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Page 00000001 The Metabone: An interactive sensory control mechanism for virtuoso trombone Mark A Bromwich Department of Misic, The Univesity of H-ddersfield, UK. smusmab @hud. ac.uk Abstract The aim of he lpoject was U crete a campletely new instrument aid peformance avironment tlang as a stating point the dynamics aid d arateristics f the trombone Custom designed proximity sensors were employed, augmented by cammercially produced transducers. These sensors were built into the performance space sa that the instrumentalist could affect various sound transformation parameters by using a modified irombone slide aid a custom designed anechoic mute. The first performance df the resulting dectro-acoustic piece entitled Zero in the Bone was gven by the Trombonist B ary Vbb hi April 1997 as part of he University ff Huddersfield's Electric Spring programme. 1 Background The Metabone poj ect is a continuation of theauthors fsearch into interactive perfomance avironments and eactive sound installations which has both explored sensitised heatfical peffomanne spaes (1), md interactive soundsculpture(2). 2 Instrument mechanics It was of paramount inportance that absolutely m a oustic sound emitted from he tlimbone vas leaked into the pefomannce spae. The ecdusion cf the integral acoustic cf the instrument presented a hallenge ) the pirfoiner h tha b hadt o e-lean and e-sensitize himself aurally aid kinaethetically to vhat s findamentally anew hstrument and perfonmance pae. detection by t he sensor dements 2 duminium flates measuiing 250 X 120mm were affixed ) the cnd of he trombone slide, these flaes were cnstlucted from mateial only 5 thousanths of an inch hfickness. I was fbund that using heavier gauge rmtefial nide e instrument inpossible to play due to he tombone slide bending a fill ectension. A small 50 X 50 mm xindowwas cat entrally h ihe light hand plate to allow the performer to see a laser!pot cn he inside cf the aij acent plate EBach iiae was coaed With athin layer of xtuied enanel which was equiied ) achieve reliable detection. The Polaroid ultrasonic sensois behave as specular reflectors in that hey cb mt reliably detect suafaces which ae smooth with espect u the avdelength of the ultrasonic wave This only occuts whvn hen he eflcting surface is positioned dft axis to the ultrasonic beam resulting in the beanm being reflected a an angle avay fom he source. As i is lmost impossible to achieve a ight aigle surface fom a moving trombone slide a solution was ) paint e plates wNth he textued enamel ceating a difuse surfae ensuring eliable detection. It was extremely inportant that he perfrmer had otal freedom ofmovement to interact WNthin he sensor dements so a ndio microphone ws used to transmit the amustic signal to the sound processors. The only wie attached 1) the pirfoiner was a thin headphone feed suspended from above he pefomner. 3 Implementation The cntrol voltagesfiomthe sensor dements were cannected to 2 Midi Ciretos' -multichannel analogue ) nidi cnveitors (Fig 2). Each convertor was progranmed to output only the midi controller infmnation required for teal time control Cf he SE70 digital effect units. These controller assignments wee stored in 2 IEPROM ards vhich were required 1) hold the necessay controllerinformation. Fig. 1 A custom;echoic mute was &signed and hbilt which consisted of a high dnsity polypropylene cone into vhich was inserted a 120mm ieae of aoustic dbsorbtion foam, his absorber was required rrninimise campression effects that were foundto oaur using a conventional mute(Fig 1). A Shuie radio instrument microphonewas embedded into the acoustic fxim, the rAble exiting a small holein te body ofthe mute - his hlle dso sived 1 d low aminimum ofexplessed air out of the mute. To ensue accurate orientation and
