Active adaptive control system with weight update selective leakage

DETAILED DESCRIPTION FIG.
1 shows an active adaptive control system similar to that shown in U.
S.
Pat.
No.
4,677,676, incorporated herein by reference, and uses like reference numerals therefrom where appropriate to facilitate understanding.
The system introduces a control signal from a secondary source or output transducer 14, such as a loudspeaker, shaker, or other actuator or controller, to combine with the system input signal 6 and yield a system output signal 8.
An input transducer 10, such as a microphone, accelerometer, or other sensor, senses the system input signal and provides a reference signal 42.
An error transducer 16, such as a microphone, accelerometer, or other sensor, senses the system output signal and provides an error signal 44.
Adaptive filter model 40 adaptively models the system and has a model input from reference signal 42 correlated to system input signal 6, and an output outputting a correction signal 46 to output transducer 14 to introduce the control signal according to a weight update signal 74.
Reference signal 42 and error signal 44 are combined at multiplier 72 to provide the weight update signal through delay element 73.
In a known alternative, the reference signal 42 may be provided by one or more error signals, in the case of a periodic system input signal, "Active Adaptive Sound Control In A Duct: A Computer Simulation" J.
C.
Burgess, Journal of Acoustic Society of America, 70(3), September 1981, pages 715-726, U.
S.
Pat.
Nos.
5,206,911, 5,216,722, incorporated herein by reference.
In updating the filter coefficients, and as is standard, one or more previous weights are added to the current product of reference signal 42 and error signal 44 at summer 75.
As noted above, it is known in the prior art to provide exponential decay of all of the filter coefficients in the system.
Leakage factor .
gamma.
at 77 multiplies one or more previous weights, after passage through one or more delay elements 73, by an exponential decay factor less than one before adding same at summer 75 to the current product of reference signal 42 and error signal 44, Adaptive Signal Processing, Widrow and Stearns, Prentice-Hall, Inc