CA2117803A1 - Active cancellation of noise or vibrations - Google Patents
Active cancellation of noise or vibrationsInfo
- Publication number
- CA2117803A1 CA2117803A1 CA002117803A CA2117803A CA2117803A1 CA 2117803 A1 CA2117803 A1 CA 2117803A1 CA 002117803 A CA002117803 A CA 002117803A CA 2117803 A CA2117803 A CA 2117803A CA 2117803 A1 CA2117803 A1 CA 2117803A1
- Authority
- CA
- Canada
- Prior art keywords
- signals
- signal
- residual
- cancelling
- frequency domain
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1787—General system configurations
- G10K11/17879—General system configurations using both a reference signal and an error signal
- G10K11/17883—General system configurations using both a reference signal and an error signal the reference signal being derived from a machine operating condition, e.g. engine RPM or vehicle speed
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
- G10K11/17821—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
- G10K11/17825—Error signals
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
- G10K11/1785—Methods, e.g. algorithms; Devices
- G10K11/17853—Methods, e.g. algorithms; Devices of the filter
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/10—Applications
- G10K2210/129—Vibration, e.g. instead of, or in addition to, acoustic noise
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/301—Computational
- G10K2210/3025—Determination of spectrum characteristics, e.g. FFT
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/301—Computational
- G10K2210/3045—Multiple acoustic inputs, single acoustic output
Abstract
An active noise cancellation system processes a residual signal (r), generated by the interaction of a noise signal (p) and a cancelling signal (s), in the frequency domain so as to produce a new cancelling signal. A Fourier transformer (5, 8) operating in accordance with a moving discrete Fourier transform algorithm is used to produce a frequency domain representation of the residual signal.
Description
-- W~ 93~2~688 PCT/US~3354 iS -~117 ~3 I ~
Active Ca cellation of Noise or Vibrations FIELD OF THE INVENTION
The present invention relates to active cancellatio~ of noise or vibrations~
BACgGROUND TO '~ ~ INVENTIQN
One method of effecting active noise cancellation is described in US Patent No. 4 490 841 which is hereh~
incorporated by reference. The system described there transforms a residual signal, resulting from t~
superposition of a noise signal and a cancellinc ~:: signal, from the time domain into the frequency domair~
wherein it is represented by fourier coefficients. T~e fourier coefficients are then used to calculate further set of fourier coefficients from which t~
cancelling signal is generated by an inverse fourier transformer.
Many noise or vibration cancellation systems, includi~
that referred to hereinbefore, employ fast fourie~
transforms to convert from the time domain to t~
WO 93/2168~ P~T/USg3~0335,'`- i - 2 - ~
frequency domain. The fast fourier transforms are digitally implemented and the transformation process is carried out on a block of N samples. Therefore, ~he system cannot respond properly unti` N~ t after the change. has occurred, where ~t is the time between successive samples. Thus a step change in the noise signal results in a sharp xise in the amplitude of the residual signal which is then reduced in a stepwise manner as effective cancellation is re-establishe~.
This stepwise decay of residual signal has been found to ~e undesirable by users of such s~stems.
SUMYARY OF THE IN~ENTION
It is an object of the present invention to provide an improved active noise or ~ibration cancellation system which exhibits a non-stepwise decay of residual signal during establishment of effective cancellation.
According to the present invention, there is provided an active vibration cancellation system including means responsi~e to a residual vibration signal to produce an electrical signal representative thereof, sampling means for sampling said electrical signal and a fourier I--~.......... ~ ' ' ' ' '' ' ' ' ~ WO 93/21688 P~T/US~3/033~4 ~117 ~1 -transformer means for processing the sampled electrical signal to produce a frequency domain repres~n~ation of the residual vibration signal, wherein the fourier txansformer means performs a movin~ discrete fourier transformation on the sampled electrical signal to produce said frequency domain representation of the residual vibration signal.
In an emhodLment, the frequency domain representation is only a partial representation. The partial representation may comprise a limited number of, possibly predetermined, harmonics. This avoids the need for unnecessary processing where a par~icular noise source includes only a limited number of harmonics which need to be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is block diagram of a single--input/
single-output system according to the present invention;
Figure 2 is a block diagram of a first embodiment of a multi-input/multi-output system according to the present invention; and WO 93~2l6X8 PCT/US93/0335a ^`- ` ~
~lt ~-~ iJ~
- 4 - ~
Figure 3 is a block diagram of a second e~diment of a multi-input/multi-output system according t~ ~he present ivnention.
DESCRIPTION OF E~OD~NTS
A source of noise such as an internal combustion engine 1 generates prLmary vibrations p which propagate into the neighborhood of a microphone 2. A loudspeaker 3 generates secondary vibrations s which interact with the primary vibration p in the neigh~orhood of the microphone ~.
The microphone 2 outputs an electrical signal r which represents the residual sound wave produced by the interaction of the prLmary vibrations p and the secondary vibrations s. The output from the microphone 2 is amplified by an amplifier 10 filtered by a low pass filter 11. The filter outp~t is then digitised by an A to D converter 4 to produce a signal r' at 15 which is transformed 'into the frequency domain by a first fourier transformer 5. An electrical signal representing the fourier coefficients of the signal r~
is fed to a processor 6. The processor 6 also receives - 5 - ~
a ~ynchronisation signal from a synchronisation signal generator 7 which generates the signal s~T.chronlsation signal ln dependence on the operation of the internal combustion engine 1.
