PlaySoundGround: An Interactive Musical Playground Michael St. Clair

Drama/Stanford University551 Serra Mall

Stanford, CA94305michael.a.stclair@gmail.com

Sasha LeitmanCCRMA/Stanford University

660 Lomita Ct.Stanford, CA 94305

sleitman@ccrma.stanford.edu

Abstract We describe a novel transformation of a playground -merry-go-round, teeter-totter (also referred to as a see-saw), swings, and climbing structure – from its traditionalpurpose to a collaborative and interactive musicalperformance system by equipping key structures withsensors that communicate with a computer. A set of Max/MSP patches translate the physical gestures of playgroundplay into a variety of performer-selected musicalmappings. In addition to the electro-acoustic interactivity,the climbing structure incorporates acoustic musicalinstruments.

Keywords: Real-time, Music, Playground, Interactive,Installation, Radical Collaboration, Play.

1. OverviewThe PlaySoundGround is a functioning playground (scaledto adult size) that produces musical sound whenparticipants play on and with the equipment. It is, as such,also a musical instrument that allows participants toexplore musical interaction and the creation and control ofmusical gestures by learning the musical mappings of theplay structures. As they learn the device's musicalresponses to their play, they can alter the quality of theirplay to produce desired musical effects.

The basic premise of the PlaySoundGround is that the“play” children perform in a playground and the “playing”of music share the property of creative interaction withinstructural, physical and technological constraints.Furthermore, both concepts of 'play' employ a set ofunwritten implicit social rules. The PlaySoundGroundmakes these connections explicit by endowingrecognizable, functional playground equipment with thepower to generate musical sound, extending rehearsed,

playful physical motions into the realm of artisticexpression. In doing so, it also opens up new territories forinstrument design and interactive audio art, acting as amusical instrument controlled by broad kinesthetic motionrather than fine motor movements.

Figure 1. Collaborators enjoying the merry-go-round andteeter-totter

2. DescriptionThe PlaySoundGround consists of three pieces of furniture– a merry-go-round, a teeter totter and a pair of swingsappending from a large climbing structure. Thedimensions of the play structures were scaled such that therelation between the size of the play furniture and the adult

Figure 2. Playground installed at the Burning Man ArtFestival.

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users was approximately the same as the relation betweenthe size of a children's playground and a child.

The PlaySoundGround was first installed at the BurningMan Arts Festival outside of Gerlach, Nevada. BurningMan is a one week art festival and cultural adventurewhere approximately 40,000 participants gather in atemporary city. The festival was founded by a loosegathering of artists and pranksters who envisioned aTemporary Autonomous Zone [1] free of the rules andcommerce of contemporary society. With the exceptionof a small number of arts grants and limited safetyregulations, there is no institutional control of the workthat is shared at Burning Man.

With the help of a large number of volunteers, wedesigned and built the playground using the followingmethods and materials. The merry-go-round base is madeout of a car wheel bearing. A web of square tubing andangle iron are welded to the matching wheel hub and awooden platform is bolted to the top. Hall Effect sensorsand rare earth magnets attached to the inside of the huband bearing measure the direction and speed of rotation.

The teeter totter is constructed from a 16' salvagedaluminum truck ramp. In the center of the ramp, a 1.5"steel rod is mounted to a trapezoidal fulcrum using twopillow block bearings. A Nintendo Wii Remote attached tothe side of the ramp near the fulcrum providesaccelerometer data. The swing structure is schedule-40pipe connected by specialized fittings designed forplayground structures. Removable Kee Klamps are usedto connect the swing structure to the wooden climbingstructure. A potentiometer coupled to the top of eachswing chain measures the placement, speed and directionof the swing seat. The climbing structure is a multi-tieredplatform structure designed for climbing and playing. Itsupports, and is supported by, the swings. These choicesof construction material made each piece of playgroundfurniture portable and easy to disassemble.

