Room Acoustic Ray-Tracing : Understanding, evaluating and expanding the toolset

Sammanfattning: Room acoustic simulations are an important tool, both for design of spaces with satisfactory acoustics and for use in virtual reality experiences. Auralization of acoustic simulations are becoming more and more important in the context of Virtual and Augmented reality (VR and AR respectively), as the technology is used more and more in healthcare, culture and research. In this work, ray tracing simulations for room acoustics were studied. New methods wereintroduced to improve their overall performance in terms of simulation speed and accuracy for the purpose of auralization in VR.Acoustic ray tracing simulations and auralizations of the historically important Vadstena abbey church were performed. The heritage site was reconstructed digitally based on historical sources. Analysis of the simulation results showed that the sound field was characterized by acoustic subspaceswhere the activities of the monastical congregations were better supported than in the nave. Redistribution of acoustic energy by the vaulted ceiling was found to have a significant impact on the transmission of sound into the nave. Accordingly, the distribution and redirection of acoustic energy was identified as important factors in the simulation. Scattering playsa central role in those processes and was consequently studied further in the project. It was additionally found that faster simulations were necessary to achieve good performance for VR.A room acoustic ray tracer was implemented to facilitate the development and testing of new algorithms. The ray tracer runs on the GPU and can generate an estimate of the energetic room impulse response.Using the developed ray tracer, some typical algorithms for scattering were tested and evaluated based on their simulation accuracy, simulation speed and usability. It was found that randomly determining whether rays are scattered or geometrically reflected was the overall best method. This is also the most commonly used algorithm in ray tracers today. An extension to this modelis suggested, so that so-called 1D-scatterers can be modelled more accurately. The extended algorithm was tested by simulation of a room where the orientation of 1D-scatterers on the walls had been determined to lead to audible variations in room acoustic parameters. The algorithm for directional scattering was capable of emulating those variations.Finally, a strategy to maintain simulation accuracy under strong restrictions on computational resources was presented. The method is called Iterative ray tracing, and uses a fundamental property of Monte Carlo simulations methods to improve simulation precision over time. By combining the results of multiple ray tracing passes, the overall number of rays (or samples) is increased, and thus variance is decreased while the expected outcome is maintained.In all, this research has shed light on the historical acoustics of Vadstena abbey church, developed mathematical models for the analysis of ray tracing simulations, and produced new strategies for use in room acoustic ray tracing simulations.