[This page is no longer being updated.  Go to my homepage for my current contact information or to my list of publications to download papers.  -- SCD]


Active Noise and Vibration Control (ANVC)

Active noise control, and its cousin, active vibration control, attempt to cancel an unwanted ``noise'' acoustical wave by injecting an equal-but-opposite ``anti-noise''acoustical wave into the medium, thereby attenuating the wave via destructive interference.  The origins of ANVC date back to at least 1936, when P. Leug patented the idea for sound control.  It tooks nearly fifty years, however, to obtain what might be called successful ANVC, due to the level of electronic precision required to create an anti-noise signal with any great fidelity.  Today, anti-noise headsets abound (I have a very cute set of Sony earbud-style `phones from Japan); these are mostly analog systems.  Large-scale quieting requires the use of adaptive digital signal processing technology in all but the simplest acoustic environments.

I began my study of ANVC as a summer hire at SRI International, Menlo Park, CA, in 1992.  While working in the Acoustics and Radar Technology Laboratory, I helped develop the algorithms and guide software code developers to implement a simple one-input, one-output, one-error active noise control system that illustrated some of the advantages that simple adaptive processing has over more-costly off-line calibration methods.  I also developed the multichannel extensions of the algorithms and wrote an internal SRI report that helped others to design a real-time multichannel active noise control system for reverberant room noise control.  After joining the University of Utah, I remained as a consultant to SRI, developing normalized LMS algorithms for multichannel active noise control and studying simplified partial-update schemes for the task.  Both of these latter topics have since appeared in publications.

My more-recent work in ANVC have been developed in part with Prof. Mark Bodson of the University of Utah.  Our efforts have been in two areas:  1) computationally-simple algorithms for single- and multichannel feedforward ANVC, and 2) practical algorithms for feedback ANVC for periodic noises with unknown fundamental frequency.  In the first area, we have discovered what might be called the ``right way'' to implement the multichannel filtered-X LMS algorithm, in which the complexity of the coefficient updates is essentially the same as that of the input-output calculations.  The savings in number of operations over the standard implementation is enormous--it can be more than a 90% reduction in the number of multiply/adds for systems with a large number of sensors/actuators.  This work has appeared in an ICASSP'97 paper as well as in a NOISE-CON'97 paper, and a longer version of the work is scheduled to appear in journal form.  We have also filed for a patent to protect our intellectual ideas, and the costs of the patent have been paid for by an outside firm who may license the technology.  Our student, David S. Nelson, has taken a different approach to simplify feedforward ANVC systems by using non-traditional block-convolution methods; these methods are described in a NOISE-CON'97 paper as well as a longer submission to the International Journal of Adaptive Control and Signal Processing.  In the second area, we have developed two techniques for combining frequency estimation with disturbance rejection.  One is an indirect approach, in which a frequency estimator is combined with a traditional amplitude-phase estimation.  The other is a novel direct approach in which the amplitude and the instantaneous phase of the disturbance are estimated jointly using a phased-lock-loop-type structure.  The initial work appears in an Automatica journal paper; subsequent developments have appeared at several conferences.

We have most recently been developing algorithms that compensate for the inherent delay due to the plant transfer function in feedforward and feedback active noise control systems.  My October 1997 publication in IEEE Signal Processing Letters describes a simplified method for performing this delay compensation in the modified filtered-X LMS algorithm.  These ideas are being extended by Jihee Soh, one of my Ph.D. students; some of the ideas have been presented at the 1998 DSP Workshop in Bryce Canyon, UT.  The methods were originally motivated by similar techniques that are used within the fast affine projection (FAP) algorithm.  A 1995 Asilomar Conference paper reviews this algorithm and various applications of it to active noise control tasks.

I have been involved in the development of several DSP-based active noise control systems, including a personalized, ``boom-box''-style noise control system that I helped develop as a consultant to a small Silicon Valley startup company.  The details of this system were presented in a paper at the Asilomar Conference in 1995, although the demonstration model is the only one in existence and has not been commercialized to my knowledge.  While at the University of Utah, Marc Bodson and I jointly oversaw the design and construction of a six-input, six-output active noise control system that continues to be a testbed for algorithm development.  I and my students are to develop a similar capability at SMU -- using Texas Instruments processors for the controller, of course!

