Convolution Explained

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 1/7

Printarticle

PublishedinSOSApril2005:Closewindow

Therearethreemainsourcesofconvolutionimpulseresponses.Theeasiestthingtosampleisasoftwareplugin

ConvolutionProcessingwithImpulseResponsesHowItWorksTechnique:Theory+Technical

Althoughconvolutionisoftenassociatedwithhighendreverbprocessing,thistechnologymakesmanyothernewsoundsavailabletoyouifyouunderstandhowitworks.

MartinWalker

Convolutionor'sampling'reverbsarenowextremelypopular,andit'snothardtoseewhy.Theyprovidethesoundsofrealacousticspacesthatarefarmorerealisticthanmostreverbeffects(althoughtheseremainincrediblyusefulwhenyouwantmoreflexibility),andcanalsogiveyourrecordingsthesoundofbeingpassedthroughanexoticmic,preamp,compressor,guitaramp,orindeedanyothereffect,bothhardwareandsoftware.Eachofthesespacesordevicesisencapsulatedintowhatiscalledan'impulseresponse'filethatcanbeloadedintoacompatibleconvolutionplaybackdevice.SuchdevicesrangefromfreewarePCandMacpluginstodedicatedhardwaresuchasFocusrite'sLiquidChannelorSony'sDRES777reverbprocessor.

Aswithmostothertechnologies,manypeoplewillbecontenttousetheIRs(impulseresponses)bundledwiththeirparticularplaybackdevice,andtodownloadotherfreeonesfromtheInternet.(IprovidedalistofsuitablesitesforconvolutionreverbpluginownersinmyrecentroundupofPCFreewareinSOSJuly2004).Whilecapturingyourownimpulseresponsestothestandardofcommerciallibrariesmaybedaunting,it'snotparticularlydifficulttogetrespectableresultswithalittlegear,andyoudon'thavetorestrictyourselftotheusualhalls,churches,andstudioseither.

Effectspecialistsinthefilm,TV,andvideogamesfieldsarefindingitextremelyusefultocaptureIRsonlocationforuselateronwhenplacingoverdubbeddialogueoreffectsintoarealacousticspace.Moreover,notmanypeoplehavecottonedontothefactthatyoudon'thavetorestrictyourselftoIRsofexistingspacesandgearonceyouabandonrealismandstartconvolvingotheraudiofilesthere'sabizarrenewworldoftreatmentsoutthereforyouraudiotracks.

ConvolutionInputSignals

Tocapturethesoundofarealspace,plugin,orhardwareprocessor,youneedasuitabletestsignal.Themostobviousapproachistoplaybackashortimpulsecontainingallfrequencies,sothatyoucanrecordtheresultingresponseacrossthecompleteaudiorangeasingle0dBlevelpulselastingasinglesamplecouldbeused(andI'verecommendedthisinthepastforlisteningtothesmoothnessofreverbtails).Ifyoudon'twanttocartloudspeakersabouttogeneratethispulseinthespaceyouwanttocapture,realworldalternativesincludefiringastartingpistol,poppingaballoon,orinanemergencyevenclappingyourhandsalthoughjudgingbytheresultsI'veachieved,thislatteroptionisofverylimiteduse.

However,there'sadisadvantageinallthesesignalstheirshortnessresultsinarelativelypoorsignaltonoiseratio.Inmorepracticalterms,thismeansthatthebackgroundnoiseinyourIRswillbehigh.Thebestwayroundthislimitationistoextendthetestsignal,whichiswhymostseriousexperimentersusesomesortofsweptsinewavesignaltypicallylastingtwelvesecondsorso.Tocaptureparticularlynoisyenvironmentssuchasthoseinsidefactories,onboardships/planes,andinsideothervehiclesascleanlyaspossible,youcandoublethisto24seconds,andofcourseswepttonesarealsotheeasiestwaytocapturethesoundofsoftwareplugins,micpreamps,guitaramp/speakercombos,andsoon.

Somesoftwareconvolutionplaybackdevicesofferafunctiontoconverttheswepttonerecordingsyou'vecapturedintoIRs.TheseincludetheAltiverbIRPreProcessorfromAudioEase,thelatestversionofWavesIR1,andtheonethatstarteditallonthePCsomesixyearsago,SonicFoundry'sAcousticModeler(nowSonyMedia'sAcousticMirror).Suitabletestsignalsmaybebundledwiththesoftware,orareavailableasdownloadablefiles.