Figure 3. Acoustic instrument designed by students.The climbing structure contains a number of acoustic

instruments designed by the students of Jonathan Berger'sTechnology and Art Class. The class was designed toengage the students in a radical collaboration where theyworked together to determine how many instrumentswould be built, the relation of the instruments to oneanother, and the relation of the instruments to the 2008

Burning Man theme, the American Dream. They chose touse the instruments to tell a history of the American Dreamthrough American material culture. The first level of thestructure contained instruments made of wood and glass –scratched gourds burned with buffalo designs on one sideand a set of bellows that blow air over the lips of large jugson the other side. The second level contained percussioninstruments built out of metal and housed in two concavesheet metal enclosures. The third level used plasticmaterials – rain sticks made out of pink flamingo lawnornaments and PVC pipes pitched in complimentary bluesscales struck on the top of the pipe with a flip-flop shoe.

Besides their interesting and event-appropriate visualaesthetics, these instruments granted the PlaySoundGrounda variety of additional capabilities. They increased thenumber of users that could play at once; they added arelatively sedentary mode of activity to the higher-energymodes of activity already available; they allowed users togather in more physically intimate and immediate groups(as opposed to the furniture, which was broadly spaced outfor safety's sake); and they gave users an additionalchannel of musical engagement with the amplified audioproduced by the furniture.

3. Sound ProcessingData from sensors embedded in the play structures isprocessed and interpreted in a Max/MSP patch. AnArduino prototyping platform is used to acquire data fromthe Hall effect sensors and potentiometers, while the WiiRemote communicates directly with Max/MSP viaBluetooth and is interpreted using Masayuki Akamatsu'saka.wiiremote object [2]. The Max/MSP patches run on aMac Mini, which, at Burning Man, was housed in a smallrefrigerator to protect it from the dust and heat of a desertenvironment.

Sound processing of the sensor data is also performed inMax/MSP. Audio is sent to four speakers located aroundeach piece of furniture. Generally, this audio is spatializedin relation to the movements of the users on the furniture(often applying a stereo image based on some arbitraryreference point). The speakers were constructed fromsalvaged car stereo speaker elements mounted in woodenbox enclosures, steel trash cans, and 55-gallon plasticdrums for the merry-go-round, teeter-totter, and swingsrespectively.

This audio is generated according to one of fiveselectable modes of musico-kinetic mapping. All of thesemappings have sub-settings that alter a variety ofparameters. The mappings are:

1. A simple additive synthesis system that producescomplex, organ-like chords. The melodic sequences itproduces are pseudo-random, based on one of severalMarkov chains that control transitions between pre-established pitches. The kinetic focus is on speed of

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motion and frequency of event. The users' motions triggerthe incident tones, thus controlling the melody's rhythm;their speed also alters the tones' timbres.

2. A granular synthesis system that manipulatessamples from a wide variety of popular music intocomplex sound textures or altered versions of the originalmusic. Depending on the setting, the general kinetic focusmay be on particular position, speed of motion, orfrequency of events; users' motions may controlparameters ranging from grain pitch to volume to thedensity of sound textures.

3. A system that produces sounds based on four sorts ofenvironmental noise : fire, water, electricity, and wind.The kinetic focus is on speed and position. Using acombination of spatialization, filtering techniques, andtriggered samples, these sounds change in natural-sounding ways with the users' movements; water pours andthen splashes at extrema, electricity zaps, and so on.

4. A simple sampler that, depending on its setting, usesthe players' movements to trigger either notes in a varietyof scales, percussive environmental noises, or loopedmechanical sounds. The kinetic focus is on positioningand the sequentiality of movement.

5. A "scratcher" that uses the movement of theinstrument like a virtual tape head or phonograph needle,rapidly advancing or reversing a recorded sample as usersplay.

4. Performance PracticeThe vast majority of musical interfaces, both traditionaland contemporary, are designed to be responsive to finemotor control. With few exceptions (large bells and drums,for example) musical gesture is generated and shaped byrelatively subtle oral or tactile manipulation. Recently, agrowing number of interfaces, particularly for motion-tracking of dancers [3]– have generated sound fromrelatively gross kinetic input. The vast majority of theseinstruments, from gloves to motion-capture arrays, areessentially sensor rigs for the human body rather thanphysical objects with meaningful presences in space [4].They allow free movement and provide guidance to theuser only through aural feedback.

