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.

Physically-Based Auralization - Design, Implementation, and Evaluation

Tapio Lokki

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Computer Science and Engineering, for public examination and debate in Auditorium T1 at Helsinki University of Technology (Espoo, Finland) on the 8th of November, 2002, at 12 noon.

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The aim of this research is to implement an auralization system that renders audible a 3D model of an acoustic environment. The design of such a system is an iterative process where successive evaluation of auralization quality is utilized to further refine the model and develop the rendering methods. The work can be divided into two parts corresponding to design and implementation of an auralization system and evaluation of the system employing objective and subjective criteria.

The presented auralization method enables both static and dynamic rendering. In dynamic rendering positions and orientations of sound sources, surfaces, or a listener can change. These changes are allowed by modeling the direct sound and early reflections with the image-source method. In addition, the late reverberation is modeled with a time-invariant recursive digital filter structure. The core of the thesis deals with the processing of image sources for auralization. The sound signal emitted by each image source is processed with digital filters modeling such acoustic phenomena as sound source directivity, distance delay and attenuation, air and material absorption, and the characteristics of spatial hearing. The digital filter design and implementation of these filters are presented in detail. The traditional image-source method has also been extended to handle diffraction in addition to specular reflections.

The evaluation of quality of the implemented auralization system was performed by comparing recorded and auralized soundtracks subjectively. The compared soundtracks were prepared by recording sound signals in a real room and by auralizing these signals with a 3D model of the room. The auralization quality was assessed with objective and subjective methods. The objective analysis was based on both traditional room acoustic criteria and on a simplified auditory model developed for this purpose. This new analysis method mimics the behavior of human cochlea. Therefore, with the developed method, impulse responses and sound signals can be visualized with similar time and frequency resolution as human hearing applies. The evaluation was completed subjectively by conducting listening tests. The utilized listening test methodology is explained and the final results are presented. The results show that the implemented auralization system provides plausible and natural sounding auralizations in rooms similar to the lecture room employed for evaluation.

This thesis consists of an overview and of the following 7 publications:

  1. L. Savioja, J. Huopaniemi, T. Lokki, and R. Väänänen. Creating interactive virtual acoustic environments. Journal of the Audio Engineering Society, vol. 47, no. 9, pages 675-705, September 1999. © 1999 AES. By permission.
  2. T. Lokki, J. Hiipakka, and L. Savioja. A framework for evaluating virtual acoustic environments. Presented at the 110th Convention of the Audio Engineering Society, Amsterdam, The Netherlands, May 12-15 2001, preprint no. 5317. © 2001 AES. By permission.
  3. T. Lokki, U.P. Svensson, and L. Savioja. An efficient auralization of edge diffraction. In Proceedings of the Audio Engineering Society 21st International Conference: Architectural Acoustics & Sound Reinforcement, pages 166-172, St. Petersburg, Russia, June 1-3 2002. © 2002 AES. By permission.
  4. T. Lokki and M. Karjalainen. Analysis of room responses, motivated by auditory perception. Journal of New Music Research, vol. 31, no. 2, pages 163-169, 2002.
  5. T. Lokki. Objective comparison of measured and modeled binaural room responses. In Proceedings of the 8th International Congress on Sound and Vibration, pages 2481-2488, Hong Kong, China, July 2-6 2001.
  6. T. Lokki and H. Järveläinen. Subjective evaluation of auralization of physics-based room acoustic modeling. In Proceedings of the 7th International Conference on Auditory Display, pages 26-31, Espoo, Finland, July 29 - August 1 2001. © 2001 by authors.
  7. T. Lokki and V. Pulkki. Evaluation of geometry-based parametric auralization. In Proceedings of the Audio Engineering Society 22nd International Conference: Virtual, Synthetic and Entertainment Audio, pages 367-376, Espoo, Finland, June 15-17 2002. © 2002 AES. By permission.

Errata of publications 2, 3, and 4

Keywords: auralization, room acoustic modeling, digital signal processing, virtual reality, 3D sound, spatial sound evaluation, binaural technology

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© 2002 Helsinki University of Technology

Last update 2011-05-26