JPH05333872A - Noise reducing device - Google Patents

Abstract

PURPOSE:To obtain the best noise reduction effect at all times even if a head changes in position or direction. CONSTITUTION:A canceling sound generating means 30 generates a canceling sound for canceling a noise gathered by a microphone 21 for reference input. A speaker 26 radiates the canceling sound from the canceling sound generating means 30. The noise residual in a sound field whose noise is reduced with this canceling sound is gathered by a microphone 41 for residue detection which is fitted to an accessory and fixedly installed nearby an ear 12. The residual signal of the microphone 14 for residue detection is supplied to the canceling sound generating means 30, which makes an adjustment so that the residue is minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small active noise reduction device that acoustically reduces noise.

[0002]

2. Description of the Related Art Conventionally, a device called an active noise reduction device has been known. This is because the noise radiated from the noise source reaches the human ear through a spatial path, but a sound wave having an amplitude equal to that of the noise from the noise source but having an opposite phase is emitted from, for example, a speaker, and the sound is emitted near the ear. It is a system for reducing noise in.

In this type of noise reduction device, a noise signal (this noise signal has a very strong correlation with noise from the noise source) is picked up by a reference input microphone installed near the noise source, A canceling sound forming circuit forms a sound signal for canceling noise near the ear from the noise signal. Then, this canceling audio signal is supplied to the speaker to reduce noise in the vicinity of the ear. Then, a residual detection microphone that picks up the noise residual is placed near the ear, and the detection signal from this residual detection microphone is fed back to the cancellation sound formation circuit, and noise is generated in this cancellation sound formation circuit. The adjustment is made so that the residual is minimized.

In this active noise reduction device, it is desirable to install the residual detection microphone at the ear canal entrance or near the eardrum as much as possible, and the farther away from that position, the smaller the noise reduction amount. Conventionally, when applied to an occupant of an aircraft, for example, the noise residual detection microphone is fixed near the ears of the occupant by a supporting member such as a seat or a headrest.

[0005]

However, when the residual detection microphone is installed at a position distant from the human body such as the seat or the headrest as described above, the difference in the size of the person's head and the sitting method are different. In addition, it is necessary to consider that it is necessary to allow a certain degree of freedom for the movement of the head.Therefore, the residual detection microphone must be installed away from the ear, and the residual detection microphone must be fully Was difficult to approach. As a result, there is a drawback that a sufficient noise reduction amount cannot be obtained.

Further, in the conventional system, since the residual detection microphone is physically fixed and attached apart from the human body, the area where noise is reduced is limited,
If the ears are not within that area, a certain amount of noise reduction cannot be obtained. For this reason, there is a drawback that the free movement of the head is restricted.

In view of the above points, an object of the present invention is to provide a noise reduction device which can always obtain a sufficient noise reduction amount even if the head moves or the direction changes.

[0008]

In order to solve the above-mentioned problems, the noise reduction device according to the present invention is provided with a reference input microphone 21 for picking up noise when the reference numerals of the embodiments described later are made to correspond to each other. This reference input microphone 2
From the noise picked up in 1, the canceling sound forming means 30 for forming a canceling sound for canceling this noise, and the sound signal for emitting the canceling sound in response to the audio signal from the canceling sound forming means 30 Means 26 and this sound emitting means 26
Residual detection microphone 4 for picking up a noise residual in a sound field whose noise is reduced by a cancellation sound emitted from
1 and the residual signal picked up by the residual detection microphone 41 is supplied to the canceling sound forming means 30, and the canceling sound forming means 30 is adjusted so that the residual is minimized. The residual detection microphone 41 is attached to the accessory 50. It is more preferable that this accessory is a thing worn on the head, for example, glasses or a hair band.

[0009]

In the present invention constructed as described above, the residual detection microphone 41 is attached to an accessory worn on the human body and installed near the ear. Since the residual detection microphone is attached to the human body, a predetermined noise reduction amount can always be obtained irrespective of head movement and direction change.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a noise reduction device according to the present invention will be described below with reference to the drawings, taking an adaptive noise reduction device for performing adaptive processing using an adaptive filter circuit as an example.

Before explaining the embodiment of the present invention, FIG.
The adaptive noise reduction apparatus will be described with reference to FIG.
In FIG. 3, 1 is a main input terminal, 2 is a reference input terminal, and the signal input through the main input terminal 1 is supplied to the combining circuit 4 via the delay circuit 3. In addition, the signal input through the reference input terminal 2 is an adaptive filter circuit 5
Is supplied to the synthesizing circuit 4 via and is subtracted from the signal from the delay circuit 3. The output of the synthesizing circuit 4 is fed back to the adaptive filter circuit 5 and is also led to the output terminal 6.

