SIST EN 301 704 V7.2.1:2003

Digital cellular telecommunications system (Phase 2+) (GSM); Adaptive Multi-Rate (AMR) speech transcoding (GSM 06.90 version 7.2.1 Release 1998)

Adaptive Multi- Rate (AMR)  Speech Transcoding

Digitalni celični telekomunikacijski sistem (faza 2+) – Prilagodljivo večhitrostno (AMR) prekodiranje govora (GSM 06.90, različica 7.2.1, izdaja 1998)

General Information

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Mandate: T-172
• Ref Project: ETSI EN 301 704 V7.2.1 (2000-05) - Digital cellular telecommunications system (Phase 2+) (GSM); Adaptive Multi-Rate (AMR) speech transcoding (GSM 06.90 version 7.2.1 Release 1998)

Standards Content (Sample)

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Adaptive Multi-Rate (AMR) speech transcoding (GSM 06.90 version 7.2.1 Release 1998)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 301 704 Version 7.2.1SIST EN 301 704 V7.2.1:2003en01-december-2003SIST EN 301 704 V7.2.1:2003SLOVENSKI
STANDARD



SIST EN 301 704 V7.2.1:2003



ETSIEN301704V7.2.1(2000-04)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);AdaptiveMulti-Rate(AMR)speechtranscoding(GSM06.90version7.2.1Release1998)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)2(GSM06.90version7.2.1Release1998)ReferenceREN/SMG-110690Q7R1KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunication(GSM),speech,AMRETSI650RoutedesLuciolesF-06921SophiaAntipolisCedex-FRANCETel.:[phone]Fax:[phone]SiretN°34862356200017-NAF742CAssociationàbutnonlucratifenregistréeàlaSous-PréfecturedeGrasse(06)N°7803/88ImportantnoticeIndividualcopiesofthepresentdocumentcanbedownloadedfrom:http://www.etsi.orgThepresentdocumentmaybemadeavailableinmorethanoneelectronicversionorinprint.Inanycaseofexistingorperceiveddifferenceincontentsbetweensuchversions,thereferenceversionisthePortableDocumentFormat(PDF).Incaseofdispute,thereferenceshallbetheprintingonETSIprintersofthePDFversionkeptonaspecificnetworkdrivewithinETSISecretariat.Usersofthepresentdocumentshouldbeawarethatthedocumentmaybesubjecttorevisionorchangeofstatus.InformationonthecurrentstatusofthisandotherETSIdocumentsisavailableathttp://www.etsi.org/tb/status/Ifyoufinderrorsinthepresentdocument,sendyourcommentto:[e-mail]opartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)3(GSM06.90version7.2.1Release1998)ContentsIntellectualPropertyRights.5Foreword.51Scope.62References.63Definitions,symbolsandabbreviations.73.1Definitions.73.2Symbols.93.3Abbreviations.124Outlinedescription.134.1Functionaldescriptionofaudioparts.134.2Preparationofspeechsamples.144.2.1PCMformatconversion.144.3PrinciplesoftheGSMadaptivemulti-ratespeechencoder.144.4PrinciplesoftheGSMadaptivemulti-ratespeechdecoder.164.5Sequenceandsubjectiveimportanceofencodedparameters.175Functionaldescriptionoftheencoder.175.1Pre-processing(allmodes).175.2Linearpredictionanalysisandquantization.175.2.1Windowingandauto-correlationcomputation.185.2.2Levinson-Durbinalgorithm(allmodes).195.2.3LPtoLSPconversion(allmodes).205.2.4LSPtoLPconversion(allmodes).215.2.5QuantizationoftheLSPcoefficients.225.2.6InterpolationoftheLSPs.235.2.7MonitoringresonanceintheLPCspectrum(allmodes).245.3Open-looppitchanalysis.255.4Impulseresponsecomputation(allmodes).285.5Targetsignalcomputation(allmodes).285.6Adaptivecodebook.285.6.1Adaptivecodebooksearch.285.6.2Adaptivecodebookgaincontrol(allmodes).