Restoring Audio with iZotope RX

iZotope with Nat Johnson

Tools, tips and techniques.
2008 iZotope, Inc. All rights reserved. iZotope and iZotope RX are either registered trademarks or trademarks of iZotope, Inc. in the United States and/or other countries. Other product or company names mentioned herein may be the trademarks of their respective owners.
INTRODUCTION...4 IntendedAudienceforThisGuide.... 4 WHAT IS AUDIO RESTORATION?...5 WhataretheGoalsofGoodAudioRestoration?... 5 WHAT IS IZOTOPE RX?...7 GETTING SET UP TO RESTORE AUDIO...8 Equipment.... 8 Transferringmediatothecomputer... 10 Recordingfromanalogformats... 10 SUGGESTIONS FOR THE RESTORATION PROCESS.13 HOW TO IDENTIFY AUDIO PROBLEMS...14 UsingtheSpectrogramandWaveformDisplay.. 14 HowtoSpotAudioProblems... 17 ChangingSpectrogramSettings... 21 BROADBAND NOISE REDUCTION..24 WhatisBroadbandNoise?... 24 BasicTechniquesforusingRXsDenoiser... 24 HUM AND TONAL NOISE....31 FindingandRemovingHum... 31 UsingDenoiserforTonalNoiseRemoval... 35 REMOVING CLIPPING....36 HowdoesRXsDeclipperwork?... 36 RepairingClipping.... 36 REMOVING CLICKS AND POPS...39 UsingRXsDeclicker.... 39 REMOVING INTERMITTENT NOISES AND GAPS..43 UsingRXSpectralRepair.... 45 GENERAL RX TOOLS...47 ComparingSettings... 47 BatchProcessing.... 48 EQandGain.... 49 WorkingwithPresets.... 50 KeyboardShortcutsandassigningyourown... 51
Restoring Audio with iZotope RX Page 2 of iZotope, Inc.
EXPORTING AND DELIVERING AUDIO...52 iZotopeMBIT+DitheringPanel(RXAdvancedonly).. 54 iZotope64BitSRCPanel(RXAdvancedOnly)... 56 SUMMARY....58 APPENDIX: REPAIRING THE INCLUDED AUDIO FILES..60 Example1:RemovingBroadbandNoisefromaConcertRecording.. 61 Example2:UsingDenoiserandEQonaShellacRecordingofSpokenWord. 63 Example3:RestoringanHistoricalSpeech:MakingVoiceMoreIntelligible. 64 Example4:CleaningupaPhoneInterviewwithSpectralRepair.. 65 Example5:RemovingClicksandPopsfromaConcertonRecord. 67 Example6:RemovingClippingfromaPhoneInterview... 69 Example7:RemovingGuitarStringSqueakswithSpectralRepair.. 71 Example8:FillingaGapinAudiowithSpectralRepair.. 73

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2008 iZotope, Inc.

INTRODUCTION

Today,audioandvideorecordingscanbemadebynearlyanyone.Fromthesimplecamcorder tosophisticatedstudiosandsoundstages,agrowingnumberofrecordingsareproduceddaily. Andasourworldbecomesincreasinglyandaudiblycongested,sotherateofruinedrecordings isrising!Humanerror,unexpectedelectricalormechanicalinterferenceandunwelcome intrusionsfromaircraft,cellphones,pets,peopleandMotherNatureregularlyimpacteventhe mostseasonedprofessional.Whetheryoureaprofessionalorjustgettingstarted,youhave probablyrunintodifficultaudiosituationslikethisandwishedyoucouldcorrectwhatseemed likeanimpossibledilemma. Thepurposeofthisguideistohelpyoudeveloppracticalandeffectivewaystoremovenoise andfixaudioproblemsusingiZotopeRX.Wehopethisguidewillhelpyouunderstandthe basics(andbeyond)ofaudiorestorationandhelpyoutoapplythemtoyourownprojects.
Intended Audience for This Guide
IfyoudontknowanythingaboutaudiorestorationanddonthaveiZotopeRX,westillhopethis guidewillhelpyou.FeelfreetodownloadthetrialversionofRXtofollowalongandtryout theseconceptsforyourself. IfyoudontunderstandaudiorestorationbutdohaveRX,youreinluck.RXgivesyouacomplete rangeofaudiorestorationtoolsandthisguideshowsyouhowtousethem. IfyouhaveRXandknowthebasicsofrestoringaudio,thisguidewillstillshowyoutricksor techniquesthatarepossibleinRX.Justsayyeah,Iknewthatwhenappropriatefortheother parts.

Try It For Yourself!

BesuretodownloadourRXRestorationGuideaudioexamplesandtryyourhandatrestoring them.AttheendofthisguideyoullfindanAppendixthatwillwalkyouthroughhowtodothe repairs.Itsagreatwaytoapplywhatyoulllearnfromreadingthisguide.

