Linear predictive coding (LPC) of speech - Forward线性预测编码（LPC）语音了.docx

SpeechProcessingProject1.inearPredictivecodingusingVoiceexcitedVocoderECE5525OsamaSarairehFall2005Dr.VetonKepuskaThebasicformofpitchexcitedLPCvocoderisshownbelowThespeechsignalisfilteredtonomorethanonehalfthesystemsamplingfrequencyandthenA/Dconversionisperformed.Thespeechisprocessedonaframebyframebasiswheretheanalysisframelengthcanbevariable.Foreachframeapitchperiodestimationismadealongwithavoicingdecision.AlinearpredictivecoefficientanalysisisperformedtoobtainaninversemodelofthespeechspectrumA(z).InadditionagainparameterG,representingsomefunctionofIhespeechenergyiscomputed.Anencodingprocedureisthenappliedfortransformingtheanalyzedparametersintoanefficientsetoftransmissionparameterswiththegoalofminimizingthedegradationinthesynthesizedspeechforaspecifiednumberofbits.Knowingthetransmissionframerateandthenumberofbitsusedforeachtransmissionparameters,onecancomputeanoise-freechanneltransmissionbitrate.Atthereceiver,thetransmittedparametersaredecodedintoquantizedversionsofthecoeifficentanalysisandpitchestimationparameters.Anexcitationsignalforsynthesisisthenconstructedfromthetransmittedpitchandvoicingparameters.Theexcitationsignalthendrivesasynthesisfilter1/A(z)correspondingtotheanalysismodelA(z).Thedigitalsampless(n)arethenpassedthroughanD/Aconverterandlowpassfilteredtogeneratethesyntheticspeechs(t).Eitherbeforeoraftersynthesis,thegainisusedtomatchthesyntheticspeechenergytotheactualspeechenergy.Thedigitalsamplesaretheconvertedtoananalogsignalandpassedthroughafiltersimilartotheoneattheinputofthesystem.LMearDrediCtiVeCOdin父(LPC)OfSDeeChThelinearpredictivecoding(LPC)methodforspeechanalysisandsynthesisisbasedonmodelingtheVocaltractasalinearAll-Pole(IIR)filterhavingthesystemtransferfunction:T = pitd periodimpulse trainInnovationsu(n)。UVSpeech SignalLPC FilterWI)whitenoisesimplespeechproductionWherepisthenumberofpoles,GisthefilterGain,andakaretheparametersthatdeterminethepoles.Therearetwomutuallyexclusivewaysexcitationfunctionstomodelvoicedandunvoicedspeechsounds.Forashorttime-basisanalysis,voicedspeechisconsideredperiodicwithafundamentalfrequencyofFo,andapitchperiodoflFo,whichdependsonthespeaker.Hence,Voicedspeechisgeneratedbyexcitingtheallpolefiltermodelbyaperiodicimpulsetrain.Ontheotherhand,unvoicedsoundsaregeneratedbyexcitingtheall-polefilterbytheoutputofarandomnoisegenerator.Thefundamentaldifferencebetweenthesetwotypesofspeechsoundscomesfromthewaytheyareproduced.Thevibrationsofthevocalcordsproducevoicedsounds.Therateatwhichthevocalcordsvibratedictatesthepitchofthesound.Ontheotherhand,unvoicedsoundsdonotrelyonthevibrationofthevocalcords.Theunvoicedsoundsarecreatedbytheconstrictionofthevocaltract.ThevocalcordsremainopenandtheconstrictionsofthevocaltractforceairouttoproducetheunvoicedsoundsGivenashortsegmentofaspeechsignal,letssayabout20msor160samplesatasamplingrate8KHz,thespeechencoderatthetransmittermustdeterminetheproperexcitationfunction,thepitchperiodforvoicedspeech,thegain,andthecoefficients3pk.Theblockdiagrambelowdescribestheencoder/decoderfortheLinearPredictiveCoding.Theparametersofthemodelaredeterminedadaptivelyfromthedataandmodeledintoabinarysequenceandtransmittedtothereceiver.Atthereceiverpoint,thespeechsignalisthesynthesizedfromthemodelandexcitationsignal.Theparametersoftheall-polefiltermodelaredeterminedfromthespeechsamplesbymeansoflinearprediction.TobespecifictheoutputofIheLinearPredictionfilterisPS()=工ap(k)s(nk)k=landthecorrespondingerrorbetweentheobservedsampleS(n)andthepredictedvalueAs(h)ise(h)=s(ri)一s(h)byminimizingthesumofthesquarederrorwecandeterminethepoleparameters/7(Jofthemodel.Theresultofdifferentiatingthesumabovewithrespecttoeachoftheparametersandequationtheresulttozero,isasepofplinearequationsP%(Z)Q(机幻=_噎(MWherem=I2.pk=whereGS(Mpresenttheautocorrelationofthesequence$()definedasNQ(M=s()s5+m)H=OtheequationabovecanbeexpressedinmatrixformasRd=一曝whereRSSaisapxpautocorrelationmatrix,GsiSaPXlautocorrelationvector,andaisapx1vectorofmodelparameters.rowcol=size(data);ifcol=1data=data"endnfrane=0;msfr=round(srl(X)Ofr);%Convertmstosamplesmsfs=round(sr/1000*fs);%Convertmstosamplesduration=Iength(data);speech=filler01-preemp,1,data)'%Preemphasizespeechnsoverlap=msfs-nsfr;ramp=0:1/(nsoverlap-1):1J'%Computepartofwindowforframeindex=1:msfr:duration-msfs+1%framerate=20rnsframeData=speech(frameindex:(frameIndex+ms-1);%framesize=3Omsnframe=nfrane+l;CiiitoCor=XcorriframeData);%ComputethecrosscorrelationautoCorVec=autoCor(msfs+0:LJ);TheseequationscanbesolvedinMATLBbyusingtheLevinson-Durbinalgorithm.%Levinson'smethoderr(1)=autoCorVec(I);k(l)=O;=;farindex=1:Lnumerator=/7A.'*autoCorVec(index+1:-1:2);denominator=-1*err(index);k(index)=nuneratordenoninator;%PARCORcoeffsA=A+k(index)*flipud（八）;k(index)J;err(index+l)=(1-k(index)2)*err(index);Thegainparameterofthefiltercanbeobtainedbytheinput-outputrelationshipasfollowPs(n)=-Za