Audio-Precision音频分析仪测试介绍演示教学课件

APIntroduction&THD+N

AnalyzerinputandXLRconnectorAPPanelAudiospecificationsTHD+N1APintroduction

Analyzerinputcableconnection -Singleendedoutput(MP3headphone) 2–Signal,3–Ground. e.g.,ChannelA:2–Leftoutput,3–Ground ChannelB:2–Rightoutput,3–Ground -Differentialoutput(loudspeaker) 2–Non-invertingsignal,3–Invertingsignal

2APintroduction

XLRConnector

3APintroduction

XLRConnector

-Inreferencetoitsoriginalmanufacturer,JamesH.Cannon,founderofCannonElectricinLosAngeles,California(nowpartofITTCorporation),theconnectoriscolloquiallyknownasacannonplugorcannonconnector.

-Themostcommonisthe3-pinXLR3,usedalmostuniversallyasabalancedaudioconnectorforhighqualitymicrophonesandconnectionsbetweenequipment. -XLRplugsandsocketsareusedmostlyinprofessionalaudioandvideoelectronicscablingapplications.HomeaudioandvideoelectronicsnormallyuseRCAconnectors.4APintroduction

AP1Panel5APintroduction

THD

+

NvsLevel

Curve6APintroduction

AnalyzerPanel7APintroduction

SweepDefinitions

Panel8APintroduction

FrequencyResponse -FrequencyResponsemeasurementsaremadebysteppingorsweepingasinewaveoscillator,atafixedamplitude,acrossthespectrumofinterest. -UsuallystatedintermsofdBvariationfromsomereferencemidbandfrequency(e.g.,1KHz). -Thetestmaybeeasilymodified.Thefrequencyrangeanddirectionofsweepcanbechangedfromthe20KHz~20HzstoredbyenteringnewvaluesforSTARTandSTOPunderSWEEP(F9)DEFINITIONSpanel.9APintroduction

SignaltoNoiseRatio -Signaltonoiseratio,asarelativemeasurement,mustbemadewithreferencetoaspecificoutputamplitudefromthedeviceundertest. -Theratedoutputamplitudemustbecalibratedasthe0dBrreferenceoftheanalyzer.Thentheresidualoutputamplitude(noise)ismeasuredandexpressedindBrelativetothereference.10APintroduction

Crosstalk

-Signalsfromonechannelleakingintoanotherchannel.Normally,thishappensbetweenleftandrightstereochannels.

-Ageneratordrivesonechannelandthischannel'soutputvalueisnoted;meanwhiletheotherchannelissetforzerovolts.Themeasuredchannelleftopen. -Whateversignalisinducedintothetestedchannelismeasuredatitsoutputwithanrmsvoltmeterandnoted.Aratioisformedbydividingtheunwantedsignalbytheabove-notedoutputtestvalue,andtheanswerexpressedindB.

11APintroduction

HarmonicDistortionConcepts

-Harmonicdistortionmaybemeasuredandexpressedastotalharmonicdistortion(THD),orastotalharmonicdistortionplusnoise(THD+N). -THDisthedistortionthatoccursonharmonicsoftheoriginalsignal.Noiseisthemorerandom,uncorrelateddistortion. -Inallcases,stimulusfromaverypuresinewavegeneratorisfedtotheinputofdeviceundertest.Thegeneratormusthavesignificantlylowerdistortionsthanthatofdevice.

12APintroduction

HarmonicDistortionConcepts

-THDreferstomeasurementmethodswhichindividuallymeasuretheamplitudeofeachsignificantharmonicinanarrowbandwidth,thencombinestheminroot-mean-squarefashiontoproduceasinglenumber.

-THD+N,referstothemeasurementtechniqueinwhichthefundamentalcomponentisremovedbyabandreject(norch)filterandallremainingenergymeasured,includingharmonicsandnoise.

13APintroduction

HarmonicDistortionConcepts -BandwidthandTHD+N ThemeasuredTHD+Nofadevicewillvarywiththemeasurementbandwidth.Youwillalmostalwayswanttorestrictthemeasurementbandwidthusinghigh-passandlow-passfilters,andyoumustincludethebandwidthusedwhenyoustatetheresult.THD+Nistypicallymeasuredandreportedina20Hz"20kHzbandwidth. 14APintroduction

HarmonicDistortionConcepts -LevelandTHD+N ThemeasuredTHD+Nofadevicewillalsovarywithlevelandthefrequencyoftheappliedsignal.AudioTHD+Nistypicallymeasuredandreportedatamid-rangefrequency(1kHzorso)attheeitherthedevice'snominaloperatingleveloratitsmaximumoutputlevel(MOL). -ATHD+NversusfrequencysweeporaTHD+NversusamplitudesweepswillshowhowaDUTperformsundervaryingstimulus.15T