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How to Spot Audio Problems
Whileyourearsaregreatforlocatingproblemsinaudio,nothingbeatsbeingabletosimply glanceatafileandimmediatelygetasenseofwhatyouneedtofix.Betteryet,ifyoureworking witha2hourlongliveconcert,youcanlearntoquicklyzeroinonproblemslikeclippedsections, intermittentnoisesandmorewithouthavingtolistentotheentirerecordingfirst.Visual analysiswillneverreplaceyourears,butitcancertainlycomplimenttheminmanyways. LetstakealookatsomecommonaudioproblemsinRXswaveformandspectrogramdisplays. LearningtoidentifytheseproblemsbysightwillhelpyougreatlyasyoulearntouseRXsaudio restorationmodules. Hum Humisusuallytheresultofelectricalnoisesomewhereinrecordedsignalchain.Itcanusually beheardaudiblyasalowfrequencytone,usuallybasedateither50Hzor60Hzdependingon whethertherecordingwasmadeinNorthAmericaorEurope.Ifyouzoomintothelow frequenciesusingRX'sSpectrogramDisplay,youwillbeabletoseehumasaseriesofhorizontal lines,usuallywithabrightlineat50or60Hzandseverallessintenselinesaboveitatharmonics. Seebelow:
Insituationslikethisexample,whichhasonlyafewharmonics,RX'sHumRemovalmoduleisa goodtoolforthejob.HumRemovalletsyousettheprimaryfrequencyofthehumandcontrol suppressionofupto7harmonicsabovethelowfrequency.RXsDenoiserisalsoalogicalchoice touseforremovinghum,youmaywanttotrybothtoseewhichgivesyouthebestresults. Buzz Insomecases,theelectricalnoisewillextendupintohigherfrequencies,thiswilloftenmanifest itselfasabackgroundbuzz.Seetheexamplebelow:

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Insituationslikethisexample,wherethehum'sharmonicsextendintohighfrequencies,try usingtheDenoisermoduleinRX.Denoisercanworkwiththistypeofnoiseaswellandfeatures aTonalNoisesuppressioncontrol,whichcanoftencontrolhighfrequencybuzzmoreeffectively thanHumRemoval. TheabovescreenshotshowsRXsSpectrogramDisplayinahighertimeresolutionmode thatmakesseeingtonalnoiseeasier.Readontolearnhowtoadjustspectrogramsettings. HissandotherBroadbandNoise Unlikehumandbuzz,broadbandnoiseisspreadthroughoutthefrequencyspectrumandnot concentratedatspecificfrequencies.Tapehissandnoisefromfansandairconditionersare goodexamplesofbroadbandnoise.InRX'sSpectrogramDisplay,broadbandnoiseusually appearsasspecklesthatsurroundtheprogrammaterial.Seeimagebelow:
RX'sDenoisermoduleisthegototoolforremovingnoisesofthistype. Clicks,Popsandothershortimpulsenoises Clicksandpopsarecommononrecordingsmadefromvinyl,andcanalsobeintroducedby somekindsofdigitalerrors,includingrecordingintoaDAWwithimproperbuffersettings.These shortimpulsenoisesappearinRX'sspectrogramasverticallines.Theloudertheclickorpop,the brighterthelinewillappear.Belowisanexampleofclicksandpopsfromarecordingmadefrom

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vinyl:
RX'sDeclickerincludesbothautomaticandmanualtoolsforremovingclicksandpops. Clipping Clippingisacommonproblemthatoccurswhenaloudsignaldistortsoninputtoasound card/converter,mixingconsole,fieldrecorderorotherpieceofequipment.Theresultis overloaddistortion.ThisclippingcanusuallybeseenmosteasilyfromRX'swaveformdisplay (movethesliderbelowthespectrogramtothelefttosuperimposethewaveformdisplay).As youwillseeintheimagebelow,theclippingappearsas"squaredoff"sectionsofthewaveform.

RXhasadedicatedDeclippertoolwhichcaninmanycasesrebuildthesquaredoffpeakscaused byclippingandrestoretherecordingtoanaturalsoundingstate.Noteverykindofdistortion canberemoved,butRXsDeclipperworkswellonarangeofanaloganddigitalclipping. Sometimesheavilylimitedaudiowillalsoappearsquaredoffwhenzoomedoutzoom inbytimetoseeifindividualwaveformtopsareclipped. IntermittentNoises Intermittentnoisesaredifferentthannoiseslikehissorhum,theymayappearinfrequentlyand maynotbeconsistentinpitchorduration.Examplesincludecoughs,sneezes,footsteps,car horns,cellphonerings,etc.Thepicturesbelowrepresenttwodifferentexamplesofthese

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noises:drinkingglassesclinkingtogether,andanelectronicbeepfromacarignition.
Becausenoiseslikethisareoftenunpredictable,theyusuallyneedtoberemovedmanually. RX'sSpectralRepairtoolprovidesanumberofdifferentmodesthatallowyoutoselectand removeintermittentnoisesandreplacethemwithresynthesizedcontentbasedonthe surroundingaudio.

