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DESCRIPTION JPH07162987

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DESCRIPTION JPH07162987
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
noise reduction device for reducing noise by generating the same signal as noise whose phase is
reversed.
[0002]
2. Description of the Related Art For example, in the interior of a car, noise may be generated due
to the rotation of an engine, which may cause an unpleasant feeling. A conventional device for
reducing such noise installs a micro horn at a point where noise is desired to be reduced, and
generates an adaptive filter tap value by an adaptive filter that generates noise in the opposite
phase to the noise input to the micro horn. The noise is reduced by adaptive control by the signal
that compensates for the transfer characteristic until the signal reaches the micro horn.
[0003]
In other words, the conventional noise reduction device transmits the transfer characteristic of
the propagation path in which the sound wave propagates from the speaker and the speaker that
converts the signal from the adaptive filter that cancels the noise into the sound wave to the
microphone. The characteristic compensation unit is made to record and control the adaptive
filter.
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[0004]
For this reason, for example, when the number of passengers changes, the transfer characteristic
from the speaker to the micro horn changes, and the transfer characteristic compensated by the
transfer characteristic compensator does not match the actual transfer characteristic, and the
noise reduction effect decreases. It was
An object of the present invention is to provide a noise reduction device in which the noise
reduction effect is not reduced even if the condition in the vehicle changes.
[0005]
SUMMARY OF THE INVENTION The means adopted by the present invention for solving the
above-mentioned problems will be described. A tap value of an adaptive filter that generates a
signal that reduces noise input to a microhorn, and a transmission that compensates for a
transfer characteristic until an output from the microhorn and a signal generated by the adaptive
filter reach the microhorn An audio frequency band for generating a signal of an audio frequency
band to be superimposed on a signal for reducing noise, in a noise reduction device adapted to
reduce noise signals from the microphone by adaptive control with a signal from a characteristic
compensation unit. Generating means, a speaker for converting a signal for reducing noise into a
sound wave by the signal generated by the audio frequency band generating means, and a
transfer characteristic measuring means for measuring transfer characteristics between the
microphones; and the transfer characteristic measuring means Means for rewriting the transfer
characteristics of the transfer characteristic compensation unit with the transfer characteristics
measured by Equipped with a.
[0006]
The signal generated by the sound frequency band generating means is superimposed on the
signal generated to reduce noise, converted into sound waves by the speaker, and sent out. The
transfer characteristic measuring means measures the transfer characteristic between the
speaker and the microphone by the signal generated by the audio frequency band generating
means.
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[0007]
The transfer characteristic rewriting unit rewrites the transfer characteristic of the transfer
characteristic compensating unit used to generate the signal for reducing the noise with the
transfer characteristic measured by the transfer characteristic measuring means. As described
above, an audio frequency band signal is superimposed on a signal generated to reduce noise and
transmitted from a speaker, and measurement and measurement are performed using an audio
frequency band signal on which the transfer characteristic between the speaker and the
microphone is superimposed. Since the transfer characteristics for generating a signal for
reducing noise are rewritten in the transfer characteristics, a high noise reduction effect can
always be obtained.
[0008]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present
invention will be described with reference to FIGS. FIG. 1 is a block diagram of an embodiment of
the present invention, FIG. 2 is a specific example of a transfer characteristic recording unit and a
recorded value update unit of the same embodiment, and FIG. 3 is a specific example of a
transfer characteristic compensation unit.
[0009]
In FIG. 1, 10 is a noise source, 11 is a pickup circuit for picking up noise from the noise source
10, 12 and 16 are analog-to-digital converters (A / D), 13 are digital-to-analog converters (D / A),
14 Denotes a speaker, 7 denotes an adaptive filter, 8 denotes a transfer characteristic
compensation unit, and 9 denotes a tap value updating unit for updating the tap value of the
adaptive filter 7.
[0010]
The micro horn 15 is installed at a point where noise is to be reduced.
The adaptive filter 7 corrects a portion different from the noise from the noise source 10 which
is input to the micro horn 15 and the signal picked up by the pickup circuit 11 is sent out from
the speaker 14 and the signal which reaches the micro horn 15 is a noise source It generates a
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signal of the same amplitude as the noise of 10 and in antiphase.
