Multi-filter-set active adaptive control system

A multi-filter-set active adaptive control system includes a plurality of output transducer arrays introducing control signals to combine with a system input signal to yield a system output signal. A plurality of error transducers sense the system output signal and provide a plurality of error signals to a plurality of sets of adaptive filters. A plurality of sets of D/A converters are provided at the outputs of the adaptive filters outputting correction signals therethrough. A plurality of sets of A/D converters are provided at the filter inputs and error inputs of the adaptive filters. Various filter sets and combinations are provided.

BACKGROUND AND SUMMARY 
The invention relates to active adaptive control systems, and more 
particularly to a multi-filter-set system. 
The invention arose during continuing development efforts directed toward 
active acoustic attenuation systems. Active acoustic attenuation involves 
injecting a canceling acoustic wave to destructively interfere with and 
cancel an input acoustic wave. In an active acoustic attenuation system, 
the input acoustic wave is sensed with an input transducer, such as a 
microphone or an accelerometer, which supplies an input reference signal 
to an adaptive filter control model. The output acoustic wave is sensed 
with an error transducer which supplies an error signal to the model. The 
model supplies a correction signal to a canceling output transducer, such 
as a loudspeaker or a shaker, which injects an acoustic wave to 
destructively interfere with the input acoustic wave and cancel or control 
same such that the output acoustic wave at the error transducer is zero or 
some other desired value. 
An active adaptive control system minimizes an error signal by introducing 
a control signal from an output transducer to combine with the system 
input signal and yield a system output signal. The system input signal is 
sensed with an input transducer providing a reference signal. The system 
output signal is sensed with an error transducer providing an error 
signal. An adaptive filter model has a model input from the reference 
signal, an error input from the error signal, and outputs a correction 
signal to the output transducer to introduce the control signal matching 
the system input signal, to minimize the error signal. 
The present invention is applicable to active adaptive control systems, 
including active acoustic attenuation systems. The present invention 
provides a system for implementing multichannel active control systems 
using multiple filters having multiple independent A/D and D/A converters. 
This system facilitates use of active control for applications requiring 
large amounts of processor computation time and/or memory by sharing the 
computational requirements between multiple controllers. The invention 
significantly reduces parallel processing requirements by using 
multi-filter-set combinations. The invention may be used to implement 
multichannel control systems such as shown in U.S. Pat. Nos. 5,216,721 and 
5,216,722, incorporated herein by reference.

DETAILED DESCRIPTION 
FIG. 1 shows a multichannel active adaptive control system 10. A plurality 
of output transducer arrays 12, 14, etc. are provided, each array having 
at least one output transducer such as a loudspeaker, shaker, or other 
actuator or controller. The output transducer arrays introduce control 
signals to combine with a system input signal to yield a system output 
signal, as in incorporated U.S. Pat. No. 5,216,721 for example at 
canceling loudspeakers 14 and 210 introducing signals to combine with 
system input signal 6 to yield system output signal 8, and also for 
example as shown in U.S. Pat. No. 4,677,676, incorporated herein by 
reference, showing canceling loudspeaker 14, input signal 6, and output 
signal 8. A plurality of error transducers 16, 18, 20, 22, etc., such as 
microphones, accelerometers, or other sensors, sense the system output 
signal and provide a plurality of error signals. A plurality of A filters 
24, 26, etc. are provided, one for each output transducer array 12, 14, 
etc. Each of the A filters is preferably an LMS, least mean square, FIR, 
finite impulse response, filter, for example as shown at 12, 302, etc. in 
the incorporated '721 patent, and as shown at 12 in the incorporated '676 
patent, though other types of adaptive filters may be used, including 
RLMS, recursive least mean square, IIR, infinite impulse response, filters 
such as shown at 40, 202 in the incorporated '721 patent, and at 40 in the 
incorporated '676 patent, as well as other adaptive filters. A.sub.11 
filter 24 models the transfer function or acoustic path to output 
transducer 12. A.sub.21 filter 26 models the transfer function or acoustic 
path to output transducer 14. A plurality of D/A, digital to analog, 
converters 28, 30, etc. are provided, one for each output transducer array 
12, 14, etc. Each A filter outputs a correction signal through its 
respective D/A converter to its respective output transducer array to 
introduce the control signal. A plurality of sets of A/D, analog to 
digital, converters are provided, one set for each A filter. Each set has 
a plurality of A/D converters, one for each error transducer. In FIG. 1, a 
first set is provided by A/D converters 32, 34, 36, 38, and a second set 
is provided by A/D converters 40, 42, 44, 46. Each A filter has a 
plurality of error inputs, one for each A/D converter of its respective 
set. A.sub.11 filter 24 has error inputs 48, 50, 52, 54. A.sub.21 filter 
26 has error inputs 56, 58, 60, 62. Each error input receives a respective 
error signal through its respective A/D converter from its respective 
error transducer. 
