ITU-T J.41 (11 1988)(英) Characteristics of equipme

INTERNATIONALTELECOMMUNICATIONUNION)454*TELECOMMUNICATIONSTANDARDIZATIONSECTOROFITU4%,%6)3)/.!.$3/5.$42!.3-)33)/.#(!2!#4%2)34)#3/&%15)0-%.4&/24(%#/$).'/&!.!,/'5%()'(15!,)493/5.$02/'2!--%3)'.!,3&/242!.3-)33)/./.KBITS#(!..%,3)454Recommendation*(ExtractfromtheLUEOOK)NOTES1ITU-TRecommendationJ.41waspublishedinFascicleIII.6oftheBlueBook.ThisfileisanextractfromtheBlueBook.WhilethepresentationandlayoutofthetextmightbeslightlydifferentfromtheBlueBookversion,thecontentsofthefileareidenticaltotheBlueBookversionandcopyrightconditionsremainunchanged(seebelow).2InthisRecommendation,theexpression“Administration”isusedforconcisenesstoindicatebothatelecommunicationadministrationandarecognizedoperatingagency.ITU1988,1993Allrightsreserved.Nopartofthispublicationmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromtheITU.FascicleIII.6-Rec.J.411RecommendationJ.41FascicleIII.6-Rec.J.41CHARACTERISTICSOFEQUIPMENTFORTHECODINGOFANALOGUEHIGHQUALITYSOUNDPROGRAMMESIGNALSFORTRANSMISSIONON384kbit/sCHANNELS(Malaga-Torremolinos,1984;amendedatMelbourne,1988)1General1.1ThisRecommendationgivesthecharacteristicsofequipmentforthecodingof15kHzmonophonicanaloguesound-programmesignalsintoadigitalsignalof384kbit/s.Forstereophonicoperation,twomonophonicdigitalcodecscanbeutilized.Twomonophonicdigitalsignalsthatformastereophonicsignalshouldberoutedtogetheroverthesametransmissionsystems(path)toavoidanydifferenceintransmissiondelay.1.2Equipmentforcodingofanaloguesound-programmesignals,asspecifiedinthisRecommendation,canbe:a)Astand-aloneencoder/decoderwithadigitalinterfaceat384kbit/s.Theencoderoperationandthedecoderoperationmaybeperformedintwoseparateequipmentsorinthesameequipment.b)Acombinedencoder-multiplex/decoder-demultiplexwithadigitalinterfaceat1544or2048kbit/s.Theencoder-multiplexoperationandthedecoder-demultiplexoperationmaybeperformedintwoseparateequipmentsorinthesameequipment.Incaseb),itisnotmandatorytoprovideanexternaldigitalsoundprogrammeaccessportat384kbit/s.1.3TwomethodsofencodinghavebeenspecifiedbytheCMTT[1]andtheseformthebasisforthisRecommendation.2TransmissionperformanceThetransmissionperformanceperencoder/decoderpairshallbesuchthatthelimitsspecifiedinRecommendationJ.21(CCIRRecommendation505)arenotexceededbythreeencoder/decoderpairsconnectedintandemataudiofrequencies.Note–Whentransmittingstereophonicsoundprogrammesignals,itisnecessarythattheencoderanddecoderaredesignedsuchthattheywillmeetthespecifiedrequirementsforphasedifference.Inordertoavoidanyunnecessarycomplexity,thesamplingofchannelsAandBshouldbeperformedsimultaneously.3Methodofencoding3.1Therecommendedencodinglawsareasspecifiedin[1].3.2Theseencodinglawsarebasedonauniformlyquantized14-bitpersamplePCMtechniquewithcompandingandemployeither:a)eleven-segment14-to11-bitinstantaneousA-lawcompanding,orb)five-range14-to10-bitnearinstantaneouscompanding.Forprovisionalrulesforthroughconnectionbetweenthetwocompandingmethods,seeNote4in[1].3.3OthercodingtechniqueswhichmaybeusedbybilateralagreementoftheAdministrationsconcernedarealsolistedinAnnexA.However,thesetechniquesdonotformpartofthisRecommendation.2FascicleIII.6-Rec.J.413.4Equipmentcharacteristicscommontobothmethodsofencodingare:Nominalaudiobandwidth:0.04to15kHz.Audiointerface:seeRecommendationJ.21,§2.Samplingfrequency(CCIRRecommendation606):32(1±5×10–5)kHz.Pre/de-emphasis:RecommendationJ.17with6.5dBattenuationat800Hz.Note–Pre-emphasisandde-emphasisarenotusedbytheAdministrationsofCanada,JapanandtheUnitedStatesontheirnationalcircuitsandoninternationalcircuitsbetweeneachother,butareusedoninternationalcircuitstoothercountries.4Equipmentusinginstantaneouscompanding4.1Codingtable4.1.1ThecodinglawisspecifiedinTable1/J.41.4.1.2Theallocationofcharactersignals(PCMcodewords)isalsogiveninTable1/J.41.Twovariants(AandB)ofcharactersignalsareallowed.Note–InthecaseofdigitalinterconnectionbetweenvariantsAandB,theconversionfromonesetofcharactersignalstotheotherinTable1/J.41canbeimplementedwithoutanyperformancedegradation.Inthecaseofanalogueinterconnection,asmallreductionintheS/Nratio,intheorderof3dB,isexpected.4.2BitratesNominalsourcecodingbitrate(32kHz×11bits/sample)352kbit/sErrorprotection32kbit/sTransmissionbitrate384kbit/s4.3OverloadlevelTheoverloadlevelforasine-wavesignalatzerodBinsertionlossfrequency(2.1kHz)ofthepre-emphasisis+15dBm0s.4.4DigitalsignalformatThecharactersignalbitsequencesforvariantsAandBareshowninFigure1/J.41.4.5BiterrorprotectionOneparitybitisaddedtoeach11-bitcharactersignal.FascicleIII.6-Rec.J.413TABLE1/J.4111segment,14to11bitinstantaneouscompandingA-lawPCMforsound-programmesignals(positivehalfonly)a)11bitcodingAllocationofcharactersignalsNormalizedanalogueinputNormalizedanalogueoutputCompresseddigitalcodeSegmentNo.Effectiveresolution(bits)1234VariantAb)567891011SXYZVariantBc)ABCDEFG8160to81924096to412881764112895768190111111111000000100110111111100000004080to40962048to206440882056767640210011011111100000