.
The fourier coefficients received by the processor ~
are modified in a manner described hereinafter to provide modi~ied fourier coefficients which are fed to a second, inverse fourier transformer 8. The second fourier transformer generates a di~ital tLme domain si~r.al s' at 16 in dependence up~n the fourier coefficients supplied to it. A D to A converter q ~onstructs an analog signal from the digital time domain signal. The constructed analog signal is fil~ered by a low pass filter 13, amplified b~ an amplifier 14 and fed to the loudspeaker ' which produces the secondary vibrations s in accordance therewith. The operation of the processor 6 is such that the secondary vibrations s will tend to be equal in amplitude but opposite in phase to the prLmary vibrations p in the neighbourhood of the microphone 2.
WO 93/21688 PCT/US93/0335'' ~
Q ~
The operation of the first fourier transformer 5 will now be described in more detail. The digitised residual signal r forms a set of N complex nun~ers r~k}
where k = 0, 1, 2, ..., N~ t is selected such that the~Nyquist criterion is satisfied for the highest frequency harmonic of interest. The well known discrete fourier transfo~l (DFT) of r~k} is the set of complex number R{m}, m = 0, 1, 2, ..., N-1 defined by:
~
_~ .
Rm 2 rk W , m - 0, 1, 2, ........... , N-l (1) k=0 where W = exp (~j 2 nlN) and m represents the harmonic being considered. Conventionally, the set of values R{m} would be calculated for each block of N
samples. However, the set of complex numbers R{m}
could be recalculated as~each sample is digitised by adding the new sample to the set r{k} and discarding the oldest sample; that is create a ~moving~ DFT. In practice, recalculating the set R{m} in this way `^ WO93/2168~ PCT/US93/03354 ~
.~ 1 1 7 `~
introduces an unacceptable overhead into the processing. However, if Rm(k) is the mth frequency component of the DFT of the kth sequence of r, i.e.
k ~ k + N-l} then R (k+l) expressed recursively in terms of Rm (k) as follows:
R (k~ R ( ) - rk + rk~N~ (2) ';
-~ Thus, it can be seen that producing the fourier coefficients of the residual signal in the manner defined by equation (2) eliminates much of the -~ ~ processing overhead which would be expected iI the fourier coefficients were to be calculated directly from the N samples on each occasion. Furthermore, the new fourier coefficient for each harmonic is only dependent on the previous va}ue for that harmonic, the kth sample of the residual signal r, and the (k+N)th sample ~f the ! residual`lsignal r.; The fact that the fourier transform for a given harmonic is not a function of any other harmonic makes this approach well WO 93/21688 PCT/US93/0335~
6 ~
- 8 - ~
suited to systems where only selected harmonics require cancellation.
Equation (2) is known from "Efficient DFT-Based Model Reducti~ns for Continuous Systems", IEEE Transactions on Automatic Control, vol. 36, No. 10, ppll~8-1193 and "On-Line ~etermination of Reduced-Order Models of Linear Systems Via the Moving Discrete Fourier Transform (MDFT)", ICAS '8~, ppl756-1799. However, it has not been proposed, heretofore, to apply moving discrete fourier transforms to the active canceilation of noise or vibrations. The independance of the calculations for each harmonic from that of any others is a major benefit in noise cancellation systems which must process signals in real tLme. Reducing the amount - of processin~, required to produce a given effect~
results in the extension of the cancelling capabilities of a system based on a particular procPssor or the option to use devices of a lower specification to achieve the same'effect.
~-`
jl_ P~r/uss3/033s4 WO 93/21688 ;v~ J
A system embodying the present invention responds to rapid change in the primary vibrations by producing a smooth decay in the resultant residual signal rather than the stepped decay found with the prior art.
. `
The operation of the processor 6 will now be described in more detail. The transfer function of the pa~h between the output 16 of the second fourier transformer 8 and the input 15 of the first fourier transformer 5 is stored for use by the processor 6. The transfer function may be predetermined or dynamically determined by the processor from detected changes in the signal r' in response to known changes in the signal s'. Thus the transfer function of the path between output 16 of the second fourier transformer 8 and input 15 of the first fourier transformer ~, T~, can be defined as foll~ws:
.
TF = change in siqnal s' , j .
resulting change in signal r' .
= a + ib i m + jn where a is the amplitude change of the sine components PC~/U~93/0335 WO 93/21S~8 - 10 - ,,~,"
of the signal s', b is the amplitude change of the cosine component of the signal s~, m is the resultant amplitude in the sine component of the signal r~ and n is the amplitude change in the cosin- component o the signal ~. Thus for a measured signal r~ of (p+jq) where p is the amplitude of the sine component Ot' r~
and q is the amplitude of the cosine component of r', the required change in siynal s~
ptam+bn~+q(an-bm~+j~ bm-an~+q(am+bn~1 m2 + n2 The processor 6 receives the fourier components from the fourier transformer S and calculates the necessarv change in fourier components cf the signal s based -thereon and on the known transfer function of the path between the output 16 o the second fourier transformer 8 and the input lS of the first fourier transformer 5.
The fourier components of the changed signal s~ are then fed to the second, inverse fourier transformer 8 ~, :
;' ' !
in order to produce a digital time àomain signal, which, after conversion to analog form by the D to A
converter 9, is used to produce the cancelling signal s ,` .
