Introduction
Digitalaudioisatechnologythatusesdigitalmeanstorecord,store,edit,compressorplaysound.Anewsoundprocessingmethodformedbythedevelopmentoftechnology.
Themainapplicationareasofdigitalaudioaremusicpost-productionandrecording.
Thestorageofcomputerdataisaccessedintheformof0and1,thendigitalaudiofirstconvertstheaudiofile,thenconvertstheselevelsignalsintobinarydataforstorage,andsavesitduringplayback.Thesedataareconvertedintoanaloglevelsignalsandthensenttospeakersforbroadcast.Digitalsoundisessentiallydifferentfromthesoundingeneraltape,radio,andtelevisionintermsofstorageandplaybackmethods.Incontrast,ithasthecharacteristicsofconvenientstorage,lowstoragecost,nosounddistortionduringstorageandtransmission,andveryconvenienteditingandprocessing.
Basicknowledge
Knowingthis,itisnotenoughforfamiliaritywithcomputeraudio.Wehavetounderstandafewbasicknowledgeaboutdigitalaudio:
SamplingRate
Simplyput,itishowmanydataisneededtorecordasoundof1secondlengththroughthemethodofwaveformsampling.The44KHzsamplingrateofthesoundistospend44,000datatodescribethesoundwaveformof1second.Inprinciple,thehigherthesamplingrate,thebetterthesoundquality.
Compressionrate
Usuallyreferstotheratioofthesizeofthemusicfilebeforeandaftercompression,whichisusedtosimplydescribethecompressionefficiencyofdigitalsound.
Bitrate
isanotherreferenceindexofdigitalmusiccompressionefficiency,whichrepresentstheaveragebitvaluepersecondrequiredtorecordaudiodata(bitisthesmallestdatainthecomputerUnit,referstoanumberof0or1),usuallyweuseKbps(inlayman'sterms,1024bitspersecond)astheunit.ThebitrateofdigitalmusicinCDis1411.2Kbps(thatis,recording1secondofCDmusicrequires1411.2×1024bitsofdata),andthebitrateofMP3digitalmusic,whichisclosetoCDsoundquality,isabout112Kbps～128Kbps.
Quantizationlevel
Simplyput,itisthebinarydataofhowmanybitsaredescribedinthedataofthesoundwaveform,usuallywithbitastheunit,suchas16bit,24bit.The16-bitquantizationlevelrecordssounddatausing16-bitbinarynumbers.Therefore,thequantizationlevelisalsoanimportantindicatorofdigitalsoundquality.Wedescribethequalityofdigitalsound,usuallydescribedas24bit(quantizationlevel),48KHzsampling,forexample,thequalityofstandardCDmusicis16bit,44.1KHzsampling.
Technology
DolbySurround
(DolbySurround)
"DolbySurround(DolbySurround)istheoriginalDolbyMulti-SoundTheconsumerversionofthemovieanalogformat.IntheproductionofDolbysurroundsoundtrack,theaudioinformationof4channels-left,center,rightandsurroundchannelsarematrix-encodedandrecordedontwosoundtracks.BothThesoundtrackcanbecarriedbystereoformatprogramsourcessuchasvideotapesandTVbroadcastprogramsandenterthehome.Afterdecoding,theoriginal4channelinformationcanberestoredandsurroundsoundisgenerated.HundredsofhomevideotapesandmanyTVprogramsareencodedbyDolbySurround."DolbySurround,asthefirst-levelsurroundsoundstandard,provides4channelsofsurroundsoundsupport,whichiscurrentlyrarelyused.
DolbyProLogicII
(DolbySurroundProLogicII)
"DolbySurroundProLogicIIisanimprovementMatrixdecodingtechnology,ithasabettersenseofspaceanddirectionwhenplayingDolbysurroundformatprograms.Forstereoformatmusicprograms,itcancreateaconvincingthree-dimensionalsoundfield,andisasurroundsoundexperienceTheidealtechnologytoenterthefieldofcaraudio.TraditionalsurroundsoundprogramsarefullycompatiblewithDolbyProLogicIIdecoder,andDolbyProLogicIIencodedprograms(includingseparateleftsurround/rightsurroundchannels)canalsobeproducedtoplayTheadvantageofsoundreproduction(DolbyProLogicSurrounddecoderiscompatiblewithDolbyProLogicIIencodedprograms)."Inshort,DolbySurroundProLogicIIisamethodusedtoachievesurroundsound,Itcanusefewerchannelstosimulatethesurroundsoundeffect,andtheactualperformanceisalsorelativelygood,butitdoesnotmakemuchsenseforuserswithatruemulti-channelaudiosystem.
