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Using IP for Broadcast Studio Audio
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SkipPizzi
ExecutiveSummaryArevolutioniscurrentlytakingplaceinthefieldofaudiostudiodesign.Itinvolvesafundamental
rethinkingofthewaysignalsaredistributedandmanagedthroughoutthebroadcastfacility.
AnewapproachtothisprocessutilizesadigitaltransmissionformatsimilartothatusedontheInternet
forpurposesoftransportanddistributionofcontentaroundanaudioproductionenvironment.
ThisformatisknownastheInternetProtocol,generallyreferredtoasIP,anditistheverycoreoftheInternet.IPisthecommonformatusedforanykindofdatathatflowsontheInternet(including
streaming
media),
and
on
private
extensions
of
the
Internet,
such
as
the
LANs
employed
in
enterprise
networksandsmalloffice/homeoffice(SOHO)networks,bothwiredandwireless.Itsetstherulesfor
thisentiredatanetworkinginfrastructure,bothhardwareandsoftware,whichhasemergedandbeen
sobroadlyembracedoverthelastquartercenturyormore.Sincemostaudiofacilitieshavealready
convertedtodigitalaudio,itthereforemakessensetonowexaminetheuseofIPthere,aswell.
GiventhatIPisthelinguafrancaofcontemporarydatanetworking,itcanprovidesignificanteconomiesofscaleforspecializedapplicationssuchasprofessionaldigitalaudiodistribution.Thisexploitsthesame
processthathasmadethegeneralpurposedesktopcomputeranefficientandcosteffectiveplatform
forthecreationandstorageofprofessionalaudiocontent.IPAudiodistributionissimplyanextension
ofthatthinkingandtechnology,replacingthepurposebuilt(andrelativelyexpensive)mixers,routers
andswitchersthathavetraditionallybeenusedbyaudiostudiosformanagingmultipleaudiosignalsas
theypassthroughaproductionorbroadcastfacility.IPalsoallowsthefullandcontinuingforceof
MooresLawtobeappliedtoaudiodistribution,justasthePChasdoneforotheraudioprocesses.
Beyondsimplecosteffectiveness,however,IPAudiooffersotherimportantbenefits.Theseincludehigh
scalability(i.e.,theabilitytoeasilyaccommodategrowthandotherconfigurationchanges),convenience
(i.e.,easyandfastinstallation)andfutureproofing(i.e.,highlikelihoodoffittingwellintoanyscenario
forfuturefacilityrequirements).Puttingalltheseelementstogethercreatesavaluepropositionthatis
hardtoignorewhenconsideringoptionsfornewfacilitydesignsorexistingstudioupgrades.
ManyotherindustrieshavealreadyconvertedtheirlegacycommunicationsprocessestoIPbased
replacementsystems.StudioaudiosystemsusingIPbasedtechnologyarenowsufficientlymatureto
allowaudioproducersandbroadcasterstodothesame,providingthemwithsubstantialsavingswhile
simultaneouslypositioningthemwelltoaccommodateindeterminatefutureneeds.
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IntroductionThispaperconsidersthereplacementoftraditionalformsofaudiosignaltransportinthebroadcast
studiowithnetworkedaudiocarriedviaInternetProtocol(IP).Itexaminesthevalueandprocessofsuch
conversion,thechallengestodoingso,andthelikelyfutureofthisenvironment.
ThisstudywascommissionedbyAxiaAudioinearly2008.
ABriefHistoryThebroadcastaudiostudiohasalonglegacyrelationshipwiththetelecommunicationsworld.The
earliestaudiofacilitiesandstandardpracticesweredevelopedbyBellSystemandWesternElectric
engineersintheearly20th
century,andthetwoworldshaveneverstrayedfarfromeachothersince.
Inparticular,broadcastaudiohasretainedacloseconnectiontothetelecomenvironment,sinceso
muchofbroadcastingscontentcomesand/orgoesfromthestudioviatelcoprovidedpaths.
Thusit
is
not
surprising
that
the
next
generation
of
studio
audio
technology
should
once
again
follow
a
pathblazedbytelecommunicationstechnologies.
Inthiscase,thetechnologyinvolvesdigitalnetworkingspecificallyusingthepopularandnownearly
ubiquitousInternetProtocol(IP).Thisprotocol,coupledwitheithertheTransmissionControlProtocol(TCP)orUniversalDatagramProtocol(UDP)datatransportformat,providesthebulkofdatacommunicationcarriedontheInternet.Itspopularityforthatpurposehasalsomadeitusefulforother
localized,nonInternetdatanetworkingpurposes.Thisisprimarilyduetothevolumeofdevelopment
andresultinghardwareandsoftwarethatsupportsTCP/IPorUDP/IP,andthegreateconomyofscale
thatresults.
