Paul Calamia will present his preFPO on Tuesday May 13 at 10AM in Room 402. The members of his committee are: Tom Funkhouser, Advisor; Peter Svensson (Norwegian Univ. of Science and Technology) and Perry Cook, Readers; Szymon Rusinkiewicz and Adam Finkelstein, Non-Readers. Everyone is invited to attend his talk. His abstract follows below. --------------------------- Title: Advances in Virtual-Acoustic Simulations through Edge Diffraction and Multiresolution Modeling Abstract: In recent years there has been growing interest in modeling sound propagation in complex, three-dimensional (3D) environments. With diverse applications for the military, the gaming industry, psychoacoustics researchers, architectural acousticians, and others, advances in computing power and 3D audio-rendering techniques have driven research and development aimed at closing the gap between the auralization and visualization of virtual spaces. To this end, this thesis focuses on improving the physical and perceptual realism of sound-field simulations in virtual environments through two distinct approaches: accurate and efficient computation of edge diffraction, and multiresolution modeling. To model sound propagation in virtual environments, acoustical simulation tools commonly rely on geometrical-acoustics (GA) techniques which assume asymptotically high frequencies, large flat surfaces, and ray-like paths. Such techniques can be augmented with diffraction modeling to compensate for the effect of surface size on the strength and directivity of a reflection, to allow for propagation around obstacles and into shadow zones, and to maintain soundfield continuity across reflection and shadow boundaries. Using a time-domain, line-integral diffraction expression known as the Biot-Tolstoy-Medwin (BTM) formulation, this thesis explores various aspects of diffraction calculations for virtual-acoustic simulations. Specifically, we first present analytical approximations for the BTM formulation which allow for accurate numerical computations for receivers at or near shadow and reflection boundaries, locations where the original diffraction integral experiences a singularity. We then describe an edge-subdivision strategy that allows for fast diffraction calculations with low error relative to a numerically more accurate solution. We present a novel method to find GA components using diffraction parameters which ensures continuity at reflection and shadow boundaries. Finally, to address the considerable increase in propagation paths due to diffraction, we describe a simple procedure for identifying and culling insignificant diffraction components during a virtual-acoustic simulation. The secondary thrust of this thesis involves the extension of GA techniques to highly detailed 3D models through a multiresolution approach. Such models, e.g. those created for architectural renderings or resulting from laser scans of building interiors, often exist as noisy meshes that comprise faces which are too small and too numerous for use with GA methods. To address these issues, we have developed a system in which image sources that give rise to specular reflections can be merged using frequency-dependent clustering criteria. The result is a significantly reduced set of aggregate image-sources which characterize a model's geometry and its reflection properties in a frequency-dependent, multiresoultion representation.