Inthisarticle:ConvolutionInputSignalsLateralThinkingConvolutionEnginesThirdpartyIRFilesCommercialIRCollectionsConvolutionSoftwareReviews

InSOSPureSpaceIRLibrariesSpectralRelativityIRLibraryWebResourcesKaleidoskopyIRLibraryHints&TipsImpulsePower!

SoundOnSound:Est.1985

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 2/7

chain,sincethiscanbecapturedentirelywithinasinglesoftwareapplication,asshowninthetopdiagramusingWavelabasanexample.Capturingthesoundofahardwaredeviceisonlyslightlymoredifficult,requiringasoundcardsendreturnlooptobesetup,whilecapturingthesoundofarealacousticspacegenerallyrequiresaloudspeakerandmicrophonecombination,althoughsomeacousticnoisescanalsobeusedinplaceoftheloudspeaker.

Formorerealisticsampledinstrumentlibraries,Tascam'sGigastudio3usesitsGigapulseconvolutionenginetoprovidePedalUpandDownresonancesforitslatestGigapianoIIlibrary.Youcanalsousethesameconvolutiontechnologytomodeldifferentmicresponses,asshownhere.

Theycanevenbegeneratedbysomeutilities.Forinstance,forPCusersthere'sVoxengo'sDeconvolver(reviewedinSOSOctober2004),whichisageneric$23utilitywhichcangenerateswepttonetestsignalsthatyoucantransfertoanyaudioplaybackdeviceforuseinthefield.YoucanthenuseanyDATorotheraudiorecordertocapturesuitableresponserecordings,andDeconvolvercanconverttheserecordingsbackintoimpulseresponses.Sincemostpeoplewillendupwithloadsoftestrecordings,therearebatchprocessingoptionsinthesoftwaretoconvertthemallinonehit.

LateralThinking

Apartfromtheobviousacousticspaces,youcanalreadyfindquiteafewimpulseresponsescapturedfrommicpreamps,guitaramps,loudspeakers,speakersimulators,tapemachines,andsoon.Thesecanbeagreatwaytoaddsonicinteresttoanotherwiseblandelectronicsound,andtheirtypicallyshortIRsoftenactlikecomplexEQswithresponsesfarmorecomplexthanmostresonatorplugins.

However,alittlelateralthinkingrevealsthatthereareplentyofothersoundsthatcanbepressedintoservicetoprovideverymusicalresults.Youcouldforinstancecapturetheuniquecollectionofresonancesbelongingtothebodyofanacousticguitarorviolin,orthesympatheticresonancesofapianosoundboard,andapplythemtootherinstrumentsorsounds.Sincetheseresonances'ring'slightlylongerthantheoriginalsound,thiswillalsoimpartsome'timesmearing'towhateveryou'retreating,likeaveryshortreverb.Whilethiswon'tconvertanelectricguitar/pianosoundintoanacousticone,theresultwillcertainlyhavesomeoftheacousticinstrument'scharacteristics,aswellasaddingextralifeandinterest.

OtherpossiblesourcesforIRsamplingincludetelephonesandhumanspeechingeneral,soyoucangiveonesoundsomeofthecharacteristicsofanotherthiscanbeaveryfruitfulareaforanyoneworkingonfilmorgamesoundtracks,orindeedmusiciansinsearchofnewandexcitingsounds.

However,youdon'thavetohaveanendresultinmind,andsomeofthemostinterestingresultscanbeachievedifyoucompletelythrowcautiontothewindandloadanyWAVfileintoaconvolutionplugintoactasanIR.Ofcoursetheresultswillbeunpredictable,butforthesonicexperimenterthisisallpartoftheexcitementdrumloopsandsyntharpeggioscanbeturnedintounusualechounitspadsoundsresultindrones,ambientwashes,andbackgroundtexturesandshortfilesprovideexoticcombfiltering.