325.7Algebraiccodebook.335.7.1Algebraiccodebookstructure.335.7.2Algebraiccodebooksearch.355.8Quantizationoftheadaptiveandfixedcodebookgains.395.8.1Adaptivecodebookgainlimitationinquantization.395.8.2Quantizationofcodebookgains.395.8.3Updatepastquantizedadaptivecodebookgainbuffer(allmodes).415.9Memoryupdate(allmodes).416Functionaldescriptionofthedecoder.426.1Decodingandspeechsynthesis.426.2Post-processing.456.2.1Adaptivepost-filtering(allmodes).456.2.2High-passfilteringandup-scaling(allmodes).467Detailedbitallocationoftheadaptivemulti-ratecodec.468Homingsequences.518.1Functionaldescription.518.2Definitions.518.3Encoderhoming.528.4Decoderhoming.52SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)4(GSM06.90version7.2.1Release1998)9Bibliography.56AnnexA(informative):Documentchangehistory.57History.58SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)5(GSM06.90version7.2.1Release1998)IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.TheinformationpertainingtotheseessentialIPRs,ifany,ispubliclyavailableforETSImembersandnon-members,andcanbefoundinSR000314:"IntellectualPropertyRights(IPRs);Essential,orpotentiallyEssential,IPRsnotifiedtoETSIinrespectofETSIstandards",whichisavailablefromtheETSISecretariat.LatestupdatesareavailableontheETSIWebserver(http://www.etsi.org/ipr).PursuanttotheETSIIPRPolicy,noinvestigation,includingIPRsearches,hasbeencarriedoutbyETSI.NoguaranteecanbegivenastotheexistenceofotherIPRsnotreferencedinSR000314(ortheupdatesontheETSIWebserver)whichare,ormaybe,ormaybecome,essentialtothepresentdocument.ForewordThisEuropeanStandard(Telecommunicationsseries)hasbeenproducedbytheSpecialMobileGroup(SMG).Thepresentdocumentdescribesthedetailedmappingfrominputblocksof160speechsamplesin13-bituniformPCMformattoencodedblocksof95,103,118,134,148,159,204,and244bitsandfromencodedblocksof95,103,118,134,148,159,204,and244bitstooutputblocksof160reconstructedspeechsampleswithinthedigitalcellulartelecommunicationssystem.ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version7.x.ywhere:7indicatesRelease1998ofGSMPhase2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.NationaltranspositiondatesDateofadoptionofthisEN:31March2000DateoflatestannouncementofthisEN(doa):30June2000DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):31December2000DateofwithdrawalofanyconflictingNationalStandard(dow):31December2000SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)6(GSM06.90version7.2.1Release1998)1ScopeThepresentdocumentdescribesthedetailedmappingfrominputblocksof160speechsamplesin13-bituniformPCMformattoencodedblocksof95,103,118,134,148,159,204,and244bitsandfromencodedblocksof95,103,118,134,148,159,204,and244bitstooutputblocksof160reconstructedspeechsamples.Thesamplingrateis8000samples/sleadingtoabitratefortheencodedbitstreamof4.75,5.15,5.90,6.70,7.40,7.95,10.2or12.2kbit/s.Thecodingschemeforthemulti-ratecodingmodesistheso-calledAlgebraicCodeExcitedLinearPredictionCoder,hereafterreferredtoasACELP.Themulti-rateACELPcoderisreferredtoasMR-ACELP.Inthecaseofdiscrepancybetweentherequirementsdescribedinthepresentdocumentandthefixedpointcomputationaldescription(ANSI-Ccode)oftheserequirementscontainedinGSM06.73[6],thedescriptioninGSM06.73[6]willprevail.TheANSI-Ccodeisnotdescribedinthepresentdocument,seeGSM06.73[6]foradescriptionoftheANSI-Ccode.Thetranscodingprocedurespecifiedinthepresentdocumentisapplicablefortheadaptivemulti-ratefullrateandhalfratespeechtrafficchannels(TCH)intheGSMsystem.InGSM06.71[5],areferenceconfigurationforthespeechtransmissionchainoftheGSMadaptivemulti-rate(AMR)systemisshown.Accordingtothisreferenceconfiguration,thespeechencodertakesitsinputasa13-bituniformPCMsignaleitherfromtheaudiopartoftheMobileStationoronthenetworkside,fromthePSTNviaan8-bitA-laworµ-lawto13-bituniformPCMconversion.TheencodedspeechattheoutputofthespeechencoderisdeliveredtoachannelencoderunitwhichisspecifiedinGSM05.03[3].Inthereceivedirection,theinverseoperationstakeplace.2ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.• Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.• Foraspecificreference,subsequentrevisionsdonotapply.• Foranon-specificreference,thelatestversionapplies.• Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.• ForthisRelease1998document,referencestoGSMdocumentsareforRelease1998versions(version7.x.y).[1]GSM01.04:"Digitalcellulartelecommunicationssystem(Phase2+);Abbreviationsandacronyms".[2]GSM03.50:"Digitalcellulartelecommunicationssystem(Phase2+);TransmissionplanningaspectsofthespeechserviceintheGSMPublicLandMobileNetwork(PLMN)system".[3]GSM05.03:"Digitalcellulartelecommunicationssystem(Phase2+);Channelcoding".[4]GSM06.94:"Digitalcellulartelecommunicationssystem(Phase2+);VoiceActivityDetection(VAD)forAdaptiveMulti-Ratespeechtrafficchannels".[5]GSM06.71:"Digitalcellulartelecommunicationssystem(Phase2+);AdaptiveMulti-Ratespeechprocessingfunctions;Generaldescription".[6]GSM06.73:"Digitalcellulartelecommunicationssystem(Phase2+);ANSI-CcodefortheAdaptiveMulti-Ratespeechcodec".[7]GSM06.74:"Digitalcellulartelecommunicationssystem(Phase2+);TestsequencesfortheGSMAdaptiveMulti-Ratespeechcodec".SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)7(GSM06.90version7.2.1Release1998)[8]ITU-TRecommendationG.711(1988):"CodingofanaloguesignalsbypulsecodemodulationPulsecodemodulation(PCM)ofvoicefrequencies".[9]ITU-TRecommendationG.726:"40,32,24,16kbit/sadaptivedifferentialpulsecodemodulation(ADPCM)".3Definitions,symbolsandabbreviations3.1DefinitionsForthepurposesofthepresentdocument,thefollowingtermsanddefinitionsapply.adaptivecodebook:Theadaptivecodebookcontainsexcitationvectorsthatareadaptedforeverysubframe.Theadaptivecodebookisderivedfromthelong-termfilterstate.Thelagvaluecanbeviewedasanindexintotheadaptivecodebook.adaptivepostfilter:Thisfilterisappliedtotheoutputoftheshort-termsynthesisfiltertoenhancetheperceptualqualityofthereconstructedspeech.Intheadaptivemulti-ratecodec,theadaptivepostfilterisacascadeoftwofilters:aformantpostfilterandatiltcompensationfilter.AdaptiveMulti-Rate(AMR)codec:Speechandchannelcodeccapableofoperatingatgrossbit-ratesof11.4kbit/s(“half-rate”)and22.8kbit/s(“full-rate”).Inaddition,thecodecmayoperateatvariouscombinationsofspeechandchannelcoding(codecmode)bit-ratesforeachchannelmode.algebraiccodebook:Afixedcodebookwherealgebraiccodeisusedtopopulatetheexcitationvectors(innovationvectors).Theexcitationcontainsasmallnumberofnonzeropulseswithpredefinedinterlacedsetsofpositions.AMRhandover:HandoverbetweentheFRandHRchannelmodestooptimiseAMRoperation.anti-sparsenessprocessing:Anadaptivepost-processingprocedureappliedtothefixedcodebookvectorinordertoreduceperceptualartifactsfromasparsefixedcodebookvector.channelmode:Half-rateorfull-rateoperation.channelmodeadaptation:Thecontrolandselectionofthe(FRorHR)channelmode.channelrepacking:RepackingofHR(andFR)radiochannelsofagivenradiocelltoachievehighercapacitywithinthecell.closed-looppitchanalysis:Thisistheadaptivecodebooksearch,i.e.,aprocessofestimatingthepitch(lag)valuefromtheweightedinputspeechandthelongtermfilterstate.Intheclosed-loopsearch,thelagissearchedusingerrorminimizationloop(analysis-by-synthesis).Intheadaptivemulti-ratecodec,closed-looppitchsearchisperformedforeverysubframe.codecmode:Foragivenchannelmode,thebitpartitioningbetweenthespeechandchannelcodecs.codecmodeadaptation:Thecontrolandselectionofthecodecmodebit-rates.Normally,impliesnochangetothechannelmode.directformcoefficients:Oneoftheformatsforstoringtheshorttermfilterparameters.Intheadaptivemulti-ratecodec,allfilterswhichareusedtomodifyspeechsamplesusedirectformcoefficients.fixedcodebook:Thefixedcodebookcontainsexcitationvectorsforspeechsynthesisfilters.Thecontentsofthecodebookarenon-adaptive(i.e.,fixed).Intheadaptivemulti-ratecodec,thefixedcodebookisimplementedusinganalgebraiccodebook.fractionallags:Asetoflagvalueshavingsub-sampleresolution.Intheadaptivemulti-ratecodecasub-sampleresolutionof1/6thor1/3rdofasampleisused.full-rate(FR):Full-ratechannelorchannelmode.frame:Atimeintervalequalto20ms(160samplesatan8kHzsamplingrate).SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)8(GSM06.90version7.2.1Release1998)grossbit-rate:Thebit-rateofthechannelmodeselected(22.8kbsor11.4kbs).half-rate(HR):Half-ratechannelorchannelmode.in-bandsignalling:SignallingforDTX,LinkControl,Channelandcodecmodemodification,etc.carriedwithinthetrafficchannel.integerlags:Asetoflagvalueshavingwholesampleresolution.interpolatingfilter:AnFIRfilterusedtoproduceanestimateofsubsampleresolutionsamples,givenaninputsampledwithintegersampleresolution.inversefilter:Thisfilterremovestheshorttermcorrelationfromthespeechsignal.Thefiltermodelsaninversefrequencyresponseofthevocaltract.lag:Thelongtermfilterdelay.Thisistypicallythetruepitchperiod,oritsmultipleorsub-multiple.LineSpectralFrequencies:(seeLineSpectralPair).LineSpectralPair:TransformationofLPCparameters.LineSpectralPairsareobtainedbydecomposingtheinversefiltertransferfunctionA(z)toasetoftwotransferfunctions,onehavingevensymmetryandtheotherhavingoddsymmetry.TheLineSpectralPairs(alsocalledasLineSpectralFrequencies)aretherootsofthesepolynomialsonthez-unitcircle.LPanalysiswindow:Foreachframe,theshorttermfiltercoefficientsarecomputedusingthehighpassfilteredspeechsampleswithintheanalysiswindow.Intheadaptivemulti-ratecodec,thelengthoftheanalysiswindowisalways240samples.Foreachframe,twoasymmetricwindowsareusedtogeneratetwosetsofLPcoefficientinthe12,2kbit/smode.Fortheothermodes,onlyasingleasymmetricwindowisusedtogenerateasinglesetofLPcoefficients.Inthe12,2kbit/smode,nosamplesofthefutureframesareused(nolookahead).Theothermodesusea5mslookahead.LPcoefficients:LinearPrediction(LP)coefficients(alsoreferredasLinearPredictiveCoding(LPC)coefficients)isagenericdescriptivetermfortheshorttermfiltercoefficients.mode:Whenusedalone,referstothesourcecodecmode,i.e.,tooneofthesourcecodecsemployedintheAMRcodec.