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GapsandDropOuts Sometimesarecordingmayincludeshortsectionsofmissingorcorruptedaudio.Theseare usuallyveryobvioustoboththeeyeandtheear!Seebelow:
RX'sSpectralRepaircanbeusedtoresynthesizegapsinaudio,sometimesofuptoahalfsecond longormore,byusinginformationaroundthegaptofillinthemissinginformationusing patternsandadvancedresynthesis.
Changing Spectrogram Settings
Inaddition,therearecountlesswaystoalterthe spectrogramandhowfilescanbedisplayed. Sometimeschangingspectrogramsettingscan showaudioinadifferentlight,helpingyouto identifyproblemsandzeroinonnoise.For example,justchangingthecolorsofRXs spectrogramcanbringdifferenteventstothe forefront. RXalsohastheuniqueabilitytosaveyour Spectrogrampreferencesaspresetsforeasy recalllater. RXsSpectrogramDisplayshowingvinylclicks andhisswithfourdifferentcolorsettings

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Spectrogram Settings
iZotopeRXoffersadvancedspectrogramoptionsundertheView|SpectrogramSettingsmenu. HereisanindepthdescriptionoftheSpectrogramSettingscontrols: SpectrogramTypeRXofferssomedifferentmethodsfordisplayingtimeandfrequency informationinthespectrogram.RXhasadvancedspectrogrammodesthatallowyoutosee sharpertime(horizontal)andfrequency(vertical)resolutionatthesametime.Thereisalwaysa tradeoffofdisplayqualityversusprocessingtime,sokeepinmindthatsomemodeswilltake longertodrawonthescreenthanothers.
STFT(shorttimeFouriertransform)Thisreferstothemethodthat'susedtotransform theaudiodataintothespectrogramdisplay.Thistypeofspectrogramisthemost commononeandcanbefoundinothereditors.Ithasafixeduniformtimefrequency resolution.ThisisthesimplestmodeinRX. AutoAdjustableSTFTThismodeautomaticallyadjustsFFTsize(i.e.timeand frequencyresolutionofaspectrogram)accordingtothezoomlevel.Forexample,ifyou zoominhorizontally(time)you'llseethatpercussivesoundsandtransientswillbemore clearlydefined.Whenyouzoominvertically(frequency),you'llseeindividualmusical notesandfrequencyeventswillappearmoreclearlydefined.ThisisRXsdefaultmode. MultiresolutionThismodecalculatesthespectrogramwithbetterfrequency resolutionatlowfrequenciesandbettertimeresolutionathighfrequencies.This mimicspsychoacousticpropertiesofourperception,allowingthespectrogramdisplay toshowyouthemostimportantinformationclearly. AdaptivelySparseThismodeautomaticallyvariestimeandfrequencyresolutionofa spectrogramtoachievethebestspectrogramsharpnessineveryareaofa timefrequencyplane.Thisoftenletsyouseethemostdetailsforathoroughanalysis, butit'stheslowestmodetocalculate.

FFTsizeFFTisafastFouriertransform,aprocedureforcalculationofasignalfrequency spectrum.ThehighertheFFTsize,thegreaterthefrequencyresolutioni.e.notesandtonal eventswillbeclearer.However,choosingalargernumberherewillmaketimeeventsless sharplydefinedbecauseofthewaythistypeofprocessingisdone.Choosing"AutoAdjustable" or"Multiresolution"modesallowyoutogetagoodcombinationoffrequencyandtime resolutionwithouthavingtochangethissettingasyouwork. EnablereassignmentThiscontrolenablesaspecialtechniqueforspectrogramcalculationthat allowsveryprecisepitchtrackingforanyharmoniccomponentsofthesignal.Whenused togetherwithFrequencyoverlap/Timeoverlapcontrols,thisoptioncanprovidevirtually unlimitedtimeandfrequencyresolutionsimultaneouslyforsignalsconsistingoftones. WindowTheWindowcontrolletsyouchoosedifferentweightingwindowsthatareusedfor

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theFFTanalysis.Thisgetsintosomecomplexmathematics,buttryingeachofthesewillhave differentspectrumsmoothingpropertiesandprevent"spectralleakage"indifferentways. HannisRXsdefaultwindowsetting. FrequencyScaleUsingdifferentfrequencyscalescanhelpyouseeusefulinformationmore easily.Differentscaleshavedifferentcharacteristicsfordisplayingthevertical(frequency) informationinthespectrogramdisplay.
Linearthissimplyshowsfrequenciesspreadoutinauniformway.Thisismostuseful whenyouwanttoanalyzehigherfrequencies. Logarithmicthisscaleputsmoreattentiononlowerfrequencies. MeltheMelscale(derivedfromthewordMelody)isafrequencyscalebasedonhow humanspercievesound.Thisselectionisoneofthemoreintuitivechoicesbecauseit correspondstohowweheardifferencesinpitch. BarktheBarkscaleisalsobasedonhowweperceivesound,andcorrespondstoa seriesofcriticalbands.
Frequencyoverlap(a.k.a.zeropaddingfactor)controlstheamountofoversamplingonthe frequencyscaleofspectrogram.WhenusedtogetherwiththeReassignmentoption,itwill increasetheresolutionofthespectrogramvertically(byfrequency). TimeoverlapThiscontrolsthetimeoversamplingofthespectrogram.Inmostcases,overlap of4xor8xisagoodsettingtostartwith.Howeverusinghigheroverlaptogetherwiththe Reassignmentoptionwillincreasethetimeresolutionofaspectrogram,makingtransientevents appearmoreclearly. ColorMapRX'sspectrogramdisplayallowsyoutochoosebetweenseveraldifferentcolor schemes.Thereisnorightorwrongcolorsettingtousewerecommendyoutrythemall. Sometimescertaincolormodeswillmakedifferenttypesofnoisestandoutmoreclearly. Experiment! Highqualityrenderingturningthiscontroloffmakesspectrogramrenderingslightlyfaster,but you'lllosesomedetailandclarityinthespectrogramimage. ReduceQualityAboveRX'sspectrogramusesveryaccuraterenderinglettingyouseeaudio problems,suchasclicks,evenatzoomedoutstate.Howeverdoingsuchrenderingforlongfiles canbesomewhatslow.So,whenthelengthofthevisiblespectrogramisabovethespecified numberofseconds,thespectrogramcalculationischangedtoafastandlessaccuratepreview mode.Whentheuserzoomsin,thespectrogramcalculationbecomesaccurateagain.