A plurality of sets of C filters are provided, one set for each A filter. 
Each set has a plurality of C filters, one for each error transducer. In 
FIG. 1, a first set is provided by C filters 64, 66, 68, 70, and a second 
set is provided by C filters 72, 74, 76, 78. Each set of C filters has an 
input from the input to the respective A filter. Each C filter of each set 
has an output combined with the output of a respective A/D converter of 
the respective set of A/D converters. The output of C filter 64 is 
multiplied with the output of A/D converter 32 at multiplier 80, and the 
output resultant product provides weight update signal 82, as in the 
incorporated '721 and '676 patents. The output of C filter 66 is 
multiplied by the output of A/D converter 34 at multiplier 84, and the 
output resultant product provides weight update signal 86. The output of C 
filter 68 is multiplied by the output of A/D converter 36 at multiplier 
88, and the output resultant product provides weight update signal 90. The 
output of C filter 70 is multiplied by the output of A/D converter 38 at 
multiplier 92, and the output resultant product provides weight update 
signal 94. The output of C filter 72 is multiplied by the output of A/D 
converter 40 at multiplier 96, and the output resultant product provides 
weight update signal 98. The output of C filter 74 is multiplied by the 
output of A/D converter 42 at multiplier 100, and the output resultant 
product provides weight update signal 102. The output of C filter 76 is 
multiplied by the output of A/D converter 44 at multiplier 104, and the 
output resultant product provides weight update signal 106. The output of 
C filter 78 is multiplied by the output of A/D converter 46 at multiplier 
108, and the output resultant product provides weight update signal 110. 
Weight update signals 82, 86, 90 and 94 are summed at summer 112, and the 
output resultant sum is provided as the weight update signal to A filter 
24. Weight update signals 98, 102, 106 and 110 are summed at summer 114, 
and the output resultant sum is the weight update signal to A filter 26. 
The C filters model the transfer function or acoustic path from the 
respective output transducer to the respective error transducer. For 
example, C.sub.11 filter 64 models the transfer function to the first 
error transducer 16 from the first output transducer 12, C.sub.21 filter 
66 models the transfer function to the second error transducer 18 from the 
first output transducer 12, C.sub.31 filter 68 models the transfer 
function to the third error transducer 20 from the first output transducer 
12, C.sub.41 filter 70 models the transfer function to the fourth error 
transducer 22 from the first output transducer 12, C.sub.12 filter 72 
models the transfer function to the first error transducer 16 from the 
second output transducer 14, C.sub.22 filter 74 models the transfer 
function to the second error transducer 18 from the second output 
transducer 14, C.sub.32 filter 76 models the transfer function to the 
third error transducer 20 from the second output transducer 14, and 
C.sub.42 filter 78 models the transfer function to the fourth error 
transducer 22 from the second output transducer 14. The C filters are 
preferably provided using a random noise source as shown at 140 in FIG. 19 
of the incorporated '676 patent, with a copy of the respective transfer 
function or acoustic path filter model provided as shown at 144 in FIG. 19 
of the incorporated '676 patent, and also as shown at 352, 354, etc. in 
FIG. 8 of the incorporated '721 patent. It is preferred that each set of C 
filters have its own random noise source, for example as shown at 140a, 
140b in FIG. 8 of the incorporated '721 patent. Alternatively, the output 
transducer to error transducer transfer function or acoustic path may be 
modeled without a random noise source as in U.S. Pat. No. 4,987,598, 
incorporated herein by reference. 