Page 00000002 C2 c A RlLlui A scý 1 R2 ij R2U2 A^ L2 The m idi antroller information wis fed I the sund processors via a nidi wantrolled router which in turn wis switched ly the host computer. Opcode's Studio Vision Pro was chosen to storethe necessary program change information and also o ste pie cmposed electroacoustic sDundfiles - used as carierinfonmation fcr thevocoder pitches used h the piece Audio synchronisation cues were also stoied as digital aidio soundfiles fed to the peformer via a Iuadphone system, timing ihformation wes given t heperformer in the form of a midi dick track. The pogrann dso held isible cueing infoimation in the frm f simple mte ai/off messages connected to a midi to light interfce feding ligh rightness LED's mounted in the sensor dements. A snall powered HeNe laser assists t Ie performer to establish physical orientation within the performance space The laser system was used nh cnjunction with he Ultrasonic aensois ensuring that the perfoiner entered, moved aid exited the Utrasonic beams cleanly and acuratey, the inglebeam being plit into 2 via a system cf miror eflectors to hdicate the 2 sansor paths. 2 X 110mm Acoutistile dbsorbeis weie mnunted 3 metres avay, diiectly oppositethe dtrasonictransduces (each transducer operating at the same frequency of 30 lHz ) his stopped the ultrasonic beams from flecting aound he perfoimane spae and interacting with ach ether. A way was needed to emiotely switch input souices to he SE70 processors from the various console auxiliay outputs. A solution was to connect he live trombone agnal 1 3 channels of the MM1 console,as he auxiliay sends ae muted with the channel nutes then paches could be d&signed t ahieve the input routing without using a d dicated aidio switcher. Stereo outputs from he 2 effect processors vere outed to he MM1's direct channeloutputs at he required time by sending program change messages u nute heredundant channels. 3.1 Sensor Elements
Page 00000003 Eements with a wide range dc p oximity dtection weie iequited to gve he performer differing degies cf sensitivity for t Ie various sections cf the iec. Tihese wewe: 2 MidiSensors, capacitive sensors, wae used with a detection range of between 0 ad 100mm fig 3). 2 M\di Cestute,ultranonic sensors, with a range of between 1 aid 3 meters gave the largest dtection nange. The Mdi Gstues cb mt hold their sensing voltages when exiting the ultraonic beams so a positional dtector and a smple aid hold mechanism was designed and uilt to fcilitate he this voltage nuncry iequitement.An infraed photoreflective switch vas employed, mounted adjaunt to eich dtrasonic sensor, iis switch detection was used Irigger he simple and hlld dicuitiy. The HeNe hser was nunted centrally between he dtasonic and hfimred detectors (Fig 4) 2 Radio Shack metal chectors were customisedto gve a medium sensingrange cf proximity detection (Fig 3). Modifications wete required to wnvert the pulse width frequency cutput cf hemetal dtectorcircuitry to the 0- 3.2V output voltage required, frthe Midi Creators. A frequency to voltageconvertorcircuit ws designed aidbuilt 1 give a Inear sonsing ange ofbetween 10 aid400mm 3.2 Computer system Macintosh Quada 650 c/w 24Mb nam,500Mb ID and Digidesign Audiomedia 2 mith Qpcode Studiovision po V.3. 1 softwae. 3.3 AudioSystem 2 Roland SE70 dgital nulti efects modules, Tascan MNMI mixing console mith Mdi nuting. Soundca# sKeies 20OB mixing console,Alice MicPak preamplifier, Iawmer L251 Spectral cmpressor. 3.4 Midi system Opcode Studio 3intefae Akai IE3OP midi routAer 2 Mdi Creators - 14 dunnel malogue to nidi interfce dw 2 EEPROM caids holding the 8 dannels of nidi cntroller data, Peavey PC1600 Mdi ContIoller, M\diLight-8 dmnel midi to light interface Midibalanced line transmitted dctver. Fig. 4 4 Conclusions The combintion of Wkabone and VtFa-environment poved to bea poweifully expiessive medium in wvhichthe perfomer was both adullenged, in trms Cf the d giee Cf hysical sdill required, and nancipated by the bhad xirtuoso qualities thA the e nvironment offed. CGnent eseach hto he implementation of radio ad infrared Iransmission/ecption systems will povide ageter dgiee dC jhysicalfrieedom fr the instrumentalist, and htanish mnuch Cf he abling fom he peifomnane cnvironment. Refeences  Bromwich, Maik. "AS hgle performier Connolled Interfae for Electronic DancolMusicTheare". In proceedings of he 1995 hternational Computer hMsic Confeence, San Fransisco:Computer Music Association 1995  Bromwich, Maik, "An Interutive Sound Sclptue f4or theVisually I mpaiwed" h Ensemble Research proceedings 1996, University Cf Yok The sculptuie 'A Passage to Indid' is in the pemanent collection of Wakefield City Art Cillety, Wakefield,England Fig. 3