birds on the wire – olivier messiaen's livre du saint...

BirdsonthewireWFSlivetransmissionprojectreport

1 Planning

TheideaofaWFSlivetransmissionwasoriginallydevisedbyProf. StefanWeinzierl ofTUBerlinandDomorganistProf.WinfriedBnig.

Thegoalwastocaptureaconvincingrepresentation of the room ambiance of CologneCathedralaswellasnearfieldimagesoftheorganworksandremotestops,toallowforaspatiallycorrectrecreationoftheliveconcertexperience in the WFS auditorium of theTechnischeUniversittBerlin(TU).ThesignalsweretobetransmittedtoBerlininrealtime,andpristineaudioquality.

InMay2008,theauthorwasapproachedbytheTUtoprovidethenecessarynetworkinfrastructureandtoactasprojectmanagerfortheColognesideoftheproduction.

ThesoundengineeringworkwastobetakencareofbyTonmeisterHansSchlosseroftheRobertSchumannHochschule in Dsseldorf(RSH),andateamofhisstudents.Asoundtruck and all necessary audio equipmentwouldbekindlyprovidedbyRSH.

With the help of WFS specialist Dipl.Ing.Frank Melchior (of the Fraunhofer Institutefor Digital Media Technology IDMT,Ilmenau), we had established that up to 24discretesignalsofuncompressedaudiowouldbedesirableforthetransmission.It was decided early on that the actualtransmission should happen via an AudiooverIPlink,possiblybasedonUDP/RTP.At a sampling rate of 48 kHz and a wordlengthof32bits,thedataaddsuptoabandwidth of roughly 37 Mbit/s. There exists afiberopticslinkfromtheSilberkammerinthe

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BirdsonthewireOlivierMessiaen'sLivredu

SaintSacrmentintheworld'sfirst

wavefieldsynthesislivetransmission

JrnNettingsmeierLortzingstr.1145128Essen

On July 29 2008, a world premiere took place between Cologne Cathedral and Technische UniversittBerlin(TU):thefirstliveconcerttransmissionusingthewavefieldsynthesistechnique.

OrganistProf.WinfriedBnigperformedOlivierMessiaen's"LivreduSaintSacrment"onthetwoKlaisOrgansofthecathedralforanaudienceofaround1500.Atthesametime,600peoplein BerlinlistenedtoalivereconstructionoftheconcertonthewavefieldsynthesisarrayattheTU,supervisedbyTonmeisterProf.Dr.StefanWeinzierl.

ThisistheprojectreportfortheColognesideoftheproduction.


Dom basement to the Domforum and theDombauverwaltung(adjacentbuildingsacrosstheRoncallisquare),buttheavailableuplinkisameagre4Mbit/sADSLline.RentalofoneormoreadditionalDSLlineswasnotfeasible,sincethelocalISPhadnoprovisions for line trunking, which wouldhave been undesirable anyway due to theincreasedpossibilityofoutoforderpackets.Moreover, their quotation for only onetemporaryDSLlinkat18Mbit/scameclosetoexceedingourtotalbudget.So we decided to cooperate with the

Kunsthochschulefr Medien(KHM)(whichhad hosted the Linux Audio Conference in2008,andwhosestafftheauthorhadworkedwithbefore)totryapointtopointopticallinktotheDomviainfraredlaser.TheKHMhasdirectlineofsighttotheDomspiresatadistanceofabout850m.Fortheuplink,theCitizenMediaresearchproject at KHMkindlyletussharetheir2Gbit/sconnection.Aftermanyfailedattemptstoobtainasuitabletransmissionsystemfromseverallargenational rental companies, OPTEL, a laser linkvendor fromHamburg, came to the rescue.Notusuallyintherentalbusiness,theyfoundthe project sufficiently challenging andinterestingtoprovideuswithapairofspare

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Illustration1:The"Querhausorgel",themainorgan of Cologne Cathedral (Klais, Bonn, 1948,1956,2002)

Illustration 3: The "Schwalbennestorgel" onthenorthernwallofthecentralnave(Klais, Bonn, 1998). Mechanical and (optional) electric action for remote control from themainorganconsole.