. ~
to effect cancellation.
; WO 93/~168S PCT/US93/0335~ ':
;~ l .L i ' a J
I
I, `:
11 ., j Referring to Figure 2, a two channel system is shown wherein a plurality of microphones 22 are associated with respective loudspeakers 23, for instance in the headrests of the seats in an airliner. Each of the microphones 22 is coupled to a respective analog to digital converter 24 via perspective amplifiers 30 and low-pass fitters 31. The first fourier transformer 5, operating in accordance with a MDFT algorithm, receives signals from the analog to digital converters 2~ and outputs electrical signals representing the fourier coefficients of the signals r' at the inputs to the first fourier transformer 5, which a~e derived from the residual signals r detected by the microphones 22, to ; the processor 6. Since each microphone 22 is substantially only affected by its associated speaker 23, the processor 6 operates as describeà
hereinbefore, carrying out the necessary ~rocessing of - each signal r' independently. The modified fourier coefficients are fed to a second fourier transformer 8 .
which outputs tLme domain signals to respective digital to analog convert~rs 2g. The analog signals created by the digital to analog converters 29 sre then passed WO 93/21688 PC~/US93/03354i `3~
through respective low-pass fitters 32 and amplifier6 33 to the speakers 13.
Referring ~o Figure 3, which shows a third e~bodiment of the present invention, suitable for cancelling noise within a volume such as the cabin of a car, a plurality of microphones 42 are distributed about a volume in which noise is to ~e can~elled. A sLmilar number of loudspeakers 43 are also distributed alound the volume. The arrangement of microphones 42 and speakers 4~ is such that each microphone 42 is influenced by more than one of the loudspeakers 43.
The outputs from the microphones 42 are again amplified and filtered by amplifiers S0 and low-pass filters 51 and then digitised by respective analogue to digital converters 44. However, a time division multiplexer 40 is interposed between the analogue to digital converters 44 and the first fourier transformer 5. The first fourier transformer operates in accordance with a MDFT algorithm. The signals output by the first fourier transformer 5 are again passed to a processor 6. The procC-~sor 6 processes these signals taking into account the fact that each microphone 42 responds to ~~ WO 9~/21688 PCrtUSg3/03354 ~;
~ 1 1 7 ~ O ~7 _ 13 -more than one speaker 43. The operation of the processor 6 will be described in mo.e detail hereinafter.
The modif~led fourier coefficients output from the processor 6 ~re treated in substantially the same manner as described with reference to Figure 2.
However, a demultiplexer 31 is interposed between the second fourier transformer 8 and the digital to analog converters 49. The constructed analog signals ou~put from the digital to analog converters 49 are filtered and amplified by respective low-pass filters 52 and amplifiers 53.
Since each microphone 42 responds to more than one speaker 43, the processor 6 determines the desired change in the signals s~ at the output of the second fourier transformer 8, according to the following algorithm:
WQ 93/~1688 PCT/US93/0335~, ~
2 1 ~ 7 'J ~3 3 5~ \ / 11 12 lj\ i \
.~ ~ ; T~21 T}22 T 2j ~ ~ 2 i TFi1 TFi~ TFij rj where Si to Si are the necessary changes in the signals output by the second fourier transformer 8 to drive respective speakers 1 to i, r~ to rj are the signals r' deriYed from the residual signals r from the microphones 1 to j and TFll to TFij are the transfer functions of each path from the output of the second fourier transformer 8 to the input of the first fourier transformer 5.
For instance, the first row of the transfer function matric contains the transfer functions of the paths including speaker 1 and respectively each of the ;
microphones 1 to j.
~~
In certain circumstances, the functions of the fourier ~.
. ` 21 l 7 ;~ ~? 3 transformers 5 8 and the processor 6 may be combined, for instance into a microcomputer running under the control of a suitable program.
It is ~preciated that the system described with reference to Figure 2 may be Lmplemen~ed using a multiplexer and demultiplexer and that the syst~m described with refeL-ence to Figure 3 may be implemented using the arrangement of elements shown in Figure 2.
Whilst the present invention has been described with reference to an internal combustion engine, microphones and loudpsea~ers, the present invention may ~e employed to cancel the noise or other cyclic vibrations from various signals and that other forms of transducers may be used in place of microphones and loudspea~ers.
s
Active Ca cellation of Noise or Vibrations FIELD OF THE INVENTION
The present invention relates to active cancellatio~ of noise or vibrations~
BACgGROUND TO '~ ~ INVENTIQN
One method of effecting active noise cancellation is described in US Patent No. 4 490 841 which is hereh~
incorporated by reference. The system described there transforms a residual signal, resulting from t~
superposition of a noise signal and a cancellinc ~:: signal, from the time domain into the frequency domair~
wherein it is represented by fourier coefficients. T~e fourier coefficients are then used to calculate further set of fourier coefficients from which t~
cancelling signal is generated by an inverse fourier transformer.
Many noise or vibration cancellation systems, includi~
that referred to hereinbefore, employ fast fourie~
transforms to convert from the time domain to t~
WO 93/2168~ P~T/USg3~0335,'`- i - 2 - ~
frequency domain. The fast fourier transforms are digitally implemented and the transformation process is carried out on a block of N samples. Therefore, ~he system cannot respond properly unti` N~ t after the change. has occurred, where ~t is the time between successive samples. Thus a step change in the noise signal results in a sharp xise in the amplitude of the residual signal which is then reduced in a stepwise manner as effective cancellation is re-establishe~.
