ITU-T J.42 (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%-%$)5-15!,)493/5.$02/'2!--%3)'.!,3&/242!.3-)33)/./.KBITS#(!..%,3)454Recommendation*(ExtractfromtheLUEOOK)NOTES1ITU-TRecommendationJ.42waspublishedinFascicleIII.6oftheBlueBook.ThisfileisanextractfromtheBlueBook.WhilethepresentationandlayoutofthetextmightbeslightlydifferentfromtheBlueBookversion,thecontentsofthefileareidenticaltotheBlueBookversionandcopyrightconditionsremainunchanged(seebelow).2InthisRecommendation,theexpression“Administration”isusedforconcisenesstoindicatebothatelecommunicationadministrationandarecognizedoperatingagency.ITU1988,1993Allrightsreserved.Nopartofthispublicationmaybereproducedorutilizedinanyformorbyanymeans,electronicormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromtheITU.FascicleIII.6-Rec.J.421RecommendationJ.42FascicleIII.6-Rec.J.42CHARACTERISTICSOFEQUIPMENTFORTHECODINGOFANALOGUEMEDIUMQUALITYSOUND-PROGRAMMESIGNALSFORTRANSMISSIONON384-kbit/sCHANNELS(Malaga-Torremolinos,1984;amendedatMelbourne,1988)1General1.1ThisRecommendationgivesthecharacteristicsofequipmentforthecodingof7kHzmonophonicanaloguesound-programmesignalsintoadigitalsignal.Twomonophonicdigitalsignalscanbecombinedtoforma384-kbit/ssignalalreadyspecifiedinRecommendationJ.41.1.2Equipmentforcodingofanaloguesound-programmesignals,asspecifiedinthisRecommendation,canbe:a)Astandaloneencoder/decoderwithadigitalinterfaceat384kbit/s.Theencoderoperationandthedecoderoperationmaybeperformedintwoseparateequipmentsorinthesameequipment.b)Acombinedencoder-multiplexdecoder-demultiplexwithadigitalinterfaceat1544or2048kbit/s.Theencoder-multiplexoperationandthedecoder-multiplexoperationmaybeperformedintwoseparateequipmentsorinthesameequipment.Incaseb)itisnotmandatorytoprovideanexternaldigitalsound-programmeaccessportat384kbit/s.2TransmissionperformanceThetransmissionperformanceperencoder/decoderpairshallbesuchthatthelimitsspecifiedinRecommendationJ.23(CCIRRecommendation503)arenotexceededbythreeencoder/decoderpairsconnectedintandemataudiofrequencies.3Methodofencoding3.1Therecommendedencodinglawsareasspecifiedin[1].3.2Theseencodinglawsarebasedonauniformlyquantized,14-bitpersamplePCMtechniquewithcompandingandemployeither:a)eleven-segment14to11bitinstantaneousA-lawcompanding,orb)five-range14to10bitnear-instantaneouscompanding.3.3Equipmentcharacteristicscommontobothmethodsofencodingare:Nominalaudiobandwidth:0.05to7kHzAudiointerface:seeRecommendationJ.23,§2.Samplingfrequency:16(1±5×10–5)kHz.Pre/de-emphasis:RecommendationJ.17with6.5dBattenuationat800Hz.Note–Pre-emphasisandde-emphasisarenotusedbytheAdministrationsofCanada,JapanandtheUnitedStatesofAmericaontheirnationalcircuitsandoninternationalcircuitsbetweeneachother,butareusedoninternationalcircuitstoothercountries.4Equipmentusinginstantaneouscompanding4.1Codingtable4.1.1ThecodinglawisspecifiedinTable1/J.41.2FascicleIII.6-Rec.J.424.1.2Theallocationofcharactersignals(PCMcodewords)isalsogiveninTable1/J.41.Twovariants(AandB)ofcharactersignalsareallowed.Note–InthecaseofdigitalinterconnectionbetweenvariantsAandB,theconversionfromonesetofcharactersignalstotheothersetinTable1/J.41,canbedonewithoutanyperformancedegradation.Inthecaseofanalogueinterconnection,areductionintheS/Nratio,intheorderof3dB,isexpected.4.2BitratesNominalsourcecodingbitrate(16kHz×11bit/sample)176kbit/sErrorprotection(16kHz×1bit/sample)16kbit/sTransmissionbitratepersound-programmesignal192kbit/sChannelbitratefor2sound-programmesignals384kbit/s4.3OverloadlevelTheoverloadlevelforasine-wavesignalatzerodBinsertionlossfrequency(2.1kHz)ofthepre-emphasisis+15dBm0s.4.4DigitalsignalformatThecharactersignalbitsequencesforvariantsAandB,areshowninFigure1/J.41.4.4.1VariantAWhentransmittingtwomonophonicdigitalsignalsasone384kbit/ssignal,withrespecttothecodewordinterleavingshowninFigure1/J.41,thefirsttwo12bitcodewordsareallocatedto7kHzchannelNo.1andthesecondtwo12bitcodewordsareallocatedto7kHzchannelNo.2.4.4.2VariantBThe12bitcodewordassignmentswhentransmittingtwomonophonicdigitalsignalsasone384-kbit/ssignalisunderstudy.4.5BiterrorprotectionOneparitybitisaddedtoeach11-bitcharactersignal.4.5.1VariantAThefivemostimportantbitsofeachsampleareprotectedagainsterrorsbymeansofaparitybit.Intheconverterofthetransmittingpart,theparitybitisaddedasthe12thbittoeachcodeword.Itsvalueisfixedsothatthe6bitparityblockalwayscontainsonlyanoddnumberofonevalues.Inorderthatevenbiterrorstructurescanalsoresultinparityviolations,theprotectedandunprotectedbitsofeachcodewordareinterleavedinascendinganddescendingsequence,asshowninFigure1/J.41.4.5.2VariantBTheaddedparitybitshallbebasedonthe7mostsignificantbitsofthe11-bitPCMword.ThesearebitsS,X,Y,Z,A,B,C.Theparityof“ones”bitshallbeeven.Sincethechordbits(X,Y,Z)alwayscontainaone,theminimumnumberofonespersampleis2,resultinginaminimumonesdensityof1/6.4.5.3ErrorconcealmentIfaparityviolationisdetected,ane