(Seealsocodecmodeandchannelmode.)open-looppitchsearch:Aprocessofestimatingthenearoptimallagdirectlyfromtheweightedspeechinput.Thisisdonetosimplifythepitchanalysisandconfinetheclosed-looppitchsearchtoasmallnumberoflagsaroundtheopen-loopestimatedlags.Intheadaptivemulti-ratecodec,anopen-looppitchsearchisperformedineveryothersubframe.out-of-bandsignalling:SignallingontheGSMcontrolchannelstosupportlinkcontrol.residual:Theoutputsignalresultingfromaninversefilteringoperation.shorttermsynthesisfilter:Thisfilterintroduces,intotheexcitationsignal,shorttermcorrelationwhichmodelstheimpulseresponseofthevocaltract.perceptualweightingfilter:Thisfilterisemployedintheanalysis-by-synthesissearchofthecodebooks.Thefilterexploitsthenoisemaskingpropertiesoftheformants(vocaltractresonances)byweightingtheerrorlessinregionsneartheformantfrequenciesandmoreinregionsawayfromthem.subframe:Atimeintervalequalto5ms(40samplesat8kHzsamplingrate).vectorquantization:Amethodofgroupingseveralparametersintoavectorandquantizingthemsimultaneously.zeroinputresponse:Theoutputofafilterduetopastinputs,i.e.duetothepresentstateofthefilter,giventhataninputofzerosisapplied.zerostateresponse:Theoutputofafilterduetothepresentinput,giventhatnopastinputshavebeenapplied,i.e.,giventhatthestateinformationinthefilterisallzeroes.SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)9(GSM06.90version7.2.1Release1998)3.2SymbolsForthepurposesofthepresentdocument,thefollowingsymbolsapply:()AzTheinversefilterwithunquantizedcoefficients()AzTheinversefilterwithquantizedcoefficients()()HzAz=1ThespeechsynthesisfilterwithquantizedcoefficientsaiTheunquantizedlinearpredictionparameters(directformcoefficients)aiThequantifiedlinearpredictionparametersmTheorderoftheLPmodel1Bz()Thelong-termsynthesisfilter()WzTheperceptualweightingfilter(unquantizedcoefficients)γγ12,TheperceptualweightingfactorsFzE()Adaptivepre-filterTTheintegerpitchlagnearesttotheclosed-loopfractionalpitchlagofthesubframeβTheadaptivepre-filtercoefficient(thequantifiedpitchgain)HzAzAzfnd()(/)(/)=γγTheformantpostfilterγnControlcoefficientfortheamountoftheformantpost-filteringγdControlcoefficientfortheamountoftheformantpost-filtering()HztTiltcompensationfilterγtControlcoefficientfortheamountofthetiltcompensationfilteringµγ=tk1'Atiltfactor,withk1'beingthefirstreflectioncoefficient()hnfThetruncatedimpulseresponseoftheformantpostfilterLhThelengthof()hnfrih()Theauto-correlationsof()hnf()AznγTheinversefilter(numerator)partoftheformantpostfilter()1AzdγThesynthesisfilter(denominator)partoftheformantpostfilter()rnTheresidualsignaloftheinversefilter()Aznγ()hntImpulseresponseofthetiltcompensationfilterβscn()TheAGC-controlledgainscalingfactoroftheadaptivepostfilterαTheAGCfactoroftheadaptivepostfilter()Hzh1Pre-processinghigh-passfilterwnI(),wnII()LPanalysiswindowsLI1()LengthofthefirstpartoftheLPanalysiswindowwnI()LI2()LengthofthesecondpartoftheLPanalysiswindowwnI()LII1()LengthofthefirstpartoftheLPanalysiswindowwnII()LII2()LengthofthesecondpartoftheLPanalysiswindowwnII()rkac()Theauto-correlationsofthewindowedspeechsn'()()wilagLagwindowfortheauto-correlations(60Hzbandwidthexpansion)SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)10(GSM06.90version7.2.1Release1998)f0ThebandwidthexpansioninHzfsThesamplingfrequencyinHzrkac'()Themodified(bandwidthexpanded)auto-correlations()EiLDThepredictionerrorintheithiterationoftheLevinsonalgorithmkiTheithreflectioncoefficientaji()ThejthdirectformcoefficientintheithiterationoftheLevinsonalgorithm()′Fz1SymmetricLSFpolynomial()′Fz2AntisymmetricLSFpolynomial()Fz1Polynomial()′Fz1withrootz=−1eliminated()