This stepwise decay of residual signal has been found to ~e undesirable by users of such s~stems.
SUMYARY OF THE IN~ENTION
It is an object of the present invention to provide an improved active noise or ~ibration cancellation system which exhibits a non-stepwise decay of residual signal during establishment of effective cancellation.
According to the present invention, there is provided an active vibration cancellation system including means responsi~e to a residual vibration signal to produce an electrical signal representative thereof, sampling means for sampling said electrical signal and a fourier I--~.......... ~ ' ' ' ' '' ' ' ' ~ WO 93/21688 P~T/US~3/033~4 ~117 ~1 -transformer means for processing the sampled electrical signal to produce a frequency domain repres~n~ation of the residual vibration signal, wherein the fourier txansformer means performs a movin~ discrete fourier transformation on the sampled electrical signal to produce said frequency domain representation of the residual vibration signal.
In an emhodLment, the frequency domain representation is only a partial representation. The partial representation may comprise a limited number of, possibly predetermined, harmonics. This avoids the need for unnecessary processing where a par~icular noise source includes only a limited number of harmonics which need to be suppressed.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is block diagram of a single--input/
single-output system according to the present invention;
Figure 2 is a block diagram of a first embodiment of a multi-input/multi-output system according to the present invention; and WO 93~2l6X8 PCT/US93/0335a ^`- ` ~
~lt ~-~ iJ~
- 4 - ~
Figure 3 is a block diagram of a second e~diment of a multi-input/multi-output system according t~ ~he present ivnention.
DESCRIPTION OF E~OD~NTS
A source of noise such as an internal combustion engine 1 generates prLmary vibrations p which propagate into the neighborhood of a microphone 2. A loudspeaker 3 generates secondary vibrations s which interact with the primary vibration p in the neigh~orhood of the microphone ~.
The microphone 2 outputs an electrical signal r which represents the residual sound wave produced by the interaction of the prLmary vibrations p and the secondary vibrations s. The output from the microphone 2 is amplified by an amplifier 10 filtered by a low pass filter 11. The filter outp~t is then digitised by an A to D converter 4 to produce a signal r' at 15 which is transformed 'into the frequency domain by a first fourier transformer 5. An electrical signal representing the fourier coefficients of the signal r~
is fed to a processor 6. The processor 6 also receives - 5 - ~
a ~ynchronisation signal from a synchronisation signal generator 7 which generates the signal s~T.chronlsation signal ln dependence on the operation of the internal combustion engine 1.
.
The fourier coefficients received by the processor ~
are modified in a manner described hereinafter to provide modi~ied fourier coefficients which are fed to a second, inverse fourier transformer 8. The second fourier transformer generates a di~ital tLme domain si~r.al s' at 16 in dependence up~n the fourier coefficients supplied to it. A D to A converter q ~onstructs an analog signal from the digital time domain signal. The constructed analog signal is fil~ered by a low pass filter 13, amplified b~ an amplifier 14 and fed to the loudspeaker ' which produces the secondary vibrations s in accordance therewith. The operation of the processor 6 is such that the secondary vibrations s will tend to be equal in amplitude but opposite in phase to the prLmary vibrations p in the neighbourhood of the microphone 2.
WO 93/21688 PCT/US93/0335'' ~
Q ~
The operation of the first fourier transformer 5 will now be described in more detail. The digitised residual signal r forms a set of N complex nun~ers r~k}
where k = 0, 1, 2, ..., N~ t is selected such that the~Nyquist criterion is satisfied for the highest frequency harmonic of interest. The well known discrete fourier transfo~l (DFT) of r~k} is the set of complex number R{m}, m = 0, 1, 2, ..., N-1 defined by:
~
_~ .
Rm 2 rk W , m - 0, 1, 2, ........... , N-l (1) k=0 where W = exp (~j 2 nlN) and m represents the harmonic being considered. Conventionally, the set of values R{m} would be calculated for each block of N
samples. However, the set of complex numbers R{m}
could be recalculated as~each sample is digitised by adding the new sample to the set r{k} and discarding the oldest sample; that is create a ~moving~ DFT. In practice, recalculating the set R{m} in this way `^ WO93/2168~ PCT/US93/03354 ~
.~ 1 1 7 `~
introduces an unacceptable overhead into the processing. However, if Rm(k) is the mth frequency component of the DFT of the kth sequence of r, i.e.
k ~ k + N-l} then R (k+l) expressed recursively in terms of Rm (k) as follows:
R (k~ R ( ) - rk + rk~N~ (2) ';
-~ Thus, it can be seen that producing the fourier coefficients of the residual signal in the manner defined by equation (2) eliminates much of the -~ ~ processing overhead which would be expected iI the fourier coefficients were to be calculated directly from the N samples on each occasion. Furthermore, the new fourier coefficient for each harmonic is only dependent on the previous va}ue for that harmonic, the kth sample of the residual signal r, and the (k+N)th sample ~f the ! residual`lsignal r.; The fact that the fourier transform for a given harmonic is not a function of any other harmonic makes this approach well WO 93/21688 PCT/US93/0335~
6 ~
- 8 - ~
suited to systems where only selected harmonics require cancellation.
