Ideal three-dimensional resonators are “labeled” (identified) by infinite sequences of resonance modes, whose distribution depends on the resonator shape. We are investigating the ability of human beings to recognize these shapes by auditory spectral cues. Rather than focusing on a precise simulation of the resonator, we want to understand if the recognition takes place using simplified “cartoon” models, just providing the first resonances that identify a shape. In fact, such models can be easily translated into efficient algorithms for real-time sound synthesis in contexts of human-machine interaction, where the resonator shape and other rendering parameters can be interactively manipulated. This paper describes the method we have followed to come up with an application that, executed in real-time, can be used in listening tests of shape recognition and together with human-computer interfaces.

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This paper describes the structure and potential of a real-time sound model of “rolling”. The work has it’s background and motivation in the ecological approach of psychoacoustics. Scope of interest is the efficient and clear (possibly exaggerated) acoustic expression, cartoonification, of certain ecological attributes rather than realistic simulations for their own sake. To this end, different techniques of sound generation are combined in a hybrid hierarchical structure. A physics-based algorithm (section 2) of impact-interaction at the audio-core is surrounded by higher-level structures that explicitely model macroscopic characteristics (section 5). Another connecting audio-level algorithm, the “rolling-filter”, reduces the (3-dimensional) geometry of the rolling-contact to the one dimension of the impactinteraction-model (section 3).

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For reasons of practical handling as well as optimization of the processes of development and implementation, it is desirable to realize realtime models of sound emitting physical processes in a modular fashion that reflects an intuitively understandable structure of the underlying scenario. At the same time, in discrete– time algorithms based on physical descriptions, the occurance of non–computable instantaneous feedback loops has to be avoided. The latter obstacle prohibits the naive cross-connection of input– output signal processing blocks. The following paper presents an approach to gain modularity in the implementation of physicsbased models, while preventing non–computable loops, that can be applied to a wide class of systems. The strategy has been realized pratically in the development of realtime sound models in the course of the Sounding Object [1] European research project.

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Continuous sensory–motor loops form a topic dealt with rather rarely in experiments and applications of ecological auditory perception. Experiments with a tangible audio–visual interface around a physics-based sound synthesis core address this aspect. Initially dealing with the evaluation of a specific work of sound and interaction design, they deliver new arguments and notions for non-speech auditory display and are also to be seen in a wider context of psychoacoustic knowledge and methodology.

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In discrete-time digital models of contact of vibrating objects stability and therefore control over system energy is an important issue. While numerical approximation is problematic in this context digital algorithms may meat this challenge when based on exact mathematical solution of the underlying equation. The latter may generally be possible under certain conditions of linearity. While a system of contacting solid objects is non-linear by definition, piece-wise linear models may be used. Here however the aspect of “switching” between different linear phases is crucial. An approach is presented for exact preservation of system energy when passing between different phases of contact. One basic principle used may be pictured as inserting appropriate ideal, massless and perfectly stiff, “connection rods” at discrete moments of phase switching. Theoretic foundations are introduced and the general technique is explained and tested at two simple examples.

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The question, if a vibrating object can be forced to follow a given movement profile at one point forms a case of an inverse problem. It is shown that for the specific setting of an object described by modal data, this question may be solved by a newly developed method. The new technique has several strengths, such as allowing to compute modal data for the constrained scenario and forming a basis for precise and stable simulations. The latter potential is shown at a short example, a stiff string being hammered against a fixed board by a hammer of infinite mass.

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