Our main research topic is “inverse problems for acoustic field” and “signal processing for sound field recording, transmission, and reproduction”. Details are described below.

Inverse problems for acoustic field

We tackle with inverse problems for acoustic field, such as sound field imaging, analysis, source localization, and estimation of room acoustic parameters. We pursuit new methodologies with various approaches (optimization, machine learning, etc.) and develop systems to achieve these purposes.

Signal processing for sound field recording, transmission, and reproduction

We deal with a broad range of problems for sound field recording, transmission, and reproduction. By using these methodologies, we develop new systems for telecommunication, virtual reality, and so on.


Sparse representation for sound field analysis

rep_wfr_sprep_sparse_sp
Left: Plane-wave-decomposition-based reconstruction, Right: Sparse-sound-field-decomposition-based reconstruction

A sound field is generally analysed by decomposing it into plane-wave functions; however, this method suffers from spatial aliasing artifacts with severe effects at high frequencies. The analysis based on the sparse representation developed in the literature of compressed sensing enables to reduce these artifacts, which can be regarded as super-resolution in sound field analysis.

References

  • S. Koyama and H. Saruwatari, “Sound field decomposition in reverberant environment using sparse and low-rank signal models,” in Proc. IEEE Int. Conf. Acoust., Speech., Signal Process. (ICASSP), Shanghai, Mar. 2016, pp. 345-349. [LINK]
  • S. Koyama, et al., “Sparse sound field representation in recording and reproduction for reducing spatial aliasing artifacts,” in Proc. IEEE Int. Conf. Acoust., Speech., Signal Process. (ICASSP), Florence, May 2014, pp. 4443-4447. [LINK]

Sound field recording and reproduction


Left: original sound field, Right: reproduced sound field with circular loudspeaker array

Sound field recording and reproduction is intended to high-fidelity reconstruction of a sound space in a physical sense. By using arrays of multiple microphones and loudspeakers and an appropriate signal transform, high-accuracy sound field reproduction is achieved.

References

  • S. Koyama, et al., “Analytical approach to wave field reconstruction filtering in spatio-temporal frequency domain,” IEEE Trans. Audio, Speech, Lang. Process., vol. 21, no. 4, pp. 685-696, 2013. [LINK]
  • S. Koyama, et al., “Wave field reconstruction filtering in cylindrical harmonic domain for with-height recording and reproduction,” IEEE/ACM Trans. Audio, Speech, Lang. Process., vol. 22, no. 10, pp. 1546-1557, 2014. [LINK]
  • S. Koyama, et al., “Analytical approach to transforming filter design for sound field recording and reproduction using circular arrays with a spherical baffle,” J. Acoust. Soc. Amer., vol. 139, no. 3, pp. 1024-1036, 2016. [LINK]