Conversely,youcanalsotryloadingimpulseresponsesintovariousotherpluginstoproduceyetmoreoutlandishresults.Candidatesincludevocodersthatcanloadaudiofilesforuseascarrierwaves(suchastheoneinPropellerheadReason,ProsoniqOrangeVocoder,ortheWavesMorphoder),additivesoftwaresynthslikeCamelAudioCameleon5000andWhiteNoiseAdditive,orother'morphing'pluginssuchastheProsoniqMorphVSTplugin.Alloftheseusethecharacteristicsofonesoundasthebasisfortreatinganotherit'snotconvolution,butit'stheresultsthatcount.

ConvolutionEnginesTherearenowquiteafewconvolutionpluginssupportingdifferentformatsandplatforms,andtherearealsoconvolutionfunctionsbuiltintovariousstandaloneapplicationslikeAdobeAudition,BiasPeak,SteinbergNuendo,andMagixSamplitude.ThereseemstobeafarwiderrangeavailableforPCsthanforMacs,andsomeofthebestareonlyavailableononeformatortheother.Forinstance,AudioEase'AltiverbandAppleSpaceDesignerareonlyavailabletoMacusers,whilethehighlyregardedVoxengoPristineSpaceandTascamGigapulse(andofcoursethefreewareSIR)arePConly.DigidesignProToolsuserswillnodoubtbeinterestedinlookingatTrilliumLabsTLSpace(whichisavailableforbothMacandPC),whileWavesIR1alsocoversbothMacandPC,includingRTASandMASoptions.ProsoniqRayverbisalsocrossplatform,butasmentionedinthemaintestisratherdifferentfromaconvolutionreverb.There'sevenaconvolutionengineavailableforLinuxandUnix(BruteFIR),andafewinnovativeplugins,suchasDelayDots'SpectrumworxandSpectralMorpher,offerconvolutionalongsideotherfrequencydomaineffects.Itseemsthatalmosteverymonthanewconvolutionpluginofsomedescriptionisreleased,aswellasnewupdatesforsomeoftheexistingones.AnuptodatelistthatI'vefoundusefulcanbeseenatSpiritCanyonAudio'swebsite,whichdescribesallthelatestcontendersandwhatplatformstheyeachsupport.Youcanreaditatwww.spiritcanyonaudio.com/convolvers.php.

ThirdpartyIRFiles

AlthoughthemoreexpensiveIRhostslikeWaveIR1arebundledwithworldclasslibrariesofreverbresponses,others(likeVoxengo'sPristineSpaceandthefreewarePCutilitySIR,forinstance)comewithnone,tokeepbothcostsanddownloadtimesdown.However,mostusersareinterestedinaddingtotheirIRcollection,andtherearenowquiteafewwebsitesofferingfreelydownloadableIRfilescreatedbyusersmanyofthecommercialconvolutionplugindevelopershostuploadsofferedbytheirusers,andtherearealsositeslikeNoisevaultmaintainedbyenthusiasticusers.

Sincecapturingtheessenceofrealspacesisquiteanarttodotoahighstandard,themajorityofsuchfilestendtobecapturesofhardwaredevicessuchasreverbsandamplifiers,andtherearesomegemstobefoundifyou'vegotafastmodemandplentyoftime.However,freeIRstendtobeofwildlyvaryingquality,sothereareafewthingstolistenoutforwhenauditioningthemifyouwanttopickoutandusethebest.

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 3/7

Youdon'thavetolimityourselftoreverbwhenusingconvolutionplugins.Anyaudiofilescanbeloadedinasanimpulseresponse,providingavastrangeofcomplexeffects.Hereyoucanseesomeofthe863effectsoftheSpectralRelativitylibrary(reviewedinthisarticle)loadedintothefreewareSIRplugin.

First,thevastmajorityoffilestendtobe16bit,andallofthesecompromisethedynamicrangeof24bitsignalsbeingtreated.Second,andrathermoreobviousinmanycases,I'venoticedmanysignsofpoorsetup,withhighlevelsofbackgroundnoise,missingreverbtailends,orstillvaguelyaudibletesttonewhines(againmostobviousneartheend).

CommercialIRCollections

Althoughtheytookalongtimetoappear,therearenowalsosomeexcellentcommercialthirdpartyIRlibraries,andI'llbelookingatafewofthesefortheremainderofthisarticle.However,beforeyouthinkofinvestinginanyoftheseyoushouldbeawareofvariouspotentialrestrictionstotheiruseifyouwanttoavoidfrustration.

