Dab Plus Brochure 200803
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Transcript of Dab Plus Brochure 200803
DAB+
The additional audio codec in DAB
2007 (Updated March 2008)
Contents
Why 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
astandard’scompetitivenessinarapidlychangingmarketplace.The
internationalorganisationresponsiblefortheEureka147standards,
WorldDMB(formerlyknownastheWorldDABForum)hascarefully
monitoreddevelopmentsinaudiocoding.AlthoughWorldDMBremains
astrongadvocateofstability,itsSteeringBoardtookthedecisionthat
thebenefitsofaddinganadditionalhighlyefficientcodectoEureka147’s
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
102563“DigitalAudioBroadcasting(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
“radioservice”insteadoftheDABterm“audioservice”.
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
they will 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+wasashort“zapping”delay.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-AACv2–audiocodingfortoday’sdigitalmediaworld(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
therelativelylowbitratesusedforaudioservices,thetune-intimeforDAB+
ismuchquickerthanforDMB,althoughaDMBservicewithnormalframe
ratevideowillhaveahigherbitrateitwillalsohaveasimilartuningtimeto
DAB+.
AllthefunctionalityavailableforDABservicesisalsoavailableforDAB+,but
itisnotavailableforDMB(itisnotneededforamobiletelevisionservice):
servicefollowing(e.g.,toFM,AM,DRMoranotherDABradioservice),
trafficannouncements,PADmultimedia(dynamiclabelssuchastitleartist
informationornewsheadlines;stillimagessuchasweatherchartsorCD
covers,etc.),servicelanguageandprogrammetypeinformationetc.
Theresistancetotransmissionerrorsofbothsystemsissimilar,sincethey
arebasedoncomparableerrorcorrectionschemes,butthedetailsofthe
twoschemeshavebeenoptimisedforthetwofunctions.
Performance of DAB+
Duringthestandardisationprocess,fieldtestswereconductedintheUK
andAustralia.Theyshowedthatthegeographicalcoverageareaofradio
servicesusingHE-AACv2isslightlylargerthanthatforradioservicesusing
MPEGAudioLayerII.
AudioservicesusingHE-AACv2performedabout2-3dBbetteratthethreshold
ofaudibility.Thismeansthatinsomeareasclosetothecoverageareawhere
This figure shows a comparison of the relative overhead (used for error correction and transport protocol) of additional audio coding (assuming no PAD information) and DMB (PAD information not possible) in case of a radio service.
100
Subchannel bit rate in kbps
DMB:at least 25% overhead
additional audio coding about 10% overhead
90
80
70
60
50
40
30
20
10
0
8 24 40 56 72 88 104 120 136 152 168 184
additional audio coding
DMB
Relative overhead of additional audio coding and DMB
MPEGAudioLayerIIservicesalreadyshowedaudibleartefacts,HE-AACv2
radioservicesshowednoaudibleartefacts.TheerrorbehaviourofMPEGAudio
LayerIIisdifferenttothatofHE-AACv2.WithMPEGAudioLayerII,theweaker
theDABsignalgets,themoreaudibleartefactscanbeheard.
HE-AACv2producesnoaudibleartefacts,butwhenthesignalgetstooweak,
anincreasednumberofaudioframeswillbelostandthiscausesshortperiods
ofsilence(fade-outandfade-in).Testlistenerspreferredthiserrorbehaviour.
ComparedtoradioservicesusingMPEGAudioLayerII,radioservicesusing
HE-AACv2willfaillater(theycancopewithaslightlylowerDABsignalquality),
butthemarginfromerrorfreereceptiontolossofreceptionissmaller.
Todeterminetheaudioqualityatlowbitrates,listeningtestswereperformedby
theEBU(EuropeanBroadcastingUnion)in2003.Forstereophonicaudio,the
listeningtestsshowthatatanaudiobitrateof48kbps,HE-AACoffersgoodto
excellentquality,atanaudiobitrateof64kbpsitoffersexcellentquality.
Atthetimeofthesetests,HE-AACv2wasnotyetavailable.ThePS(parametric
stereo)tool,whichwasaddedaftertheEBUtestswerecompleted,significantly
increasestheperceivedaudioqualityatlowerbitrates.
Itshouldbenotedthatthebitratescitedfromtheselisteningtestsarepure
audiobitratesandnotDABsub-channelbitrates.Inordertocarryaudioina
DABmultiplexusingthenewspecificationa10%overheadshouldbetaken
intoaccount.
AudiocomparisontestsperformedinAustraliain2005confirmedthat
HE-AACv2providessimilarperceivedaudioqualityataboutonethirdof
thesub-channelbitrateneededbyMPEGAudioLayerII.
Broadcasterswillwanttomakefurthertestsbeforetakingoperational
decisionsabouttheappropriatebitrateforaparticularservice.
DAB+ Roll OutManycountriesaroundtheworldhaveacknowledgedthebenefitsofDAB+
fortheirindividualmarkets.TheAustraliangovernmenthasannounced
DAB+astheofficialdigitalradiostandardinthecountry,withacommercial
rolloutplannedforJanuary2009.OthercountriessuchasItaly,Germany,
Switzerland,theCzechRepublic,theNetherlands,Malta,Malaysiaand
ChinahavealsoexpressedtheirinterestinrollingoutcommercialDAB+
services.Testsandtrialsarebeingcarriedoutaroundtheworld(seethe
mapbelow).ManufacturersarealsoensuringDAB+’squickrolloutwithan
increasingnumberofDAB+receiversinthemarket.InmatureDABmarkets
manyreceiverswillbeDAB+upgradeable.
Countries with DAB and DAB+
DAB Commercial Launch DAB Commercial Launch andDAB+ Trial /TestDAB Trial /Test DAB+ Trial /Test
R U S S I A N F E D E R A T I O N
ME
XI
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I T A L Y
SOUTH AFR ICA
I N D I A
C H I N A
A U S T R A L I A
P E R U
S. KOREA
S P A I N
F R A N C E
GERMANY
UN I TEDK INGDOM
PORTUGAL
GREECE
SWEDEN
NORWAY
SWITZ.
REP. OFIRELAND
BELGIUM
LUX.
NETHER-LANDS
DENMARK
HUNGARY
CZECH REP .
KUWAIT
C A N A D A
U N I T E D S T A T E S
O F
A M E R I C A
NEWZEALAND
A L A S K A( U S ) ICELAND
MALTA
SINGAPORE
MALAYSIA
HONG KONG
CHINESETAIPEI
C A L I F O R N I A
I T A L Y
S P A I N
F R A N C E
GERMANY
UN I TE DK INGDO M
PORTUGAL
GREECE
SWEDEN
NORWAY
SWITZ.
REP. OFIRELAND
BELGIUM
LUX.
NETHER-LANDS
DENMARK
HUNGARY
CZECH REP .
ICELAND
MALTA