Publications on Active Noise and Vibration Control -- Scott C. Douglas

Journal Publications

  1. S.C. Douglas, ``Analysis of the Multiple-Error and Block Least-Mean-Square Adaptive Algorithms,'' IEEE Trans. Circuits and Systems II: Analog and Digital Signal Processing, vol. 42, no. 2, pp. 92-101, February 1995.
  2. S.C. Douglas, ``Adaptive Filters Employing Partial Updates,'' IEEE Trans. Circuits and Systems II: Analog and Digital Signal Processing, vol. 44, no. 3, pp. 209-216, March 1997.(Postscript, 452K, 20 pages)
  3. S.C. Douglas, ``An Efficient Implementation of the Modified Filtered-X LMS Algor ithm,'' IEEE Signal Processing Letters, vol. 4, no. 10, pp. 286-288, October 1997. (Postscript, 102K, 6 pages)
  4. M. Bodson and S.C. Douglas, ``Adaptive Algorithms for the Rejection of Sinusoidal Disturbances with Unknown Frequency,'' Automatica, vol. 33, no. 12, pp. 2213-2221, December 1997.(Postscript, 339K, 17 pages)
  5. S.C. Douglas, ``Fast Implementations of the Filtered-X LMS and LMS Algorithms for Multichannel Active Noise Control,'' accepted for publication in IEEE Trans. Speech and Audio Processing; to appear.(Postscript, 298K, 27 pages)
  6. D.S. Nelson, S.C. Douglas, and M. Bodson, ``Fast Exact Adaptive Algorithms for Feedforward Active Noise Control,'' submitted to International Journal of Adaptive Control and Signal Processing,January 1999.

Patent

  1. S.C. Douglas, ``Method and Apparatus for Multichannel Active Noise and Vibration Control,'' patent pending.

Conference Publications

  1. S.C. Douglas and J.A. Olkin, ``Multiple-input, Multiple-output, Multiple-error Adaptive Feedforward Control Using the Filtered-X Normalized LMS Algorithm,'' Proc. Second Conference on Recent Advances in Active Control of Sound and Vibration, Blacksburg, VA, pp. 743-754, April 1993.
  2. S.C. Douglas,``Mean-Square Analysis of the Multiple-Error and Block LMS Adaptive Algorithms,'' Proc. IEEE International Conf. on Acoustics, Speech, and Signal Processing, Adelaide, Australia, vol. 3, pp. 429-432, April 1994.(Postscript, 178K, 4 pages)
  3. S.C. Douglas, ``Simplified Stochastic Gradient Adaptive Filters Using Partial Updating,'' Proc. Sixth IEEE Digital Signal Processing Workshop, Yosemite, CA, pp. 265-268, October 1994.
  4. A. Karakasoglu, C. Hung, J.F. Abbott, and S.C. Douglas, ``A Low-Cost Multichannel Active Noise Control System for Personal Quietude,'' Proc. 29th Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove, CA, vol. 2, pp. 1275-1279, November 1995.
  5. S.C. Douglas, ``The Fast Affine Projection Algorithm for Active Noise Control,'' Proc. 29th Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove, CA, vol. 2, pp. 1245-1249, November 1995. (Postscript, 317K, 5 pages)
  6. M. Bodson and S.C. Douglas, ``Rejection of Disturbances with a Large Periodic Component of Unknown Frequency,'' Proc. SPIE Symposium on Smart Structures and Materials--Mathematics and Control in Smart Structures, San Diego, CA, vol. 2715, pp. 64-75, February 1996.
  7. M. Bodson and S.C. Douglas, ``Adaptive Algorithms for the Rejection of Periodic Disturbances with Unknown Frequency,'' Proc. 13th IFAC World Conference, San Francisco, CA, vol. K, pp. 229-234, July 1996.
  8. M. Bodson and S.C. Douglas, ``Narrowband Disturbance Rejection Using Adaptive Feedback Algorithms,'' Proc. SPIE Symposium on Smart Structures and Materials, San Diego, CA, vol. 3039, pp. 45-56, March 1997.
  9. S.C. Douglas, ``Fast Exact Filtered-X LMS and LMS Algorithms for Multichannel Active Noise Control,'' Proc. IEEE International Conf. Acoust., Speech, Signal Processing, Munich, Germany, vol. 1, pp. 399-402, April 1997. (Postscript, 142K, 4 pages)
  10. S.C. Douglas, ``Reducing the Computational and Memory Requirements of the Multichannel Filtered-X LMS Adaptive Controller,'' Proc. National Conference on Noise Control Engineering (NOISE-CON), University Park, PA, vol. 2, pp. 209-220, June 1997. (Postscript, 393K, 12 pages)
  11. D.S. Nelson, S.C. Douglas, and M. Bodson, ``Fast Block Adaptive Algorithms for Feedforward Active Noise Control,'' Proc. National Conference on Noise Control Engineering (NOISE-CON), University Park, PA, vol. 2, pp. 197-208, June 1997. (Postscript, 194K, 12 pages)
  12. M. Bodson, J.S. Jensen, and S.C. Douglas, ``Active Noise Control for Periodic Disturbances,'' Proc. 17th American Control Conference, Philadelphia, PA, vol. 4, pp. 2616-2620, June 1998.
  13. S.C. Douglas and J.K. Soh, ``Delay Compensation Methods for Stochastic Gradient Adaptive Filters,'' Proc. 8th IEEE Digital Signal Processing Workshop, Bryce Canyon, UT, paper no. 108, August 1998.(Postscript, 152K, 4 pages)