Forexample,whilethemajorityofuswouldideallylikeauniversalaudiofileformattobeusedforIRs,it'snotsurprisingthatcommercialdeveloperswhobundlehugeIRlibrarieswiththeirconvolutionproductstendtouseavarietyofproprietaryformatsforthemafterall,suchlibrariesareahugeinvestmentoftime,expertise,andmoney,anddevelopersdon'twantthempassedaroundtheglobeforallandsundrytousewithotherproducts.

Fortunately,mostconvolutionpluginsthatusetheirownIRfileformatcanalsoacceptmorestandardones,whichmakesitfairlyeasytousethemwithcommerciallibraries.ThetwomostwidelyadoptedIRimportformatsareWAVfilesforPCandAIFFfilesforMac.SincemanyMac/PCaudioapplicationsacceptbothofthesefiletypesit'sgenerallyfairlyeasytoconvertlibrariesfromonetotheotherifnecessary,toloadthemintoaparticularconvolutionplugin.AudioEaseAltiverbisslightlymoretricky,sinceitonlyacceptsaleftrightpairofSDII(SoundDesignerIIformat)files,althoughonceagainMacDAWsoftwaresuchasBiasPeak,MOTUDigitalPerformer,andAppleLogicshouldbeabletoperformtheconversionforyou.

However,afewconvolutionpluginsmightyetgiveunexpectedresultswithcommerciallibraries.Forinstance,whileWaves'IR1hasanexcellentreputationforitsaudioqualityandworldclasslibrary,itcurrentlyrestrictsitsIRstoamaximumofsixsecondsinlength,andsimplytruncatesanylongerresponsesatthispoint.Wavestoldmethiswasbecausemanyhostsdon'tallowreallocationofmemorylateron,soIR1grabssixsecond'sworthwhenit'sinitiallyloadedwhen96kHzstereoIRsaresupported,aswellasmultipleinstancesoftheIR1plugin,thiswaschosenasareasonablecompromise.

Unfortunately,thisrestrictionwillpreventyoufromusingmanyoftheexcellentresponsesfromthecommercialIRlibrariesreviewedhere,exceptthoseinthedeliberatelyshortercollectionprovidedbyKaleidoskopy.Nuendo'sAcousticStampconvolutionenginesimilarlyhasanarbitrary12secondlimit,althoughthishasfarfewerlibraryimplications.AnotherthingtolookoutforisthattheReversefunctionofTrilliumLane'sTLSpacetruncatesanyIRlongerthanfiveseconds.

Prosoniq'sRayverbisslightlyunusualinnotbeingastandardconvolutionplayer.Instead,ituses'inverseraytracing'tomodelrealacousticspaces,andprovidescomprehensivecontroloveritsroommodel.Thismakesitextremelyversatileforreverbpurposes,andyoucanstillimportandanalysethirdpartylibraryfiles(althoughbothMacandPCversionsonlyacceptAIFFfiles),buttheywillbeinterpretedbyRayverb'salgorithms,andwillprobablysoundcompletelydifferentfromwhattheirdevelopersoriginallyintended.

ConvolutionSoftwareReviewsInSOSAudioEaseAltiverb:May2002.

www.soundonsound.com/sos/may02/articles/altiverb.asp

DelayDotsSpectrumWorx:August2004.

www.soundonsound.com/sos/aug04/articles/delaydotsspectworx.htm

DelayDotsSpektralBundle:PluginFolderJune2002.

www.soundonsound.com/sos/jun02/articles/plugin0602.asp

EmagicSpaceDesigner:December2003.

www.soundonsound.com/sos/dec03/articles/spacedesigner.htm

ProsoniqRayverb:October2004.

www.soundonsound.com/sos/Oct04/articles/prosoniqrayverb.htm

SIR(SuperImpulseResponse):PCMusicianJune2004.

www.soundonsound.com/sos/jul04/articles/pcmusician.htm

SonyMediaSoftwareAcousticMirror:January1998.

www.soundonsound.com/sos/jan98/articles/acoustic.htm

TascamGigapulse:inTascamGigastudio3reviewJanuary2005.

www.soundonsound.com/sos/jan05/articles/gigastudio3.htm

VoxengoPristineSpace:September2004.

www.soundonsound.com/sos/sep04/articles/voxengo.htm

WavesIR1:May2004.

www.soundonsound.com/sos/may04/articles/wavesir1.htm

PureSpaceIRLibraries

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 4/7

Ifyou'reconsideringbuyingIRlibraries,notallconvolutionplaybackpluginsmaybetotallysuitable.WavesIR1forinstanceonlysupportsresponsesuptosixsecondsinlength,andanylibraryresponselongerthanthiswillbetruncatedasshown.