Illustration 2:Oneof the twohighpressuretubastopsontheTriforium,abovethemain entrance(Klais,2006)


laserdevicesandextensivetechnicalsupportforthedurationoftheproject.

Abouttwomonthsbeforetheconcert,theauthorcontactedtheDombauhttetoaskforapermissiontoinstallthelaserandrunafibercabledownthespiretotheplannedlocationofthesoundtruck,andtodeterminewaystomountmicrophonearrays intheDomitself.Dombaumeisterin Prof. Dr. SchockWernercalledameetingwithsomeofherseniorstaffmembersafewdayslater,wherewepresentedtheproject.Wewontheirsupport,quicklyarrived at a consensus and developed a firstconceptformicrophoneplacementandcablerunswiththeassistanceofthetechnicalstaffoftheDom.Nowtherealworkcouldbegin.

1.1 Microphonedistribution

Tonmeister Hans Schlosser and his studentscheckedoutthelocationoneweekbeforetheconcert, to estimate required cable lengthsandtodecideonthedistributionoftheremotemicpreampsandthefinalmicrophoneplacement.In total, we used 20 discrete signals. FiveSchoepsMK5omnisintwoABpairsandanadditionalmonospotmikehadtobeusedonthemainorganduetoitscomplicatedlayout,whileanextraM/Spair(SchoepsMK5/MK8)covereditsRckpositiv.OnesubcardioidABpair(SchoepsMK21)was facing the new Schwalbennestorgel("swallow'snest", sinceit clings to thewallsuspendedfromtheroofonfoursteelcables)fromacrossthemainnave.Twomonohypercardioids(SchoepsCCM41)were aimed at the highpressure tuba stopsovertheentrance.AllthesesignalsweretoberenderedontheWFSarrayaspointsourcesattheappropriatelocations.

Inaddition,eightfiguresofeight(SennheiserMKH 800) were used in a Hamasakistylearray to capture uncorrelated ambianceinformation (four were oriented towards thesidewallsandfourtotheceiling);theywouldlaterberenderedasplanewavesarrivingfromthefourcornersoftheWFSarray.Finally, one Sennheiser MD421 covered theannouncer.

Duringtheirvisit,theRSHteamdecidedthattheambientHamasakisquareshouldberelocatedfromitsoriginallyplannedpositioninthesoutherntransepttotheapsisofthecentralnave,toreducetheamountofdirectsoundfrombothorgans.

2 Networkinstallation

Twoweeksbeforetheshow,theauthorarrivedattheDomearlyinthemorningtorunanopticalcabledownfromthe Vierungsturm (theintersectionspire,atthecrossingoftranseptandcentralnave)ataround70metrestotheground, which was to connect the streamservertothelaserlink.

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Illustration 4: The laser link seen from theintersectionspire.Theotherendwaslocatedto the left of the staggered facade (the Overstolzenhaus,KHMlibrarybuilding).


Ropeaccesstechniqueshadtobeusedintheuppersectiontoprovidesufficientanchoringforhighwindconditions,butrestofthecablerunwaseasilyaccessiblebystaircasesandviafixed scaffolds. With the help of Head ofScaffoldingWolfgangSchmitz,thecablewassecuredinplaceinlessthanthreehours.

Chief electrician Lothar Reinhardt hadalreadytakencareofrunningapowersupplytotheroof,andaroundnooneverythingwasready for the installation of the lasers. Theinitial setup was performed by two skilledOPTELtechnicians,andthelaserlinkwasupinlessthan4hours.Meanwhile,KHMadministratorBobO'Kanehadpatchedourfibrethroughtotheinternet.Itmaysoundabitchildish,buttheveryfirstpingfromtheDom'sgloomystoragebunkertoBerlinwasquiteanexperience!

2.1 Powerissues

However,afterhalfadayofstableperformance,thelinkdied.ChecksonthenextdayrevealedthatamediaconverterattheDomwasgettingstuckregularly.

Some quickly deployed watchdog scriptsshowed a regular outage pattern: the linkwould die in the mornings, some timebetween8and11hours, and comebackatnight,between23and3hours.

