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1、SpeechSignalRepresentationsPart1:DigitalSignalProcessingHsin-minWangReferences:1X.Huangetal.,SpokenLanguageProcessing,Chapters5-62J.R.Delleretal.,Discrete-TimeProcessingofSpeechSignals,Chapters4-63J.W.Picone,“Signalmodelingtechniquesinspeechrecognition,”proceedingso
2、ftheIEEE,September1993,pp.1215-12471Introduction￠Currentspeechrecognitionsystemsaremainlycomposedof:?Afront-endfeatureextractor(featureextractionmodule)?Discoversalientcharacteristicssuitedforclassification?Basedonscientificand/orheuristicknowledgeaboutpatternstorec
3、ognize?Aback-endclassifier(classificationmodule)?Setclassboundariesaccuratelyinthefeaturespace?StatisticallydesignedaccordingtothefundamentalBayes’decisiontheory2AnalogSignaltoDigitalSignalAnalogSignalDigitalSignal:Discrete-timeDiscrete-timeSignalorDigitalSignalsign
4、alwithdiscreteamplitudex[n]=x(nT),T:samplingperiod;at=nTsamplingperiod=125μsF=1samplingrate=>samplingrate=8kHzsT3TwoMainApproachestoDigitalSignalProcessing￠FilteringSignalinSignaloutFilterx[]ny[n]Amplifyorattenuatesomefrequencycomponentsofx[n]￠ParameterExtractionSig
5、nalinParameterParameteroutx[]nExtractioncc?c11??21??L1???????e.g.:?c12??c22??cL2?1.SpectrumEstimation????????????2.ParameterforRecognition???????c??c??c??1m??2m??Lm?45.1DigitalSignalsandSystems5SinusoidalSignalsx[n]=Acos(ωn+φ)f:normalizedfrequency0≤f≤1?A:amplitude(振
6、幅)?ω:angularfrequency(角頻率),fω=2π?:phase(相角)φ[]?π?period:T=25samplesxn=Acos?ωn???2?frequency:f=0.046SinusoidalSignals–periodicvs.non-periodicx[n]isperiodicwithperiodNifandonlyifx[n+N]=x[n]Acos()ω(n+N)+φ=Acos(ωn+φ)2πωN=2πω=NAcos()ωn+φisnotperiodicforallvaluesofw￠Examp
7、les?x[]n=cos(πn/4)isperiodicwithperiodN=81?x[]n=cos(3πn/8)isperiodicwithperiodN=162?x[]n=cos(n)isnotperiodic37SinusoidalSignals–periodicvs.non-periodic(cont.)x1[n]=cos()πn/4?π??ππ?=cos?(n+N1)?=cos?n+N1??4??44?π?N1=2π?k?N1=8k(bothN2andkareintergers)4∴periodN1=8x2[n]=
8、cos(3πn/8)?3π??3π3π?=cos?(n+N2)?=cos?n+N2??8??88?3π16?N2=2π?k?N2=k(bothN2andkareintergers)83∴periodN2=16x3[n]=cos()n=cos(n+N3)?N3=2π?kcan'
