ANU

Acoustic/ Audio Signal Processing



I am actively engaged in Audio and Acoustic research- using signal processing as a tool in audio and acoustic applications.

Head Related Transfer Function (HRTF)

The ability of humans to perceive the spatial location of a sound is of great practical and research importance. The recent advances in computational power and acoustic measurement techniques have make the study of the HRTF a rapidly growing area with potential uses in virtual reality audio applications. This research will focus on applying binaural techniques in communication systems, for situations where the listener must hear more than one communication channel at a time. Implementations of this kind of system can be used for pilots, air control towers and spatial audio teleconferencing.

Publications:

  1. Wen Zhang, Rodney A. Kennedy, and Thushara D. Abhayapala, ``Iterative Extrapolation Algorithm for Data Reconstruction over Sphere'', in In Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), pp. 3733-3736, April 2008, Las vegas, USA. (download / IEEE Xplore)

  2. Wen Zhang, Rodney Kennedy, and Thushara D. Abhayapala, “Signal Estimation from Incomplete Data on the Sphere”, In In Proc. IEEE 9th Australian Communication Theory Workshop, AusCTW07, Christchurch, New Zealand, Feb. 2008.
  3. W. Zhang, T.D. Abhayapala, R.A. Kennedy, ``Horizontal Plane HRTF Reproduction Using Continuous Fourier-Bessel Functions'', in Proc. 31st AES International Conference, London, Uk, June 2007.

Spatial Soundfield Reconstruction

The ability to control a sound field within a given region of space is a fundamental problem in signal processing. The multi-frequency nature of sound adds complexity that is not commonly observed in other signal processing problems. The aim of this work is to present an auditory system that is capable of reproducing an arbitrary sound field within a region of space using an array of loudspeakers. Reverberation and having multi-zone regions add further complexity to the problem.

Publications:

  1. Y. Jennifer WU and T.D. Abhayapala, ``Soundfield reproduction using theoretical continuous loudspeaker'', in In Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), (accepted) Vol. X, pp. ,  April 2008, Las vegas, USA.
  2. T. Betlehem, and T.D. Abhayapala, ``Theory and design of soundfield reproduction in reverberant rooms,”  Journal of the Acoustic Society of America, Vol. 117, Issue 4, Apr. 2005.
  3. T. Betlehem, and T.D. Abhayapala, “A Modal Space Approach to Soundfield Reproduction in Reverberant Rooms”, in Proc. "IEEE International Conference on Acoustics, Speech, and Signal Processing , ICASSP’2005, vol. III , pp. 289-292, March 2005.
  4. T. Betlehem, and T.D. Abhayapala, “Spherical Harmonic Analysis of Equalization in a Reverberant Room,” in Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing, ICASSP’2004, vol. 689–92, May 2004.
  5. D. Excell, ``Reproduction of a 3D Soundfield Using an array of loudspeakers", Honours Thesis, Department of Engineering, Australian national University, June 2003.
  6. D.B. Ward and T.D. Abhayapala, “Reproduction of a plane-wave sound field using an array of loudspeakers,” IEEE Trans. Speech and Audio Proc. , vol. 9, no. 6, pp 697-707, Sep. 2001.
  7. D. B. Ward and T.D. Abhayapala, “Performance bounds on sound field reporduction using a loudspeaker array,” in Proc. 2001 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, pp. 187--190, Oct. 2001.

Spherical Microphone Arrays/ Spatial Recording

Spherical microphone arrays have been introduced to use in spatial sound recording and beamforming applications. Over the last 5 years, there has been a strong interest in theory and design of spherical microphone arrays due to their possible use in various applications such as in recording directional sounds for surround sound creation, speech enhancement and surveillance. The theory of such arrays is based on decomposition of soundfields to spherical harmonics which are the natural basis functions for valid soundfields over three dimensional space.

Publications:

  1. T.D. Abhayapala, ``Generalized framework for spherical microphone arrays: Spatial and Frequency Decomposition'', in In Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), (accepted) Vol. X, pp. ,  April 2008, Las vegas, USA
  2. Thushara D. Abhayapala, Michael C.T. Chan, ``Limitation and Errior Analysis of Spherical Microphone Arrays'', In Proc. 14th International Congress on Sound and Vibration (ICSV14) , pp. Cairns, Australia, July 2007
  3. Michael Chan, Honours Thesis, Department of Engineering, Australian national University, June 2003. (download)
  4. T.D. Abhayapala and D. B. Ward, “Theory and Design of High Order Sound Field Microphones using Spherical Microphone Array,” in Proc. IEEE Int. Conf. Acoust. Speech Sig. Process. (ICASSP’2002), Vol. 2, 1949-1952, May 2002.
  5. T.D. Abhayapala “Modal Analysis and Synthesis of Broadband Nearfield Beamforming Arrays” PhD Thesis (see page 101), 1999

