Audio Metering: Measurements, Standards and Practice PDF
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Audio Metering Measurements, Standards and Practice This page intentionally left blank Audio Metering Measurements, Standards and Practice Eddy B. Brixen AMSTERDAMlBOSTONlHEIDELBERGlLONDONlNEWYORKlOXFORD PARISlSANDIEGOlSANFRANCISCOlSINGAPORElSYDNEYlTOKYO FocalPressisanImprintofElsevier FocalPressisanimprintofElsevier TheBoulevard,LangfordLane,Kidlington,Oxford,OX51GB,UK 30CorporateDrive,Suite400,Burlington,MA01803,USA Firstpublished2011 Copyright(cid:1)2011EddyB.Brixen.PublishedbyElsevierInc.AllRightsReserved. TherightofEddyB.Brixentobeidentifiedastheauthorofthisworkhasbeenassertedin accordancewiththeCopyright,DesignsandPatentsAct1988 Nopartofthispublicationmaybereproducedortransmittedinanyformorbyanymeans, electronicormechanical,includingphotocopying,recording,oranyinformationstorageand retrievalsystem,withoutpermissioninwritingfromthepublisher.Detailsonhowtoseek permission,furtherinformationaboutthePublisher’spermissionspoliciesandourarrangementwith organizationssuchastheCopyrightClearanceCenterandtheCopyrightLicensingAgency,canbe foundatourwebsite:www.elsevier.com/permissions Thisbookandtheindividualcontributionscontainedinitareprotectedundercopyrightbythe Publisher(otherthanasmaybenotedherein). Notices Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperience broadenourunderstanding,changesinresearchmethods,professionalpractices,ormedical treatmentmaybecomenecessary. Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluating andusinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuch informationormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers, includingpartiesforwhomtheyhaveaprofessionalresponsibility. Tothefullestextentofthelaw,neitherthePublishernortheauthors,contributors,oreditors,assume anyliabilityforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability, negligenceorotherwise,orfromanyuseoroperationofanymethods,products,instructions,or ideascontainedinthematerialherein. BritishLibraryCataloguinginPublicationData AcataloguerecordforthisbookisavailablefromtheBritishLibrary LibraryofCongressControlNumber:2010938289 ISBN:978-0-240-81467-4 ForinformationonallFocalPresspublications visitourwebsiteatfocalpress.com PrintedandboundintheUnitedStates 1011121110987654321 Table of Contents Preface.............................................................................................................vii 1 Acoustic Sound........................................................................................1 2 From AcousticSound toElectrical Signals............................................9 3 Digital Representation...........................................................................11 4 Signal Types...........................................................................................19 5 HowLargeIsanAudioSignal?............................................................33 6 The dB Concept.....................................................................................39 7 The Ear, Hearing, and LevelPerception...............................................47 8 TimeWeighting.....................................................................................57 9 FrequencyWeighting andFilters..........................................................61 10 Determinationof Loudness...................................................................75 11 Characteristics of LevelMeters.............................................................83 12 The Standard Volume Indicator (VU Meter)........................................87 13 Peak Program Metere PPM.................................................................91 14 LoudnessMetering................................................................................95 15 Calibration ofLevelMeters................................................................107 16 Relationships Between Scales.............................................................111 17 Dynamic Scales...................................................................................117 v vi Table of Contents 18 Polarity andPhase Reading.................................................................121 19 Display ofLevelDistribution..............................................................129 20 Multi-Channel and SurroundSound....................................................135 21 Standards andPractices.......................................................................151 22 Summation ofAudio Signals..............................................................163 23 Digital Interface...................................................................................169 24 Where toConnect aMeter..................................................................181 25 Fast FourierTransformation................................................................193 26 Spectrum Analyzer..............................................................................201 27 Other Measurement Systems...............................................................205 28 MeasurementSignals...........................................................................213 29 Sound LevelMeters.............................................................................215 30 NRand NC Curves..............................................................................219 31 RoomAcoustics Measures..................................................................225 Glossary.........................................................................................................243 Index..............................................................................................................259 Preface What is dynamic range e and how loud is it? These are the eternal questions that concerneveryonewhoworkswiththe practical aspectsofsound. Thisbookwaswrittentogiveeverybodywithaninterestinaudioanexpla- nation ofthe conditions thatdetermine the answers tothese 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 indescribing the magnitude ofsound. 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 chapteron room acoustics hasbeen added. HOW SHOULD THIS BOOK BE READ? AudioMeteringcanbeusedasareferencebook.Thebeginningcontainsatable of contentsand the end ofthe book providesa glossary and anindex. Readingthebookfromcovertocoverishighlyrecommended.Thesubject matterofthebookhasbeenorganizedsothatthemostbasicmaterialisplaced atthebeginning,whilethemoregenerallydescriptivematerialisfoundtowards the end ofthe book. Enjoy Eddy Bøgh Brixen Smørum, Denmark, September2010 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 tothe 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”isanEnglish-basedword.“Audio”isderivedfromLatin,andrefersto thingsthatarerelatedtohearing.Sounddoesnotnecessarilyhavetobeaudible. Infrasound and ultrasound, which are below and above the normal range of humanhearing,respectively, are examples ofinaudible sounds. InEnglish,wetendtousetheterms“sound”and“audio”indiscriminately. When discussing acoustical topics in this book, we will be dealing with “sound,” andthat iswherewewillbegin. WHAT IS SOUND? Sound is normally understood to mean elastic molecular oscillations in air or other media such as water, iron, or concrete. These oscillations result in pres- sure variations that are of such a magnitude that they can be sensed by humanhearing. However, sound can also be converted to, for example, variations in the electrical current in a conductor, or magnetic variations on an audio tape, or a sequence of numeric values. We call these forms intermediate formats, becausewe later convertthem into acousticsound. SPEED OF SOUND Soundpropagatesbyanoscillatingsolidbodysettingtheparticlesnexttoitin motion, and those next to them, and so on. Sound thus spreads with a certain 1 AudioMetering.DOI:10.1016/B978-0-240-81467-4.10001-2 Copyright(cid:1)2011EddyB.Brixen.PublishedbyElsevierInc.Allrightsreserved.
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