In this noise reduction apparatus, the main input terminal 1 receives the desired signal s and the noise n0 uncorrelated with the desired signal s. On the other hand, noise n1 is input to the reference input terminal 2. Noise n1 of this reference input
Is uncorrelated with the desired signal, but is correlated with noise n0.

The adaptive filter circuit 5 has a reference input noise n1.
Is filtered to output a signal y that approximates noise n0. As the output signal y of this adaptive filter circuit 5,
It is also possible to obtain a signal having a phase opposite to that of the noise and having the same amplitude. In the synthesizing circuit 4, a process of subtracting the output signal of the adaptive filter circuit 5 from the output signal of the delay circuit 3 is performed.
The delay circuit 3 is for adjusting the time of the signals to be subtracted in consideration of the processing time in the adaptive filter circuit 5.

The adaptive algorithm in the adaptive filter circuit 5 works so as to minimize the subtraction output (residual output) e which is the output of the synthesis circuit 4. That is, now s, n
Assuming that 0, n1 and y are statistically stationary and the average value is 0, the residual output e is e = s + n0-y. The expected value of the square of this is that s is n0,
Also, because it is y ^{uncorrelated, E [e 2] = E} [s 2] + E [(n0 -y) 2] + 2E [s (n0 -y)] = E [s 2] + E [(n0 - y) ² ]. Assuming that the adaptive filter circuit 5 converges,
The adaptive filter circuit 5 is adjusted so that E [e ² ] is minimized. At this time, since E [s ² ] is not affected, Emin [e ² ] = E [s ² ] + Emin [(n 0 -y) ² ]. That, E E by [e ^2] is minimized [(n0 -y) ^2] is minimized, the output y of the adaptive filter circuit 5 will estimate the noise n0. And
The expected value of the output from the combining circuit 4 is only the desired signal s. That is, adjusting the adaptive filter circuit 5 to minimize the total output power is equivalent to the subtraction output e becoming the least-squares estimated value of the desired speech signal s.

The adaptive filter circuit 5 may be realized by an analog signal processing circuit or a digital signal processing circuit. FIG. 4 shows an example in which the adaptive filter circuit 5 is realized by using a digital filter. This example uses the so-called LMS (Least Mean Square) method as an adaptive algorithm.

In this example, as shown in FIG. 4, an FIR filter type adaptive linear combiner 300 is used. this is,
A plurality of delay circuits DL1, DL2, ... DLm (m is a positive integer) each having a delay time Z ⁻¹ of a unit sampling time, input noise n1 and each delay circuit DL1, DL
2, ... DLm is provided with weighting circuits MX0, MX1, MX2, ... MXm for multiplying the output signal of DLm by a weighting coefficient, and an adder circuit 310 for adding the outputs of the weighting circuits MX0 to MXm. The output of the adder circuit 310 is y.

The weighting coefficients supplied to the weighting circuits MX0 to MXm are formed on the basis of the residual signal e from the synthesizing circuit 4 in the LMS arithmetic circuit 320 composed of, for example, a microcomputer. The algorithm executed by the LMS arithmetic circuit 320 is as follows.

Now, the input vector X _k at time k is
As shown in FIG. 4, X _k = [x _0k x _1k x _2k ... x _mk ] ^T , the output is y _k , and the weighting coefficient is w _jk (j = 0,1,2, ... m). Then, the relationship of input and output is as shown in the following Equation 1.

[0019]

[Equation 1] Becomes

Then, the weight vector W _{k at} time _k
Is defined as W _k = [w _0k w _1k w _2k ... w _mk ] ^T , the input / output relationship is given by y _k = X _k ^T · W _k . Here, if the desired response is d _k , the residual e _k is expressed as follows. e _k = d _k −y _k = d _k −X _k ^T · W _{k In the} LMS method, the weight vector is updated sequentially by the formula W _{k + 1} = W _k +2 μ · e _k · X _k . Here, μ is a gain factor (step gain) that determines the speed and stability of adaptation.

In the active noise reduction device which is the object of the present invention, the synthesis circuit 4 serves as an acoustic synthesis means. That is, the adaptive filter circuit 5 forms a noise canceling voice signal -y having a phase opposite to that of noise and an equal amplitude, and supplies this to a speaker or the like to acoustically add to the main voice to reduce noise. The residual e in this case is picked up by the residual detection microphone.

FIG. 1 is a block diagram of an embodiment of a noise reduction device according to the present invention. In this example, an adaptive filter circuit using a digital filter is used. Then, as the main input, only the noise source 11 is considered.
The noise from the noise source 11 is transmitted to the ear 1 as shown in the figure.
2 is propagated.

