DAB+ the additional audio codec in DAB

download DAB+ the additional audio codec in DAB

of 12

  • date post

    22-Mar-2016
  • Category

    Documents

  • view

    228
  • download

    5

Embed Size (px)

description

In the digital age, broadcasting standards need to balance the benefits of stability and innovation.

Transcript of DAB+ the additional audio codec in DAB

  • DAB+ The additional audio codec in DAB

    2007 (Updated March 2008)

  • ContentsWhy DAB+

    Features of DAB+

    Possible scenarios with DAB+

    Comparison of DAB+ and DMB for radio services

    Performance of DAB+

    DAB+ roll out

    Markus Prosch,WorldDMB Technical Committee Audio Codec Task Force Chairman. Markus Prosch is a research engineer at Fraunhofer IIS, Erlangen, Germany.

    WorldDMB Forum Project Office30LeicesterSquare,London,WC2H7LA,UnitedKingdomTel:+442072884640Fax:+442072884643www.worlddab.org

  • Why DAB+?Inthedigitalage,broadcastingstandardsneedtobalancethebenefits

    ofstabilityandinnovation.Stabilitygivesconfidencetobroadcasters,

    manufacturersandconsumers.Andyet,enhancingastandardtotake

    advantageoftechnologicalinnovationcanoffernewbenefitsandprotect

    astandardscompetitivenessinarapidlychangingmarketplace.The

    internationalorganisationresponsiblefortheEureka147standards,

    WorldDMB(formerlyknownastheWorldDABForum)hascarefully

    monitoreddevelopmentsinaudiocoding.AlthoughWorldDMBremains

    astrongadvocateofstability,itsSteeringBoardtookthedecisionthat

    thebenefitsofaddinganadditionalhighlyefficientcodectoEureka147s

    optionsweresosignificantthatthisinnovationshouldbeincorporated.

    The benefits of DAB+ include: LatestMPEG-4audiocodecdeliversexceptionalperformanceefficiency

    Morestationscanbebroadcastonamultiplex

    Greaterstationchoiceforconsumers

    Moreefficientuseofradiospectrum

    Lowertransmissioncostsfordigitalstations

    NewreceiversbackwardscompatiblewithexistingMPEGAudio

    LayerIIbroadcasts

    CurrentMPEGAudioLayerIIservicesandconsumersunaffected

    Compatiblewithexistingscrollingtextandmultimediaservices

    Robustaudiodelivery

    Optimisedforlivebroadcastradio

    Broadcasters/regulatorscanselecteitherstandardMPEGAudio

    LayerII,ortheadditionalaudiocoding,orboth,tosuittheircountry

    Fastre-tuningresponsetime(lowzappingdelay)

    MPEGSurroundispossible

  • Untilnow,DABdigitalradiohasalwaysbeenbroadcastusingMPEGAudio

    LayerIIcoding.IntheyearssincetheDABdigitalradiostandardwas

    firstdefined,moreefficientcodingschemesandalgorithmshavebeen

    devised.Theseallowaudiowithequivalentorbettersubjectivequalitytobe

    broadcastatlowerbitrates.OtherbroadcasttechnologiessuchasDVB-H

    (digitalvideobroadcastingforhandheld),DRM(DigitalRadioMondiale;i.e.

    digitallong,mediumandshortwave)orMediaFLOusetheaudiocoding

    MPEG-4HE-AACv2andareabletocarrymultipleaudioservicesinthe

    digitalcapacityneededforasingleradioserviceusingMPEGAudioLayerII.

    WorldDMBcreatedaTaskForceofitsTechnicalCommitteetodevelopthe

    additionalstandard.Afterexaminingtheoptions,DAB+usingMPEG-4HE-

    AACv2wasadopted.DAB+waspublishedinFebruary2007asETSITS

    102563DigitalAudioBroadcasting(DAB);TransportofAdvancedAudio

    Coding(AAC)audio.

