Convincing simulation of diffraction around obstacles is critical in modeling sound propagation in virtual environments. Due to the computational complexity of large-scale wavefield simulations, ray-based models of diffraction are used in real-time interactive multimedia applications. Among popular diffraction models, the Biot-Tolstoy-Medwin (BTM) edge diffraction model is the most accurate, but it suffers from high computational complexity and hence is difficult to apply in real time. This paper introduces an alternative ray-based approach to approximating diffraction, called Volumetric Diffraction and Transmission (VDaT). VDaT is a volumetric diffraction model, meaning it performs spatial sampling of paths along which sound can traverse the scene around obstacles. VDaT uses the spatial sampling results to estimate the BTM edge-diffraction amplitude response and path length, with a much lower computational cost than computing BTM directly. On average, VDaT matches BTM results within 1–3 dB over a wide range of size scales and frequencies in basic cases, and VDaT can handle small objects and gaps better than comparable state-of-the-art real-time diffraction implementations. A GPU-parallelized implementation of VDaT is shown to be capable of simulating diffraction on thousands of direct and specular reflection path segments in small-to-medium-size scenes, within strict real-time constraints and without any precomputed scene information.
The demonstrated scene complexity is primarily limited by our reflection path generation system, which uses the exponential-complexity image source method, as well as by our use of a parallelized but not hierarchical implementation for checking segment-triangle intersections. Future work is planned to improve both of these elements.