Broadband/Nearfield Beamforming

Beamforming is an important area of research with applications in acoustics, wireless communications, sonar, and radar. A broadband beamformer at the receiver is based on a time-sampled sensor array—a finite set of wavefield samples taken throughout space and time. Weighted linear combinations of these space-time samples are used to filter far-field sources based on their angle of arrival and frequency content. More formally, the response of a broadband beamformer can be expressed as a beam pattern—a 2D function of angle and frequency/wave number. A perfect beam pattern is designed to reject noise and interfering sources, but depending on sensor positions and time sampling, this desired pattern may not be achievable by a particular array. The beamformer design problem is to find an achievable pattern as close as possible to the desired pattern.

Publications:

  1. M.I.Y. Williams, T.D. Abhayapala, and R.A. Kennedy, ``Generalized Broadband Beamforming using a Modal Subspace Decomposition,” in EURASIP Journal on Advances in Signal Processing,  Vol.  2007,  Article ID 68291, 9 pages, doi:10.1155/2007/68291
  2. Michael Williams, Thushara D. Abhayapala, Rodney Kennedy, ``Generalized Broadband Beamforming Using a Modal Decomposition'', in Proc. IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP), Vol. 4, pp. 1021-1024, May 2006, Toulouse, France.
  3. T.D. Abhayapala, R.A. Kennedy, and R.C. Williamson, “Nearfield broadband array design using a radially invariant modal expansion,” J. Acoust. Soc. Amer., vol. 107, pp 392–403, Jan. 2000.
  4. R.A. Kennedy, D.B. Ward, and T.D. Abhayapala, “Nearfield beamforming using radial reciprocity,” IEEE Trans. Sig. Proc., vol. 47, pp. 33–40, Jan. 1999.
  5. T.D. Abhayapala, R.A. Kennedy, and R.C. Williamson, “Farfield array weight redesign for nearfield beamforming,” in Proc. 6th IEEE Int. Workshop on Intelligent Signal Processing and Communication Systems, pp. 537–540, 1998.
  6. R.A. Kennedy, T.D. Abhayapala, and D.B. Ward, “Broadband nearfield beamforming using a radial beampattern transformation,” IEEE Trans. Sig. Proc., vol. 46, pp. 2147–2156, Aug. 1998.
  7. T.D. Abhayapala, R.A. Kennedy, and R.C. Williamson, “Broadband beamforming using elementary shape invariant beampatterns,” in Proc. IEEE Int. Conf. Acoust. Speech Sig. Process. ICASSP98, vol. 5, pp. 2041–2044, 1998.
  8. D. B. Ward, R. A. Kennedy, and T.D. Abhayapala, “A beamforming paradox: Using far-field techniques to design a near-field microphone array,” J. Acoust. Soc. Amer., vol. 102, pp. 3208, 1997.
  9. R.A. Kennedy, D.B. Ward, and T.D. Abhayapala, “Nearfield beamforming using nearfield farfield reciprocity,” in Proc. IEEE Int. Conf. Acoust. Speech Sig. Process. ICASSP97, vol. 5, pp. 3741–3744, 1997.
  10. R. A. Kennedy, T.D. Abhayapala, and D. B. Ward, “Nearfield broadband array beamforming using wave equation transformation,” J. Acoust. Soc. Amer., vol. 100, pp. 2696, 1996.
  11. R.A. Kennedy, T.D. Abhayapala, D.B. Ward, and R.C. Williamson, “Nearfield broadband frequency invariant beamforming,” in Proc. IEEE Int. Conf. Acoust. Speech Sig. Process. ICASSP96, vol. 2, pp. 905–908, 1996
  12. T.D. Abhayapala “Modal Analysis and Synthesis of Broadband Nearfield Beamforming Arrays” ANU PhD Thesis, 1999

Source Localisation

The problem of estimation of direction of arrival (DOA) of broadband sources has applications in audio/acoustic and wireless communication systems.

Publications:

  1. T. D. Abhayapala, "Broadband Source Localization by Modal Space Processing", in the book titled Advances in Direction-of-Arrival Estimation, edited by S. Chandran, Artech House, 2006, ISBN 1-59693-004-7.
  2. T.D. Abhayapala, and H. Bhatta “On Coherent Broadband Source Localization by Modal Space Processing”, Proc. IEEE 10th International Conference on Telecommunications (ICT’2003), vol. 2, pp. 1617–1623, February 23 - March 1, 2003, Tahiti.



© 2007 Thushara D. Abhayapala. Web page template designed by Andreas Viklund