DolbyDigital
(DolbyDigital)
"DolbyDigitalisDolbyDigital(AC-3)audiocoding/decodingtechnologyIntheapplicationofconsumerformatssuchasDVDandDTV.Intheprocessofcontinuousdevelopmentandpopularization,DolbyDigitalisfinallyfinalizedasa5.1-channelmode,whichisalsothestandardsupportedbymosthometheatersorPCmultimediadesktoptheaters.DolbyDigitalItcanprovidefivefull-bandchannels,includingleft,center,andrightscreenchannels,independentleftandrightsurroundchannels,andanindependent".1"channelforbassenhancement,whilethecenterChannelsareoftenusedtoenhancedialogue,andsurroundchannelsaremainlyusedtocreateathree-dimensionaleffectoftheoverallsoundfield.DolbyDigitalwasfirstappliedtofilmsoundeffects,andthepre-recordedandsynthesizedaudiodatain5.1formatisstoredinthefilmperforation.DolbyDigitalwasthenusedinDVDvideodiscsandbecameanintegralpartofthehometheatersystem.Asfarasthecurrentmarketisconcerned,ithasbecomethemostwidelyusedsurroundaudiostandard,andmostDVDprogramssupportthisThemostbasicsurroundaudioformat.
DolbyDigitalSurroundEX
(DolbyDigitalSurroundEX)
Dolby®DigitalSurroundEX)IsathirdsurroundchanneladdedtotheDolbyDigitalstandard.Afterthethirdsurroundchannelisdecoded,itisplayedthroughthesurroundspeakersinstalleddirectlybehindtheaudienceseatinthetheaterorhometheatersystem(Alsoknownastherearcenter),andtheleft/rightsurroundchannelaudioinformationisplayedthroughthesurroundspeakersarrangedontheleftandrightoftheseat.Consideringthecompatibilityofthesystem,thisrearcenterchannelismatrix-encodedRecordedintheleft/rightsurroundsoundtrackofaconventional5.1system,sothatwhenthemovieisplayedinaconventional5.1systemtheatersystem,therewillbenoinformationloss.Dolby®DigitalSurroundEX(Dolby®DigitalSurroundEX)Theadvantageliesintheadditionofanewsurroundchannel,whichgreatlyimprovestherearsoundeffect.Atpresent,moreandmorehigh-qualityDVDdiscshavebeguntosupportthisnewstandard.
DTS
DolbyDigitalstoresthesoundeffectdatainthemiddleoftheperforationsonthefilm.Becauseofspaceconstraints,alargenumberofcompressionmodesmustbeused,soitalsosacrificespartofthesoundquality.Dolby'sexperimentalcompetitor,DTS,Trytofindawaytoplacetheaudiotrackseparatelyinanotherstoragedevice(usuallyaCDROM),andthensynchronizewiththeimage.Oneofthebenefitsofthisisthatitisconvenientforthetheatertochangedifferentlanguageversions,anditisalsomoreconvenienttouse.Thecoloreffectisbetter.AftertheadventofDVDvideodiscs,DolbyDigitalandDTShavesuccessivelybecomethetwomajoraudioformats.Thelattercanhaveadataflowof1536KbpsonDVD.ComparedwiththegeneralflowofDolbyDigital(AC-3)from384Kbpsto448Kbps,theadvantagesarenotmentioned.Yu.EvenifAC-3ispulledtothelimitof640Kbps,DTSisstillmorethandoubled.ThisallowsDTStohearmoresounddetailsthanDolbyDigital,andthesoundeffectisevenbetter.However,becauseDTSneedstotakeupalotofdataspaceonthevideodisc,generallyasingleDVD-5formatvideodisclesssupportsDTSaudiotracks.