Foralittlebackground,notethataprotocolinthedatanetworkingcontextissimplyanagreementon
theformatofdatathatwillbepassedbetweendevices.Thereforeitspecifiesasetofrulesforvarious
parametersofthatdata,suchasthedataratesallowed,theerrorcheckingalgorithmsemployed,any
datacompressionformatsthatmightbeused,howthestartandendofindividualmessageswillbe
determined,howconfirmationthatamessagehasbeensuccessfullydeliveredwillbecommunicated,
andsoon.
ItsalsohelpfultoreviewsomeoftheearlydevelopmentthatledtoIPsparticularpopularity.Ina
nutshell,theIPapproachisasimplificationofthecanonicalsevenlayernetworkingarchitecture1down
toastackconsistingofonlyfourlayers,asshowninTable1.
1TheOpenSystemsInterconnection(OSI)referencemodel,establishedinthelate1970s,includedApplication,
Presentation,Session,Transport,Network,DataLink,andPhysicallayers.
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APPLICATION HTTP,RTP,FTP,SMTP,TELNETTRANSPORT TCP,UDPNETWORK IP
LINK Ethernet,WiFiTable1:ThefourlayersofInternetdatatransmission,withsomeexamplesofeachlayersprotocols.
TheInternetprocessalsoincludesanaddressingprotocolforeachofitsdatapackets,theIPaddress.AnydeviceattachedtoanIPnetworkisassignedanIPaddress.Untilrecentlyi.e.,usingIPv4anIP
addresswasspecifiedasanumericstringoffouronebytenumbers(oroctets,sinceonebyteiseight
bits),eachexpressedindecimalform(from0to255)andseparatedbyperiods(e.g.,169.10.206.2).2
ThisimpliesthatthenumberofpossibleaddressesinIPv4isthatexpressedbya32bitnumber(4x8
bits),meaningthat232,orapproximately4.3billion(4.3x10
9),uniqueIPaddressesareavailable.This
maysoundlikealot,butmanyofthesearereservedforspecificuses(moreonthisbelow).
Today,the
IP
world
is
converting
to
IPv6,
which
specifies
its
IP
addresses
using
128
bit
rather
than
32
bit
numbers.3
ThenumericalexpressionofIPv6addressesalsodiffersfromIPv4s,inthatitgenerallyuses
hexadecimalnumbersintheformhhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh:hhhh, whereeachbyte(or
octet)isrepresentedbyahexadecimalpairofnumbers(from00toff,e.g.,e7),andeachpairofbytesis
separatedfromthenextpairbyacolon.Anexampleis30c1:0ab6:0000:0000:0000:8a2e:0370:2f8e.For
awhile,theremaybealotofzerosinIPv6addresses,andtheycanbeskippedwiththeinsertionofa
doublecolon,asinthisnotationofthepreviousaddress:30c1:0ab6::8a2e:0370:2f8e.
OneoftheprimaryimprovementsofIPv6overIPv4isitsallowanceoffarmoreIPaddresses.Thisisa
realissue
given
the
expectation
that
so
many
devices
in
the
future
will
require
unique
IP
addresses.
IPv6s128bitrangeprovidesmorethan3.4x1038
possibleaddresses,ormorethan5,000addressesper
squaremicrometeroftheEarthssurfaceprobablyenoughtolastforawhile.
Nevertheless,itisexpectedthatIPv4willremainthestandardformatoftheInternetforsometimeto
come,whileIPv6supportisgraduallydeployedworldwide.
ThereasonthatIPaddressesareimportanttothisdiscussionisbecausetheyessentiallyreplacethe
audiocrosspointsinatraditional,circuitswitchedenvironment.InanIPAudiosystem,alltrafficflows
along
a
single,
serialized
path,
and
each
packet
of
data
gets
to
its
intended
destination
via
the
IP
address
initsheader,ratherthanbyitsbeingsentalongadedicatedwirebyaswitcher.