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Musicalnoisesuppression Thiscontroladjuststhereductionofartifactsknownas"musicalnoise".Thiscontrolisthe advancedequivalentoftheSmoothingcontrolfoundintheBasicpanel. ResidualWhitening Thisfeaturemodifiestheamountofnoisereductionappliedatdifferentfrequenciestoshape thespectrumofthenoisethatsleftover. Whenresidualwhiteningiszero,noisesuppressionisthesameatallfrequencies,andthe suppressednoisehasasimilarspectralshapetotheoriginalnoise.Whenresidualwhiteningisat itshighestsetting,thedesiredshapeofsuppressednoisefloorismadeclosertowhitenoise, whichisusuallymoreneutralsounding.ThiscontrolincombinationwiththeMusicalNoise Suppressioncontrolcanmakeahugedifferenceincontrollingresidualartifacts. MoreAdvancedModeControls(RXAdvancedOnly): MNSalgorithmMusicalnoiseartifactsuppressionalgorithm TheSimplealgorithmperformsindependentnoisegatingineveryfrequencychannelofFFT. ReleasetimeofsubbandgatesiscontrolledbytheReleasecontrol.Thisisafastalgorithm withsmalllatency(delay)thatissuitableforrealtimeoperation. TheAdvancedandExtremealgorithmsperformjointtimefrequencyanalysisoftheaudio signalwhichresultsinbetterqualityandless"musicalnoise"artifacts.Thesealgorithms havehigherlatencyandcomputationalcomplexity.
FFTsize(ms) InRX,wecontrolFFTwindowsizeforspecificrequirements:longerwindowsmeanlowertime resolution,butbetterfrequencyresolution.Goodfrequencyresolution(longerwindows)allows forbetterseparationoftonalsignalsandnoise,butitalsoreducestimeprecisionofDenoiser whichcanleadtosoftenedtransientsandlessnoisereductionaroundtransients.Switchingto MultiResolutionmodewilldisablethiscontrol. WheneverFFTsizeischanged,it'srecommendedyouretrainDenoiserbecausetheold noiseprofilewastakenatadifferentFFTsizeandthereforebecomesinaccurate. MultiResolution Themultiresolutionprocessingselectsthebesttimefrequencyresolutionforeveryportionof thesignaltominimizesmearingoftransientsandatthesametimeachievehighfrequency resolutionwhereitisneeded.Theoverallqualityofnoisereductionisincreased,butatthecost ofmuchhighercomputationalcomplexity.TheFFTsizecontroldoesnothaveanyaffectin multiresolutionmodebecauseFFTresolutionisselectedautomatically. Kneesharpness Adjuststhesharpnessofthenoisegatesusedinthenoisereductionprocess(1issoftknee,8is sharpknee).

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Release Selectsthereleasetimeofthesubbandnoisegatesinmilliseconds.Longerreleasetimes reducemusicalnoisemoreeffectively,butcanproduceechoesofnoiseafterloudsignals. Psychoacousticsuppression Enablesapsychoacousticmodelthatdynamicallycontrolssuppressionamount.ThisallowsRX tousesoftersuppressionwherenoiseissubjectivelyinaudibletothehumanear.Thepositionof theslidercontrolstheinfluenceofpsychoacousticmodelonsuppressionlevels. Harmonicenhancement Thiscontrolallowsforsoftersuppressionofharmonicsofthesignalthatcouldbeburiedin noise.Itcanmaketheresultingsignalbrighterandmorenaturalsounding,buthighvaluesof harmonicenhancementcanresultinhighfrequencynoisebeingmodulatedbythesignalsouse itsparingly.

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REMOVING CLIPPING
Liveconcertsandonlocationinterviewsfrequentlybecomethevictimsofsignaloverloador clipping.Thisisoftentheresultoftoolittletimeavailableforsetuporsoundcheck.Inmusic recording,overlyenthusiasticsingersanddrummersarefrequentlytheworstoffenders! iZotopeRXfeaturesaDeclippertoolwhichcansaverecordingsfromsometypesofbothanalog anddigitalclippingoroverloaddistortion.
How does RXs Declipper work?
RXfeaturesauniqueDeclipperwhichusesadvancedinterpolationtechniquestointelligently rebuildthepeaksofclippedaudiorecordings.Thistoolcanbeinvaluableforfixingrecordings thatyoumayhavethoughtwereruined! However,weshouldnotethatsomedistortionsimplycannotbefixed.Thereisalwaysapointat whichadigitalconverteroranalogtapehasbeenpushedsohardthatthereisnotenough usefulinformationleftforRXtomakeagoodrepair.Youmayfindoldrecordsthathavebeen playedsomuchtheyhavegroovewalldistortionfromrecordwearthiscanbevirtually impossibletofix.Insomecases,ifDeclipperdoesnotworkforyouyoumaybeabletouseRXs SpectralRepairtooltofixshortcorruptedsegments.SeetheSpectralRepairchapterformore details.