ThefirstofthethirdpartyIRlibrariesI'mgoingtolookatcomesfromErnestCholakis,whowillalreadybewellknowntomanymusiciansforhiscreationoftheDNAGrooveTemplates.Hehasbeenexploringreverberationimpulseresponsesforthelasttenyears,andhasalreadyreleasedsampleCD'susingthisextensiveknowledge,includingtheacclaimedDroneArcheology(reviewedinSOSDecember2000).

EachPureSpaceseriesCDROMcontainsasetofimpulseresponsefilesavailablein16bitat44.1kHzor48kHzsamplerates,orin24bitat44.1,48,88.2,96,176.4,and192kHzforprofessionalsthisimmediatelyplacesthepotentialaudioqualityaboveandbeyondthatofmostotherofferingsfromthirdpartdevelopers.AvailablefileformatsareWAVforthePCandSDIIfortheMAC.

Usinghisownextensiverecordingsofspacessuchasconcerthalls,cathedrals,monasteries,andeventheambienceinsidetheGreatPyramidKufuatGiza,ErnesthasresynthesisedtheimpulseresponsesinthePureSpacelibraries,whichmeansthattheresultssufferfromnoneofthelimitationsofrealworldrecordingsforinstance,becauseofthewayErnestgenerateshisresponses,the24bitversionsofferadynamicrangeofmorethan140dB,whiletheirfrequencyresponsesarevirtuallyflat,soyoucanEQyoursourcestotastebeforeconvolvingthem.

TherearecurrentlytwolibrariesavailableClassical&MysticalandFilm&Sacredandeachcontains55impulseresponsescleverlyorganisedinorderofacoustic'size'.Eachresponsehasthreefurthernumbersassociatedwithit,thatcompareitslow,mid,andhighfrequencydecaytimestotheaverageforthatset.Whenyou'relookingforasuitablereverberationimpulseforarecording,thisapproachcanmakealotmoresensethanwadingthroughnameslikeLargeHallorStLuke'sChurchRow42.

Afterallthiscarefulpreparation,theIRsthemselvescertainlydon'tdisappoint,anddon'trunawaywiththeimpressionthatsincetheyareresynthesisedtheymightsoundunnaturalorlackcharacter.TheseareamongthecleanestandmostsilkysmoothreverbsI'veeverheard,withnoneofthegrittiness,lumpiness,ormetallicovertonesthatcharacterisemanysynthesisedreverbs.Therearesomegorgeoustailsintherewithoodlesofcharacter,andtheyencompassahugerangeofdecay'timbres'.

Itriedouttheselibrarieswithclosemikedsoloinstruments,vocals,andevenanechoicallyrecordedorchestralsnippets,andwithoutexceptiontheysoundedverynaturalindeed.Therearenosmallrooms(thesmallestspaceintheClassicalserieshasatwosecondtail)buttherearechambers,halls,churches,cathedrals,andmagicalspacesgalore.

Theseareextremelyprofessionallibrariescontainingworkcreatedovertenyears,andwithpricetagstomatch,rangingfrom$299(16bit),to$399(forthemostpopular24bitversions),to$599forthe24bit/192kHzversion.Thisisstillfarcheaperthanbuyingadecenthardwarereverb(thatstillprobablywon'tsoundasgood),butifyouwanttobuyjustoneofthetwolibrariesIwouldpersonallyoptforthemoreversatileClassical&Mystical,sincethiscontainstheshortestandlongestreverbs(plusloadsinbetween),rangingfromtwoto10seconds,andeachonesoundsquitedifferent.

