Research HOME

Due to the very nature of R&D, this page is always under construction

Research Interests

Engineering

Array & statistical signal processing techniques in the field of speech enhancement, adaptive beamforming and blind source separation as well as algorithms for adaptive noise canceller (ANC), particularly with applications to hands-free telephony and speech recognition (both single and multichannel).

Botany

Orchids especially monopodial type like Phalaenopsis, particularly on cross-breeding, classification, propagation, culture, care and development etc.

Microphone Array in Brief

Microphone array has had a long-standing achievement as far as speech enhancement is concerned. It exploits both the spatial and temporal information to enhance the target signal by suppressing the interference. Simply, it is a multidimensional signal processing technique in both space and time (hence the term spatio-temporal processing). Such capability paves the way for microphone array in countless applications like hands-free communications, speech recognition devices, hearing aids and the list goes on. There are generally two types of beamformer namely fixed and adaptive. As the name implies, the former optimizes the filter coefficients such that the beamformer forms a beam (hence the name beamformer) towards the source of interest. Examples of fixed beamformer include the delay & sum and the constrained minimum variance beamformer. Adaptive beamformer on the hand, adaptively minimizes the response from the “out-of-source” region. A very popular adaptive beamformer is the Generalized Sidelobe Canceller (GSC) introduced by Griffiths and Jim in the early 80’s. Ever since, the literature is populated with countless variations of the GSC beamformers. The reason for its popularity is because of its ease of implementation (unconstrained) and the very fact that it does work (to a certain extent).

Some Audio Demonstrations

[RW1] A synergetic spatio-temporal decorrelator was developed and the following are the associated wav files:

Real Room Environment with Multiple Babble Sources (diffuse and directional)

[RW2] The wav file for the ICASSP 2004 [C20] paper on PSD:

Real Car Environment (6 mics, speed = 110 km/h, windows down)

ICASSP_PSD (Noisy signal followed by processed signal)

[RW3] The wav files for the Convolutive BSS with Post-Processing [J5]:

Room Environment (RT=100ms with multiple babble sources, 2 mics)

Input

BSS only Output

Proposed Output

[RW4] The wav files for the WASPAA 2003 [C24] paper on subband GSC:

Real Car Environment (6 mics, speed = 110 km/h, windows down)

Input

Output

Publications

Book Chapter

[B1] S. Nordholm, H. Q. Dam, N. Grbić and S. Y. Low, “Adaptive Microphone Array Employing Spatial Quadratic Soft Constraints and Spectral Shaping” in Speech Enhancement, J. Benesty, S. Makino, and J. Chen, Eds., Springer, 2005.

Journal papers (accepted/published)

[J1] S. Y. Low, K. F. C. Yiu and S. Nordholm, ``Beamspace Blind Signal Separation for Speech Enhancement," accepted Optimization and Engineering, Springer Science 2008.

[J2] K. F. C. Yiu, S. Y. Low, K. Y. Chan and S. Nordholm, ``A multi-filter system for speech enhancement under low signal-to-noise ratios," accepted Journal of Industrial and Management Optimization, 2008.

[J3] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Post-filtering using multi-channel spectral estimation in multi-speaker environments” EURASIP JASP 2008.

[J4] H. H. Dam, S. Nordholm, S. Y. Low and A. Cantoni, “Blind Signal Separation Incorporating Step Size Optimization” IEEE Transactions on Signal Processing, August 2007.

[J5] S. Y. Low, S. Nordholm and K. L. Teo, “Use of Efficient Frontier in Microphone Arrays” IEE Electronics Letters, September 2006.

[J6] S. Y. Low, S. Nordholm and R. Togneri, “Convolutive Blind Signal Separation with Post-Processing” IEEE Transactions on Speech and Audio Processing, September 2004.

Conference papers

[C1] A. Davis, S. Y. Low and S. Nordholm, ``Multi-band Decision Voice Activity Detection for Speech Enhancement,” submitted IWAENC, Seattle, USA, September 2008.

[C2] S. Nordholm, S. Y. Low, I. Claesson and K. F. C. Yiu, “Non-uniform Optimal Subband Beamforming: An Evaluation on Real Acoustic Measurements” IEEE International Congress on Image and Signal Processing, Hainan, China, May 2008.

[C3] S. Nordholm, S. Y. Low and H. H. Dam, “A Microphone Array Solution for Duplex Hands-Free Communication Systems,” IEEE ICCE, Las Vegas, USA, January 2007.

[C4] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Post-Filtering Techniques for Directive Non-Stationary Source Combined with Stationary Noise Utilizing Spatial Spectral Processing,” APCCAS, Singapore, December 2006.

[C5] A. Davis, S. Nordholm, S. Y. Low and R. Togneri, “A multi-decision sub-band voice activity detector,” EUSIPCO, Florence, Italy, September 2006.

[C6] S. Y. Low and S. Nordholm, “Space Constrained Beamformer with a Soft Adaptation Blocking System and Non-Coherent Cancellation,” IWAENC, Paris, France, September 2006.

[C7] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Post-filtering with multichannel power spectral estimation using joint diagonalization in multi-speaker environments,” Asia Pacific Conference on Communications, Busan, South Korea, August 2006.

[C8] S. Nordholm and S. Y. Low, “Speech Signal Extraction Utilizing PCA-ICA Algorithm with a Non-Uniform Spacing Microphone Array,” IEEE Int. Conf. on Acoustics, Speech and Signal Processing, vol. 5, pp. 965-968, Toulouse, France, May 2006.