By contrast, musically-enabled playground equipmentprovides users with a powerful set of readily-intelligiblemechanical constraints on their movement. Swings, teeter-totters, and merry-go-rounds all work to restrict the rangeof human motion to a well-defined arc through space. Aninstrument that is tangible and provides tactile feedbackhas many advantages: increased capacity for precisecontrol and virtuosity, the possibility of rational mappingsbetween gestures and output, increased legibility of therelationships between gestures and musical outputs, andperhaps the satisfaction of interacting with a device. ThePlaySoundGround provided all of these besides thedevelopment of precision and virtuosity, a quality that

does not easily mesh with gross motor input: whileextremely precise control of global coordination iscertainly possible, it is difficult.

Moreover, because of the ubiquity of playgrounds inprimary education, virtually all of our target audience cameequipped with a carefully-rehearsed (if perhaps only half-remembered) lexicon of gestures for interacting with ourequipment. In other words, they knew how to operate theinstruments before they ever saw them. This, inconjunction with the participatory conventions associatedwith playgrounds, enabled our users to immediately enjoyengaging and pleasurable musico-kinetic experiences.

Our desire to facilitate their ability to rapidly gainfacility with the PlaySoundGround strongly influenced ourcompositional choices. We preferred easy-to-understandmappings between musical events and meaningful motorevents on the furniture. For instance, on the teeter-totter: amapping between upwards motion and a rising scale, amapping between height and the rate of audio graingeneration, a completed “teeter” motion and the generationof a chord. However, the desire to make the mappingslegible didn't mean that we made the audio outputsimplistic. Different settings varied the degree of controlover the resultant musical output given to the performers,the composers, and randomness. As with many play forms[5], a pleasant degree of randomness added a great deal ofspice to some of our compositions: among our mostsuccessful (as determined by informal user response) wasour patch that generated chords triggered by completedmotions (teeters, rotations, swings), with variable timbrebased on motion velocity, with pseudo-random melodiesbased on preprogrammed Markov chains.

5. User ExperienceThe PlaySoundGround also works as a novel andsurprising environment. It does so through one primarymechanism with several elements: the making-unfamiliarof previously familiar objects through repurposing oraugmentation.

First, much of the PlaySoundGround is constructedfrom junk and scrap. It turns half-recognizable elementslike loading ramps and truck bearings into entirely newobjects. In this respect, it sits in a long tradition ofinstruments and installations that rely on a junk-construction aesthetic -- most immediately, Harry Partch'swork, previous NIME work [6] and the environs of BlackRock City itself. [7]

This repurposed-and-recycled constructionmethodology provided a foundation for a higher-leveldefamiliarizing aspect of the PlaySoundGround: itsaugmentation of familiar objects with new capacities. Itdoes not contain mysterious new objects constructed fromjunk, like Partch's plantlike fantasias; it contains friendly,recognizable structures. Moreover, the fashion in which itaugments the capacities of these objects, unlike many

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methods of musical instrument augmentation, [8] does notrely on the addition of new control surfaces. Instead, itadds new functionality to the existing control surfaces ofits furniture. These new functions serve as a set of newand hidden ways of being used that, while perhaps easyand natural, are not part of the furniture's conventional usesand are not telegraphed by some added surface or marking.

There is a relationship between this stealthyenhancement of usable objects and the notion of ubiquitouscomputing [9]. The PlaySoundGround's technologicalaugmentations, however, do not add entirely new methodsof using its furniture: for instance, one may not blow onthe teeter-totter to check one's email. Instead, it enhancesthe existing lexicon of functional gestures towards theirexisting purpose. It couples musical play to the motions ofphysical play to enhance the fun of play. It gives auditoryfeedback that might influence the qualities of thesegestures, but does not alter their fundamental form.