ItturnedoutthatthevoltageofthethepowergridattheDomwas218ratherthanthestandard230V,anditwoulddipsomemorewhenthe load was high. This would cause ourmedia converter (which used a cheap wallwarttypepowersupply)tochokefrequently.Finally, after one week of heroiccompensation efforts, an onboard voltageregulatorsheditsmagicsmokeanddied.

OK, time for another media converter.Luckily,thenewoneranon12Vandsowecould feed it from the 12 volts rail of theencodingPC,whoseswitchingpowersupplyhadnotroublecompensatingforthelowgridvoltage.

2.2 Botanics

Now,justoneintermittentfaultinanetworkthatweonlyhadremoteaccesstomostofthetime1wouldhavebeenwaytooeasy.Tokeeplifeinteresting,webegantoobservemysteriouspacketlossesafewdaysafterthethe power issues had been taken care of,occurring in bursts of several secondsduration.Afterrulingoutnetworkandpowerissuesonbothends(whichtookquitesometime)itwasfoundthatatreeinbetweentheKHMand theDomhad takenadvantageoftendaysofverywetweatherandthreedaysofsunshine and had been sprouting at anamazingrate.Wehadnotanticipatedthistobeaproblem,becausethetreestoodslightly

1 Onsiteaccessat theDomwasstrictly limited toworkhours,inthiscasefrom6:30hto15:30h,andwouldrequireaonehourtrainride.

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Illustration 5: Voltage measurement at theinitial testing locationof thestreamserver: the "bunker", an appendix to the southerntranseptusedasastoragecloset.


tothesideof thelaser'slineofsight,but itturnedoutthatevenalightwindwouldbendthesoftnewbranchesintotheway,sometimesoccluding the beam for more than threesecondsat a time.Obviously, this wouldbefatalforourintendedusage.Thus,itwasbacktosquareone:thelaseratthe KHMhad to be raised by at least onemetre for the beam to stay clear of thebranches.SincetheKHMlibrarybuildingwehadinstalleditonisaprotectedhistoricsite(known as the "Overstolzenhaus", formertownestate of a Colognemerchant family),there was no chance of drilling holes intowalls,sowehadtorelyonacoupleofstoneplates to weigh down our makeshift laserscaffold, made from hastily purchased60x5mmaluminumtube.OPTELshippedusapairofcrosshairscopesand some measuring equipment for properalignment via expressat a day's notice, andwegottoplaywithlasersagain.Withsometelephone support by Optel CEO RalfMagiera, the link was reestablished a fewhourslater.

2.3 Transmissiontuning

Ontheweekendbeforetheshow,theauthorwenttoBerlintorunsomefinalperformancetests with WFS cluster admin Thilo Koch.Aftersolvingsomeinitialbufferingissuesandlocal digital clocking problems, we finallyfound a dependable setup and enjoyed 24channels of uncompressed 16bit test signalstreamed live from Cologne Cathedral. Atlonglast,wewerebeginningtorelax.

Unfortunately,therewasaminorflawinourreasoning:anetworkthatperformswellonaSunday need not necessarily behave on aweekday.

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Illustration 7: One of the RME Micstasy remote controlled preamps, secured to a columnontheTriforium.Inthebackground, theHamasakiframecanbeseen.

Illustration 6: Keeping track of themicrophone setup. To the left, the YamahaDM1000 console used for monitoring andsignalrouting.


3 Rehearsalday

Onthedaybeforetheshow,theColognecrewarrived at the cathedral around10:00h. Thesoundtruckgotcaught ina traffic jam,butafter the midday prayer at 12:30, the setupworkcouldbegin.

TheRSHstudentsgotbusyrunningaMADIfibrefromthesoundtrucktofourremotecontrollableRMEMicstasymicrophonepreampswhich were placed on the Triforium (theDom'sinnerbalcony),nexttothemainorganandacrossfromtheSchwalbennest organ.Thestreamserver(whichhadsatinaclosetduring the previous testing phase) wasrelocated to the sound truck and startedtransmitting while the microphones werebroughtonlineoneaftertheother.