[C9] H. H. Dam, S. Nordholm, S. Y. Low and K. L. Teo, “Steerable Far-field Circular Array,” Australian Communications Theory Workshop, Perth, Australia, February 2006.

[C10] S. Y. Low, S. Nordholm and K. L. Teo, “On the Use of Scalarization in Microphone Arrays,” ASOR, November 2005.

[C11] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Maximum Likelihood Estimation and Cramer-Rao Lower Bounds for the Multichannel Spectral Evaluation on Hands-Free Communication,” Asia Pacific Conference on Communications, pp. 961-964, Perth, Australia, October 2005.

[C12] M. Berg, E. Bondesson, S. Y. Low, S. Nordholm and I. Claesson, “A Combined On-Line PCA-ICA Algorithm for Blind Source Separation,” Asia Pacific Conference on Communications, pp. 969-972, Perth, Australia, October 2005.

[C13] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Multi-Channel Adaptive Beamforming With Source Spectral and Noise Covariance Matrix Estimation,” IWAENC, pp. 77-80, Eindhoven, The Netherlands, September 2005.

[C14] S. Y. Low, S. Nordholm and H. Q. Dam, “A Spatio-Temporal-Spectral for Duplex Hands-Free Communication Systems,” IWAENC, pp. 81-84, Eindhoven, The Netherlands, September 2005.

[C15] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Adaptive Beamformer for Hands-Free Communication System in Noisy Environments,” IEEE Int. Sym. on Circuits and Systems, pp. 856-859, Kobe, Japan, May 2005.

[C16] A. Davis, S. Y. Low, S. Nordholm and N. Grbic, “A Subband Space Constrained Beamformer Incorporating Voice Activity Detection,” IEEE Int. Conf. on Acoustics, Speech and Signal Processing, vol. 3, pp. 65-68, Philadelphia, USA, March 2005.

[C17] S. Y. Low and S. Nordholm, “A Blind Approach to Joint Echo and Noise Cancellation,” IEEE Int. Conf. on Acoustics, Speech and Signal Processing, vol. 3, pp. 69-72, Philadelphia, USA, March 2005.

[C18] S. Nordholm, S. Y. Low, H. Q. Dam and N. Grbic, “Speech Enhancement Using Microphone Arrays,” Joint Workshop on Hands-Free Speech Communication and Microphone Arrays, New Jersey, USA, March 2005.

[C19] S. Y. Low and S. Nordholm, “A Hybrid System Employing Blind Source Separation and Adaptive Noise Cancellation,” IEEE 6th Nordic Sym. on Signal Processing, pp. 204-207, Espoo, Finland, June 2004.

[C20] H. Q. Dam, S. Y. Low, S. Nordholm and H. H. Dam, “Adaptive Microphone Array with Noise Statistics Updates,” IEEE Int. Sym. on Circuits and Systems, vol. 3, pp. 433-436, Vancouver, Canada, May 2004.

[C21] S. Y. Low, R. Togneri and S. Nordholm, “Spatio-Temporal Processing for Distant Speech Recognition,” IEEE Int. Conf. on Acoustics, Speech and Signal Processing, vol. 1, pp. 1001-1004, Montreal, Canada, May 2004.

[C22] S. Y. Low and S. Nordholm, “A Robust Multichannel Speech Enhancement Method Based on Decorrelation,” IEEE Int. Sym. on Circuits and Systems, pp. 2875-2878, Kobe, Japan, May 2005.

[C23] H. Q. Dam, S. Y. Low, H. H. Dam and S. Nordholm, “Space Constrained Beamforming with Source PSD Updates,” IEEE Int. Conf. on Acoustics, Speech and Signal Processing, vol. 4, pp. 93-96, Montreal, Canada, May 2004.

[C24] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Speech Enhancement Using The Microphone Array and Short-Term Spectral Amplitude Estimator,” IEEE International Sym. on Intelligent Multimedia, Video and Speech Processing, Hong Kong PRC, October 2004.

[C25] H. Q. Dam, S. Nordholm, H. H. Dam and S. Y. Low, “Speech Enhancement Using Spectral Amplitude Estimator for Noisy Environments,” 6th Int. Conf. on Optimization: Techniques and Applications, Ballarat, Victoria, Australia, December 2004.

[C26] H. Q. Dam, S. Y. Low, S. Nordholm and N. Grbic, “An Adaptive Beamformer with Recursively Updated Quadratic Constraints,” IEEE Int. Conf. on Information, Communications & Signal Processing & IEEE Pacific-Rim Conf. On Multimedia, vol. 1, pp. 105-109, Singapore, December 2003.

[C27] S. Y. Low, N. Grbic, and S. Nordholm, “Subband Generalized Sidelobe Canceller - A Constrained Region Approach,” IEEE Workshop on Applications of Signal Processing to Audio and Acoustics, pp. 41-44, New York, USA, October 2003.

[C28] S. Y. Low, N. Grbic, and S. Nordholm, “Speech Enhancement Using Multiple soft Constrained Beamformers and Non-Coherent Technique,” IEEE Int. Conf. on Acoustics, Speech and Signal Processing, vol. 5, pp. 489-492, Hong Kong PRC, April 2003.

[C29] S. Y. Low, N. Grbic, and S. Nordholm, “Robust Microphone Array Using Subband Adaptive Beamformer and Spectral Subtraction,” IEEE Int. Conf. on Communication Systems, vol. 2, pp. 1020-1024, Singapore, November 2002.

Grant

[G1] Curtin Developmental Research Grant (DRG), 2006.

“To Teach Is To Touch Lives Forever”

Last Updated: 20/06/2008