A reference input transducer 116, such as a microphone, accelerometer, or 
other sensor, senses the system input signal and provides a reference 
signal as at 42 in the incorporated '721 and '676 patents. A plurality of 
A/D converters 118, 120, etc., are provided, one for each A filter. Each A 
filter has a reference input receiving the reference signal through its 
respective A/D converter from the reference input transducer 116. A.sub.11 
filter 24 models the transfer function or acoustic path to output 
transducer 12 from input transducer 116. A.sub.21 filter 26 models the 
transfer function or acoustic path to output transducer 14 from input 
transducer 116. The system is applicable to one or more input transducers, 
one or more output transducers, and one or more error transducers. One or 
more reference input signals representing the system input signal are 
provided by one or more reference input transducers such as 116. Only a 
single reference signal need be provided, and the same such reference 
signal may be input to each of the adaptive filter models. Such single 
reference input signal may be provided by a single input microphone, 
accelerometer or other sensor, or alternatively the reference input signal 
may be provided by a transducer such as a tachometer which provides the 
frequency of a periodic system input signal such as from an engine or the 
like. Alternatively, multiple reference input signals may be used. Further 
alternatively, the input reference signal may be provided by one or more 
error signals, in the case of a periodic noise source, for example 
incorporated U.S. Pat. No. 5,216,722. In FIG. 1, a first filter set 
combination is shown in dashed line at 180, and a second filter set 
combination is shown in dashed line at 182. 
FIG. 2 uses like reference numerals from FIG. 1 where appropriate to 
facilitate understanding. A plurality of sets of adaptive B filters are 
provided, one set for each A filter. Each set has a plurality of B 
filters, one for each output transducer. Each B filter is preferably an 
LMS FIR filter provided as in the incorporated '721 and '676 patents, 
though other filters may be used. A first set is provided by B filters 130 
and 132. A second set is provided by B filters 134 and 136. Each A filter 
has an output summed at a summer with the outputs of the B filters of its 
respective set, and the output of the summer provides the correction 
signal. The output of A filter 24 is summed at summer 138 with the outputs 
of B filters 130 and 132. The output of A filter 26 is summed at summer 
140 with the outputs of B filters 134 and 136. A plurality of sets of 
feedback A/D converters are provided, one set for each A filter. The 
number of feedback A/D converters in each set is one less than the number 
of output transducers. In FIG. 2, a first set is provided by A/D converter 
142, and a second set is provided by A/D converter 144. Each set has a 
single member because there are two output transducers. If there were 
three output transducers, then each set would have two members, etc. 
Each set of B filters has a first B filter with an input from the summer of 
its respective A filter prior to passing through its respective D/A 
converter. For example, in the first set of B filters, B filter 130 has an 
input from summer 138 prior to the correction signal passing through D/A 
converter 28. B filter 134 has an input from summer 140 prior to the 
A.sub.21 correction signal passing through D/A converter 30. The remaining 
B filters of each set have an input from a respective feedback A/D 
converter receiving a correction signal from the summer of another of the 
A filters after passing through its respective D/A converter. For example, 
B filter 132 has an input from A/D converter 142 receiving the correction 
signal from summer 140 of A filter 26 after passing through D/A converter 
30. B filter 136 has an input from feedback A/D converter 144 receiving 
the correction signal from summer 138 of A filter 24 after passing through 
D/A converter 28. Each input to each of the remaining B filters first 
passes through the D/A converter of the other A filter and then passes 
through the feedback A/D converter of the respective remaining B filter. 
In FIG. 2, a first filter set is shown at 184, and a second filter set is 
shown at 186. 
FIG. 3 uses like reference numerals from above where appropriate to 
facilitate understanding. A reference input transducer array is provided 
by one or more reference input transducers 116, 117, etc. A.sub.11 filter 
24 models the transfer function or acoustic path to output transducer 12 
from reference input transducer 116. A.sub.12 filter 25 models the 
transfer function or acoustic path to output transducer 12 from reference 
input transducer 117. A.sub.21 filter 26 models the transfer function or 
acoustic path to output transducer 14 from reference input transducer 116. 