Reference numeral 21 is a reference input microphone,
It is arranged near the noise source 11 and picks up noise that is correlated with the noise input to the ear. This reference input microphone 2
The signal obtained by being picked up by 1 and converted into an electric signal is supplied to the A / D converter 23 via the amplifier 22, is converted into a digital signal, and is adaptive filter circuit 30.
Is supplied to. Then, the output signal of the adaptive filter circuit 30 is converted back into an analog audio signal by the D / A converter 24 and supplied to the speaker 26 via the amplifier 25. Then, the noise canceling sound is emitted by the speaker 26 and acoustically synthesized with the noise sound wave from the noise source 11, and the noise from the noise source 11 is reduced in the vicinity of the ear 12.

A residual wireless transmission unit 40 having a residual detection microphone 41 is installed near the ear 12. In this example, as shown in FIG. 2, this unit 40 is attached to the frame 51 of the spectacles 50, and the residual detection microphone 41 is located near the entrance of the ear canal when the spectacles are worn. Has been done.

The residual wireless transmission unit 40 includes an amplifier 42 and a wireless transmission circuit 4 in addition to the residual detection microphone 41.
Equipped with 3. The power supply for driving the wireless transmission unit 40 may be mounted on the unit 40, may be built in the spectacle frame 51, or may be mounted on the frame 51. Then, the residual difference at the ear canal entrance of the ear 12 collected by the residual detection microphone 41 is
It is supplied to the wireless transmission circuit 43 via the amplifier 42 and is transmitted to the wireless reception circuit 27 as a radio wave. The residual error received by the wireless reception circuit 27 is supplied to the adaptive filter circuit 30. The adaptive filter circuit 30 adjusts its output signal -y so that the residual is minimized.

In this way, noise is adaptively reduced so that the noise at the ear canal entrance of the ear 12 is minimized. In this example, the residual detection microphone 41 is used.
Is attached to the spectacles 50 worn by a human, and the ear 1
It is fixedly installed on the human body in the vicinity of the ear canal entrance regardless of the movement of the head, so that a predetermined amount of noise reduction is always obtained without giving inconvenience to the movement of the human head or the movement of the human himself. be able to. Furthermore, in this example, since the residual signal is transmitted wirelessly, there is no troublesome signal line and free movement can be secured.

In the above example, the residual detection microphone 4 is used.
The wireless transmission unit 40 provided with 1 is attached to a frame of eyeglasses, and the residual detection microphone 41 is provided near the ear 12.
However, the member to which the wireless transmission unit 40 is attached is not limited to this, and it is an accessory used by humans, such as a hat, a hair band, an earring, and the like. Anything can be used as long as it can be installed in the vicinity.

Further, the residual detection microphone 41 and the wireless transmission circuit 43 are provided separately, and a signal line is used to connect the two.
The wireless transmission circuit 43 may be portable. In that case, the battery can be provided on the portable radio transmission circuit side, and the power supply voltage for operating the residual detection microphone 41 can also be supplied via the cord. Further, in the above example, the residual signal is transmitted by radio waves, but wireless transmission means using infrared rays, ultrasonic waves, laser light or the like may be used.

Needless to say, the residual signal may be transmitted to the applied filter circuit 30 via a signal line instead of being transmitted wirelessly.

[0030]

As described above, according to the present invention, in the active noise reduction device, the residual detection microphone can be attached to the accessory and fixedly installed near the ear. Therefore, even if the head moves or the direction changes, the initial noise reduction effect can always be obtained. Further, since the noise reduction area is always near the ear, the head and body can be moved freely. In particular, when the residual signal is transmitted wirelessly, the degree of freedom of movement is increased, and since there are no troublesome signal lines, various operations can be performed freely.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a noise reduction device according to the present invention.

FIG. 2 is a diagram for explaining an example of a main part of the present invention.

FIG. 3 is a diagram for explaining an example of an adaptive noise reduction device.

FIG. 4 is a diagram showing an example of an adaptive filter circuit.

[Explanation of symbols]

 11 Noise Source 12 Ear 21 Microphone for Reference Input 26 Speaker for Emitting Canceling Sound 30 Applied Filter Circuit 40 Residual Wireless Transmission Unit 41 Residual Detection Microphone 42 Wireless Transmission Circuit

Claims (4)

[Claims] 1. A reference input microphone for picking up noise, a canceling sound forming means for forming a canceling sound for canceling the noise from the noise picked up by the reference input microphone, and the canceling sound. Sound emitting means for receiving the audio signal from the forming means and emitting the canceling sound, and collecting a noise residual in a sound field whose noise is reduced by the canceling sound emitted from the sound emitting means. And a residual signal picked up by the residual detection microphone is supplied to the cancellation sound forming means, and the cancellation sound forming means minimizes the residual error. The noise reduction device, wherein the residual detection microphone is attached to an accessory. 2. The noise reduction device according to claim 1, wherein a residual signal from the residual detection microphone attached to the accessory is wirelessly transmitted to the cancellation sound forming means. 3. The noise reduction device according to claim 1, wherein the accessory is worn on the head of a human body. 4. The noise reduction device according to claim 1, wherein the canceling sound forming means is composed of an adaptive filter circuit.