Repairing Clipping

ChoosingaDeclippingMode Inmostcases,itisbesttostartwiththeDeclippermodule'sSinglebandmode.Fortrickier clipping,youmayneedtouseMultibandmode(orMultiresolutionmodeinRXAdvanced). Welldiscussthislaterinthechapter. UsingtheHistogramtosettheClippingThreshold ThemostimportantpartofsettingDeclipperisfiguringoutatwhatlevelintherecordingthe clippingishappeningsoyoucansettheClippingThresholdcontrol.Dependingonhowthe recordingwasmade,whethertheclippingisanalogordigitalinnature,andotherfactors, clippingcanappearatdifferentdBlevels. ThehistogrammeterintheDeclippermoduleallowsyoutoanalyzeclippinginyourfile.Selecta sectionthatisclipped,andhittheComputebutton(ifyoureusingthepluginversionof Declipper,themeterwillautomaticallyupdateduringplayback).Agraphwillappearshowing theaveragelevelsoftheaudioovertheselectedtime.Thisiscalledahistogram.

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Ifclippingispresentintheselection,itwillusuallyappearasahorizontallineinthehistogram thatextendsallthewayacrossthemeter.Thisiswherethepeaksinthefileareconcentrated, usuallyindicatingclipping. Tosetthemodule'sthreshold,movetheredlineinthehistogram,ortheClippingThreshold slider,untiltheredlineinthehistogramisjustbelowthelinewhereclippingisconcentrated.

iftheclippingpointisbelow8dBFS,thehistogramwillbeempty.Yourfilemay needtobenormalized.YoucanalsoraisetheoverallgainofthefileusingRX'sGain module.
MakeupGain Thiscontrolaccommodatestheincreasedpeaklevelscausedbythedeclippingprocess.When RXrebuildstheclippedpeaks,theywilloftengohigherthanzero.Iftherebuiltpeaksgoabove zerodBinRX,yourrecordingwillclipagainwhenyouexportit.Themakeupgaincontrollets yousettheresultinggainofthedeclippingprocesssothatthewaveformisbroughtdownbelow zero. WhenusingDeclipper,startbysettingmakeupgainataround6.0dB.Ifyou'reremoving clippingduringashortselectionofafile,youmaywanttosetthiscontrolhighertopreventa noticeablevolumedropintheprogrammaterialduringthedeclippedsection. Choosingaqualitymode TherearethreequalitymodesinRX'sDeclipper:Low,Medium,andHigh.Lowqualitymode processesveryquickly;Highqualitymodeprocessesslowlybutinsomecasescanachievebetter results.Inmanycasesyouwillfindthat"Low"qualitymodegivesyougreatresults.Tosavetime, alwaysstartbypreviewingtheLowqualitymodesfirst.

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WhenusingDeclipperasaplugin,thehigherqualitymodesmayintroducealotoflatencyor causedropouts.Ifthishappens,youcanswitchtoalowerqualitymodeforrealtimeuse,then changetohighqualitymodewhenyourereadytobouncedownorrenderyourtrack.
Toavoidfluctuationsinvolume,youmaywanttoapplyDeclippertoyourentirefile ratherthanjustshortclippedsections.SingleBandmodewillnotadverselyaffectthequality ofthenonclippedmaterial. WhentouseMultibandandMultiresolutionmodes Usually,Singlebandmodeisagoodstartforanyaudiofile,butifthequalityofsingleband declippingisinsufficient,youmaywanttotryothermodes,suchasMultibandor Multiresolutiondeclipping. BothMultibandandMultiResolutionmodeshavesimilarparameterstoSingleBandmode. HowevertheyalsoallowyoutoselectthenumberoffrequencybandsRXusestoperform interpolation.Ahighernumberofbandsdoesnotnecessarilymeanhigherquality,youmayneed tosearchforagoodsoundwiththisparameterasitisextremelysituationdependent.For example,multiresolutionmodecanbeusedincertainscenarioslikehighfemalevocalswith reverberationthathaveonlyamoderateamountofclipping.Werecommendyoutrymultiple modesandpreviewtheresultsintheCompareSettingswindow.

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REMOVING CLICKS AND POPS
Clicksandpopscanoccuratalmostanystageintherecordingprocessandcanappearinnearly anymedium:surfacenoisefrommechanicalmedia(especiallydiscs),staticelectricity, powerlineinterference,inadvertentphysicalcontactwithamicrophone(includingthoseon camcorders)ortelephonehandsetand/orbadaudioconnectorcables.Occasionally,digital errorswillresultinafew,unexpectedclicksaswell.Yourchallengewillbetoreduceorremove clicksandpopswithoutdisturbingprogramcontent.ThankfullyRXprovidessomeeasytouse, highqualitytoolsfordoingjustthat.