Fz2Polynomial()′Fz2withrootz=1eliminatedqiThelinespectralpairs(LSPs)inthecosinedomainqAnLSPvectorinthecosinedomain()qinThequantifiedLSPvectorattheithsubframeoftheframenωiThelinespectralfrequencies(LSFs)Txm()AmthorderChebyshevpolynomialfifi12(),()ThecoefficientsofthepolynomialsFz1()andFz2()fifi12''(),()Thecoefficientsofthepolynomials()′Fz1and()′Fz2fi()Thecoefficientsofeither()Fz1or()Fz2()CxSumpolynomialoftheChebyshevpolynomialsxCosineofangularfrequencyωλkRecursioncoefficientsfortheChebyshevpolynomialevaluationfiThelinespectralfrequencies(LSFs)inHz[]ftfff=1210ThevectorrepresentationoftheLSFsinHz()z()1n,()z()2nThemean-removedLSFvectorsatframen()r()1n,()r()2nTheLSFpredictionresidualvectorsatframenp()nThepredictedLSFvectoratframen()()r21n−ThequantifiedsecondresidualvectoratthepastframefkThequantifiedLSFvectoratquantizationindexkELSPTheLSPquantizationerrorwii,,,,=110LSP-quantizationweightingfactorsdiThedistancebetweenthelinespectralfrequenciesfi+1andfi−1()hnTheimpulseresponseoftheweightedsynthesisfilterOkThecorrelationmaximumofopen-looppitchanalysisatdelaykOiti,,,=13Thecorrelationmaximaatdelaystii,,,=13()Mtiii,,,,=13ThenormalizedcorrelationmaximaMiandthecorrespondingdelaystii,,,=13HzWzAzAzAz()()(/)()(/)=γγ12Theweightedsynthesisfilter()Azγ1Thenumeratoroftheperceptualweightingfilter()12AzγThedenominatoroftheperceptualweightingfilterSIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)11(GSM06.90version7.2.1Release1998)T1Theintegernearesttothefractionalpitchlagoftheprevious(1stor3rd)subframesn'()Thewindowedspeechsignal()snwTheweightedspeechsignal()snReconstructedspeechsignal()′snThegain-scaledpost-filteredsignal()snfPost-filteredspeechsignal(beforescaling)()xnThetargetsignalforadaptivecodebooksearch()xn2,x2tThetargetsignalforalgebraiccodebooksearchresnLP()TheLPresidualsignal()cnThefixedcodebookvector()vnTheadaptivecodebookvectorynvnhn()=()()∗Thefilteredadaptivecodebookvector()ynkThepastfilteredexcitation()unTheexcitationsignal()unTheemphasizedadaptivecodebookvector'()unThegain-scaledemphasizedexcitationsignalTopThebestopen-looplagtminMinimumlagsearchvaluetmaxMaximumlagsearchvalue()RkCorrelationtermtobemaximizedintheadaptivecodebooksearchb24TheFIRfilterforinterpolatingthenormalizedcorrelationterm()Rk()RktTheinterpolatedvalueof()Rkfortheintegerdelaykandfractiontb60TheFIRfilterforinterpolatingthepastexcitationsignal()untoyieldtheadaptivecodebookvector()vnAkCorrelationtermtobemaximizedinthealgebraiccodebooksearchatindexkCkThecorrelationinthenumeratorofAkatindexkEDkTheenergyinthedenominatorofAkatindexkdHx=t2Thecorrelationbetweenthetargetsignal()xn2andtheimpulseresponse()hn,i.e.,backwardfilteredtargetHThelowertriangularToeplizconvolutionmatrixwithdiagonal()h0andlowerdiagonals()()hh139,,Φ=HHtThematrixofcorrelationsof()hndn()Theelementsofthevectordφ(,)ijTheelementsofthesymmetricmatrixΦckTheinnovationvectorCThecorrelationinthenumeratorofAkmiThepositionoftheithpulseϑiTheamplitudeoftheithpulseNpThenumberofpulsesinthefixedcodebookexcitationEDTheenergyinthedenominatorofAkSIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)12(GSM06.90version7.2.1Release1998)()resnLTPThenormalizedlong-termpredictionresidual()bnThesignalusedforpresettingthesignsinalgebraiccodebooksearch()snbThesignsignalforthealgebraiccodebooksearch()′dnSignextendedbackwardfilteredtargetφ'(,)ijThemodifiedelementsofthematrixΦ,includingsigninformationzt,()znThefixedcodebookvectorconvolvedwith()hn()EnThemean-removedinnovationenergy(indB)EThemeanoftheinnovationenergy()~EnThepredictedenergy[]bbbb1234TheMApredictioncoefficients()RkThequantifiedpredictionerroratsubframekEIThemeaninnovationenergyRn()Thepredictionerrorofthefixed-codebookgainquantizationEQThequantizationerrorofthefixed-codebookgainquantizationen()Thestatesofthesynthesisfilter()1Az()enwTheperceptuallyweightederroroftheanalysis-by-synthesissearchηThegainscalingfactorfortheemphasizedexcitationgcThefixed-codebookgain′gcThepredictedfixed-codebookgaingcThequantifiedfixedcodebookgaingpTheadaptivecodebookgaingpThequantifiedadaptivecodebookgainγgcccgg=′Acorrectionfactorbetweenthegaingcandtheestimatedone′gcγgcTheoptimumvalueforγgcγscGainscalingfactor3.3AbbreviationsForthepurposesofthepresentdocument,thefollowingabbreviationsapply.FurtherGSMrelatedabbreviationsmaybefoundinGSM01.04[1].ACELPAlgebraicCodeExcitedLinearPredictionAGCAdaptiveGainControlAMRAdaptiveMulti-RateCELPCodeExcitedLinearPredictionEFREnhancedFullRateFIRFiniteImpulseResponseFRFullRateHRHalfRateISPPInterleavedSingle-PulsePermutationLPLinearPredictionLPCLinearPredictiveCodingLSFLineSpectralFrequencyLSPLineSpectralPairLTPLongTermPredictor(orLongTermPrediction)MAMovingAverageSIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)13(GSM06.90version7.2.1Release1998)4OutlinedescriptionThepresentdocumentisstructuredasfollows:Section4.1containsafunctionaldescriptionoftheaudiopartsincludingtheA/DandD/Afunctions.Section4.2describestheconversionbetween13-bituniformand8-bitA-laworµ-lawsamples.Sections4.3and4.4presentasimplifieddescriptionoftheprinciplesoftheAMRcodecencodinganddecodingprocessrespectively.Insubclause4.5,thesequenceandsubjectiveimportanceofencodedparametersaregiven.Section5presentsthefunctionaldescriptionoftheAMRcodecencoding,whereasclause6describesthedecodingprocedures.Insection7,thedetailedbitallocationoftheAMRcodecistabulated.4.1FunctionaldescriptionofaudiopartsTheanalogue-to-digitalanddigital-to-analogueconversionwillinprinciplecomprisethefollowingelements:1)AnaloguetouniformdigitalPCM−microphone;−inputleveladjustmentdevice;−inputanti-aliasingfilter;−sample-holddevicesamplingat8kHz;−analogue−to−uniformdigitalconversionto13−bitrepresentation.Theuniformformatshallberepresentedintwo'scomplement.2)UniformdigitalPCMtoanalogue−conversionfrom13−bit/8kHzuniformPCMtoanalogue;−aholddevice;−reconstructionfilterincludingx/sin(x)correction;−outputleveladjustmentdevice;−earphoneorloudspeaker.Intheterminalequipment,theA/Dfunctionmaybeachievedeither−bydirectconversionto13-bituniformPCMformat;−orbyconversionto8-bitA-laworµ-lawcompoundedformat,basedonastandardA-laworµ-lawcodec/filteraccordingtoITU-TRecommendationsG.711[8]andG.714,followedbythe8-bitto13-bitconversionasspecifiedinsubclause4.2.1.FortheD/Aoperation,theinverseoperationstakeplace.InthelattercaseitshouldbenotedthatthespecificationsinITU-TG.714(supersededbyG.712)areconcernedwithPCMequipmentlocatedinthecentralpartsofthenetwork.Whenusedintheterminalequipment,thepresentdocumentdoesnotonitsownensuresufficientout-of-bandattenuation.Thespecificationofout-of-bandsignalsisdefinedinGSM03.50[2]inclause2.SIST EN 301 704 V7.2.1:2003



ETSIETSIEN301704V7.2.1(2000-04)14(GSM06.90version7.2.1Release1998)4.2Preparationofspeechsampl
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