acoustic-phonetics.ppt

BriefIntroductiontoAcousticPhoneticsHuiqinMaSep15 2010 AcousticparametersFundamentalfrequency F0 Hz Pitch auditory Amplitude dB Loudness auditory Formants frequenciesaboveF0 Hz Quality auditory DifferentqualitybetweenvowelAandvowelB differentformantpatternsLength Duration s Speechsoundconsistsofsmallvariationsinairpressurewhichareaudiblebtw20to20 000perturbations Hz Everytimethevocalcordsopenandclose thereisapulseofairfromthelungs Inthecaseofvoicedsounds thevibratingvocalcordschopupthestreamoflungairsothatpulsesofhighpressurealternateswithpulsesoflowerpressure Whenvariationsinairpressureintheformofsoundwavesreachtheearofthelistener theycausetheeardrumtovibrate Soundwave Soundiscausedbyperturbationofairpressure itisanalternatingpatternofhighandlowpressureareas Theredlinerepresentstheaveragebackgroundairpressure theairpressurethatwouldexistiftherewerenosoundwaves Pointsabovethislinerepresenthigherpressure morecrowdedairmolecules pointsbelowrepresentlowerpressure lesscrowdedairmolecules ThewaveformshowsspeechasafunctionofAmplitude whichismeasuredindecibels dB andthefrequencyofthesoundwavesmeasuredinhertz Hz PropertiesofSineWave Thissimplestkindofwaveisoftencalledasinewave CombiningWaves Ifyou relisteningtowavesfromtwosourcesatthesametime ahighpressurefromonesourcewilltendtocanceloutalowpressurefromtheother twohighpressureswillreinforceeachotherandcreateanevenhigherpressure twolowerpressureswillreinforceeachotherandcreateanevenlowerpressure Anycomplexwavecanbetreatedasacombinationofsimplesinewaves Formostpracticalpurposesinphonetics wedon tcareabouttheactualcomplexwaveformitself We reonlyinterestedinthefrequenciesandamplitudesofthesimplewavesthatit smadeof a b c arecomponentfrequencies and d isacomplexwaveform Whenthesignal sound isperiodic thesinewavesinthecomplexwavesarewhole numbermultiples 整倍数 ofthesamefundamentalfrequency F0 Whenthesignalisnoise aperiodic thefrequenciesofthesinewaveshavenorelationship 无比例关系 tooneanother Analysisofacomplexsoundiscalledspectralanalysis Wavelength thelengthofasoundwaveisthedistanceinspacethatonecycleoccupies Onecanmeasurefromanypointinonecycletothecorrespondingpointinthenextcycle Highfrequencysoundsoccupylessspacepercycle haveashorterwavelength thandolowfrequencysounds PitchandFrequency Frequencyisthenumberofthecompleterepetitions cycles ofwaveforms orthenumberofvibrations inasecond TheunitoffrequencyismeasuredinHz Ifthevocalcordsmake200completeopeningandclosingmovementsinasecond thefrequencyis200Hz Soitispossibletodeterminethefrequencyofasoundbycountingthepeaksofairpressureinarecordofitswaveforms Frequencydeterminespitch Whenaspeechsoundgoesupinfrequency italsogoesupinpitch therateofspeechalsogoesup Thepitchofasoundmaybeequatedwithitsfundamentalfrequency Fundamentalfrequency 基频 E1 determinedbyhowmanytimesthevocalfoldsvibrateinonesecond ifthevocalcordsopenandclose100timespersecond theglottalperiodequals10millisecond theF0equals100Hz E2 firstharmonic fundamental F0 readasFnaughtorFzero isofparticularimportanceinstudiesofintonation F0determinestone Toneisconnectedwithpitchvariations Weperceivetones Pitch Vowelshavean intrinsic pitchwhichcorrelateswithvowelheight highvowelshavehighpitchandlowvowelshavelowpitch andthedifferencecanbeaslargeas20 25Hz Pitchpatternsareeithersteady risingorfalling anditischangingpitchthathasagreaterperceptualsalience Aspeakertakeslesstimetoproduceafallingpitchthanarisingpitch Alllanguagesvarypitchtoconveylinguisticinformation Amplitude Intensity Loudness Amplitudedeterminesloudness Theloudnessofasounddependsonthesizeofthevariationsinairpressure oramplitude Acousticintensityistheappropriatemeasurecorrespondingtoloudness