[0011]
The adaptive filter 7 is composed of a digital filter consisting of tapped delay lines. That is, by
using the output signal of the pickup circuit 11 having a correlation with noise as the input of the
adaptive filter 7, transmission of the filter so that the sound pressure waveform by the adaptive
filter 7 has an opposite phase to the noise at the position of the micro horn 15. It is possible to
determine the characteristics, and the adaptive processing is performed by the tap value update
unit 9.
[0012]
The transfer characteristic compensation unit 8 is affected by time delay, band limitation, and the
like before the signal generated by the adaptive filter 7 reaches the micro horn 15 through the D
/ A 13 and the speaker 14, so The compensation signal is generated so as to be compensated and
to have the same amplitude and the opposite phase as the signal from the noise source 10 at the
input of the microhorn.
[0013]
This transfer characteristic can also be constituted by a digital filter comprising a tapped delay
line.
FIG. 3 shows the configuration of the transfer characteristic compensation unit 8. Reference
numerals 80-1 to 80-J denote delay elements, which are delayed in time corresponding to
sampling intervals of sampling pulses input to the A / Ds 12 and 16. . Further, 81-0 to 81 -J are
tap values, and the output value of the delay element is multiplied by the tap value and output.
[0014]
Therefore, the output value of A / D 12 at t = tn is represented by x (n), and the output value at
the next t = tn + 1 is represented by x (n + 1), and <i = 1, 3 >> xi is Assuming that <i = 1, 3> Σxi =
x1 + x2 + x3, the compensation signal C (n) from the transfer characteristic compensator 8
output from the adder 82 is C (n) = <i = 0, J> .SIGMA.x (n-i) Ci (1)
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[0015]
The adaptive filter 7 and the tap value updating unit 9 have the same configuration as the
transfer characteristic recording unit and the recording value updating unit described later, and
therefore will be described with reference to FIG.
The adaptive filter 7 includes delay elements 70-1 to 70-Z, tap values 71-0 to 71-Z, and an adder
72, as shown in FIG. The delay element 70 delays the output signal from the time A / D 12 equal
to the generation interval of the sampling pulse.
[0016]
Therefore, the output y (n) from the adaptive filter 7 is represented by y (n) = <i = 0, Z> .SIGMA.x
(n-i) Wi (n) (2), and D / A 13 represents an analog signal. And sent from the speaker 14.
[0017]
The tap values WO (n) to Wz (n) of the adaptive filter 7 are updated each time a sampling pulse
is generated.
The tap value updating unit 9 updates the tap value. The tap value update unit 9 includes
multipliers 90, 91 and 92 and an adder 93, as shown in FIG.
[0018]
First, in the delay element 90, the output signal C (n) from the transfer characteristic
compensation unit 8 is input, and is delayed by a time equal to the generation interval of the
sampling pulse and propagated. Further, in the multiplier 91, multiplication is performed to
multiply the signal e (n) whose microhorn 15 output e (t) is converted into a digital value by the
A / D 16 by α. This α is determined by the loop characteristic of the adaptive control system.
[0019]
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Next, the update value W (n + 1) of each tap value of the adaptive filter 7 is calculated. For ease
of explanation, the case where the tap value WO (n) of the tap 71-0 is updated to WO (n + 1) will
be described as an example. The multiplier 92-0 multiplies the output of the multiplier 91 by the
output value C (n) from the transfer characteristic compensation unit 8. The adder 93-0 subtracts
the output value from the multiplier 92-0 from the tap value WO (n) at t = tn, and taps the result
as the tap value WO (n + 1) at the next t = tn + 1 Update the value
[0020]
That is, the tap values are updated as WO (n + 1) = WO (n) -αC (n) e (n) (3). The other taps Wi
are also updated to the tap values Wi (n + 1) = Wi (n)-. Alpha.C (n-i) e (n) (4).
