文献翻译——Fireface UC

外文文献资料FirefaceUC1.DS-DoubleSpeedWhenactivatingtheDoubleSpeedmodetheFirefaceUCoperatesatdoublesamplerate.Theinternalclock44.1kHzturnsto88.2kHz,48kHzto96kHz.Theinternalresolutionisstill24bit.Sampleratesabove48kHzwerenotalwaystakenforgranted,andarestillnotwidelyusedbecauseoftheCDformat(44.1kHz)dominatingeverything.Before1998therewerenoreceiver/transmittercircuitsavailablethatcouldreceiveortransmitmorethan48kHz.Thereforeawork-aroundwasused:insteadoftwochannels,oneAESlineonlycarriesonechannelwithitsoddandevensamplesbeingdistributedtotheformerleftandrightchannels.Bythis,yougetthedoubleamountofdata,i.e.alsodoublesamplerate.OfcourseinordertotransmitastereosignaltwoAES/EBUportsarenecessarythen.ThistransmissionmodeiscalledDoubleWireintheprofessionalstudioworld,andisalsoknownasS/MUX(SampleMultiplexing)inconnectionwiththeADATformat.NotbeforeFebruary1998,Crystalshippedthefirstsinglewirereceiver/transmittersthatcouldalsoworkwithdoublesamplerate.Itwasthenpossibletotransmittwochannelsof96kHzdataviaoneAES/EBUport.ButDoubleWireisstillfarfrombeingdead.Ononehand,therearestillmanydeviceswhichcanthandlemorethan48kHz,e.g.digitaltaperecorders.ButalsoothercommoninterfaceslikeADATorTDIFarestillusingthistechnique.BecausetheADATinterfacedoesnotallowforsamplingfrequenciesabove48kHz(alimitationoftheinterfacehardware),theFirefaceUCautomaticallyusesSampleMultiplexinginDSmode.Onechannelsdataisdistributedtotwochannelsaccordingtothefollowingtable:Asthetransmissionofdoubleratesignalsisdoneatstandardsamplerate(SingleSpeed),theADAToutputstilldelivers44.1kHzor48kHz.2.QSQuadSpeedDuetothesmallnumberofavailabledevicesthatusesampleratesupto192kHz,butevenmoreduetoamissingrealworldapplication(CD.),QuadSpeedhashadnobroadsuccesssofar.AnimplementationoftheADATformatasdoubleS/MUXresultsinonlytwochannelsperopticaloutput.Therearefewdevicesusingthismethod.InQuadSpeedmodetheFirefaceUCautomaticallyusesSampleMultiplexing.Onechannelsdataisdistributedtofourchannelsaccordingtothefollowingtable:Asthetransmissionofquadratesignalsisdoneatstandardsamplerate(SingleSpeed),theADAToutputstilldelivers44.1kHzor48kHz.TheSPDIF(AES)outputoftheFirefaceUCprovides192kHzasSingleWireonly.3.AES/EBU-SPDIFThemostimportantelectricalpropertiesofAESandSPDIFcanbeseeninthetablebelow.AES/EBUistheprofessionalbalancedconnectionusingXLRplugs.ThestandardisbeingsetbytheAudioEngineeringSocietybasedontheAES3-1992.Forthehomeuser,SONYandPhilipshaveomittedthebalancedconnectionanduseeitherPhonoplugsoropticalcables(TOSLINK).TheformatcalledS/P-DIF(SONY/PhilipsDigitalInterface)isdescribedbyIEC60958.Besidestheelectricaldifferences,bothformatsalsohaveaslightlydifferentsetup.Thetwoformatsarecompatibleinprinciple,becausetheaudioinformationisstoredinthesameplaceinthedatastream.However,thereareblocksofadditionalinformation,whicharedifferentforbothstandards.Inthetable,themeaningofthefirstbyte(#0)isshownforbothformats.ThefirstbitalreadydetermineswhetherthefollowingbitsshouldbereadasProfessionalorConsumerinformation.Itbecomesobviousthatthemeaningofthefollowingbitsdiffersquitesubstantiallybetweenthetwoformats.IfadevicelikeacommonDATrecorderonlyhasanSPDIFinput,itusuallyunderstandsonlythisformat.Inmostcases,itwillswitchoffwhenbeingfedProfessional-codeddata.ThetableshowsthataProfessional-codedsignalwouldleadtomalfunctionsforcopyprohibitionandemphasis,ifbeingreadasConsumer-codeddata.NowadaysmanydeviceswithSPDIFinputcanhandleProfessionalsubcode.DeviceswithAES3inputalmostalwaysacceptConsumerSPDIF(passivecableadapternecessary).4.NoiseLevelinDS/QSModeTheoutstandingsignaltonoiseratiooftheFirefacesAD-converterscanbeverifiedevenwithoutexpensivetestequipment,byusingrecordlevelmetersofvarioussoftware.ButwhenactivatingtheDSandQSmode,thedisplayednoiselevelwillrisefrom-109dBto-104dBat96kHz,and82dBat192kHz.Thisisnotafailure.Thesoftwaremeasuresthenoiseofthewholefrequencyrange,at96kHzfrom0Hzto48kHz(RMSunweighted),at192kHzfrom0Hzto96kHz.Whenlimitingthemeasurementrangefrom20Hzto20kHz(socalledaudiobandpass)thevaluewouldbe-110dBagain.ThiscanbeverifiedwithRMEsDIGICheck.ThefunctionBitStatistic&NoisemeasuresthenoisefloorbyLimitedBandwidth,ignoringDCandultrasound.Thereasonforthisbehaviouristhenoiseshapingtechnologyoftheanalogtodigitalconverters.Theymoveallnoiseanddistortiontothein-audiblehigherfrequencyrange,above24kHz.Thatshowtheyachievetheiroutstandingperformanceandsonicclarity.Thereforethenoiseisslightlyincreasedintheultrasoundarea.High-frequentnoisehasahighenergy.Addthedoubled(quadrupled)bandwidth,andawidebandmeasurementwillshowasignificantdropinSNR,whilethehumanearwillnoticeabsolutelynochangeintheaudiblenoisefloor.5.SteadyClockTheSteadyClocktechnologyoftheFirefaceUCguaranteesanexcellentperformanceinallclockmodes.Thankstoahighlyefficientjittersuppression,theAD-andDA-conversionalwaysoperatesonhighestsoniclevel,beingcompletelyindependentfromthequalityoftheincomingclocksignal.SteadyClockhasbeenoriginallydevelopedtogainastableandcleanclockfromtheheavilyjitteryMADIdatasignal(theembeddedMADIclocksuffersfromabout80nsjitter).UsingtheFirefacesinputsignalsSPDIFandADAT,youllmostprobablyneverexperiencesuchhighjittervalues.ButSteadyClockisnotonlyreadyforthem,itwouldhandlethemjustonthefly.Commoninterfacejittervaluesinrealworldapplicationsarebelow10ns,averygoodvalueislessthan2ns.ThescreenshotshowsanextremelyjitterySPDIFsignalofabout50nsjitter(topgraph,yellow).SteadyClockturnsthissignalintoaclockwithlessthan2nsjitter(lowergraph,blue).ThesignalprocessedbySteadyClockisofcoursenotonlyusedinternally,butalsousedtoclockthedigitaloutputs.Thereforetherefreshedandjitter-cleanedsignalcanbeusedasreferenceclockwithouthesitation.6.DriverandFirmware6.1.DriverInstallationAftertheFirefacehasbeenconnected,(see14.HardwareInstallation)installthedriversfromtheRMEDriverCD.ThedriverfilesarelocatedinthefolderFireface_USB.Installationworksautomaticallybyadouble-clickonthefileFirefaceUSB.pkg.RMErecommendsdownloadingthelatestdriverversionfromtheRMEwebsite.Ifdone,theprocedureisasfollows:Adouble-clickontodriver_usb_mac.zipexpandsthearchivefiletoFirefaceUSB.pkg.Instal-lationworksautomaticallybyadouble-clickonthisfile.DuringdriverinstallationtheprogramsFirefaceUSBSettingsandFirefaceUSBMixer(To-talMix)arecopiedtotheApplicationsfolder.ItisrecommendedtolinkthesetwoprogramstotheDocksothattheyarealwaysavailable.Arebootofthecomputerisnotrequired.PossiblereasonswhyaFirefaceUCisnotfoundafterdriverinstallation:TheUSBportisnotactiveinthesystem(checkinSystemProfiler,USB)TheUSBcableisnotornotcorrectlyinsertedintothesocket6.2.DriverUpdateIncaseofadriverupdateitsnotnecessarytoremovetheolddriverfirst,itwillbeoverwrittenduringtheinstallation.Incaseofproblemsthedriverfilescanbedeletedmanuallybydraggingthemtothetrashbin:/Applications/FirefaceUSBMixer/Applications/FirefaceUSBSettings/System/Library/Extensions/FirefaceUSB.kext/Users/username/Library/Preferences/FirefaceUSBfolder/Users/username/Library/Preferences/de.rme-audio.FirefaceUSBMixer.plist/Users/username/Library/Preferences/de.rme-audio.TotalmixFX.plist/Users/username/Library/Preferences/de.rme-audio.Fireface_USB_Settings.plist/Library/LaunchAgents/de.rme-audio.firefaceUSBAgent.plist6.3.FirmwareUpdateTheFlashUpdateToolupdatesthefirmwareoftheFirefaceUCtothelatestversion.Itrequiresanalreadyinstalleddriver.StarttheprogramFirefaceUSBFlash.TheFlashUpdateTooldisplaysthecurrentrevisionoftheFirefaceUCsfirmware,andwhetheritneedsanupdateornot.Ifso,simplypresstheUp-datebutton.Aprogressbarwillindicatewhentheflashprocessisfinished(VerifyOk).IfmorethanoneFirefaceisinstalled,allunitscanbeflashedbychangingtothenexttabandrepeatingtheprocess.Aftertheupdatetheunitneedstobereset.ThisisdonebypoweringdowntheFirefaceforafewseconds.Arebootofthecomputerisnotnecessary.Whentheupdatefails(status:failure),theunitssecondBIOSwillbeusedfromthenextcoldbooton(SecureBIOSTechnology).Thereforetheunitstaysfullyfunctional.Theflashprocessshouldthenbetriedagainonadifferentcomputer.TheSafetyBIOScanalsobeactivatedmanually:Pushtherotaryencoderbuttonwhileswitch-ingontheunit.Thismethodisalsousefultotemporarilydeactivateanewerfirmware.Withpressedbuttontheolderversionofthefirmwarewillbeloaded.7.ConfiguringtheFireface7.1.SettingsDialogConfiguringtheFirefaceUCisdoneviaitsownsettingsdialog.StarttheprogramFirefaceUSBSettings.ThemixeroftheFireface(TotalMix)canbeconfiguredbystartingtheprogramFire-faceUSBMixer.TheFirefaceshardwareoffersanumberofhelpful,wellthought-ofpracticalfunctionsandop-tionswhichaffecthowthecardoperates-itcanbeconfiguredtosuitmanydifferentrequire-ments.ThefollowingisavailableintheSettingsdialog:LevelofanalogI/OsConfigurationofdigitalI/OsSynchronizationbehaviourCurrentsamplerateStateofinputandoutputAnychangesperformedintheSettingsdialogareappliedimmediately-confirmation(e.g.byexitingthedialog)isnotrequired.However,settingsshouldnotbechangedduringplaybackorrecordifitcanbeavoided,asthiscancauseunwantednoises.UsethedropdownmenuPropertiesFortoselecttheunittobeconfigured.Ontherightofitthecurrentfirmwareanddriverversionisshown.LevelLineInDefinesthereferenceleveloftherearanaloginputs5-8.Theavailablesettingsare-10dBV,+4dBuandLoGain.LineOutDefinesthereferenceleveloftherearanalogoutputs1-6.Theavailablesettingsare-10dBV,+4dBuandHiGain.PhonesDefinesthereferenceleveloftheanalogoutputs7/8.Theavailablesettingsare-10dBV,+4dBuandHiGain.ClockModeSampleRateUsedtosetthecurrentsamplerate.ThisisthesamesettingasintheAudioMIDISetup,justaddedhereforyourconvenience.Atongoingrecord/playbacktheselectionisgreyedout,sonochangeispossible.ClockSourceTheunitcanbeconfiguredtouseitsownclock(Internal=Master),oroneoftheinputsignals(Word,Optical,SPDIFcoax.,=Slave).Iftheselectedsourceisntavailable,theunitwillchangetothenextavailableone(AutoSync).Ifnoneisavailablethentheinternalclockisused.Thecurrentclocksourceisdisplayedtotheright.InputStatusIndicatesforeachinput(Word,optical,SPDIFcoax.)whetherthereisavalidsignal(Lock,NoLock),orifthereisavalidandsynchronoussignal(Sync).Thesecondrowshowsthesamplefrequencymeasuredbythehardware.InClockModetheclockreferenceisshown(Current).Seealsochapter31.1.OutputFormatWordThewordclockoutputsignalusuallyequalsthecurrentsamplerate.SelectingSingleSpeedcausestheoutputsignaltoalwaysstaywithintherangeof32kHzto48kHz.Soat96kHzand192kHzsamplerate,theoutputwordclockis48kHz.OpticalTheopticalTOSLINKoutputcanoperateasADATorSPDIFoutput.TheChannelStatusisfixedtoConsumerstate.Note:Theopticalinputdetectstheincomingformatautomatically.SPDIFcoax.ThecoaxialSPDIFoutputcanhavetheChannelStatusConsumerorProfessional.Forfurtherdetailspleaserefertochapter.ClockModes-SynchronizationInthedigitalworld,alldevicesmustbeeitherMaster(clocksource)orSlave(clockreceiver).Wheneverseveraldevicesarelinkedtheremustalwaysbeasinglemasterclock.Adigitalsystemcanonlyhaveonemaster!IftheFirefacesclockmodeissettoInternal,allotherdevicesmustbesettoSlave.TheFirefaceUCutilizesaveryuser-friendly,intelligentclockcontrol,calledAutoSync.InAuto-Syncmode,thesystemconstantlyscansalldigitalinputsforavalidsignal.Ifanyvalidsignalisfound,theFirefaceswitchesfromtheinternalquartz(ClockModeCurrentInternal)toaclockextractedfromtheinputsignal(ClockModeCurrentADATetc).Thedifferencetoausualslavemodeisthatwhenevertheclockreferencefails,thesystemwillautomaticallyuseitsin-ternalclockandoperateinMastermode.AutoSyncguaranteesthatrecordandrecord-while-playwillalwaysworkcorrectly.Incertaincaseshowever,e.g.whentheinputsandoutputsofaDATmachineareconnecteddirectlytotheFirefaceUC,AutoSyncmaycausefeedbackinthedigitalcarrier,sosynchronizationbreaksdown.Remedy:switchtheFirefaceclockmodeovertoMaster(ClockSourceInternal).TheFirefaceUCsADATandSPDIFinputsoperatesimultaneously.Becausethereisnoinputselector,theFirefaceUChastobetoldwhichoneofthesignalsisthesyncreference(adigitaldevicecanonlybeclockedfromasinglesource).TheClockSourceselectionisusedtodefineapreferredinputfortheautomaticclocksystem.Thisinputwillstayactiveaslongasavalidsignalisfound.Tocopewithsomesituationswhichmayariseinstudiopractice,definingasyncreferenceisessential.Oneexample:AnADATrecorderisconnectedtotheADATinput(ADATimmediatelybecomestheAutoSyncsource)andaCDplayerisconnectedtotheSPDIFinput.TryrecordingafewsamplesfromtheCDandyouwillbedisappointed-fewCDplayerscanbesynchronized.Thesampleswillinevitablybecorrupted,becausethesignalfromtheCDplayerisreadwiththe(wrong)clockfromtheADATi.e.outofsync.Inthiscase,theClockSourceshouldbesettemp