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1、AbstractAbstractWiththerapiddevelopmentandthewidespreadapplicationsofthedigitalcommunication,thelowbitratespeechcodingplaysanimportantroleinnarrowbandcommunications,especiallyinmilitaryorsecurecommunications,andincivilianuseaswell.Mixedexcitationline
2、arprediction(MELP)vocoderisoneofthemostpotentialalgorithminmodernlowbitratespeechcoding.MELPisbasedonthemodelofLPCvocoderandincludesfiveadditionalfeatureswhicharemixedexcitation,aperiodicpulses,pulsedispersion,adaptivespectralenhancementandFouriermag
3、nitudesscalingofthevoicedexcitation.BasedonthemodelofMELP,averylowbitratespeechcodingalgorithmworkingat1.2kbpsisdesignedandimplementedinthethesis.Firstly,becauseofthelowbitratespeechcodersat1.2kbpscanhardlygetgoodperformanceforthelackofbitstoaccurate
4、repersenttheparametersofspeechsignals,asuperframethatcomposestwosubframesisused.Secondly,foreverysubframe,theparametersofspeechsignalsareanalyzedandextracted.Thirdly,subbandvoiced/unvoicedjudgment,gainandlinearspectralfrequency(LSF)arequantizedinones
5、ubframe,andjointvecterquantizationalgorithmsareappliedtopitchandamplitudevalueofFourierseriesoftheresidualsignalsintwosubframes.Finally,the1.2kbpslowbitratespeechcodingalgorithmisportingtoandimplementedonTIC6000DSPplatformwithoptimization.Testandeval
6、uationresultshaveshownthat,thePESQscoreofthedesigned1.2kbpslowbitratespecchcodingalgorithmisjustabout0.17lowerthanthatoftheMELPat2.4kbps.ThismeansthatthereconstructedspeechqualityofthedesignedalgorithmisprettyclosetothatofMELP.WiththeDSPplatformimple
7、mentation,thealgorithmcomplexityisoptimizedtolessthan10%thecomplexityoftheoriginalalgorithmsandthisisagoodbaseforfurtherengineeringapplications.Keyword:SourceCodingLowBitRateSpeechCodingMELPSuperframeVQ目录1目录第一章绪论......................................
8、..........................................................................11.1课题来源及意义................................................................................................11.2语音编码概述...........................................................