Aftersomelistening,thestudentsdecidedtoswapsomecapsules for narrowerdirectivitypatternstoreducetheamountofreverberationpickedupbythespotmikes.

The Dom scaffolders had rigged a radiocontrolledchainhoistforuswhichwasusedtosuspendtheHamasakisquare.Twolengths

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Illustration8:Overviewofmicrophonepositions

Illustration9:TheRSHsoundtruck.


of fishing line were then strung to theTriforiumforprecisealignment.

During the day, Frank Melchior and HansSchlossertookcareofanoverwhelmingnumberofinterviewrequestsbypress,radioandTVjournalists.Theirinitiativegavetherestofthe teamtimetoconcentrate on their work,and as a welcome side effect considerablyenrichedthemediacoveragewithsoundtechnicalexpertise.

Avideo camera with software encoder wassetupontheTriforiumtoprovideliveimagingtotheremoteaudienceinBerlin.

At17:00hours,theBerlincrewfinallyhadaccess to the WFS auditorium (it had beenblockedbyregular lecturesduringtheday),andbegansettingupthereceivingmachine.After somedigital clockingissueshadbeenresolved,thefirsttestsignalswereroutedtotheWFSarray.

3.1 Networkproblems

Wequicklyfoundthatthetransmissionquality was abysmal, with at least onedropoutper second in oneof thechannels, andfrequent losses of connection. The level ofrelaxationdroppedaccordingly.Measurementsfromseveralremotenetworksestablished that contrary to all expectations,thelaserwasbyfarthefastestandmostreliablelinkinthetransmissionchain, andthatUDPpacket losses on the order of 1020%appearedtooccuronthecampusnetworkinBerlin.Itwasdecidedtogetateamtogethertocreateadedicatedlinktothereceivingmachinethatwould circumvent possible bottlenecks, butsinceit requiredthecooperationofnetworkoperationspeopleattheTU,itbecameclearthatthiscouldonlyhappenthenextmorning.Atthesametime,wefoundoutthehardway

that all the little knobs that our softwareprovidedtodealwithnetworkproblems(inputbuffering, redundant encoding, outputbuffering),eitherdidnothaveanysignificanteffectorwerenotworkingatallatthehighchannelcountswewereusing.Thus, the organ rehearsal which began at20:00h could not be used to optimize theWFSrenderingandwasinsteadspentdebuggingnetworkissues,whichunfortunatelyremainedunresolved.Ataround23:00h,theRSHcrewlefttheColognesiteafterhavingtakenanumberofimpulseresponsesfromthecathedral,whiletheauthorstayedbehindinthesoundtrucktryingtocomeupwithaplanB.

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Illustration 10: Detail of the Hamasaki square,withoneofthehorizontalfiguresofeight (a Sennheiser MKH 800). The arraywassuspendedinthecentralnaveclosetotheapsis,ataheightofaround20metres.


4 Showtime

Workresumedat09:00hthenextmorning.WhiletheBerlinteamwerehopingforaresponsefromcampusnetworkoperations,theauthor set up a 16 channel OggVorbis encoderwith160kbit/spersignalasanalternativetransmissionsystem,inthehopethatitsHTTPbasedtransportlayerwouldbeabletocompensateforpacketlossesatthecostofincreasedlatency(whichdidnotmatterforourintendedapplication).TheVorbisstreamwasrelayedviaanoffsiteIcecastserverthathadoriginallybeenintendedtoserveastereoonlystreamoveraseparateDSLlineasafallback

solutionincasethemainuplinkwentdown.

At this point, wehad one 24channel PCMstreamandone16channelVorbisstreamgoingout,butbothcouldnotbereceivedproperlyat theTUend: thePCMstreamduetocontinuingnetworkproblems,andtheVorbisone due to problems with multichannelsupport in the decoders weused. AspecialteamwasdispatchedinBerlintoworkonasolution. Finally, CCRMA wizard FernandoPabloLopezLezcano,thenguestprofessorattheTU,cametotherescueandfoundareliable way to decode the 16 channel Vorbisstream, using his private laptop to save theshow.