SinceErnestsellshisCDsdirectlytotheenduserwww.numericalsound.com,hecangivethemanindividualregistrationnumberand'installerlockcode',whichpreventsthecasualcopierfromunpackingandinstallingthefiles.EachfileontheCDalsoemployshisuniqueSonicTracedigitalwatermarkprotectionsystem,whichencryptstheuser'snameintoeachandeveryreverbimpulse,soitcanbetracedtotheoriginalownerevenwhenusedinmultitrackaudiorecordings.Finally,there'salsoan11pointlicenseagreementtosignbeforeuse,whosetermsmaydismayafewpotentialusers,socheckitoutbeforebuying.Otherthanthat,thePureSpacelibrariesaresuperbresourcesforprofessionals,andwon'tdisappoint.

SpectralRelativityIRLibrary

Describedas'exoticambientimpulsesforelectronicmusicians',SpectralRelativityisavast635MBcollectionofover80016bit/44.1kHzfiles.Theyaredeliberatelynotintendedtoproviderealisticreverbs,andalthoughsomecanprovidestrangeandoftenetherealreverbtreatmentswhenusedasimpulseresponses,mostcreatesometimesbizarreandsometimesverybeautifultonalcolours,drones,andambientwashes.

ThefirstfoldercontainsColors88extremelyshortfilesrangingfromninesamplesto64mS.Theseinvolvepreciouslittletimesmearing,insteadofferingahugerangeofEQs,butwithfarmoreexoticresponsesthansimplecombfilters.Likemostoftheotherimpulsesinthiscollectiontheyarebestused100percentwetformaximumeffect,althoughtherearenorules.

ThenextfolderisnamedCosmic,andhereweenteraweirdandwonderfulworldofimpulsesthatlastanywhereupto16seconds.Some,likethedeepanddoomladenBlackSun,theplummetingmetallicdronesofSpiralDescent,andhaunting

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 5/7

echoesofNearMiss,couldbedescribedasweirdscifireverbs,whilewithsomeofthelongeronesthetimesmearingbecomessogreatthattheoutputsignalsbecomebarelyrecognisable.

Theresultsareperfectforambientwashesandbackgroundtextures,andIfoundvocalrecordingstobeparticularlyeffectivesources,asyoucangeneratehauntinghumanlikedrones.Forinstance,HeliopauseandLunarMonolithprovideinspiring2001styleangelicchoirsfromalmostanysourcesignal,whilePlanetaryNebulacreatespitchedmetallicdrones.

TheFantasy&Fictionfolderevokesimagesfromliteratureandthemedia,withplentyofscifiandfantasyfilmsandbooksmakinganappearance.IparticularlyenjoyedtheshortmetallicsmearsofGomJabbar,themultiplegatedrepeatsofPickledPeppers,andthereverseflangeddronesofSkynet.Horror&Paranormalgivesus,amongmanyothers,thewhisperingAngels&Demons,theeeriehollownessofBurningMan,thelongmoaningofHeartOfDarkness,andthemenacingHidingInTheAttic.

ThecontentsoftheImpressionsfolderaredesignedtoevokeanimageinthelistener'smind.IfoundthefallingpitchesofBombsAwayquitehauntingwhentreatingcompletesongs,asweretheevenweirderCetaceanMatingCallandthehighpassanimationsofDustInTheGroove.ThosewithdarkerleaningsshouldlovetheIndustrialfolder,includingthepulsingmetallicArmorPlate,thegatednoiseofCrackedPiston,andthepowerofFeelItThroughTheFloor.Isimplyhaven'tgotenoughspacetocovertheremainingMiscellaneousfolders,the102weirdobjectsinthePeriodicTablecollection,the83hightechwashesandfiltersoftheScience&Technologysection,andthe167combinedinhabitantsofWeirdandWeirderStill.

Iabsolutelylovedthiscollection,andit'sobviouslybeenareallabourofloveforitscreatorDarrenBurgan,evendowntothefilenames.ThedescriptionsofeachtreatmentinthePDFmanualareabsolutelyinvaluableinguidingyoutosuitablecandidates,althoughyou'llneverknowexactlyhowtheysoundwithaparticularsourcesignaluntilyoutryit.It'sgreatifyou'renotfeelingparticularlyinspiredIfounditalmostimpossiblenottobecomecatapultedintocreativitywithinafewminuteseverytimeIusedthislibrary.It'salsoincrediblevalueformoneyatjust$24.99,andanyonewhoownsacompatibleconvolutionreverbpluginshouldmakeittheirdutytobuyitimmediately!