2IPv4hasbeeninusesince1981,establishedwiththepublicationbyDARPAoftheseminalRFC791document,
generallycitedastheoriginalspecificationfortheInternet.Althoughotherprotocolsprecededit,formostofus,
IPv4istheonlyversionofIPtheInternethaseverused.3IfyourewonderingwhathappenedtoIPv5,itwasascribedtoaversionthatwasoriginallyintendedtobeused
forconnectionbased(ratherthanpacketbased)streamingmediaontheInternet,butworkwasabandonedonit
asstreamingmediabecamepossiblewiththedevelopmentofnewprotocolsoverIPv4.
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IPBeyondtheInternetAsnotedearlier,IPisusedtodayonmanylocalareanetworksthatarenotconnectedtotheInternet.
ThisiswhytherearealargenumberofIPaddressesthatarereservedfornonInternetusesonprivate
networks.4AnumberofIPaddressrangesareinternationallyagreedtobereservedforthispurpose,the
largestcontiguousgroupofwhichspansfrom10.0.0.0to10.255.255.255.Thisgroupaloneprovides
some16millionpossibleaddressesthatarenotaccessiblefromtheInternet(routersareprogrammed
toignore
the
addresses
on
incoming
Internet
traffic),
and
are
only
available
from
within
alocal
network.
ThisalsoimpliesthataprivateIPaddresshasnoneedtobegloballyunique,andsothesesame
addressescanbeusedbyanyentityonitsinternalnetwork,therebyconservingthenumberofIP
addressesrequiredworldwide.
DevicesassignedsuchprivateaddressescanstillaccesstheInternetifnecessary,viaaproxyserveror
NetworkAddressTranslation(NAT)device.5
TheprivateaddressspaceisparticularlyusefulforstudioaudioapplicationsofIP,sincethedevicesso
interconnectedaretypicallynotintendedtobeaccessibledirectlyviathepublicInternet.
IPbutnotInternetisalsothecaseforanothermajoremergingtechnologycalledIPTV,whichusesIP
fordistributionoftelevisionprogramming,butoverdedicatednetworksoperatedbytelcos(providinga
multichannelservicecompetitivewithdigitalcableandsatelliteTV),nottheopenInternet.6
StreamingChangesAllAlthoughoriginallydevelopedforstandarddatacommunication,subsequentenhancementstothe
Internetallowedittobeusedformediatransmission,aswell,whichiswellknownastheprocesscalled
streamingmedia.
ThisdevelopmentfundamentallyalteredtheusageoftheInternet,andhassubsequentlyhadsignificant
impactonallfacetsofthemediaindustry,astheystruggletocopewiththechangesitbrings,andto
takeadvantageofthenewopportunitiesitengenders.
Besidesspawningmanycurrentlyburgeoningonlinemediabusinesses,streamingtechnologyisalsothe
basisforIPstudioaudio.Thisallowstheaudiostudioenvironmenttoleverageseveralkeypropertiesof
anIPbasedenvironment,whichprovidesubstantialimprovementovermoretraditionalapproaches:
4ThesenetworksuseaddressesintheprivateIPaddressspace,asspecifiedintheInternetEngineeringTask
Forces(IETF)RFC1918,andadministeredbytheInternetAssignedNumbersAuthority(IANA).5NotethatinIPv6therewillbenoprivateaddressspaceorNAT,giventhefargreaternumberofgloballyuniqueIP
addressesitprovides.6Meanwhile,TVcontentsentviaIPthatdoestravelviatheopenInternet(InternetTV)isalsosoaringin
popularity,increasinglyusedfordistributionofbroadcastcontentaswellascontentcreatedbyconsumers(user
generatedcontent,orUGC).
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x Scalability:PerhapsthemostfundamentalchangebetweenIPbasedaudiosystemsand
traditionalapproachesanalogordigitalistheabilityofIParchitecturestoadapttochange
andgrowth.Forexample,atraditionalaudioenvironmentmusthaveitsspatialorimaging
format(e.g.,mono,stereoorsurround)predetermined,alongwiththenumberofsimultaneous
audiochannelsitwillrequires(e.g.,one,twoormore).AnIPAudioenvironmenthasnosuch
requirement,andcaneasilyadapttoanyformat.Similarly,atraditionalcrosspointaudio
routingswitcher
must
have
its
input
and
output
(I/O)
configuration
fixed
in
its
hardware
design.