measuredindB Spectrogramcantellushowmuchacousticenergyisproduced Intensityisaphysicalcharacteristicofasound andloudnessisthesubjectivepropertyofasoundthatismostdirectlyrelatedtointensity Resonance 共鸣频率 Resonance 共鸣频率 Aresonatorissomethingthatissetintoforcedvibrationbyanothervibration Inspeech theresonancesofthevocaltractarecalledformantfrequenciesorsimplyformants Theresonantfrequenciesdependontheshapeandsizeofthevocaltract Vocalfoldsvibration harmonics H1 F0 H2 H3 Oral nasal andpharyngealcavities toformresonators Differentshapes sizesoftheresonators resonateandemphasizecertainharmonics formants F1 F2 F3 Formantpatterns qualityofsounds vowels sonorants Formants 共振峰 Aformantisaconcentrationofacousticenergy reflectingthewayairfromthelungsvibratesinthevocaltract Inwidebandspectrogram 0 005 formantsshowupasagroupofdarkenergybands innarrow bandspectrogram 0 025 formantsshowupasagroupofadjacentharmonics Sowide bandisbetterinviewingformants whilenarrow bandisbetterforviewingharmonics Formantsarenumbered Vowelsarecharacterizedbythreeformants F1 F2 F3 ThechangeofF1andF2meansthechangeofavowel VowelheightF1 Thehigheravowel thelesstheF1backnessF2 F1ThelargerthenumberofF2 F1 themoreforwardthevowel Stoptransition placeofarticulation Eg a stop a i stop i adjacenttoalabialstop theformantpatternofthevowelexhibitsaloweredf2 adjacenttoanalveolarstop theformantofthevowelexhibitsaraisedf2 adjacenttoavelarstop theformatofthevowelexhibitsdivergentf2andf3 velarpinch F2andF3oftencometogetherinvelartransitions Harmonic 谐波 Harmonic referstoregular periodic waveformaccompanyingafundamentalfrequency whichhelpstoidentifyacomplextone alsocalledanovertone 倍音 Harmonicsarewhole numbermultiplesofthefundamentalfrequency e g ifthefundamentalfrequencyis200 theharmonicswillbeat400Hz 600Hz 800HzInthisexample 400Hzwouldbethefirstharmonic 600Hzwillbethesecondharmonic 800Hzisthethirdharmonic Harmonicimpliesperiodic otherwiseitisaperiodic Distinguishharmonicswithformantfrequencies Ifweknowthefundamentalfrequency weknowtheharmonics Varyingthefundamentalfrequencychangesthepitchofthevowel Suchisnotthecasefortheformantfrequencieswhichresultfromthepositionofthetongueandtheshapeofthemouth Whenthetongueishighandforwardinthevocaltractsuchasthevowel i i hasthehighestF2 about2250 andlowestF1 about220 Whenthebackofthetongueishighsuchasthevowel u ithasthelowerF2 about870 andhigherF1 about310 whencomparedwith i VowelNormalization 元音的规整 Men womenandchildrendifferinvocaltractlength thesedifferencesresultindifferencesinformantfrequenciesinproducingvowels Theyalsodifferinthevocalfolds femaleshaveshortervocalfoldswithlessmassthanmales sotheytendtohavehigheraveragefundamentalfrequencies Children whosevocalfoldsareevenshorter usuallyhavemuchhigherfundamentalfrequenciesthanadults Thesephysicaldifferencesinspeakersresultinconsiderabledifferencesintheformantfrequenciesforparticularvowels Vowelnormalizationreferstotheperceptualprocessoffactoringoutdifferencesduetovocaltractdifferences Infactthereisaconsiderabledegreeofoverlapofvowelspaces 元音空间有很大程度的重叠 betweenadultsandchildren Researchwithveryyoungchildrenhasprovidedevidencethattheyarecapableofnormalizingvowelsfordifferentspeakers Kuhl 1987 Lieberman 1984 Infantscanrecognizethesamevowelacrossdifferentspeakers despitetheacousticdifferences Researchershavesuggestedthatthiscapacity vowelnormalization isinnateandpresentatbirth VOT Invoicedstopconsonants thevoicingbeginsalmostsimultaneouslywhentheocclusionoftheairstreamisreleased Incontrast thereisadelayintheonsetofvocalfoldvibrationaftertheocclusionoftheairstreamisreleasedinthecaseofvoicelessconsonants Thedifferencebetweenvoicedandvoicele