    Thesignificantlyincreasedefficiency,whichisdiscussedinmoredetaillater

    inthisdocument,offersbenefitsforGovernmentsandRegulators(even

    betterspectrumefficiency),broadcasters(lowercostsperstation)and

    consumers(abiggerchoiceofstations).Itisdesignedtoprovidethesame

    functionalityasthecurrentMPEGAudioLayerIIradioservicesincluding

    servicefollowing(e.g.tothesameserviceonanotherDABensembleorits

    FMsimulcast),trafficannouncements,PADmultimediadata(e.g.dynamic

    labelssuchastitleartistinformationornewsheadlines;complementary

    graphicsandimagesetc.).

    InsomecountrieswhereDABdigitalradiohasalreadybeenlaunched,

    broadcastersarecommittedtocontinuingtouseMPEGAudioLayerII.

  • However,incountriesplanningtolaunchdigitalradiotheargumentsin

    favouroflaunchingwithDAB+arecompelling.

    ToemphasisethatDAB+isintendedforradioservices(i.e.,withstreamed

    audiobeingtheessentialcomponent),thefollowingtextusestheterm

    radioserviceinsteadoftheDABtermaudioservice.

    Features of DAB+

    DAB+usesMPEG-4HighEfficiencyAACv2profile(HE-AACv2).Thisaudio

    codecisthemostefficientaudiocompressionschemeavailableworldwide.

    Itcombinesthreetechnologies:

    ThecoreaudiocodecAAC(AdvancedAudioCoding).

    AbandwidthextensiontoolSBR(SpectralBandReplication),which

    enhancesefficiencybyusingmostoftheavailablebitrateforthelower

    frequencies(lowband)oftheaudiosignal.Thedecodergeneratesthe

    higherfrequencies(highband)byusingthelowbandandsideinformation

    providedbytheencoder.Thissideinformationneedsconsiderablylessbit

    ratethanwouldberequiredtoencodethehighbandwiththecoreaudio

    codec.

    Parametricstereo(PS):amonodown-mixandsideinformationis

    encodedasopposedtoaconventionalstereosignal.Thedecoder

    reconstructsthestereosignalfromthemonosignalusingthesideinformation.

    HE-AACv2isasupersetoftheAACcorecodec.Thissupersetstructure

    permitstouseplainAACforhighbitrates,AACandSBR(HE-AAC)for

    mediumbitratesorAAC,SBRandPS(HE-AACv2)forlowbitrates.

  • ThereforeHE-AACv2providesthehighestlevelofflexibilityforthebroadcaster.

    AdetaileddescriptionofHE-AACv2isavailableontheEBUwebsite1.An

    introductiontoMPEG-4isavailableontheMPEGIndustryForumwebsite2.

    HE-AACv2providesthesameperceivedaudioqualityataboutonethird

    ofthesub-channelbitrateneededbyMPEGAudioLayerII.Thesame

    audiocodingisalsousedinDRMandDMB.Devices,whichalsoinclude

    DMBorDRMcanbenefitfromthefactthattheaudiocodingforallthese

    technologiesisessentiallythesame.

    AllthefunctionalityavailableforMPEGAudioLayerIIservicesisalso

    availableforDAB+:servicefollowing(e.g.toFMorotherDABensembles),

    trafficannouncements,PADmultimedia(dynamiclabelssuchastitleartist

    informationornewsheadlines;stillimagessuchasweathercharts,images

    andothermultimediacontent.),service

    languageandprogrammetypeinformation

    (e.g.ClassicalMusic,RockMusic,Sport)etc.

    MPEGAudioLayerIIandHE-AACv2radio

    servicescancoexist inoneensemble.

    However, legacy receiversmight list

    HE-AAC v2 radio serviceseven though

    theywill not be able todecode them.

    Thegeographicalcoverageareaofradio

    servicesusingHE-AACv2isslightlylarger

    thanthatforradioservicesusingMPEG

    AudioLayerII.Themultimediainformation

    carriedinPADofanHE-AACv2radio

    Other systems using AAC:

    iPOD

    DRM(DigitalRadio

    Mondiale)

    3GPP/3GPP2

    T-DMB

    S-DMB(Korea)

    MediaFLO

    ISDB(Integrated

    ServicesDigital

    Broadcasting;Japan)

    DVB-H

    XMSatelliteRadio

    (USA)

    HDRadio(USA)

  • serviceismuchbetterprotectedagainsttransmissionerrorsthanPAD

    dataofaradioserviceusingMPEGAudioLayerII.