Inthisway,suchadevicereflectscircuitswitchingandparalleldesign,whereasIPAudiosystemsimplementpacketswitchingandserialdesign.ThisallowsgreatflexibilityandresponsivenessinaccommodatingchangesinI/Oconfiguration.Justastelcoshavemovedawayfromthecircuit
switchedpathsoftheirearlieryearsforsimilarreasons,studioaudiosystemscannowenjoythe
sameadvantagesofscalabilityandflexibilitytoimplementexpansioninanydimension.This
comesnotamomenttoosoon,giventhecompetitivepressurescomingtobearonbroadcasters
forincreasedcontentandlistenerchoice.
x Costeffectiveness:
At
almost
any
reasonable
size,
an
IP
based
audio
system
will
compare
favorablywiththecostofatraditionalsystembothintermsofhardware/materialspricingand
installationcost.Thereductioninwirealoneprovidessubstantialeconomy.7Maintenance
expensesaregenerallyalsolower.Thesecostdifferentialsincreasewiththesizeofthefacility,
whichiswhysomanylargerinstallationshavealreadymovedtoIPbasedsolutionsastheir
needshavecalledfornewtechnicalplants.
x Convenience:Thesmallphysicalfootprint,lowoperatingcost,easeofreconfigurationor
upgrade,andfastinstallationofIPAudiosystemsmakethemextremelyconvenientfor
engineeringandoperationsalikeattheaudiostudiofacility.Frominitialdesignto
implementationtodailyoperation,IPbasedsystemsmakelifeeasier.
x Futureproofing:Nothingstrikesfearintheheartoftheengineerormanagermorethan
makingapoormajorpurchasingdecision.MovingtoanIPbasedaudioarchitecturetakesalot
ofthepressureoff,sinceitofferssuchflexibilityandallowsbroadabilityforreconfiguration
downtheroad.Provisioningforunforeseenchangesismuchlessproblematicandcheaper.
NotethattheaboveadvantagesonlyfullyapplytosystemsthatutilizestandardIPintheirarchitecture.
Notallaudiosystemsthatusecomputernetworking(overEthernetand/oronRJ45connectors)for
interconnectionarenecessarilytrueIPbasedsystems.SomesimplyuseEthernetasaphysicallayerwith
aproprietarydataformataboveit,8whileothersmayusemoreIPlikeformatsbutwithnonstandard
7RememberthatapacketswitchedsystemlikeIPdoesnotrequireindividualwiringpathstoeachinputand
outputofeverydevice.Forexample,anaudiomixingconsoleormultitrackrecordingdevicecanhaveallofits
inputsandoutputsinterfacedtotherestofthefacilityviaasinglecableinanIPAudioenvironment.8e.g.,Cobranet
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protocolvariations.Someofthesenonstandardapproachesmayhaveofferedsomevalueinthepast
(suchasreducedoverheadandlatencyoverstandardIPnetworking),butgiventhecapacity,speedand
performanceofaproperlyconfigured,standardIPsystemtoday,thepenaltiespaidbyworkinginanon
standardenvironmentgenerallyfaroutweighanyadvantagesthatsuchvariationsmightprovide,
particularlywhenconsideredoverthelongterm.
IPAnything
Intermsofcriticalmassbehindthistrend,studioaudioiscertainlynotaloneinitsmovementtowardIP
basedprocesses,asalreadynoted.NumerousotherindustrieshavealreadyembracedatransitiontoIP
forsimilarreasonstothosecitedaboveforstudioaudio.
OnesuchdevelopmentthatiscloselyrelatedisVoiceoverIP(VoIP),whichisrapidlygaininggroundin
thetelephonyspaceasareplacementfortraditionalvoiceservice,inbothconsumerandenterprise
applications.AgaintheleveragingofIPasamechanismtousegeneralizedsystemsandtransportpaths
forvariousspecifictaskshasundeniableappeal,andthisargumentisalsofindingfavorinawiderange
ofotherindustries,fromhotelTVsystemstohealthcare.EmergingdigitalTVsystems(includingnew
mobilevariants)arealsofavoringanIPdistributionmodel.
IPisfastbecomingthelinguafrancaofdigitaltechnologyandcontent,allowinganythingexpressedin
itstermstobecarriedandprocessedthroughincreasinglyavailableandcosteffectiveinfrastructures.
JustasthePCbecamethegeneralpurposecomputingplatform(deliveringunprecedentedprocessing
power,speedandcosteffectiveness),IPhasbecomethegeneralpurposedatatransportformat.
Forengineers,familiaritywithdigitalnetworkingtechnologies,includingIP,hasbecomeanear
requirementof
the
job
anyway
(for
implementing
the
on
line
services
of
aradio
station),
so
why
not
applythisknowledgetostudioaudio,too?