The Declicker can only process selections with 4000 samples or less in Manual mode. Should your selection be wider than 4000 samples, you may need to remove the problem withSpectralRepair(whichwelldiscussinthenextchapter).
Iftheresultisnotsatisfactory,tryadjustingInterpolationOrderorotherparameters.Iftheclick or popis verylong, Declicker may cause a minor drop in level. You may want to try the RX SpectralRepairtoolinstead.
Processing on one channel only
Intheexamplebelow,wewantedtoremoveaclick,presentintheleftchannelalone,without disturbingthesoundintherightchannel.Thefragileprogramcontent(aboychoirsinginga cappellainanemptycathedral)requiredpreciseanddelicateprocessing. RXcanisolateeithertheleftorrightchannelandprocessinjustthatchannelwhenrequired.In astereoprogram,youcanselecteitherleftchannelalone,rightchannelaloneorbothtogether whenchoosingaportionofyourfileforprocessing.Selecttheleftchannelalonebydraggingthe mouseatthetopofthedisplay,therightchannelalonebydraggingatthebottomofthedisplay orbothchannelsbyselectinginthemiddle.Youcanalsodeselectachannelbyclickingthegray rectangletotheleftofthechannelinthedisplay.

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Therearemanytricksofthetradeandthemoreyoutry,theeasierandquickerdeclicking willbecome.Forexample,withmaterialcontainingclicksandpopsofvaryingsizestry runningDeclickerinseveralpasses.Beginbyrepairingshortclicks,andthencontinueonto longerones.Also,youmighttryfirstapplyingtheautomaticdeclickerandthenmovingonto manualdeclickerforthoseclicksmissedinautomaticmode(orviceversa).

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REMOVING INTERMITTENT NOISES AND GAPS
Intermittentnoisescanincludeawiderangeofintrusivesoundsthatdontfallintothecategory ofbroadbandortonalnoise.Thiscanincludecellphoneringsataviolinrecital,squeakingdoor hingesinterruptinganinterview,ortrafficnoisethatmarsdialogrecordingforafilm. Gaps,dropoutsandshortsectionsofcorruptedaudioarealsoacommonaudioproblem.These cancomefromeverythingfromaloosemiccabletodigitalerrors. Thereareseveralthingsthatmakethesenoisesespeciallyhardtofix: Theycanbewildlyunpredictableinfrequencyandtiming. Unlikebroadbandnoiseorclicks,noiseslikethiscantberemovedwithanautomated process. Theycanbeverytimeconsumingtofix. Mosttraditionalnoisereductiontoolsandaudioeditorscannoteffectivelyremovethem withoutleavingmanyartifactsordamagedaudio. Thankfully,iZotopeRXincludesadvancedSpectralRepairtoolsthatallowyoutofixthese difficultproblems.InthischapterwellexploreusingtheSpectralRepairmoduletoremove intermittentnoisesandfillgaps.WestronglyrecommendyoutrytheSpectralRepairexamples includedintheAppendixandaudiodemofilesthataccompanythisguide.

CommonControls Spectral Repairs modes share several common controls that affect the way the selection is repaired. SurroundingRegionLengthletsyouchoosehowfarbeforeandaftertheselection SpectralRepairwilllookwhenfiguringouthowtomaketherepair.Tryingdifferent settingswillhelpyoufindthebestrepairforyourparticularproblem. Before/AfterWeightingdetermineswhetherSpectralRepairusesmoreinformation frombeforeoraftertheselectiontomaketherepair.Forexample,youmayneedto repairasustainedsectionofaudiorightbeforeanothereventonthetimeline.Toavoid smearingofthatothereventintoyourrepair,settheWeightingcontrolallthewayto thelefttoonlyuseaudiobeforetheselectiontomaketherepair. NumberofbandsselectsthenumberoffrequencybandsthatRXusestomakethe repair.Ahighernumberofbandscanprovidebetterfrequencyresolution,butwillalso useawidersurroundingarea. Multiresolution(RXAdvancedonly)thismodeallowsforbetterfrequencyresolutionat lowfrequenciesandbettertimeresolutionathighfrequenciessimultaneously.

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GENERAL RX TOOLS

Comparing Settings

Theabilitytoeasily,repeatedlyandaccuratelycomparesettings,visuallyandaurally,withinthe fiveRXmodulesisavaluabletoolaswellasatruetimesaverinwhateverprojectyouundertake. YoullfindtheCompareSettingsfeaturetobeanextremelyusefulreferencewhencontrastinga widerangeofchoiceswiththeoriginal.Takingnotesonyoursettingsandsavingyourown presetscanbeanexcellentpathtowardefficientandeffectiveaudiorestorationprocedure. SendingsettingstotheCompareSettingsWindow Findasettinginthemoduleyoufeelworksforaspecificsituationandthenclickonthe Comparebutton.RXautomaticallyopenstheCompareSettingswindowwhileprocessingthe resultofyoursettingsinthebackground.Viewandchangeyoursettingsandclickagainon Compare.RXwilladdanewitemtothelisteachtimeyouclickonCompare.Byclickingon OriginalwithyournewSettings,youllhaveaninstantcomparisonwitheverySettinglistedin thewindow. Repeatthisstepwithothercontrolsettingsorprocessingmodesinthemodule.Thesewillbe listedwithdefaultnames,butyoucanusetheRenamebuttontochooseyourownnamesfor theitemsinyourComparelist.NoticethattheSpectrogramdisplay,aswellasthesound, changeseachtimeyouselectaSettingintheCompareSettingswindow.

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SUMMARY
ThankyouforreadingRestoringAudiowithiZotopeRX.Wehopethatthisguidehasgivenyou thebackgroundyouneedtosuccessfullyrestoreaudiowithavarietyofproblems.Nowthat youvereadtheguide,besuretodownloadouraudioexamplesandmoveontotheAppendix, whereyoullfinddescriptionsofhowtorepairrealworldaudioproblemsusingwhatyouvejust learnedfromtheGuide.

