Page  00000001 THE BALLANCER - GESTURALLY CONTROLLED PHYSICS-BASED SOUND Matthias Rath Universita di Padova Department of Information Engineering rath@dei.unipd.it ABSTRACT Hands-on demonstration of the Ballancer, a tangible audio-visual "game" and experimental platform, that exemplifies gestural realtime control of a physically-based sound generation algorithm. 1. BACKGROUND In the last decades auditory perception has been increasingly recognized in its relevance as a mean to supply us with ecological information about our surroundings. This widening of the psychoacoustic view, beyond the traditional focus on the perception of abstract sound properties such as pitch and loudness, towards the auditory perception of attributes of sound sources has given strong impulses to the field of auditory display. The "Sounding Object" European project (IST-2000-25287) [3] has been occupied with the development of realtime sound models of familiar everyday sound-emitting processes that can be imbedded in, and form a basis for, new human-computer interfaces. These developments make use of a combination of traditional and newer techniques of sound generation, from e.g. subtractive synthesis to physical modeling, that have mainly emerged from research motivated by, and first exploited in, the field of electro-acoustic music. In a current musical context composers can today rely on an impressive range of techniques and tools of electronic sound production as an enrichment and pendant of the classical instrumentarium, while the significance of interpretation and improvisation in musical traditions appears to point out wide room for questions and research in the electro-acoustic musical practice. The aspect of the, in particular gestural, control of, or interaction with, sound is here seen as highly relevant. In this sense, electro-acoustic music and auditory display in HCI have arrived at very same issues, somewhat "from opposite direction". 2. THE BALLANCER SYSTEM The sound generation core of the Ballancer [2] device is a realtime sound model of rolling interaction of solid objects, which is used to render the sonic behavior of a virtual ball rolling along a track. The device is controlled by means of a physical representation of the rolling track, Figure 1. The Ballancer with the graphical representation of the virtual ball. (The marble on the control track here serves only demonstration purposes.) a Im wooden stick (see figure 1). As a computer realisation of a familiar everyday metaphor of gestural interaction with sonic feedback, the Ballancer is intuitive to understand for users/players, i.e. without dedicated explanation or training. By facilitating psychoacoustic experiments, as have been performed and reported recently [1], it furthermore allows new examinations into mechanisms of auditory perception and the role of sonic feedback in human interaction. 3. REFERENCES [1] M. Rath. Interactive Realtime Sound Models for Human-Computer Interaction - A Sound Design Concept and Applications. PhD thesis, Department of Computer Science, University of Verona, 2004. available online under <http://www.di.univr.it/dol/main?ent=pubbdip>, "research reports". [2] M. Rath and D. Rocchesso. Informative sonic feedback for continuous human-machine interactioncontrolling a sound model of a rolling ball. IEEE MULTIMEDIA SPECIAL ISSUE ON INTERACTIVE SONIFICATION, April 2005. [3] Davide Rocchesso and Federico Fontana, editors. The Sounding Object. Mondo Estremo, Firenze, Italy, 2003. < http://www.soundobject.org >.