    AnimportantdesigncriterionforDAB+wasashortzappingdelay.Both

    thetimeittakestoswitchfromoneradioservicetoanotherstationonthe

    sameDABensembleaswellasthetimeittakestotunetoaradioservice

    onanotherDABensemblewasminimized.

    CurrentlyallDABradioservicesaremonoorstereo.However,DAB+also

    providesthemeanstobroadcastsurroundsoundinabackwards

    compatibleway.UsingMPEGSurrounditispossibletobroadcasta

    stereosignal togetherwith surroundside information (e.g.5kbpsside

    information).Standardstereoradioswillignorethissideinformation

    anddecode the stereosignal.MPEGSurround receiverswill evaluate

    thesideinformationandreproducesurroundsound.Soatacomparatively

    lowadditionalbitrate,thebroadcastercanincreasetheaudioexperience

    onsurroundsoundreceivers,andstillprovidehighqualitysoundtoall

    otherradios.

    1 EBUTechreview:MPEG-4HE-AACv2audiocodingfortodaysdigitalmediaworld(2006) http://www.ebu.ch/en/technical/trev/trev_305-moser.pdf2AnMPEGIFWhitePaper:UnderstandingMPEG-4:Technologies,Advantages,andMarkets http://www.m4if.org/public/documents/vault/MPEG4WhitePaperV2a.zip

  • Possible scenarios with DAB+

    ThefollowingfiguresshowhowthebitrateofaDABensemblemaybe

    assignedto:

    A40kbpssubchannelwithHE-AACv2providesasimilaraudioquality

    (evenslightlybetterinmostcases)toMPEGAudioLayerIIat128kbps.

    Comparison of DAB+ and DMB for radio servicesDMBisanaudio/videostandard,asopposedtoaradioplusmultimedia

    standard,andsoisoptimisedforthatpurpose.Somefeaturesthatareimportant

    forradioservicesarenotpossibleforDMBservices.DMBisdesignedand

    optimisedformobiletelevision,anditisnotrecommendedforradioservices.

    Multiplex with HE-AAC v2 (DAB+)

    28 radio services using HE-AAC v2 at 40 kbps and 1 audio service using HE-AAC v2 at 32 kbps.

    Multiplex with MPEG Audio Layer II (DAB)

    9 radio services using MPEG Audio Layer II at 128 kbps

    Multiplex with MPEG Audio Layer II and HE-AAC v2 (DAB and DAB+)

    5radioservicesusingMPEGAudioLayerIIat128kbpsand12radioservicesusingHE-AACv2at40kbpsand1radioserviceusingHE-AACv2at32kbps

  • OneconsiderationisthatDMBismissingsomefeatureswhichareexpected

    forradioservicese.g.servicefollowing,dynamictextlabels,etc.

    DMBusesMPEGTransportStreamtocarrytheaudio,video(andpossibly

    alsomultimedia)objectsandcontainsmechanismstosynchronizethemto

    ensurethingslikelip-syncarecorrect.Thesemechanismsrequireadditional

    overheadwhichcanbesignificantattherelativelylowbitratesusedfor

    audioservices.Theadditionalbit rate required for thevideoobjectmust

    alsobefactoredin.

    Incontrast,DAB+isoptimisedforradioservices(includingPADinformation)

    andthushasamuchloweroverhead(seefigure).

    Anotherconsiderationisthetimetakenforareceivertoplaytheaudioafter

    serviceselectionbytheuser.TheerrorprotectionschemeofDMBrequiresa

    fixedamountofdatatobereceivedbeforedecodingmaybegin,andsothe

    delayisinverselyproportionaltothebitrateoftheservice.Incontrast,the

    errorprotectionschemeforDAB+isdesignedtohaveafixedtimedelay.At