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About the Authors
InadditiontothehardworkofiZotopesdevelopment,QAandcontentdevelopmentteams,we alsowishtoextendourthankstoNatJohnsonwhosewriting,restorationexpertiseandaudio examplescontributedgreatlytothisguide.

Nat Johnson

WhilestillamusicstudentinBoston,NatJohnsonbeganacareerinradiobroadcastingand soundrecordingwhenhejoinedtheConcertNetworkasanannouncerandmusicprogrammer. Duringthisperiod,hewasofferedtheopportunitytorecordaseasonofliveperformancesfor SarahCaldwellsOperaCompanyofBoston.Soonthereafter,NatjoinedthestaffatWGBHTV andRadioandwasassignedtheunique,tripleroleofannouncer,producerandaudioengineer andwherehebecameengagedwiththerecordingandmixingofmultitrackrecordings, includingbroadcastsbytheBostonSymphonyandPopsOrchestras. WhileinEnglandproducinganalbumforWGBHattheBBCStudiosinLondon,Natreceivedan invitationfromRayDolbytotourDolbyLaboratoriesatClaphamandlater,asaproducerfor RCARecords,continuedhisassociationswithDolbyinNewYorkdevelopingProLogicsurround remasteringprojectsforCD.In1999,whilesupervisingclassicalandfilmmusicreissuesat BMG/RCA,JohnsoninitiatedauniqueaudiophileseriesofhighendCDsemployingWeiss24/96 A/DconvertersandSonicSolutionsHighDensityeditingsystem.In2000,Natwasnominated foraGrammyasProducerofthe94CDRubinsteinCollectionforBMG/RCA. In2004,Natfoundedhisowncompany,RockportRestorationStudiosinRockport, Massachusetts,specializingintherestorationandpreservationofearlysoundrecordings.At present,heisheadingaprojecttorestoreallknownextantrecordingscontainingthespeeches andWhiteHouseconversationsofPresidentFranklinD.Roosevelt.

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Appendix: Repairing the Included Audio Files

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Example1:RemovingBroadbandNoisefromaConcertRecording
DETAILS: PlayerorganrecordinginBoston:VierneOrganSymphonyNo.1Allegro(STEREO).Originallyrecordedon Ampex440B,analoguetape,nonoisereductionusedatsession. COMMENTS: Theprincipalproblemwasasteady,lowlevelbackgroundnoiseresemblingtapehiss.Thechallengewasto reducethenoisewithoutsacrificingupperregisterharmonicsduringquietpassagesinthemusic.Thus,the settingsinDenoiser(particularlythreshold)Iusedwereconservative.Nat TIP:Zoomingintoselectedquietpassageswiththespectrogram,examiningthewaveformandcheckingyour programaurallywhilecomparingagainsttheoriginalcanbeacheckthatyourprogrammaterialisntbeing compromisedduringprocessing.Foraneasycomparison,IdrecommendopeningtwoinstancesofRX simultaneouslyonewiththeoriginalaudioandonewithyourprocessedversion.TIP:Leavingalittlenoise behindispreferabletohearingnobackgroundsoundatall! GOALS: TrainRXsDenoiserusingasampleofjustnoise.ThenuseDenoisertoreducebackgroundhissand lowlevelhum. Trynottodamagethemusicalqualityoftheperformancesometimesleavingsomenoisebehindis betterthantakingthelifeoutoftherecording!YoumaywanttobeconservativewiththeNoise suppressioncontrols,andturntheSmoothingorMusicalNoiseReductioncontrolsuptoprevent artifacts.

TrainDenoiserwiththejustnoisesignalpresentbeforetheorganstartsplaying

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BeforeandAfternoisereduction

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Example 2: Using Denoiser and EQ on a Shellac Recording of Spoken Word
DETAILS: ThisexamplecomesfromEugeneField'spoem"Departure,readbyGeorgeBroderick.Thefirstnumbered recordofEldridgeR.Johnson'sConsolidatedTalkingMachineCompany,thediscwasassignedcatalognumber A1.RecordedNovember1900,take3.Originalwasa7shellactransferreddirectlyfrommuseumcopy. (MONO)
COMMENTS: Thisveryearlydisc,manufacturedwithprimitiveshellacpressingmaterial,wasintolerablynoisyanduntilRX Denoiserbecameavailable,therewasnoknownwaytoreducethisdegreeofoverwhelmingbackground interferencewithoutlosingsomeofthevoiceaswell.Iusedathresholdofonly4.6onDenoiserwhichwas sufficienttodrivedownthebackgroundgrungeandliftupthevoice.PreviewandOutputNoiseOnlyweremost usefultoolsduringmyexperimentationwithdifferentsettings.NatJohnson BackgroundinformationontherecordingplustheentireRXrestorationcanbefoundonlineat http://www.gracyk.com/johnson.shtml. GOALS: UseDenoisertogetridoftheheavybackgroundnoise.Trytoimprovetheintelligibilityofthevoice withoutobscuringthepoemwithnoisereductionartifacts. UsingRXsEQwillgetridofthehighfrequencydistortionwithoutdamagingthevoiceinthe recording.Usingalowpassfilterthatcutseverythingaboveabout4,000Hzwilldonicely.
The Spectrogram Display before and after Denoiser and EQ are applied

