## The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc. | |

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium T2 at the Aalto University School of Science and Technology (Espoo, Finland) on the 15^{th} of January, 2010, at 12 noon.

Overview in PDF format (ISBN 978-952-248-265-5) [1495 KB]

Dissertation is also available in print (ISBN 978-952-248-264-8)

The goal of this research is to develop efficient algorithms for physics-based room acoustics modeling and real-time auralization. Given the room geometry and wall materials, in addition to listener and sound source positions and other properties, the auralization system aims at reproducing the sound as would be heard by the listener in a corresponding physical setup. A secondary goal is to predict the room acoustics parameters reliably.

The thesis presents a new algorithm for room acoustics modeling. The acoustic radiance transfer method is an element-based algorithm which models the energy transfer in the room like the acoustic radiosity technique, but is capable of modeling arbitrary local reflections defined as bidirectional reflectance distribution functions.

Implementing real-time auralization requires efficient room acoustics modeling. This thesis presents three approaches for improving the speed of the modeling process. First, the room geometry can be reduced. For this purpose an algorithm, based on volumetric decomposition and reconstructions of the surface, is described. The algorithm is capable of simplifying the topology of the model and it is shown that the acoustical properties of the room are sufficiently well preserved with even 80 % reduction rates in typical room models. Second, some of the data required for room acoustics modeling can be precomputed. It is shown that in the beam tracing algorithm a visibility structure called "beam tree" can be precomputed efficiently, allowing even moving sound sources in simple cases. In the acoustic radiance transfer method, effects of the room geometry can be precomputed. Third, the run-time computation can be optimized. The thesis describes two optimization techniques for the beam tracing algorithm which are shown to speed up the process by two orders of magnitude. On the other hand, performing the precomputation for the acoustic radiance transfer method in the frequency domain allows a very efficient implementation of the final phase of the modeling on the graphics processing unit. An interactive auralization system, based on this technique is presented.

This thesis consists of an overview and of the following 4 publications:

- Samuel Siltanen, Tapio Lokki, Lauri Savioja, and Claus Lynge Christensen. 2008. Geometry reduction in room acoustics modeling. Acta Acustica united with Acustica, volume 94, number 3, pages 410-418.
- Samuli Laine, Samuel Siltanen, Tapio Lokki, and Lauri Savioja. 2009. Accelerated beam tracing algorithm. Applied Acoustics, volume 70, number 1, pages 172-181.
- Samuel Siltanen, Tapio Lokki, Sami Kiminki, and Lauri Savioja. 2007. The room acoustic rendering equation. Journal of the Acoustical Society of America, volume 122, number 3, pages 1624-1635. © 2007 Acoustical Society of America. By permission.
- Samuel Siltanen, Tapio Lokki, and Lauri Savioja. 2009. Frequency domain acoustic radiance transfer for real-time auralization. Acta Acustica united with Acustica, volume 95, number 1, pages 106-117.

**Keywords:**
room acoustics modeling, auralization, virtual reality

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Last update 2011-05-26