Equation (2) is known from "Efficient DFT-Based Model Reducti~ns for Continuous Systems", IEEE Transactions on Automatic Control, vol. 36, No. 10, ppll~8-1193 and "On-Line ~etermination of Reduced-Order Models of Linear Systems Via the Moving Discrete Fourier Transform (MDFT)", ICAS '8~, ppl756-1799. However, it has not been proposed, heretofore, to apply moving discrete fourier transforms to the active canceilation of noise or vibrations. The independance of the calculations for each harmonic from that of any others is a major benefit in noise cancellation systems which must process signals in real tLme. Reducing the amount - of processin~, required to produce a given effect~
results in the extension of the cancelling capabilities of a system based on a particular procPssor or the option to use devices of a lower specification to achieve the same'effect.
~-`
jl_ P~r/uss3/033s4 WO 93/21688 ;v~ J
A system embodying the present invention responds to rapid change in the primary vibrations by producing a smooth decay in the resultant residual signal rather than the stepped decay found with the prior art.
. `
The operation of the processor 6 will now be described in more detail. The transfer function of the pa~h between the output 16 of the second fourier transformer 8 and the input 15 of the first fourier transformer 5 is stored for use by the processor 6. The transfer function may be predetermined or dynamically determined by the processor from detected changes in the signal r' in response to known changes in the signal s'. Thus the transfer function of the path between output 16 of the second fourier transformer 8 and input 15 of the first fourier transformer ~, T~, can be defined as foll~ws:
.
TF = change in siqnal s' , j .
resulting change in signal r' .
= a + ib i m + jn where a is the amplitude change of the sine components PC~/U~93/0335 WO 93/21S~8 - 10 - ,,~,"
of the signal s', b is the amplitude change of the cosine component of the signal s~, m is the resultant amplitude in the sine component of the signal r~ and n is the amplitude change in the cosin- component o the signal ~. Thus for a measured signal r~ of (p+jq) where p is the amplitude of the sine component Ot' r~
and q is the amplitude of the cosine component of r', the required change in siynal s~
ptam+bn~+q(an-bm~+j~ bm-an~+q(am+bn~1 m2 + n2 The processor 6 receives the fourier components from the fourier transformer S and calculates the necessarv change in fourier components cf the signal s based -thereon and on the known transfer function of the path between the output 16 o the second fourier transformer 8 and the input lS of the first fourier transformer 5.
The fourier components of the changed signal s~ are then fed to the second, inverse fourier transformer 8 ~, :
;' ' !
in order to produce a digital time àomain signal, which, after conversion to analog form by the D to A
converter 9, is used to produce the cancelling signal s ,` .
. ~
to effect cancellation.
; WO 93/~168S PCT/US93/0335~ ':
;~ l .L i ' a J
I
I, `:
11 ., j Referring to Figure 2, a two channel system is shown wherein a plurality of microphones 22 are associated with respective loudspeakers 23, for instance in the headrests of the seats in an airliner. Each of the microphones 22 is coupled to a respective analog to digital converter 24 via perspective amplifiers 30 and low-pass fitters 31. The first fourier transformer 5, operating in accordance with a MDFT algorithm, receives signals from the analog to digital converters 2~ and outputs electrical signals representing the fourier coefficients of the signals r' at the inputs to the first fourier transformer 5, which a~e derived from the residual signals r detected by the microphones 22, to ; the processor 6. Since each microphone 22 is substantially only affected by its associated speaker 23, the processor 6 operates as describeà
hereinbefore, carrying out the necessary ~rocessing of - each signal r' independently. The modified fourier coefficients are fed to a second fourier transformer 8 .
which outputs tLme domain signals to respective digital to analog convert~rs 2g. The analog signals created by the digital to analog converters 29 sre then passed WO 93/21688 PC~/US93/03354i `3~
through respective low-pass fitters 32 and amplifier6 33 to the speakers 13.
Referring ~o Figure 3, which shows a third e~bodiment of the present invention, suitable for cancelling noise within a volume such as the cabin of a car, a plurality of microphones 42 are distributed about a volume in which noise is to ~e can~elled. A sLmilar number of loudspeakers 43 are also distributed alound the volume. The arrangement of microphones 42 and speakers 4~ is such that each microphone 42 is influenced by more than one of the loudspeakers 43.
The outputs from the microphones 42 are again amplified and filtered by amplifiers S0 and low-pass filters 51 and then digitised by respective analogue to digital converters 44. However, a time division multiplexer 40 is interposed between the analogue to digital converters 44 and the first fourier transformer 5. The first fourier transformer operates in accordance with a MDFT algorithm. The signals output by the first fourier transformer 5 are again passed to a processor 6. The procC-~sor 6 processes these signals taking into account the fact that each microphone 42 responds to ~~ WO 9~/21688 PCrtUSg3/03354 ~;
~ 1 1 7 ~ O ~7 _ 13 -more than one speaker 43. The operation of the processor 6 will be described in mo.e detail hereinafter.
The modif~led fourier coefficients output from the processor 6 ~re treated in substantially the same manner as described with reference to Figure 2.
However, a demultiplexer 31 is interposed between the second fourier transformer 8 and the digital to analog converters 49. The constructed analog signals ou~put from the digital to analog converters 49 are filtered and amplified by respective low-pass filters 52 and amplifiers 53.
