[This page is no longer
being updated. Go to my
homepage for my current contact information or to my list of publications
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
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
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.
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)
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)
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)
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,
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.
S.C. Douglas, ``Method and Apparatus for Multichannel Active Noise and
Vibration Control,'' patent pending.
S.C. Douglas and J.A. Olkin, ``Multiple-input, Multiple-output, Multiple-error
Adaptive Feedforward Control Using the Filtered-X Normalized LMS Algorithm,''
Second Conference on Recent Advances in Active Control of Sound and Vibration,
Blacksburg, VA, pp. 743-754, April 1993.
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)
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.
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.
Douglas, ``The Fast Affine Projection Algorithm for Active Noise Control,''
29th Asilomar Conf. on Signals, Systems, and Computers, Pacific Grove,
CA, vol. 2, pp. 1245-1249, November 1995.
(Postscript, 317K, 5 pages)
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.
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.
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.
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.
142K, 4 pages)
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,
(Postscript, 393K, 12 pages)
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,
(Postscript, 194K, 12 pages)
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.
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)