ItsbecomingclearthatIPistrulythewayofthedigitalmediaworld,particularlyforanyindustrythat
valuesconnectedness,agilityandcosteffectiveness.Intheradioenvironment,itsnotanoverstatement
tosaythatIPAudioisthefutureofstudioaudiosignalflow.Arguingotherwiseisdifficult:Thereisand
willcontinuetobesomuchdevelopmentwithintheIPenvironment,itonlymakessensetoharnessthe
powerofthateffort,whilealsolettingMooresLawhaveitsfulleffectonthehardwaresideforstudio
audioequipment,justastheseforceseffectsarebeingenjoyedbysomanyotherindustriestoday.
Whatsthecatch?ThisisnottosaythattherearentsomechallengestotheoptimaluseofIPforstudioaudiotransport.
PrimaryamongtheseisthelatencythattheencapsulationprocessofaudiodataintoIPpacketscan
cause,andtheirserialroutingthroughapacketswitchednetworkpronetodatacollisions.As
mentionedearlier,variousmethodshavebeenputforthbydeveloperstoamelioratethis,butproper
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configurationofavailabledevicesusedontodayshighspeedEthernetnetworksisusuallyadequateto
resolveanysuchdifficultiesinIPAudiosystems.
SuchconfigurationofstandardIPequipment(e.g.,Ethernetroutersandswitches,buffersizesand
networkspeeds)canbesettooptimallyservethespecificneedsofastudioaudiosystem,ratherthan
generalizedInternetdatatraffic.Forthisreasonaswellasforobvioussecuritypurposesitis
importanttouseaseparate,dedicatednetwork(eitherphysicalorvirtual)forallstudioaudioIP
applications.Thisnetworkcancarryallaudiocontent,controlsignalsandmetadatarelatedto
production,butshouldbeisolatedfromthegeneraldatanetworkofthefacility.Inaddition,there
generallyshouldnotbeadirectconnectionofthestudioaudiosystemtothepublicInternet.When
Internetconnectionsarerequiredforaccesstooffsiteaudiosourcesordestinations,theyshouldbe
routedthroughaproxyserverorotherisolatingpath.SomevendorswillalsosetIPpacketprioritization
atahigherlevelforaudiocontentpacketsthanforgeneralnetworkdata.ThishelpsIPAudio
performanceevenonnetworksthatarenotdedicatedtoIPAudiousageonly.
Anotherissueisasimpleoneofconnectorstandards.SinceIPAudiogenerallytravelsonCAT5orbetter9
Ethernetcables,
the
RJ45
connector
is
used
for
all
terminations.
But
some
IP
Audio
system
implementersalsouseRJ45foranalogorAES3digitalaudioI/Oandpatching.Whilethiscanminimize
thenumberofdifferentconnectortypesusedinafacility,andreducethephysicalspacerequiredfor
connectorpanels,thereisnostandardfortheconfigurationofanRJ45connectorforthispurpose.So
individualIPAudioimplementershavedesignedtheirownunilateralformats,againpossiblylimiting
broadcasterstotheuseofonlycertainmanufacturersproductsinanIPAudiofacility,orrequiringthe
useofadapters.
Ofcourse,theneedtoretaincompatibilitywithanalogandAES3digitalaudiowilllikelyremainforsome
timeto
come
at
any
IP
based
audio
facility.
At
the
very
least,
live
microphone
signals
will
need
to
be
convertedfromtheirnativeanalogaudio(orinsomecases,perhapsAES3)format,andinsomecases
analogordigitalaudiofromotherdevicesorremotesourceswillalsohavetobeaccommodated.How
thisconversionprocessisaccomplishedisakeyfactorinthedesignofanIPAudiosystem.
Forthetimebeingatleast,theaboveoptimizationprocessesarguefortheselectionofasinglevendor
forthesupplyofIPAudioequipmenttoagivenbroadcastfacility,oratleasttheverificationthat
compatibilityamongdifferentvendorsIPAudioequipmentisassured.Workingwithasinglesupplier
alsoensuresthatupdatesandupgradeswillbedeliveredinatimelyfashion,andevenspecialfixesfora
particularproblem
encountered
at
agiven
facility
can
be
quickly
provided.
9CAT5eorCAT6
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ImplementationandintegrationThisbringsustoactualIPAudiosystemconsiderations.Giventheadvantagesofscaleprovidedbythese
systems,itmakessensetomaketheIPAudiodomainaslargeaspossiblewithinagivenfacility.That
impliesthataudiosignalsinotherformsshouldbeconvertedtoIPpacketsassoonaspossible.