Since each microphone 42 responds to more than one speaker 43, the processor 6 determines the desired change in the signals s~ at the output of the second fourier transformer 8, according to the following algorithm:
WQ 93/~1688 PCT/US93/0335~, ~
2 1 ~ 7 'J ~3 3 5~ \ / 11 12 lj\ i \
.~ ~ ; T~21 T}22 T 2j ~ ~ 2 i TFi1 TFi~ TFij rj where Si to Si are the necessary changes in the signals output by the second fourier transformer 8 to drive respective speakers 1 to i, r~ to rj are the signals r' deriYed from the residual signals r from the microphones 1 to j and TFll to TFij are the transfer functions of each path from the output of the second fourier transformer 8 to the input of the first fourier transformer 5.
For instance, the first row of the transfer function matric contains the transfer functions of the paths including speaker 1 and respectively each of the ;
microphones 1 to j.
~~
In certain circumstances, the functions of the fourier ~.
. ` 21 l 7 ;~ ~? 3 transformers 5 8 and the processor 6 may be combined, for instance into a microcomputer running under the control of a suitable program.
It is ~preciated that the system described with reference to Figure 2 may be Lmplemen~ed using a multiplexer and demultiplexer and that the syst~m described with refeL-ence to Figure 3 may be implemented using the arrangement of elements shown in Figure 2.
Whilst the present invention has been described with reference to an internal combustion engine, microphones and loudpsea~ers, the present invention may ~e employed to cancel the noise or other cyclic vibrations from various signals and that other forms of transducers may be used in place of microphones and loudspea~ers.
s
Claims (31)
WHAT IS CLAIMED IS:
1. An active noise or vibration cancelling system for cancelling a substantially periodic noise signal, including:
processing means for producing a cancelling signal for cancelling said noise signal in dependance on a frequency domain representation signal;
means for producing a residual signal representative of the sum of said noise signal and said cancelling signal;
means for sampling said residual signal to produce a sampled signal representative of said residual signal;
and transformer means for transforming said sampled signal by moving discrete fourier transformation to produce a frequency domain representation signal of said residual signal to control said processing means.
processing means for producing a cancelling signal for cancelling said noise signal in dependance on a frequency domain representation signal;
means for producing a residual signal representative of the sum of said noise signal and said cancelling signal;
means for sampling said residual signal to produce a sampled signal representative of said residual signal;
and transformer means for transforming said sampled signal by moving discrete fourier transformation to produce a frequency domain representation signal of said residual signal to control said processing means.
2. A system according to claim 1, wherein said processing means includes a processor for producing a frequency domain representation signal of a cancelling signal in dependance on said frequency domain representation signal of said residual signal, and inverse transformer means for producing said cancelling signal from said frequency domain representation signal of a cancelling signal.
3. A system according to claim 1, wherein the frequency domain representation signal is a partial representation of said residual signal in the frequency domain.
4. A system according to claim 3, wherein the frequency domain representation signal represents the components of said residual signal at predetermined harmonics of a noise fundamental frequency.
5. A system according to claim 1, wherein said means for sampling includes means for digitizing said sampled signal, whereby said sampled signal is in digital form.
6. A system according to claim 1, wherein said transformer means processes said sampled signal according to the algorithm:
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of 2 residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp (-j2.pi./N).
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of 2 residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp (-j2.pi./N).
7. An active noise or vibration cancelling system for cancelling a substantially periodic noise signal including:
processing means for producing a plurality of cancelling signals for cancelling substantially periodic noise signals, having a common source, at different respective locations in dependance upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of the sum of said cancelling signals and one of said noise signals at each of said locations;
a plurality of means for sampling respective said residual signals to produce a plurality of sampled signals; and transformer means for transforming said sampled signals by moving discrete fourier transformation to produce a frequency domain representation signal for each of said residual signals for controlling said processing means.
processing means for producing a plurality of cancelling signals for cancelling substantially periodic noise signals, having a common source, at different respective locations in dependance upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of the sum of said cancelling signals and one of said noise signals at each of said locations;
a plurality of means for sampling respective said residual signals to produce a plurality of sampled signals; and transformer means for transforming said sampled signals by moving discrete fourier transformation to produce a frequency domain representation signal for each of said residual signals for controlling said processing means.
8. A system according to claim 7, wherein said processing means includes a processor for producing frequency domain representative signals of cancelling signals in dependance upon said frequency domain representative signals of said residual signals and inverse transformer means for producing said cancelling signals from said frequency domain representing signals of a cancelling signal.
9. A system according to claim 7, wherein the frequency domain representation signals are partial representations of said residual signals in the frequency domain.
10. A system according to claim 9, wherein the frequency domain representation signals represent the components of said residual signals at predetermined harmonics of a noise fundamental frequency.
11. A system according to claim 7, wherein said means for sampling includes means for digitizing said sampled signals, whereby said sampled signals are in digital form.
12. A system according to claim 7, wherein said transformer means processes said sampled signals according to the algorithm:
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, r(k+N) is the (k+N) the sample of the residual noise signal, N is the number of samples processed, and W is exp(-j2.pi./N).
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, r(k+N) is the (k+N) the sample of the residual noise signal, N is the number of samples processed, and W is exp(-j2.pi./N).
