Analysis and Synthesis of Directional Reverberation

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School of Electrical Engineering | Doctoral thesis (article-based) | Defence date: 2021-09-20
Degree programme
104 + app. 88
Aalto University publication series DOCTORAL DISSERTATIONS, 107/2021
The reproduction of acoustics is one of the key challenges in spatial sound reproduction. In order to reach high levels of realism and immersion, reproduced signals must be processed through a set of filters accounting for real-life phenomena. From the scattering and absorption of sound on walls to its diffraction around objects and our head, the propagation of sound waves in a room creates a complex sound field around a listener. While recreating all of the underlying parts of sound propagation is not yet within our reach for real-time applications, spatial sound techniques aim to minimize the computational cost by focusing the efforts on the most perceptually critical components. In this dissertation, the reproduction of reverberant sound fields is investigated through the development of analysis methods, reverberation algorithms, and decorrelation techniques. A particular emphasis is given to the perception and reproduction of directional characteristics present in late reverberation. Most reverberation algorithms consider that the sound energy is evenly distributed across space in all directions, after an initial period of time, since the diffusion of energy leads to more homogeneous and isotropic sound fields. However, previous work has demonstrated that insufficient diffusion in a room leads to anisotropic, and directional, late reverberation. In this dissertation, a complete framework is proposed for the objective and subjective analysis of directional characteristics as well as a novel delay-network reverberation method capable of producing direction-dependent decay properties. The reverberator is also expanded to offer efficient frequency- and direction-dependent processing. The proposed algorithm contains all the required elements for the auralization of reverberant sound fields, which may be modulated in real-time to support six-degrees-of-freedom sound reproduction. The decorrelation of audio signals, which occurs naturally during the diffusion of energy in a sound field, is another important aspect of sound reproduction. This dissertation considers the use of velvet-noise sequences, a special type of sparse noise signals, as decorrelation filters and offers a method to optimize their characteristics. Velvet noise is also proposed for the reproduction of an existing impulse response using a small set of time- and frequency-dependent information, along with a reverberator using velvet noise to improve the echo density of a delay network reverberator. Overall, the results contained in this dissertation offer new insights into the perceptual ramifications of reverberant sound fields containing directional characteristics and their reproduction. The methods presented bring applications in the context of immersive sound reproduction, such as in virtual and augmented reality.
Supervising professor
Välimäki, Vesa, Prof., Aalto University, Department of Signal Processing and Acoustics, Finland
Thesis advisor
Politis, Archontis, Dr., Tampere University, Finland
Schlecht, Sebastian J., Prof., Aalto University, Finland
Välimäki, Vesa, Prof., Aalto University, Finland
acoustics, reverberation, decorrelation, digital signal processing, signal analysis
Other note
  • [Publication 1]: Benoit Alary, Archontis Politis, and Vesa Välimäki. Velvet-noise decorrelator. In Proceedings of the 20th International Conference on Digital Audio Effects, Edinburgh, UK, pp. 405–411, September 2017.
    Full text in Acris/Aaltodoc:
  • [Publication 2]: Sebastian J. Schlecht, Benoit Alary, Vesa Välimäki, and Emanüel A.P. Habets. Optimized velvet-noise decorrelator. In Proceedings of the 21st International Conference on Digital Audio Effects, Aveiro, Portugal, pp. 87–94, September 2018.
    Full text in Acris/Aaltodoc:
  • [Publication 3]: Vesa Välimäki, Bo Holm-Rasmussen, Benoit Alary, and Heidi Maria Lehtonen. Late reverberation synthesis using filtered velvet noise. Applied Sciences, vol. 7, no. 5, May 2017.
    DOI: 10.3390/app7050483 View at publisher
  • [Publication 4]: Jon Fagerström, Benoit Alary, Sebastian J. Schlecht, and Vesa Välimäki. Velvet-noise feedback delay network. In Proceedings of the 23rd International Conference on Digital Audio Effects, Vienna, Austria, pp. 219–226, September 2020.
    Full text in Acris/Aaltodoc:
  • [Publication 5]: Benoit Alary, Pierre Massé, Sebastian J. Schlecht, Markus Noisternig, and Vesa Välimäki. Perceptual analysis of directional late reverberation. Journal of the Acoustical Society of America, vol. 149, no. 5, pp. 3189– 3199, May 2021.
    Full text in Acris/Aaltodoc:
    DOI: 10.1121/10.0004770 View at publisher
  • [Publication 6]: Benoit Alary, Archontis Politis, Sebastian J. Schlecht, and Vesa Välimäki. Directional feedback delay network. Journal of the Audio Engineering Society, vol. 67, no. 10, pp. 752–762, October 2019.
    Full text in Acris/Aaltodoc:
    DOI: 10.17743/jaes.2019.0026 View at publisher
  • [Publication 7]: Benoit Alary and Archontis Politis. Frequency-dependent directional feedback delay network. In Proceedings of the 2020 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Barcelona, Spain, pp. 176–180, September 2020.
    Full text in Acris/Aaltodoc:
    DOI: 10.1109/ICASSP40776.2020.9054717 View at publisher