[0021]
As described above, by updating the tap value, the sound wave transmitted from the speaker 14
has the same amplitude and the same amplitude as the noise from the noise source 10 at the
input of the micro horn 15, and the noise in the vicinity of the micro horn Reduce. As apparent
from the above description, when the transfer characteristic (tap values CO to Cj) recorded in the
transfer characteristic compensation unit 8 changes due to, for example, a change in the number
of passengers, a high noise reduction effect can not be obtained. .
[0022]
In the present invention, when the transfer characteristic changes, the recorded transfer
characteristic is rewritten to the actual transfer characteristic to obtain a high noise reduction
effect. In FIG. 1, 1 is a tone generation unit, 2 is a transfer characteristic recording unit, 3 is a
transfer characteristic rewrite unit, 4 is an error detection unit, 5 is a recorded value update unit,
17 is A / D, and 18 is D / A. is there.
[0023]
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The tone generation unit 1 generates a tone including high frequency components from low
frequencies in order to prevent the vehicle occupant from feeling unpleasant during the
measurement of transfer characteristics which will be described later. The signal generated by
the tone generation unit 1 is converted to a digital signal by the A / D 17 and input to the
transfer characteristic recording unit 2 and the recorded value update unit 5, and further
converted to an analog signal by the D / A 18 to obtain a speaker 14. Is input to
[0024]
The transfer characteristic recording unit 2 and the recorded value update unit 5 are configured
by the circuit shown in FIG. 2 and perform the same operations as the adaptive filter 7 and the
tap value update unit 9 described above to obtain tap value memory of the transfer characteristic
recording unit 2. The transfer characteristic is recorded in W71. Note that the error detection
unit 4 detects the difference between the error e (n) input to the recorded value update unit 5
and the signal output from the A / D 16 and the transfer characteristic recording unit 2 as an
error e (n). There is.
[0025]
Therefore, when the musical tone is generated from the musical tone generating unit 1 and the
error detected by the error detecting unit 4 is fed back to the transfer characteristic recording
unit 2 through the recorded value updating unit 5, the recorded characteristic is updated. The
signal output from 2 is output from the microhorn 15, and the same signal as the A / D
converted signal is obtained, and the error detected by the error detection unit 4 is eliminated.
[0026]
That is, the signal generated by the tone generation unit 1 is obtained by compensating the
transfer characteristics of the speaker 14 and the microphone 15 by the transfer characteristic
recording unit 2.
The transfer characteristic rewriting unit 3 reads the transfer characteristic recorded in the tap
value memory W71 of the transfer characteristic recording unit 2 when the error detected by the
error detection unit 4 becomes smaller, and the transmission described in FIG. It copies to the tap
value memory 81 of the characteristic compensation part 8, and rewrites a transmission
characteristic.
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[0027]
The operation of measuring the transfer characteristic described above and rewriting the transfer
characteristic of the transfer characteristic compensation unit can be performed even in a state
where noise is actually generated. In this case, although the noise is adaptively controlled by the
adaptive filter 7 and is not output to the microhorn 15, the musical tone generated by the
musical tone generator 1 is output from the microhorn 15 as it is and the transfer characteristic
is measured.
[0028]
In addition, the start of the operation of generating a musical tone and measuring the transfer
characteristic to rewrite the transfer characteristic of the transfer characteristic compensation
unit automatically, for example, when an error output from the micro horn exceeds a certain
fixed value. The operation may be started. In the embodiment, a musical tone is generated to
measure the transfer characteristic, but any signal may be used as long as it is a signal of a voice
band in which the transfer characteristic can be measured.
[0029]
As mentioned above, although one Example of this invention was described, this invention is not
limited to this Example, Various deformation | transformation according to the main point of the
invention are possible.
[0030]
As described above, according to the present invention, the following effects can be obtained.
A voice frequency band signal is superimposed on a signal generated to reduce noise and
transmitted from a speaker, and the transfer characteristic between the speaker and the
microphone is measured by a voice frequency band signal superimposed and noise is measured
by the measured transfer characteristic. Since the transfer characteristic for generating the signal
to be reduced is rewritten, a high noise reduction effect can always be obtained.
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