Thebestplacetodothisinmoststudioconfigurationsisatthecentralpatchbayand/orthestudio
mixing
console(s).
Microphone
outputs
and
signals
from
other
legacy
audio
sources
can
be
immediatelyconvertedtodigitalaudioform(iftheyarentalready)andpacketizedasIP.OnceintheIP
domain,thesesignalscanbeaddressedandroutedtoanyotherlocationonthenetwork.Thiscan
includedestinationswithintheconfinesofafacilityviaLAN,oranywhereintheworldviaWAN.
Anotheradvantageofthisapproachisthatamixingconsolecanactasarouter.Inotherwords,because
anyinputontheconsolecanhaveauniqueIPaddress,itcanbeconnectedtoanyIPAudiosourceon
thenetwork.(Evenmoreamazingtoveteranaudioengineersisthatthiscanbeaccomplishedeven
thoughtheentireconsoleisconnectedtothenetworkviaasinglecable.)Acentralswitchingcontrol
unit(typicallyaPC)canassigntheseI/Oconnections,orthemixingconsoleitselfcanhaveacontrol
interfaceforthispurpose.Inaddition,standalonehardwareswitchcontrollerscanbedistributedaround
thefacility,essentiallyduplicatingtheappearanceandfunctionoftraditionalroutercontrolpanels.Inall
cases,however,allthatisbeingdonetoachievetheroutingistheadditionofappropriateIPaddresses
totheheadersofIPAudiopacketsonthenetwork.10
Ofcourse,themixingconsolecanalsobeequippedwithtraditionalanalog(mic/line)orAES3inputson
someinputsaswell,toaccommodatelocalaudiosourcedevices.Thesesourcesareinturnconvertedto
IPbytheconsole,andviatheirroutingtotheconsolebusordirectoutputs,thesesignalsmayinturnbe
madeavailableasIPsourcestotherestofthenetworkagainviathesinglecableconnectingthe
consoletothenetwork.(SeeFigure1.)
ConsideralsohowPCbasedaudioplayout/automationsystemscanbeinterfacedtosuchasystem.
RatherthantheiraudiooutputsbeingdirectedthroughPCsoundcardstotraditionalaudioinputs,the
automationsystemcanbefittedwithanIPdriverthatprovidesasoftwareinterfacebetweenthePC
audioandtheIPnetworkdirectlyintheIPAudiodomain.Thisnotonlymaintainshighaudioquality,but
cutscostsintheautomationsystemsinceno(oratleastfewer)soundcardsarerequired.TheIP
interfacecanalsocarrycontroldataandPADaswell,eliminatingtheneedforseparatedatalinks
betweendevices.
10Ideally,theIPfeedsto/fromanymixingconsoleinanIPAudiosystemareusedonlyforthoseitemsthatneed
accesstotheconsolesaudiomanipulationfeatures.Simpleinputtooutputconnectionscanbehandledbythe
coreIPAudioarchitecturewithouttakingupconsoleresources(orevenusingupacrosspoint,intraditional
switchingterms).TheconsolecanbeconsideredasanIPapplianceoraudioengine,whichcanhostanysortof
audioleveladjustment,mixing,processingorcoding/transcoding thatthefacilityrequires,applyingallsuch
processesefficientlyandwithintheIPdomain.
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Moreover,asingleIPdriverinterfacebetweenanautomationsystemandanIProutingarchitecturecan
carrymanyindependentaudiochannels(perhapsupto24),whereasatraditionalswitchingsystem
wouldrequireacrosspoint(pluswiring)foreachsoundcardinputandoutput.Thecombinedhardware
savings(soundcards+crosspoints+wire+installation)inalargefacilitycouldbesubstantial.
AnyIPAudiosystemtodaywillalsoincludeoneormorestandardEthernetswitches,whichareusedto
interconnecttheEthernetconnectionsfromeachfacilityordevicethatprovidesaudioI/OviaIP.These
switchesarestandardtelecomdevices,whichreplacethemorecommonEthernethubsorroutersused
forsimilarRJ45terminationsintypicalhomeorsmallofficesituations.SwitchesarepreferredinIP
Audioapplicationsbecausetheyhavemoreintelligencethanhubs,whichallowsthemtoinspectdata
packetstodeterminetheirsourceanddestination,andforwardthemappropriately.Throughthis
intelligentcontrol,eachmessageisonlysenttotheintendeddevice,therebyconservingnetwork
bandwidthandprovidingbetterperformance(includingreducedlatency).