WebResourcesAcoustics.netisthenewandofficialsourceofIRsfortheWavesIR1range,withlotsofinfoabouthowWaves

captureandcreatetheirownlibraries,plentyofIR1impulsestodownload,plusauserforum.

www.acoustics.net

AudioEaseprovideasimilarresourceforAltiverbusers.

www.audioease.com

EchoChamberisaGermansitewithfreeIRdownloads.

www.memi.com/echochamber/responses

NoisevaultisthebiggestfreewareIRdownloadsource.Italsohasarticlesoncreatingyourown,andveryhelpfulforums

http://noisevault.com

CKSDEhasbothcommerciallibrariesandfreedownloads.

www.cksde.com

PureSpaceambientimpulses.

www.numericalsound.com/purespac.html

SpiritCanyonAudio'swebsiteishometotheIRlibrariesreviewedinthisfeature,plusarangeoffascinatingfreeReaktorv4ensemblesusedtoprovidesomeoftheirtextures.

www.spiritcanyonaudio.com

FokkevanSaane'ssitehaslotsofIRsofeverydayobjectssuchastelephones,buckets,factories,domesticenvironments,andmusichardware.

www.xs4all.nl/~fokkie/IR.htm

KaleidoskopyIRLibrary

ThissecondIRLibraryfromSpiritCanyonAudioisaslightlymoresubtlecollectionthanSpectralRelativity,intendedtobeusefulinawiderrangeofmusicalstyles.Itmanagesthisbyrestrictingitsfilelengthssothattheendresultsaren'tso'smearedout',whichmeansthatpercussivesourceslikedrumsandmostloopsdon'tlosetheirsenseoftiming.Thistimeallthefilesare24bit,whichwillpleaseaudiopuristswhowanttomaintainthemaximumdynamicrangeintheirmusic,andthereare2025ofthemtotalling684MB.

Ahugeselectionoffilesarespecificallyintendedforuseatcertaintempos,providingexoticbeatsync'edeffects.TheIRsaregroupedintofoldersaccordingtotempo,covering80150bpm,eachfoldercontainingaround90IRs.Toprovidethemaximumrhythmiccompatibility,there'ssomeoverlapbetweenthefoldercontents,withquiteafeweffectsprovidedinmultipleversionstosyncwithmultipletempos.Ifyouwantanevenclosermatchforaspecifictempo,youcanimporttheclosestversionintoyourfavouriteaudioeditorandtimestretchittofitexactly.

OfthishugesectionofthelibraryIparticularlylikedthefeedbackclusterechoesofLargePrintEdition,thetinklingchimeslinesofBinkertell,andtheguitarhistrionicsofHeavyOnTheHarmonics.Thebeautyofallthese

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 6/7

WeacceptthefollowingpaymentmethodsinourwebShop:

AllcontentscopyrightSOSPublicationsGroupand/oritslicensors,19852015.Allrightsreserved.

Thecontentsofthisarticlearesubjecttoworldwidecopyrightprotectionandreproductioninwholeorpart,whethermechanicalorelectronic,isexpresslyforbiddenwithoutthepriorwrittenconsentofthePublishers.GreatcarehasbeentakentoensureaccuracyinthepreparationofthisarticlebutneitherSoundOnSoundLimitednorthepublisherscanbeheldresponsibleforitscontents.

Theviewsexpressedarethoseofthecontributorsandnotnecessarilythoseofthepublishers.

Alwaysbearinmindthatwhenusingconvolutionplugins,theirCPUoverheadisdirectlyrelatedtothelengthoftheimpulseresponsehereyoucanseeVoxengo'sPristineSpacetakingjusttwopercentofmyPentiumIV2.8GHzprocessorwitha100mSimpulse,butninepercentwhenrunninga10secondone.

PublishedinSOSApril2005

treatmentsisthatwhileyoucanusethem100percentwetforunbelievabletransformations,addingalittleprocessingunderablanddrumloop,forexample,canturnitintosomethingreallyunique.