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Illustration11:Duringtheconcert.Viewfromthetriforiuminthesouthernpartofthetransept.The videoscreensaroundthealtardisplaytextualcommentstoeachmovement, as intendedbythe composer.


Intheearlyafternoon,wehadadependablelinkatlonglast.TheeveningmasswastransmittedasatestcaseandusedbytheWFSoperatorstoalignthevirtualsourcesinBerlin.Unfortunately,notallorganworkswereinuseduringthemass,sothelastfewsourceshadtobefinetunedafterthebeginningoftheconcert.

The concert itself was transmitted withoutmajorproblems,althoughwehadthreedropouts, oneduring the introductoryaddress, averyunfortunateoneinthemiddleoftheperformanceandoneduringthefinalapplause.WelatertracedthemtoaconfigurationerroroftheIcecaststreamserver.Ithadbeenoptimizedforuseasatwochannelfallback,anditsclientbuffer(i.e.itsleniencetowardsclockdriftornetworkissuesontheclientside)hadnot been increased to allow for the higherchannel count. Effectively, this resulted inonly a fewseconds of drift tolerance, afterwhichtheclientwouldbekickedoff.

Unfortunately,thenatureoftheproblemwasnotimmediatelyrecognized,andwewronglydecided to bring down the video stream torule out networkcongestionas a reason forthedropouts. Fortunately,thevideoservicecould be reestablished quickly after theBerlincrewhadriggedadedicatedwirelesslink.

Aftertheshow,theRSHcrewbegantoteardowntheequipment. As soon as thepublichadleftthevenue,theHamasakisquarewasbrought down and dismantled. Meanwhile,the recordings (which amounted to around24GB)wereuploadedtoabackuplocationattheKHMviathelaserlink,forlaterresearchanpossiblyanotherpublicreplayontheWFSarrayinBerlin.Forsafetyreasons,theauthordecidedtopostponethetheropeworkontherooftothefollowingday,tobetackledafteragoodnight'ssleep.

Thedayaftertheshow,thefibretothespirewasreeledin,thelasersweretakendownandshippedbacktoOPTELandvariouspiecesofborrowed computing equipment were returned.At18:00hours,theworkinColognewascompleted.

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Illustration13:Teardownaftertheshow.

Illustration 12:DomorganistProf.Winfried Bnigattheconsoleofthemainorgan,which also provides access to all stops of theSchwalbennestorgel. In the foreground, part theorgan'sRckpositivisvisible.


5 Conclusion

SincetheBerlinaudiencehadbeenprimedastothehighlyexperimentalnatureofthewholeundertakingandthetechnical challengesinvolved,thebriefoutagesduringtheperformancewerereceivedsympathetically.Thesonicresultwasgenerallywellappreciatedandenjoyedby theconcert attendants in theWFSauditorium, although the material itselfprovedchallengingforpartsoftheaudienceonbothsides.

ThedifferentpartiesinvolvedintheColognesideof theproductioncooperatedextremelywell, andsimilarfutureundertakingscanbeexpected to be met with continued interestandsupport.

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6 Appendix

6.1 Credits

Specialthanks(inalphabeticalorder)to:

Juan-Pablo Caceres,composer,JackTripcodeveloperandlectureratCCRMA,forlotsofonlinesupport(evenwhilehewasonvacation)

Karl Heyes, Icecast/IceS developer, forremotesupportinsettingupa16channelVorbisencoder

Bob O'Kane,KHMnetworkadministrator,forbeingreallyhelpfulatreallyshortnotice, networksupportandlotsof littlehardwaregadgetstosavetheday

Ralf Magiera at OPTEL, Hamburg, forprovidingthelaserhardware,andfortheirenthusiasticsupport

Wolfgang Schmitz,headscaffolderattheDombauhtte,andhisteam,forhelpingtorunthefibrelinkdownthespire,andforproviding a chain hoist for the ambientmicrophonearray

Prof. Dr. Barbara Schock-Werner,MasterBuilderofCologneCathedral,forhergenerousandprofessionalsupport

Dr.-Ing. Thomas Schumacher, architectattheDombauverwaltung,forinterestinginsightsandlotsofovertimeonourbehalf

Lothar Reinhardt, head electrician(Dombauhtte), and his team, for powersupplyandcountlesslittlefavors

Martin Rumori, research associate atKHM, for organisational support and ahelpinghandintightsituations

6.1.1 ProjectPartners:

Dommusik, the musical department ofCologneCathedral

Institut fr Audiokommunikation atTechnischeUniversittBerlin

Institut fr Musik und Medien at theRobertSchumann Hochschule (RSH),Dsseldorf

Kunsthochschule fr Medien (KHM),Kln

OPTEL Optical Communication, Hamburg

CITIZEN MEDIA, collaborative researchproject(http://istcitizenmedia.net)

ohrenstrand.net, das Berliner Klangstrandbad(http://www.ohrenstrand.net)

Inventionen musicfestival,Berlin(http://www.inventionen.de/)

5th Sound and Music Computing Con-ference (SMC08), Berlin (http://www.smc08.org/)

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6.1.2 CrewKln

Dipl.-Ing. Frank Melchior, FraunhoferInstitut Digitale MedientechnologieIDMT:wavefieldsynthesisconsulting

Jrn Nettingsmeier, freelance eventengineer: executive producer in Kln,networking and stream supervision,riggingandropeaccess.

Tonmeister Hans Schlosser, assistantprofessor at RSH: lead sound engineerandrecordingsupervisor

StudentsofSoundandVideoEngineeringatRSH:

Simon Hildenbrand:remotepreampandHDrecordingoperator

Katrin Krber: microphones, cabling,photodocumentation

Jindrich Maner:microphones,cabling

Benjamin Simon:microphones,cabling

Simon Spillner:cabling,cameraoperator,soundtruckdriver

Josuel Theegarten:microphones,cabling

Michal Zllner:soundtruckoperator

6.1.3 CrewBerlin

Andr Bartetzki: AssistantWFSsoundoperator

Thilo Koch, research associate: WFSclusteradministrator,networkengineer

Andreas Lehmann:networksupport

Prof. Fernando Pablo Lopez-Lezcano:streamingsupervision

Eddie Mond, research associate: WFSdecodingsupervisor

Wilm Thoben, research associate: coordination

Tonmeister Prof. Dr. Stefan Weinzierl:Project supervisor and WFS soundoperator

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6.2 Technicalinformation

6.2.1 Domnetwork

ThelocalnetworkattheDomconsistedofa100Mbit/sEthernetswitchinthesoundtruck,whoseuplinkwasconnectedto thelaseronthe spire via a media converter and 150metresoffibre.Weuseda4wayfibrecabledrumbyALVAAudio(marketedasaMADIcable),withtwoliveandtwodarkfibresforbackup.Withitslight weight andveryruggedsheath, it waswellsuitedtothejob;aftertwoweeksintheopen, it showed no UV damage or strainmarksfromwindloadandwaseasytohandle.Theinstallationwasdonefromtoptobottomwith the drum slowly unwinding as it wasabseiled to the ground. This mode ofinstallationwaschosentoreducethestrainofpulling the fibre over a significant length. Inplaceswherethefibrehadtoberunoversharp edges, pieces of rubber hose cutlengthwise were slipped over it for extraprotection.Thecablewasanchoredevery2to5metreswithelasticstraps.Thankstotheopticalconnection,wedidnothavetoworryabouthumandsignaldegrada

tionor takesafetyprecautionsagainst lightning.

ThelaserlinkcomprisedtwoOpticomFDDunits(byOPTEL),witharawbandwidthof155Mbit/s.Itisfullytransparentandbehavesjustlikeanyother100BaseFXsegment.Endtoendping times were on the order of 0.2msec, and even at 95Mbit/s load, packetlosseswerewell below0.01%undernormalweatherconditions.On the KHM side, the laser was patchedthroughtoaLinuxNATrouterwhichwasinturnsittingontheCitizenMediagigabitbackbone.After another 4 hops, the data entered theDFN XWIN (german scientific backbone)andwasfinallytransmittedtoBerlin.

