语音自适应和差分编码方法.ppt

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1、SpeechSignalProcessing—Lecture7SpeechCodingMethodsBasedonSpeechWaveformRepresentationsandSpeechModels—AdaptiveandDifferentialCoding1QuantizationDilemmaWanttochoosequantizationstepsizelargeenoughtoaccommodatemaximumpeak-to-peakrangeofx(n);atthesametimen

2、eedtomakethequantizationstepsizesmallsoastominimizethequantizationerrorthenon-stationarynatureofspeech(variabilityacrosssounds,speakers,backgrounds)compoundsthisproblemgreatly2SolutionstoQuantizationDilemmaSolution1-letΔvarytomatchthevarianceoftheinput

3、signal=>Δ(n)Solution2-useavariablegain,G(n),followedbyafixedquantizerstepsize,Δ=>keepsignalvarianceofy(n)=G(n)x(n)constantCase1:Δ(n)proportionaltoσx2=>quantizationlevelsandrangeswouldbelinearlyscaledtomatchσx2=>needtoreliablyestimateσx2Case2:G(n)propor

4、tionalto1/σx2togiveσy2≈constantneedreliableestimateofσx2forbothtypesofadaptivequantizationAdaptiveQuantization:3TypesofAdaptiveQuantizationClassification1:instantaneous-amplitudechangesreflectsample-to-samplevariationsinx(n)=>rapidadaptationsyllabic-am

5、plitudechangesreflectsyllable-to-syllablevariationsinx(n)=>slowadaptationClassification2:feed-forward-adaptivequantizersthatestimateσx2fromx(n)itselffeedback-adaptivequantizersthatadaptthestepsize,Δ,onthebasisofthequantizedsignal,,(orequivalentlythecod

6、ewords,c(n))4FeedForwardAdaptationVariablestepsizeassumeuniformquantizerwithstepsizeΔ(n)x(n)isquantizedusingΔ(n)=>c(n)andΔ(n)needtobetransmittedtothedecoderifc’(n)=c(n)andΔ’(n)=Δ(n)=>noerrorsinchannel,andDon’thavex(n)atthedecodertoestimateΔ(n)=>needtot

7、ransmitΔ(n);thisisamajordrawbackoffeedforwardadaptation5Feed-ForwardQuantizertimevaryinggain,G(n)=>c(n)andG(n)needtobetransmittedtothedecoderCan’testimateG(n)atthedecoder=>ithastobetransmitted6FeedForwardQuantizersfeedforwardsystemsmakeestimatesofσx2,t

8、henmakeΔorthequantizationlevelsproportionaltoσx,orthegainisinverselyproportionaltoσx7FeedForwardQuantizertheparameterαcontrolstheeffectiveintervalofx(n)thatcontributestotheestimateofα=0.99=>bringsuplevelinlowamplituderegions=>syllabicra