Therearefivefoldersdevotedtosingleshoteffects,andineachonethecontentshavebeensubdividedintoshort,medium,andlongIRs,indicatingtheamountoftimesmearing.TheModulatorsaretheshortest,andIparticularlylikedthemachinegunburstof60HzMassage,theswellingchordaldronesofBadYearBlimp,thecartooncoughanddrillingofDon'tLookNow,thebouncingjuddersofLogisticalLogic,thetelephonicechoesofFondlingTheLeadedCrystal,andtheshimmeringmetallicovertonesofTungstenGlow.

ThemediumandlongReverbfolderscontainsuchgemsastherisingmetallicpitchesofI'mHuntingWabbit,thedistantringingtonesofStainlessSteelBalls,andthepianoclustersofAluminiumDiminished.TheRoomscontainveryshorttailsandevensomevaguelynormalreverbtreatmentssuchasthechimedecaysofMessagesInTheGroundLoopHum,thedistantslapbackofHubcapWallpaper,andthetwintonesofTwelveStoryAtrium.

ThetimesmearingoftheWeirdfoldersisstillgenerallylessthanonesecond,butthetreatmentsaremoreextreme,withmorepitchshiftingandpanningeffects.IparticularlylikedthetimepiecechimingofAtTheToneItWillBeTwoO'Clock,thehauntingechoesofBrainStemDysfunction,andthedistantcavernsofFloatingCity.

Overall,whileSpectralRelativityexcelsincreatinglongerdronesandtreatmentsthatareoftenaspringboardforcreativity,Kaleidoskopyseemstoworkbetteratjumpstartingexistingsongsthatneedrejuvenating,sinceyoucangenerallystillrecognisetheoriginalmaterialbeneath,underitsnewsuitofclothes.Kaleidoskopyisjust$34.99,oryoucanbuyitasabundlewithSpectralRelativityforjust$49.99.Togethertheyareatourdeforceofinventivebeautyandweirdness,andshouldbeownedbyanyonewhowantstoexplorenewsonicterritory.

Hints&Tips

ThemostimportantgeneralpieceofadviceIcangiveyouaboutusingIRpluginsandtheirlibrariesisthattheCPUoverheadisnearlyalwaysdirectlyrelatedtothelengthoftheresponsebeingused.Thismakessense,sinceeachsampleofincomingaudiomustbeprocessedforthefulllengthoftheconvolution'tail'thelongerthisis,themorecalculationsarebeingcarriedoutatanypointintime.Soifyoudon'twanttorunoutofprocessingpowerinyoursongs,trytokeepyourreverbdecaytimeswithinreason.

Ifyoufancyhavingagoatcapturingyourownimpulses,eachdeveloperthatoffersasuitableconvolutiontestsignalwillalsogenerallyprovidestepbystepinstructionsonhowbesttouseit,andtherearealsoothermoregeneralguidesontheInternet.Itshouldgowithoutsayingthattocaptureanacousticspaceaccuratelyyouneedtousehighqualitymics,preamps,amplifiers,andspeakerswithaflatfrequencyresponse.Omnidirectionalorcardioidmicresponsesgivethebestresults,althoughanypolarresponseshouldworkreasonablywell.

Ingeneral,thespeakerthatplaysyoursweepsignal(orthestartingpistol,orballoon,orwhatever)shouldbeplacedwheretheperformerwouldbe,whilethemiccapturingtheacousticresponseshouldbepositionedintheaudience,althoughobviouslytheyareyourimpulseresponsessoyoucanpointthingswhereyoulikewithinreason!Ifyou'vegotamultitrackrecorderandplentyofmicsyoucaneventrycapturingIRsurroundreverbbysimultaneouslyrecordingthesweeptoneatvariousdifferentpositions,andimportingthemintosuitablesurroundconvolutionpluginslikeWavesIR360,VoxengoPristineSpace,orTascamGigapulse.

ImpulsePower!

Finally,ifyou'researchingforexotictransformations,don'tforgetthat,justlikeanyotherplugin,youcanchainthosewithconvolutionfunctions.Asingleconvolutionplugincanprovideresultsthatareeitherextremelyrealisticortotallybizarre,soimaginewhattwoorthreeofthemcansoundlikeinseries!

8/6/2015 Convolution Processing with Impulse Responses

http://www.soundonsound.com/sos/apr05/articles/impulse.htm?print=yes 7/7

Websitedesigned&maintainedbyPBAssociates|SOS|RelativeMedia