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INTERNATIONAL CONGRESS ON ACOUSTICS MADRID , 2-7 SEPTEMBER 2007 Adaptive sampling for frustum-based sound propagati on in complex and dynamic environments

Frustum tracing is a geometric method that allows to perform sound propagation simulation in general complex and dynamic scenes. We describe the underlying algorithm and analyze its behavior with regard to different sampling and scene parameters. We also present an extension of the basic technique that allows to adaptively change the sampling with regard to local geometric complexity and show that this yields the same quality as uniform high sampling at much lower simulation time. We demonstrate our results in an interactive system for intended for virtual environments and prototyping purposes running in real-time on a current high-end PC. INTRODUCTION Modelling the acoustic properties of a virtual environment is an important step in simulating the acoustic response of buildings such as auditoriums, but also for interactive applications such as games or virtual environments where spatialized sound adds a stronger immersion effect to the application. Geometric algorithms are usually the fastest choice for this simulation, but are only accurate for the early reflections in sound propagation paths. However, they allow a good approximation of the full simulation, especially with statistically added reverberations, for purposes of prototyping or where absolute accuracy is not an issue. Considering that still both a high number of paths and reflections need to be taken into account, this is a very compute intensive task. Many algorithms for this therefore take a long time to simulate or do not scale to complex 3D environments. This paper describes a new method for geometric sound propagation, frustum tracing, based on recent advances in interactive ray tracing. This allows us to perform simulations at much higher simulation speed, achieving interactive performance on a workstation system. In addition, this approach also handles general, non-densely-occluded scenes as well as complex dynamic environments. The frustum tracing approach is most closely related to previous methods using beam tracing [11], but can trade off quality for speed by using a discrete approximation to the clipping algorithm used in beam tracing. We show that even at low quality settings, our algorithm generates a good quality result, and converges to the same result as beam tracing very quickly. Finally, we also present an extension to the original algorithm that chooses the sampling parameters for frustum tracing adaptively. We show that this allows us to generate responses of higher quality in the same time as needed before. The rest of the paper is organized as follows: first, we show previous and related work, with a special focus on giving an overview of recent advances in interactive ray tracing that motivated our work. We then describe the original frustum tracing algorithm and the extension to adaptive sampling. Afterwards, we show results from an implementation of that algorithm. Finally, we conclude and list areas of future work.