81467-4 For information on all Focal Press publications visit our website at focalpress.com Printed and bound in the United States 10 11 12 11 10 9 8 7 6 5 4 3 2 1 Table of Contents Preface .............................................................................................................vii 1 Acoustic Sound........................................................................................ 1 2 From Acoustic Sound to Electrical Signals ............................................ 9 3 Digital Representation ........................................................................... 11 4 Signal Types........................................................................................... 19 5 How Large Is an Audio Signal?............................................................ 33 6 The dB Concept..................................................................................... 39 7 The Ear, Hearing, and Level Perception............................................... 47 8 Time Weighting ..................................................................................... 57 9 Frequency Weighting and Filters .......................................................... 61 10 Determination of Loudness ................................................................... 75 11 Characteristics of Level Meters............................................................. 83 12 The Standard Volume Indicator (VU Meter) ........................................ 87 13 Peak Program Meter e PPM................................................................. 91 14 Loudness Metering ................................................................................ 95 15 Calibration of Level Meters ................................................................ 107 16 Relationships Between Scales ............................................................. 111 17 Dynamic Scales ................................................................................... 117 v vi Table of Contents 18 Polarity and Phase Reading................................................................. 121 19 Display of Level Distribution.............................................................. 129 20 Multi-Channel and Surround Sound.................................................... 135 21 Standards and Practices ....................................................................... 151 22 Summation of Audio Signals .............................................................. 163 23 Digital Interface................................................................................... 169 24 Where to Connect a Meter .................................................................. 181 25 Fast Fourier Transformation................................................................ 193 26 Spectrum Analyzer .............................................................................. 201 27 Other Measurement Systems............................................................... 205 28 Measurement Signals........................................................................... 213 29 Sound Level Meters............................................................................. 215 30 NR and NC Curves.............................................................................. 219 31 Room Acoustics Measures .................................................................. 225 Glossary ......................................................................................................... 243 Index .............................................................................................................. 259 Preface What is dynamic range e and how loud is it? These are the eternal questions that concern everyone who works with the practical aspects of sound. This book was written to give everybody with an interest in audio an expla- nation of the conditions that determine the answers to these questions. Fundamental acoustics, electronics and psycho-acoustic concepts are described here. A number of topics related to digital technology are also covered and information can also be obtained here on the majority of the tools that are used in describing the magnitude of sound. This is the second edition of Audio Metering. The update is particularly concerned with loudness measures and metering. However, the basic chapters in the beginning of the book have been expanded and a complete new chapter on room acoustics has been added. HOW SHOULD THIS BOOK BE READ? Audio Metering can be used as a reference book. The beginning contains a table of contents and the end of the book provides a glossary and an index. Reading the book from cover to cover is highly recommended. The subject matter of the book has been organized so that the most basic material is placed at the beginning, while the more generally descriptive material is found towards the end of the book. Enjoy Eddy Bøgh Brixen Smørum, Denmark, September 2010 Thanks to my family and to my publisher for the patience they have displayed during the preparation of this 2nd edition of Audio Metering. Also thanks to the publisher of the first edition, Broadcast Publishing, for leaving the rights to the author. vii This page intentionally left blank Chapter | one Acoustic Sound CHAPTER OUTLINE What Is Sound?............................................................................................................................. 1 Speed of Sound............................................................................................................................ 1 Frequency........................................................................................................................................2 Wavelength .....................................................................................................................................2 Sound Pressure............................................................................................................................ 4 Conversion Relationships.......................................................................................................... 4 Sound Power ................................................................................................................................ 4 Sound Intensity.............................................................................................................................5 Sound Fields ..................................................................................................................................5 Spherical Sound Field............................................................................................................................ 5 Cylindrical Sound Field..........................................................................................................................8 Plane Sound Field...................................................................................................................................8 “Sound” is an English-based word. “Audio” is derived from Latin,