6.3 Software

Boththetransmittingandreceivingmachineswere Linux systems with fully preemptivekernels (using thecurrent realtimepatches).Sound routing was handled by JACK(http://jackaudio.org)

The original plan was to use JackTrip(http://ccrma.stanford.edu/groups/soundwire/s

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Illustration 15:Thecomponentsofthelaser link,readytobeshippedbackaftertheshow.

Illustration 14: cable drop from theintersection spire, with rubber edgeprotection.


oftware/jacktrip/)atrevision147,sinceProf.Weinzierl's institutehadusedit forprevioussmallerprojectswithverygoodresults.

JackTripallowsforredundanttransmissionofaudio packets. Unfortunately, this is accomplishedbygroupingseveralaudiochunksintosingleUDPpackets.Forinstance,atredundancylevel3,audiochunkswouldbetransmitted in groups of three as [1,2,3], [2,3,4],[3,4,5],[5,6,7]etc.,increasingpacketsizebya factor of three. Thus at 24 channels, theMTU limit will effectively preventredundancylevelshigherthan1.

WehadbrieflytoyedwithTCPtunnelingtosecure the transmission against packet loss,butdecidednottofollowthatpath, becauselistening tests had shown that the dropoutsfromoccasionalpacketlosses(veryrareduringourtests)weregenerallynotaudibleoratleastunobtrusive,andtheTCPtunnelingsoftwareweusedwasquiteoldandfragile.

Todealwithoutoforderpackets(averyfrequentphenomenonwhenstreamingUDPoverpublic networks with redundant routes), weused very large input buffers to give thedecoder timeto rearrangethedata before itwasactuallyneeded.

As described above, the network conditionsontherehearsalandshowdayspreventedusfromusingJackTrip. TheJackTripauthoriscurrentlyworkingonTCPsupportthatshouldhelpalleviatesuchproblems.JackTripdevelopmenthasbeenmadepublicasofAug1420082.

ThefallbacksolutionwasimplementedusingthecurrentIcecaststreamserverrelease3 and

2 Projectpageishttp://sourceforge.net/projects/jacktrip/.

3 Version2.3.1,http://www.icecast.org)

a customversion of the IceSstreamsourcemaintained by Karl Heyes4, which includesJACKsupport.

The decoding was done with MPlayer, itsALSA backend directly feeding an RMEHDSP/Multiface.Forsomereason,wecouldnotfindaJACKifiedplayer thatwouldcorrectly handle multichannel Vorbis streamsandopenthecorrectnumberofJACKports.Itappearsthatmostimplementationssilentlyassumetwochanneluse.

In thenearfuture,bothJackTripandrecentnetjack developments will be viablealternativestotheVorbisencodedstreamsweused,ifsufficientbandwidthisavailableandtheir redundancy and buffering schemesperformasdesigned.

Multichannel Vorbis is a very useful tooltoday,andthespecificationappearstoallowfor up to 256 discrete channels. However,clients supporting multichannel streams arestill somewhat scarce and clients should becloselyevaluatedbeforeproductionuse.

4 http://svn.xiph.org/icecast/branches/kh/ices

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6.4 References

6.4.1 Relatedpublications

Hans Schlosser, Frank Melchior, JrnNettingsmeier, Stefan Weinzierl,Mer lossedr Dom en Klle Weltpremiere einerWellenfeldsynthese Livebertragung.Workshopat VDTInternationalConvention,Leipzig2008.http://stackingdwarves.net/public_stuff/linux_audio/tmt08/Workshop_TMT08.pdf

6.4.2 Images

Illustrations 1,36, 9, 1315 by the author;1112 by Frank Melchior; 2, 7 and 10 byKatrin Krber;8byMichaelZllner,basedon a floor plan provided by the Dombauverwaltung.Usedwithpermission.

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1 Planning1.1 Microphone distribution

2 Network installation2.1 Power issues2.2 Botanics2.3 Transmission tuning

3 Rehearsal day3.1 Network problems

4 Show time5 Conclusion6 Appendix6.1 Credits6.1.1 Project Partners:6.1.2 Crew Kln6.1.3 Crew Berlin

6.2 Technical information6.2.1 Dom network

6.3 Software6.4 References6.4.1 Related publications6.4.2 Images

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