The Ball within the Box: A Sound-Processing Metaphor

The physical-modeling paradigm is already popular in the computer music community. Nevertheless, few compositions are being written using this class of techniques. It seems that composers, who often complain about the lack of intuition in most signal-processing techniques, are nevertheless "stuck with them." What prevents a composer from approaching synthesis by physical modeling? One of the reasons is the lack of generality. Until now, most physical-modeling research has focused on the challenge of simulating existing acoustical instruments. Many ad hoc techniques have been developed for reed instruments, strings, percussion, etc. It is hard for a composer to find a way to collect these techniques and use them with the freedom of choice he/she expects to have. The classical "computer music utopia" that implies having the power to do everything seems to be contradicted by the physically based approach. Therefore, computer musicians, most of whom are "utopists," keep using frequency modulation or granular synthesis as general tools for forming musical material. We feel that to escape this bottleneck, we need general models and representations of the physical sounding objects. In this article, we try to provide one such a model, which we call the Ball within the Box (BaBo). The BaBo can be thought of as a generalized model of a resonator, in the exciter-resonator classical view of physical modeling (Borin, De Poli, and Sarti 1992). It retains the main advantage of physical modeling techniques, namely, the availability of physically meaningful parameters like size, absorption, damping, diffusion, etc. At the same time, the BaBo model is sufficiently general that it can be used as instrument resonator, post-processing filter, or reverberator. Sound from Boxes