The ease of use, inviting nature, and safely transgressivequalities of the PlaySoundGround formed a coherentperformance modality, which proved infectious, spreadingto users' interactions with the acoustic instrumentsincluded in the structure. These also had hiddencapabilities, but of a slightly different type -- one does notnormally use fire bellows to create music, for instance.However, the hidden, playful augmentations in thefurniture led users to see every object in the space as aproper instrument for musical play -- even, to our chagrin,those that weren't, like our speakers, which became drumsone too many times for their liking.

6. Performance EthicThis interface relies on a relational ethic of radicalaudience participation -- audience participation so radicalthat there is no particular boundary between performersand audience members. The PlaySoundGround should beconsidered a performance space as much as a device formusical performance – both an installation and aninstrument. As such, its capacity to serve as a fully-functional playground even apart from its musicalfunctionality made this ethic immediately and intuitivelyperceptible to our users. Playgrounds are not spaces for alarge number of people to watch a single performer orsmall group of performers demonstrate their virtuosity;they are spaces for lots of people to play in all at once.Their fundamental conventions as performance spacesdemand user participation.

We worked to manifest this ethic through theconstruction process and the presentation venue as well asthe final product. The installation was constructed by alarge team of volunteers, who brought a wide array ofskills and interests to bear on the labor and were invited toparticipate in every aspect of the work. And Burning Manwas a natural choice for the presentation of a piece of thisnature: one of the central elements of the event is an ethic

of radical participation and collaboration, ensuring anaudience ready to participate in the spirit of theinstallation.

7. ConclusionThe design process was influenced by historcical andpsychological studies of play as well as by studies in gamedesign. We were inspired by philosophical discourse onplay as a phenomenon, and a few brief instances of thisinfluence are worth citing. Johan Huizinga's classicdescription of play as a generalized cultural process thatmanifests itself in a wide variety of contexts influenced ourfeeling that musical play and kinetic play were similar andcould be made simultaneous. This was enhanced byRichard Schechner's description of play as a mode ofperformance, much like theater, dance, and music, which,along with the contributions of game design scholars likeKatie Salen, led us to conceive the PlaySoundGround notsimply as an instrument, but as a performance spacedesigned to help its user-performers actively create certainkinds of experiences. Finally, Brian Sutton-Smith'sunderstanding of play as an ambiguous phenomenon thatresists being closely defined by rhetorics or forced toconform to a particular purpose lent force to our decisionto make our playground's goal entertaining aestheticexperience rather than teaching or developmental growth.

The integration of musical performance and recreationalplay in a ubiquitous and familiar performance interfacesuch as a playground provided a novel musicalenvironment that enables collaborative and socialinteraction to create music.

References[1] H. Bey, Temporary Autonomous Zone, Brooklyn, New York:

Autonomedia, 1991.[2] http://www.iamas.ac.jp/~aka/max/#aka_wiiremote[3] A Källblad, A. Friberg, K. Svensson, and E. Edelholm.

“Hoppsa Universum – An interactive dance installation forchildren,” in Proc. of the Conf. on New Instruments forMusical Expression (NIME), 2005, pp. 128 – 131.

[4] http://www.sensorband.com/[5] K. Salen and E. Zimmerman, Rules of Play, Cambridge,

Massachusetts: MIT Press, 2003.[6] K Moriwaki, J. Bruker-Cohen. “MIDI Scrapyard Challenge

Workshops,” in n Proc. of the Conf. on New Instruments forMusical Expression (NIME), 2008, pp. 168 – 171.

[7] D. Pendell, Inspired Madness, Berkeley, California: FrogBooks, 2006.

[8] S. Schiesser and C. Traube, "On making and playing anelectronically augmented saxophone," in Proc. of the Conf.on New Instruments for Musical Expression (NIME), 2006,pp. 308-313.

[9] R. Gold “This is not a pipe,” in Association of ComputingMachinery (ACM), 2006, pp. 72. 1993

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