语音均匀和非均匀编码方法.ppt

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1、SpeechSignalProcessing—Lecture6SpeechCodingMethodsBasedonSpeechWaveformRepresentationsandSpeechModels—UniformandNon-UniformCodingMethods1TopicstobeCoveredBriefintroductiontospeechcodingCharacteristicsofspeechwaveformUniformquantizationNon-uniformquantization2SpeechInformatio

2、nRatesFundamentallevel:10-15symbols/secondforcontinuousspeech32-64symbolsperlanguage=>6bits/symbolInformationRate=60-90bpsatthesourceWaveformlevelSpeechbandwidthfrom4–10kHz=>samplingratefrom8–20kHzNeed12-16bitquantizationforhighqualitydigitalcodingInformationRate=96-320Kbps=

3、>morethan3ordersofmagnitudedifferenceinInformationRatesbetweentheproductionandwaveformlevels3DigitalSpeechCodingA-to-DConverterAnalysis/CodingChannelorMediumD-to-AConverterDecoding/SynthesisChannelorMediumxa(t)x(n)y(n)y(n)ya(t)4IntroductiontoWaveformCodingFs=1/T>twicethehigh

4、estfrequencyintheinputsignalxa(t)mustfirstbelowpassfilteredsincespeechisnotinherentlylowpasstelephonebandwidth-200-3200Hz(filteringrange)-Fs=6400Hz,8000Hzwidebandspeech-100-7000Hz(filteringrange)-Fs=16000HzT=1/Fs5noticehighfrequencycomponentsofvowelsandfricatives(upto10kHz)=

5、>needFs>20kHzwithoutlowpassfilteringneedonlyabout4kHztoestimateformantfrequenciesneedonlyabout3.2kHzfortelephonespeechcodingSpeechSpectra6TelephoneChannelResponseitisclearthat4kHzbandwidthsufficientformostapplicationsusingtelephonespeechbecauseofinherentchannelbandlimitation

6、sfromthetransmissionpath7SpeechProbabilityDensityFunctionneedtoestimateprobabilitydensityandpowerspectrumfromspeechwaveformsprobabilitydensityestimatedfromlongtermhistogramofamplitudesgoodapproximationisaGammadistribution,oftheform:simplerapproximationisLaplaciandensity,ofth

7、eform:8MeasuredSpeechDensitiesdistributionnormalizedsomeanis0andvarianceis1(x=0,σx=1)GammadensitymorecloselyapproximatesmeasureddistributionforspeechthanLaplacianLaplacianisstillagoodmodelandisusedinanalyticalstudiessmallamplitudesmuchmorelikelythanlargeamplitudes—by100:1rat

8、io9SpeechACandPowerSpectrumcanestimatelongtermautocorrelationandpowerspectr