13. An active noise or vibration cancelling system for cancelling a substantially periodic noise signal including:
processing means for producing a plurality of cancelling signals for cancelling a substantially periodic noise signal in a predetermined space in dependence upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of spacially distributed sums of said cancelling signals and said noise signal;
a plurality of means for sampling said respective residual signals to produce a plurality of sampled signals; and transformer means for processing said sampled signals by moving discrete fourier transformation to produce a frequency domain representation signal for each of said residual signals to control said processing means.
processing means for producing a plurality of cancelling signals for cancelling a substantially periodic noise signal in a predetermined space in dependence upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of spacially distributed sums of said cancelling signals and said noise signal;
a plurality of means for sampling said respective residual signals to produce a plurality of sampled signals; and transformer means for processing said sampled signals by moving discrete fourier transformation to produce a frequency domain representation signal for each of said residual signals to control said processing means.
14. A system according to claim 13, wherein said processing means includes a processor for producing frequency domain representative signals of cancelling signals in dependence upon said frequency domain representative signals of said residual signals, and inverse transformer means for producing said cancelling signals from said frequency domain representing signal of a cancelling signal.
15. A system according to claim 13, wherein the frequency domain representation signals are partial representations of said residual signals in the frequency domain.
16. A system according to claim 15, wherein the frequency domain representation signals represent the components of said residual signals at predetermined harmonics of a noise fundamental frequency.
17. A system according to claim 13, wherein said means for sampling includes means for digitizing said sampled signals, whereby said sampled signals are in digital form.
18. A system according to claim 13, wherein said transformer means processes said sampled signals according to the algorithm:
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp(-j2.pi./N).
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp(-j2.pi./N).
19. An active noise or vibration cancelling system including:
processing means for producing a plurality of cancelling signals for cancelling substantially periodic noise signals, having a common source, at different respective locations in dependence upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of the sum of said cancelling signals and one of said noise signals at each of said locations;
a plurality of means for sampling respective said residual signals to produce a plurality of sampled signals;
means for time division multiplexing said sampled signals to form a multiplex signal; and transformer means for transforming said multiplex signal by discrete fourier transformation to produce a frequency domain representation of each of said residual signals to control said processing means.
processing means for producing a plurality of cancelling signals for cancelling substantially periodic noise signals, having a common source, at different respective locations in dependence upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of the sum of said cancelling signals and one of said noise signals at each of said locations;
a plurality of means for sampling respective said residual signals to produce a plurality of sampled signals;
means for time division multiplexing said sampled signals to form a multiplex signal; and transformer means for transforming said multiplex signal by discrete fourier transformation to produce a frequency domain representation of each of said residual signals to control said processing means.
20. A system according to claim 19, wherein said processing means includes a processor for producing frequency domain representative signals of cancelling signals in dependance upon said frequency domain representative signals of said residual signals and inverse transformer means for producing said cancelling signals from said frequency domain representing signals of said cancelling signals.
21. A system according to claim 19, wherein the frequency domain representation signals are partial representations of said residual signals in the frequency domain.
22. A system according to claim 21, wherein the frequency domain representation signals represent the components of said residual signals at predetermined harmonics of a noise fundamental frequency.
23. A system according to claim 19, wherein said means for sampling includes means for digitizing said sampled signals, whereby said sampled signals are in digital form.
24. A system according to claim 19, wherein said transformer means processes said multiplex signal according to the algorithm:
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp(-j2.pi./N).
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp(-j2.pi./N).
25. An active noise or vibration cancelling system including:
processing means for producing a plurality of cancelling signals for cancelling a substantially periodic noise signal in a predetermined space in dependence upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of spatially distributed sums of said cancelling signals and said noise signal;
a plurality of means for sampling respective said residual signals to produce a plurality of sampled signals;
means for time division multiplexing said sampled signals to form a multiplex signal; and transformer means for transforming said multiplex signal by moving discrete fourier transformation to produce a frequency domain representation signal for each of said residual signals to control said processing means.
processing means for producing a plurality of cancelling signals for cancelling a substantially periodic noise signal in a predetermined space in dependence upon frequency domain representation signals;
a plurality of means for producing respective residual signals representative of spatially distributed sums of said cancelling signals and said noise signal;
a plurality of means for sampling respective said residual signals to produce a plurality of sampled signals;
means for time division multiplexing said sampled signals to form a multiplex signal; and transformer means for transforming said multiplex signal by moving discrete fourier transformation to produce a frequency domain representation signal for each of said residual signals to control said processing means.
26. A system according to claim 25, wherein said processing means includes a processor for producing frequency domain representative signals of cancelling signals in dependance upon said frequency domain representative signals of said residual signals and inverse transformer means for producing said cancelling signals from said frequency domain representing signals of said cancelling signals.
27. A system according to claim 25, wherein the frequency domain representation signals are partial representations of said residual signals in the frequency domain.
28. A system according to claim 27, wherein the frequency domain representation signals represent the components of said residual signals at predetermined harmonics of a noise fundamental frequency.
29. A system according to claim 25, wherein said means for sampling includes means for digitizing said sampled signals, whereby said sampled signals are in digital form.
30. A system according to claim 25, wherein said transformer means processes said multiplex signal according to the algorithm:
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp(-j2.pi./N).
where: Rm(k) is the mth frequency component of the discrete fourier transform of the kth sequence of r which is a sampled signal representative of a residual noise signal, Rm(k+1) is the mth frequency component of the discrete fourier transform of the (k+1)th sequence of r, rk is kth sample of the residual noise signal, N is the number of samples processed, r(k+N) is the (k+N) the sample of the residual noise signal, and W is exp(-j2.pi./N).