Figure1:ConceptualblockdiagramofatypicalIPAudiobasedbroadcaststudiofacility,showingonestudioandTechnicalOperationsCenter(TOC).
Ethernetswitchescomeinunmanagedormanagedforms,thelatterallowinguserconfigurationof
variousparametersoftheswitchsoperation.InsmallerIPAudiofacilities,unmanagedswitchescan
performadequately,whilelargerfacilitiesmaybenefitfrommanagedswitches.Someswitchesalso
TOC
Local
Audio
Sources
(Mic/line
Analogor
AES3)
Softwareinterface
(audio
+
control)
IPAudio
Converter
IncomingRemoteAudio+
ControlSignals
ProgramOutput
toAudio
Processors,
ConventionalSTL
Monitoring,etc.(AES3orAnalog)
To/from Interne
RadioServersLANorWAN
Ethernet
Switch
(Core)
PCbasedAudio
Storage/automation
System
(w/IPDriverSoftware)
EthernetSwitch(Edge)
Conversion
toIP
IPbasedMixing
Console
Ethernet
LAN
To/fromIPSTLs&
OtherSitesWAN
Ethernet
LAN
To/fromOther
Studiosinthe
Facility
LAN
STUDIO
UsingIPforBroadcastStudioAudio
TOC
Local
Audio
Sources
(Mic/line
Analogor
AES3)
Softwareinterface(audio+control)
IPAudio
Converter
IncomingRemoteAudio+
ControlSignals
ProgramOutputs
toAudio
Processors,
Conventional STLs,
Monitoring,etc.(AES3orAnalog)
To/from Internet
RadioServersLANorWAN
Ethernet
Switch
(Core)
PCbasedAudio
Storage/automation
System
(w/IPDriverSoftware)
EthernetSwitch(Edge)
Conversion
toIP
IPbasedMixing
Console
Ethernet
LAN
To/fromIPSTLs&
OtherSitesWAN
Ethernet
LAN
To/fromOther
Studiosinthe
Facility
LAN
STUDIO
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includeremoteadministrationcapability.TodaysfastestswitchesoperateatGigabitspeeds,usingCAT6
cable,andthesearethemostappropriateforlowlatencyIPAudioapplications.
AsFigure1indicates,atypicalIPAudiofacilityincludesmultipleswitches,usuallyarrangedwithone
large(core)switchinacentralroom,andsmaller(edge)switchesplacedasneededinotherrooms
aroundthefacility.Suchdistributedroutingintelligenceimprovesperformance,andalsoprovides
redundancyincaseofswitchfailure.
NotealsothattheproliferationofVoIPandotherrealtimeapplicationsviaIPhavespawnedbroad
implementationofnonblockingarchitectureinrecentEthernetswitches.Thisapproachvirtually
eliminatesdatacollisionswithinaswitch,whilemaintainingcosteffectiveness,byensuringjust
adequatecapacityfornxnconnectivity11
throughtheswitchingfabric.Missioncriticalperformanceis
therebymaintainedbyusingEthernetswitchesthatimplementnonblockingdesign,andwhenproperly
implementedwithinanIPAudiosystem,switchcapacityshouldneverbeexceeded.MostIPAudio
vendorsrecommendonlynonblockingEthernetswitches,andthisisonereasonwhyusersshouldheed
vendorsrecommendationsforallswitchesusedintheirfacilities.(Again,theeconomyofscaledriven
bybroad
uptake
of
these
switches
today
provides
such
advantages
to
IP
Audio
implementers
at
very
attractiveprices.)
TheuseofEthernetswitchesbymissioncriticalandotherhighreliabilitytelecomoperationshasdriven
majormanufacturerstoprovideexcellent24x7andovernightreplacementsupport.Notealsothatasa
facilitygrows,itmayneedtoreplaceolderswitcheswithnewermodels;thefactthatEthernetisa
ubiquitousstandardmeansthatallupgradeswillremainbackwardcompatible.Meanwhile,Moores
Lawensuresthatassuchnewhardwarebecomesavailable,price/performanceratioswillcontinually
improve.
TheIPAudiodomainisalsoextendingbeyondthestudio.Figure1showshowIPAudioisconvertedback
toAES3(orevenanalog)forprogramoutputsconnectiontoconventionalStudiotoTransmitterLinks
(STLs),butthediagramalsoindicatesthatanSTLcouldcarryIPAudiotothetransmittersite(viaWANor
otherdedicatedlink).WhetherleasedfromtelcoorusingastationoperatedRFpath,ifadequate
bandwidthisavailable,multipleaudiochannels,controlandmetadatacanallbecarriedviaIPonthe
linkbidirectionally,ifdesiredwithminimallatency.12
IPAudioinUseTodayTheadvantagesofIPAudiohavebeennoticedbybroadcastersandstudioownersaroundtheworld.Itis
fairtosaythattheengineersdesigningeverynewbroadcaststudiofacilitybuilttoday(andfromthis
pointforward)areatleastconsideringtheuseofanIPAudioarchitectureandmanyofthemare
decidingtotaketheplunge.Speakingwiththemafterwardswillfindalmostunanimousagreementthat
11Inotherwords,anyinputontheswitchcanalwaysbeconnectedtoanyoutputontheswitch,underanyusage.
12BidirectionallinkscansubstantiallydecreasejitterandlatencycomparedwithunidirectionalIPpaths.
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itwastheproperchoice,andtheresnolookingback.Inmanycasesyouwillhearthatthetransition
processwasfareasierthantheyexpected.
TheinstallationofanIPAudiosystemmakesmanypeopleattheoperationhappy,fromtheCEtothe
CFO.ThetotalcostofbuildingandoperatinganIPAudiofacilityissignificantlyreduced,andyetthiscan
beaccomplishedwithoutgivingupflexibilityinfactit,too,isgreatlyincreased.Operationsareoften
minimallyinterrupted,aswell,duetothesmallfootprintandquickinstallationofIPAudiosystems.
Thisiswhybroadcastersofallstripes,andwithbudgetslargeandsmall,havemovedtoIPAudio
systems.OnthecommercialsideintheU.S.,broadcastersfromClearChanneltoGreaterMediahave
recentlyinstalledIPAudiosystems,whilenoncommercialoperatorsfromMinnesotaPublicRadioto
WYMS,Milwaukeehavedonethesame.
Infact,theclienteleforthisemergingtechnologyalmostdefiescharacterization.Itincludessmall
independentstations,collegeradio(includingnumerousruralandcommunitycolleges),ethnicand
religiousbroadcasters,satelliteradioservices,radioandtelecomnetworkoperators,contentproduction
andbroadcast
origination
sites,
corporate
facilities
and
government
agencies
along
with
some
of
the
largestandmostrespectedstationsinthecountry.
NeitherisadoptionisbyanymeanslimitedtotheU.S.IPAudioisalreadywellensconcedaroundthe
world,fromSpaintoSouthAfrica,fromItalytoIsrael,fromChinatotheCzechRepublic,andmanyother
placesinbetween.
Clearlythetechnologyhasalotofuniqueadvantagestooffer,andthesehavebeennoticedbymanyof
theleadingpurveyorsofaudiocontentanddeliverythroughouttheplanet.
ConclusionsItsnotoftenthatanewtechnologyoffersconsiderabletechnicalimprovement,easierinstallationand
maintenance,greatlyenhancedflexibilityandscalability,andreducedcostwhencomparedwithits
predecessors.YetthesearetheattributesofaproperlyimplementedIPAudiosystem.
Broadcastershavealwaysbeenacostconsciouslot,andrightlyso,butgiventodaysincreasingly
competitivelandscape,efficienciesincapitalexpendituresandoperatingcostshavebecomeevenmore
criticalanddesirable.
Meanwhile,itsbecomequiteclearthattheradioindustrywillfacesubstantialchangeinthenear
future,andmuchofitwilllikelyinvolvequantitativegrowthinservices.Morestreams,moreaudio
channels,moredata,moreresponsivenesstoaudiencedemands,andprobablymorestill,areallonthe
paththatliesaheadforbroadcasters.AnIPAudioplatformprovidesalegitimateplatformtomost
realisticallyaccommodatethesemanychallenges.
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ItbehoovesanybroadcasterfacedwiththeopportunitytoconfronttheseuncertaintiestoseekthecounselofexpertsinthefieldofIPAudio,andtobenefitfromtheexperienceofthosewhohaverecentlyundertakensimilarprojects.YouwilllikelyhearstrongencouragementtomakethemovetoIP,
justasmuchoftherestoftheworldisdoing,withgoodreason.Fairfax,VAFebruary2008
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Axia Audio, a Telos Company 2101 Superior Ave. Cleveland, Ohio, 44114, USA +1.216.241.7225 www.AxiaAudio.com