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Example3:RestoringanHistoricalSpeech:MakingVoiceMoreIntelligible
DETAILS: ThisfilecontainsthevoiceoffamedphilanthropistAndrewCarnegie,recordedIn1914(Internetsource) (MONO) COMMENTS: Someofthewordsinthisspeech,recordedbyCarnegiein1914,aresomewhatdifficulttodecipherowingtoa pronouncedScottishburr,madeevenmoremuffledbysomeonesrudimentaryattemptatnoisereduction.In addition,therewassteadystatebackgroundnoise.IbeganwithRXEQtoraisethevoiceoutofthemudusinga slightboostroughlybetween1Kand9KandthenranDenoiser.IlefttheEQcompensationinfollowing Denoisingasthisleftthespeechabitclearer.NatJohnson GOALS: Usegentlelinearphaseequalizationtoliftthevoiceoutofthebackgroundnoise. UseRXDenoisertoreducesteadystatebackgroundnoise

SelectthegapanduseSpectralRepairsPartials+Noisemode

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Whensettingsareappliedcorrectly,SpectralRepairwillfillthegapconvincingly

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For Immediate Release
Media contact: Brian McConnon Music Marcom, LLC. 610-480-8919 brian@musicmarcom.com www.musicmarcom.com
iZotope Releases RX 2: Complete Audio Repair Suite
Professional tools to repair, restore and enhance audio for music, broadcast, video and more Cambridge, MA (November 5, 2010) iZotope, Inc., a leader in audio DSP processing, has released RX 2 and RX 2 Advanced, updates to their award-winning audio repair software suites. With a range of new features and functionality, iZotope has expanded the scope of RX into any field where audio is recorded or restored by both consumers and professionals. RX 2 and RX 2 Advanced are designed to repair common and uncommon audio problems like tonal and broadband noise, hiss, buzz, hum, clicks and crackle, distortion from clipping and interfering sounds like cell phone rings, dogs barking, car horns, string squeaks, dropped drumsticks and just about anything else. RX 2 and RX 2 Advanced are crucial tools if youre recording new tracks or restoring old ones. Whether youre on location with a TV show or recording a voiceover at home for a company presentation, its a challenge to get a good recording. RX gives you all the tools you need to repair damaged audio and deliver the best recording, explains Jeremy Todd, CTO of iZotope, RX also includes specialized tools to restoring old recordings from vinyl records, tape and other sources with tools like Declick, Decrackle and automatic azimuth alignment. RX 2 and RX 2 Advanced are a complete set of the best processing tools with an immersive visual editing interface enabling you to quickly repair and deliver high-quality audio. RX 2 builds on the success of the originals Denoise, Spectral Repair, Declick, Declip and Remove Hum modules with iZotopes latest DSP algorithm improvements and the new Decrackle and Channel Operations modules. RX 2 Advanced extends the standard RX with an adaptive Denoiser mode, a Deconstruct module, third party plug-in hosting, iZotope 64-bit SRC resampling, MBIT+ dither, iZotope Radius time and pitch control, ability to export an edit history, multi-resolution mode for Spectral Repair and automatic azimuth correction. RX 2 and RX 2 Advanced include new visual editing features and functionality such as the Magic Wand, Lasso and Brush tools designed for selecting audio in the products spectrogram. Similar to working in popular graphic design programs, these tools allow natural freehand selections around problem sounds. The Magic Wand can automatically select a sound and even automatically select its harmonics. After selecting, Spectral
Repair resynthesizes audio allowing the user to seamlessly remove unwanted sounds or even fill in gaps in the recording. RX 2 and RX 2 Advanced further improve the workflow from the first release. Like the original, they are available as both a suite of plug-ins for a DAW and as a dedicated application. An extensive edit history tracks every change the user makes allowing unlimited undo and compare processing. RX 2 Advanced adds the ability to export the history to an XML file for archival or forensic documentation. The application also saves complete session information, so the user can restart the application and continue working with even the audio selection and undo history being remembered. The updated Batch Processor allows the chaining together of modules to operate on multiple files, all optimized with the use of multiple CPUs. RX 2 and RX 2 Advanced are ideal for restoration engineers, video post production engineers, forensic specialists, audio engineers, recording musicians, broadcasters, podcasters, archivists, videographers and anyone who records audio. Specifications: Windows (XP, x64, Vista, 7) Mac OS X 10.5 or later (Universal Binary) Standalone application Plug-in formats: Pro Tools 7+ (RTAS/ AudioSuite), VST, MAS, Audio Unit, DirectX Price and Availability: $349 for RX 2 and $1,199 for RX 2 Advanced Upgrade pricing is available for RX and RX Advanced owners. For product information, demo videos and ordering information, visit http://www.izotope.com/products/audio/rx/. About iZotope, Inc. iZotope is a research-driven audio signal processing company based in Cambridge, Massachusetts. Its hardware products, software products, and audio technology are used by millions of people in over 50 countries, from hobbyist musicians to GRAMMY Award winners. iZotope focuses on developing innovative audio technology for professional and consumer applications. This core technology is presented to customers in its awardwinning product line and through its extensive licensing program now including console video games and mobile platforms.