A.sub.22 filter 27 models the transfer function or acoustic path to output 
transducer 14 from reference input transducer 117. A.sub.11 filter 24 
receives the reference signal from the first reference input transducer 
116 through A/D converter 118. A.sub.12 filter 25 receives the reference 
signal from the second reference input transducer 117 through A/D 
converter 119. A.sub.21 filter 26 receives the first reference signal from 
reference input transducer 116 through A/D converter 120. A.sub.22 filter 
27 receives the second reference signal from reference input transducer 
117 through A/D converter 121. The outputs of A filters 24 and 25 are 
summed at summer 138 and supplied with the summation of the outputs of B 
filters 130 and 132 through D/A converter 28 to output transducer array 
12. The outputs of A filters 26 and 27 are summed at summer 140 and 
supplied with the summation of the outputs of B filters 136 and 134 
through D/A converter 30 to output transducer array 14. In FIG. 3, a first 
filter set is shown at 188, and a second filter set is shown at 190. 
FIG. 4 uses like reference numerals from above where appropriate to 
facilitate understanding. A plurality of sets of adaptive B filters are 
provided, one set for each A filter. Each set has a plurality of B 
filters, one for each output transducer. A first set is provided by B 
filters 150 and 152. A second set is provided by B filters 154 and 156. 
Each B filter is preferably an LMS FIR filter provided as in the 
incorporated '721 and '676 patents at 22, 314, etc. A first set of summers 
158 and 160 is provided, one for each output transducer. A first set of 
D/A converters is provided by D/A converters 28 and 30, one for each 
summer. A second set of summers is provided by summers 162 and 164, one 
for each summer of the first set. A second set of D/A converters is 
provided by D/A converters 166 and 168, one for each summer of the first 
set. A plurality of sets of feedback A/D converters is provided, one set 
for each A filter. Each set has a plurality of A/D converters, one for 
each B filter of its respective set. The number of feedback A/D converters 
in each set is equal to the number of output transducers. In FIG. 4, a 
first set of feedback A/D converters is provided by A/D converters 170 and 
172, and a second set of feedback A/D converters is provided by A/D 
converters 174 and 176. Summer 158 sums the outputs of D/A converters 28 
and 166, and supplies the resultant sum to output transducer 12. Summer 
160 sums the outputs of D/A converters 30 and 168, and supplies the 
resultant sum to output transducer 14. Summer 162 sums the outputs of B 
filters 150 and 152, and supplies the resultant sum through D/A converter 
166 to summer 158. Summer 164 sums the outputs of B filters 154 and 156, 
and supplies the resultant sum through D/A converter 168 to summer 160. B 
filter 150 has an input through feedback A/D converter 170 from the output 
of summer 160. B filter 152 has an input through feedback A/D converter 
172 from the output of summer 158. B filter 154 has an input through 
feedback A/D converter 174 from the output of summer 158. B filter 156 has 
an input through feedback A/D converter 176 from the output of summer 160. 
In FIG. 4, a first filter set is shown at 192, a second filter set is 
shown at 194, a third filter set is shown at 196, and a fourth filter set 
is shown at 198. 
FIG. 5 uses like reference numerals from above where appropriate to 
facilitate understanding. Reference input transducer 117 senses the system 
input signal and provides a second reference signal. A/D converter 118 
supplies the first reference signal from reference input transducer 116 to 
A filter 24. A/D converter 120 supplies the first reference signal to A 
filter 26. A/D converter 119 supplies the second reference signal from 
reference input transducer 117 to A filter 25. A/D converter 121 supplies 
the second reference signal to A filter 27. Summer 138 sums the outputs of 
A filters 24 and 25 and supplies the resultant sum through D/A converter 
28 to summer 158. Summer 140 sums the outputs of A filters 26 and 27 and 
supplies the resultant sum through D/A converter 30 to summer 160. In FIG. 
5, a first filter set is shown at 200, a second filter set is shown at 
202, a third filter set is shown at 204, and a fourth filter set is shown 
at 206. 
FIG. 6 uses like reference numerals from above where appropriate to 
facilitate understanding. A/D converter 118a supplies the reference signal 
from reference input transducer 116 to A filter 24 and to A filter 26. The 
output of A filter 26 is supplied through D/A converter 177a and A/D 
converter 178a to summer 140. The output of B filter 136 is supplied 
through D/A converter 177b and A/D converter 178b to summer 140. The input 
to B filter 136 is supplied from the output of summer 138 prior to passing 
through D/A converter 28. In FIG. 6, a first filter set is shown at 208, 
and a second filter set is shown at 210. 
It is recognized that various equivalents, alternatives and modifications 
are possible within the scope of the appended claims. Various filter set 
combinations have been disclosed. Other filter sets and combinations are 
possible within the scope of the invention.