DTS-ES
ThenewgenerationofDTS-ESstandard,likeDolby®DigitalSurroundEX,alsoaddssupportfor6.1.UnlikeDoblyDigitalEX,therearcenterintheDTS-ESsystemisindependent,notsynthetic.SoDTS-ESisthereal6.1system,andDoblyDigitalEXisjustachannelextensionofthe5.1system.DTS-ESisdividedintotwotypes:DTS-ESseparation6.1andmatrix6.1.WhenDTS-ESseparate6.1decoding,thedecoderconsidersthecorepartandextendedpartoftheDTSsignalasawhole,andusesarithmeticsubtractiontorecoverthesurroundleft/rightchannel.Thesurroundcenter(alsoknownasthebacksurroundcenter)isItisdirectlydecoded,soitcanproduceacompletelyseparated6.1soundfield.Whendecodingmatrix6.1,onlythecorepartofthesignalisconsideredandtheexpansionpartisignored.However,duetotheuseofDTS'spatentedpost-processingESmatrixmodule,itcanstillproducea6.1"extendedsurround"soundfield.ItcanbeseenfromthisthatthetwodecodingmethodsofESaredifferent.Currently,therearerelativelymanyDVDvideodiscprogramsthatsupportDoblyDigitalEX,andthereareonlyahandfulofvideodiscsthatsupportDTSES.
THX
THXwasoriginallythenameoftheprofessionalstandardforcinemasoundsystemsdevelopedandpromotedbyLucasfilminHollywoodintheearly1980s.Becausethisstandardisbasedonthe70mmwidescreenand6-channelsoundsystemofthebusinesscard"StarWars"producedbyLucasfilmin1972,thecompany’stechnicaldirectorThomsonHolmanspenttwoyearsanalyzingthemovietheaterThesoundeffectisnotasgoodasthatoftherecordingstudio.Finally,theabovesoundsystemwasperfectedandpromotedincinemasintheUnitedStates.MakeitthesoundstandardofeverytheaterintheUnitedStates.Sothiskindofmoviesoundstandardhasbeenrecognizedbypeopleandhasbecomeastandardinthemovieindustry.BecausethestandardandsystemtechnologyweredevelopedbyThomsonthroughexperiments,itwasnamed"TomisonHolman'sexperiment"standard,abbreviatedas"THX"standard.Thecorrespondingsoundsystemiscalled"THXsystem".Withthissoundsystem,thesoundeffectofthemovietheatercanreachthelevelofarecordingstudio.ThemainsignificanceoftheTHXstandardistospecifytheeffect,sothesurroundsoundsystemthatpassesthestandardhasoutstandingsoundperformancecapabilities.Generallyspeaking,THX-certifiedsystemshavethefollowingoutstandingfeatures:1.Highpower.Powerisaprerequisiteforundistortedplaybacksound,especiallybass.Ifthepowerisnotenough,itwillinevitablybedistortedunderhighdynamics.TheTHX-certifiedsystemoftenhasanoutputpowerofseveralhundredwatts,whichisenoughtoensurethatthereisnodistortionatthemaximumvolume.
2.Thefrequencyresponseisflatandwide.ThefrequencyresponserangeoftheTHX-certifiedsystemisverywide,whichcanensurethatdifferentsoundscanbeplayedbackintactwithoutmissinganytinydetails.
3.Themusicrestorationeffectisgood,andthesoundqualityoftheTHXcertifiedsystemisverygood,whichcanensurethatthemusichasenoughtouchingeffects.
Basedontheabovedescription,thebenefitsofTHXcertificationareobvious.Butitsshortcomingsarealsoobvious,thatis,thepriceishigh.Becauseofitshighrequirements,manufacturingcostswillriselinearly.Inaddition,thecostofTHXcertificationisatleastUS$20,000.Thisexpensivecostalsoneedstobeapportionedtoconsumers.Therefore,thehighpricehasbecometheonlydefectoftheTHXcertificationsystem.