31. An active noise or vibration cancelling system for cancelling a substantially periodic noise signal, including:
means for producing a cancelling signal for cancelling said noise signal in dependence upon a controlling signal;
means for producing a residual signal representative of the sum of said noise signal and said cancelling signal;
means for sampling said residual signal to produce a sampled signal representative of the residual signal;
transformer means responsive to said sample signal to produce a frequency domain representation signal of said residual signal utilizing a moving discrete fourier transform;
processing means for operating on said frequency domain representation signal to produce frequency domain representation of noise cancellation signals for cancelling said residual signal; and inverse transformer means, responsive to said frequency domain representation of said cancellation signals, for producing said controlling signal based upon a time domain representation of said cancellation signals.
means for producing a cancelling signal for cancelling said noise signal in dependence upon a controlling signal;
means for producing a residual signal representative of the sum of said noise signal and said cancelling signal;
means for sampling said residual signal to produce a sampled signal representative of the residual signal;
transformer means responsive to said sample signal to produce a frequency domain representation signal of said residual signal utilizing a moving discrete fourier transform;
processing means for operating on said frequency domain representation signal to produce frequency domain representation of noise cancellation signals for cancelling said residual signal; and inverse transformer means, responsive to said frequency domain representation of said cancellation signals, for producing said controlling signal based upon a time domain representation of said cancellation signals.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86691892A | 1992-04-10 | 1992-04-10 | |
| US07/866,918 | 1992-04-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2117803A1 true CA2117803A1 (en) | 1993-10-28 |
Family
ID=25348722
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002117803A Abandoned CA2117803A1 (en) | 1992-04-10 | 1993-04-09 | Active cancellation of noise or vibrations |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0697149A1 (en) |
| AU (1) | AU3976493A (en) |
| CA (1) | CA2117803A1 (en) |
| WO (1) | WO1993021688A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB9920883D0 (en) | 1999-09-03 | 1999-11-10 | Titon Hardware | Ventilation assemblies |
| DE102010029881B4 (en) | 2010-06-09 | 2012-02-02 | Schmitz-Werke Gmbh + Co. Kg | awning |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1577322A (en) * | 1976-05-13 | 1980-10-22 | Bearcroft R | Active attenuation of recurring vibrations |
| WO1983001525A1 (en) * | 1981-10-21 | 1983-04-28 | Chaplin, George, Brian, Barrie | Improved method and apparatus for cancelling vibrations |
| US4736431A (en) * | 1986-10-23 | 1988-04-05 | Nelson Industries, Inc. | Active attenuation system with increased dynamic range |
-
1993
- 1993-04-09 CA CA002117803A patent/CA2117803A1/en not_active Abandoned
- 1993-04-09 EP EP93909299A patent/EP0697149A1/en not_active Withdrawn
- 1993-04-09 WO PCT/US1993/003354 patent/WO1993021688A1/en not_active Application Discontinuation
- 1993-04-09 AU AU39764/93A patent/AU3976493A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO1993021688A1 (en) | 1993-10-28 |
| AU3976493A (en) | 1993-11-18 |
| EP0697149A1 (en) | 1996-02-21 |
| EP0697149A4 (en) | 1995-12-20 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP2889114B2 (en) | Active noise canceller | |
| EP2597638B1 (en) | Tunable active noise control | |
| EP0615340A1 (en) | Low-delay subband adaptive filter | |
| JPH08509823A (en) | Single and multi-channel block adaptation method and apparatus for active acoustic and vibration control | |
| US20080126461A1 (en) | Signal processing system employing time and frequency domain partitioning | |
| WO1994009482A1 (en) | Adaptive control system | |
| US5745581A (en) | Tracking filter for periodic signals | |
| DE60030137T2 (en) | METHOD AND DEVICE FOR INCREASING THE PERFORMANCE OF AN ADAPTIVE FILTER BY MEANS OF NON-HARMFUL INFORMATION | |
| US5638022A (en) | Control system for periodic disturbances | |
| Kuo et al. | Broadband adaptive noise equalizer | |
| CA2117803A1 (en) | Active cancellation of noise or vibrations | |
| JP3646809B2 (en) | Time domain adaptive control system | |
| EP0694234B1 (en) | Control system for periodic disturbances | |
| Kuo | Multiple-channel adaptive noise equalizers | |
| CA2138553C (en) | Control system for periodic disturbances | |
| KR100795475B1 (en) | The noise-eliminator and the designing method of wavelet transformation | |
| Pawełczyk | Feedforward algorithms with simplified plant model for active noise control | |
| JPH05313672A (en) | Noise controller | |
| Wang et al. | Integration of bass enhancement and active noise control system in automobile cabin | |
| Sherratt | Results of a DSP based adaptive cancellation filter system for the chirp, pulsar and localiser sirens | |
| JP3432845B2 (en) | Noise cancellation method | |
| Su et al. | Application of an improved wide-narrow-band hybrid ANC algorithm in large commercial vehicle cab | |
| JP2002366161A (en) | Noise controller | |
| CN117220642A (en) | Mixed control method based on subband non-delay | |
| Kasprzyk | Model identification for active noise control in the presence of primary noise |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |