JPH07199971A - Noise reduction device - Google Patents

Abstract

PURPOSE:To provide the noise reduction device which stably operates. CONSTITUTION:The noise reduction device, which reduces the noise signal from a microphone 15 by performing adaptive control over the tap value of an adaptive filter 7, generating a signal for reducing a noise inputted to the microphone 15, with the output of the microphone 15 and the signal from a transmission characteristic compensation part 8 compensating transmission characteristics up to the arrival of the signal generated by the adaptive filter 7 at the microphone 15, is equipped with a stabilization filter 1 which passes a signal in a frequency band cut in the low frequency range of a speaker 14 converting the signal reducing the noise into a sound wave and a by-pass means which branches and inputs the signal outputted by the adaptive filter 7 to the stabilization filter 1 and adds the signal outputted from the stabilization filter 1 to the output of the microphone 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reducing device for reducing noise by generating the same signal as noise in which the phase is inverted.

[0002]

2. Description of the Related Art For example, noise may be generated by the rotation of an engine in a vehicle interior, causing an unpleasant feeling. A conventional apparatus for reducing such noise is, for example, as disclosed in Japanese Patent Laid-Open No. 3-178846, a microphone is installed at a point where noise is desired to be reduced, and noise having a phase opposite to that of noise input to the microphone is provided. The noise is reduced by adaptively controlling the tap value of the adaptive filter that generates the noise by the output of the microphone and the signal that compensates the transfer characteristic until the signal generated by the adaptive filter reaches the microphone.

[0003]

As described above, the conventional noise reduction device has a transfer characteristic of a speaker for converting a signal from an adaptive filter for canceling noise into a sound wave and a propagation path for the sound wave to propagate from the speaker to the microphone. Was recorded in the transfer characteristic compensator to control the adaptive filter.

In this conventional noise reduction device, if the frequency characteristic of the speaker that generates the sound wave for reducing the noise is a very wide band characteristic, it operates stably, but the frequency of the noise generated from the noise source is reproduced by the speaker. If it contains frequency components other than the frequency band, the operation becomes unstable.

That is, when the noise includes frequency components outside the operating band of the speaker, the adaptive filter performs adaptive control so as to cancel out noise outside the band, and the signal is transmitted. However, the noise canceling signal outside the band generated by the adaptive filter is cut by the speaker and is not transmitted to the space, and the error of the frequency component outside the band is fed back despite the adaptive control.

[0006] Due to the error of the fed-back frequency component outside the band, the adaptive filter operates so as to output a signal having a larger amplitude, and as a result, the amplifier driving the speaker is saturated to cause distortion, and It may happen that the adaptive control system diverges.

It is an object of the present invention to provide a noise reduction device improved so that adaptive control with respect to noise operates stably.

[0008]

Means adopted by the present invention for solving the above-mentioned problems will be described. A transfer for compensating the tap value of the adaptive filter that generates a signal that reduces noise input to the microphone, and the transfer characteristic of the output from the microphone and the signal generated by the adaptive filter until the signal reaches the microphone. In a noise reduction device adapted to reduce a noise signal from the microphone by adaptively controlling the signal from the characteristic compensator,
A stabilizing filter that passes a signal in a frequency band cut in at least a low frequency region of a speaker that converts a signal that reduces the noise into a sound wave, and a signal that is output from the adaptive filter is branched to the stabilizing filter. Input,
Bypass means for adding the signal output from the stabilizing filter to the output from the microphone.

[0009]

In the stabilizing filter, the frequency component cut in at least the low frequency region of the speaker is passed. Bypass means inputs the signal output from the adaptive filter to the stabilizing filter, and adds the signal passed from the stabilizing filter to the output from the microphone.

As described above, since the frequency component cut by the speaker is extracted and added to the output from the microphone, the low frequency component picked up by the microphone from the noise source is canceled and adapted. There is no error in control and stable operation is possible.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 concrete example of an adaptive filter and a tap value updating unit of the embodiment, and FIG.
FIG. 3 is a configuration diagram of a stabilizing filter, a stabilizing filter compensating unit, and a transfer characteristic compensating unit.

In FIG. 1, 1 is a stabilizing filter, 2 is an adder, 3 is a stabilizing filter compensator, 10 is a noise source, and 1 is a noise source.
1 is a pickup circuit for picking up noise from a noise source 10, 12 and 16 are analog-digital converters (A / D), and 13 is a digital-analog converter (D / D).
A), 14 is a speaker, 7 is an adaptive filter, 8 is a transfer characteristic compensation unit, and 9 is a tap value updating unit for updating the tap value of the adaptive filter 7.

First, the operation of the conventional noise reduction device which does not include the stabilizing filter 1, the adder 2 and the stabilizing filter compensating unit 3 will be described. The microphone 15 is installed at a point where noise is to be reduced. The adaptive filter 7 corrects a portion where the signal picked up by the pickup circuit 11 is different from the noise from the noise source 10 input to the microphone 15, is sent out from the speaker 14, and the signal reaching the microphone 15 is the noise source. A signal having the same amplitude as the noise of 10 but an opposite phase is generated.

The adaptive filter 7 is composed of a digital filter composed of a tapped delay line, as will be described later in detail with reference to FIG. That is, the output signal of the pickup circuit 11 having a correlation with noise is adjusted by the adaptive filter 7
, The transfer characteristic of the filter can be determined so that the sound pressure waveform by the adaptive filter 7 has a phase opposite to that of the noise at the position of the microphone 15. Performed by the part 9.

The transfer characteristic compensator 8 is affected by time delay, band limitation, etc. until the signal generated by the adaptive filter 7 reaches the microphone 15 through the D / A 13 and the speaker 14. The transfer characteristic is compensated, and a compensation signal is generated at the input of the microphone so that the signal from the noise source 10 has the same amplitude and opposite phase.

This transfer characteristic can also be configured by a digital filter including a delay line with taps. FIG. 3 shows the configuration of the transfer characteristic compensating unit 8, which includes 80-1 to 80-1.
80-J is a delay element, which is delayed by a time corresponding to the sampling interval of the sampling pulses input to the A / Ds 12 and 16. Further, 81-0 to 81-J are tap values, which are output by multiplying the output value of the delay element by the tap value.

Therefore, the output value of the A / D 12 at t = t _n is x (n), and the output value at the next t = t _{n + 1} is x.
It is represented by (n + 1), and <i = 1,3> Σx _i represents <i = 1,3> Σx _i = x ₁ + x ₂ + x ₃ and the transfer characteristic compensator output from the adder 82. The compensation signal C (n) from 8 is represented by C (n) = <i = 0, J> Σx (n−i) Ci (1).

As shown in FIG. 2, the adaptive filter 7 includes delay elements 70-1 to 70-Z and tap values 71-0 to 71-0.
71-Z and an adder 72. Delay element 70
Is the time A / D1 equal to the sampling pulse generation interval
Delay the output signal from 2.

Therefore, the output y from the adaptive filter 7
(N) is represented by y (n) = <i = 0, Z> Σx (n-i) Wi (n) (2), converted into an analog signal by the D / A 13 and transmitted from the speaker 14. It

[0020] The tap value W _O of the adaptive filter 7 (n) ~W
_Z (n) is updated every time a sampling pulse is generated. The tap value updating unit 9 updates the tap value. As shown in FIG. 2, the tap value updating unit 9 is composed of multipliers 90, 91 and 92 and an adder 93.

First, in the delay element 90, the output signal C (n) from the transfer characteristic compensator 8 is input, and is delayed by the time equal to the sampling pulse generation interval and propagated.
In addition, the multiplier 91 outputs the microphone 15 e (t)
Is the signal e (n) whose A / D16 has been converted to a digital value.
Is multiplied by α. This α is determined by the loop characteristic of the adaptive control system.

Next, each tap value of the adaptive filter 7 is updated.
The value W (n + 1) is calculated. Easy to explain
Therefore, tap value W of tap 71-0_O(N) is W_O(N +
The case of updating to 1) will be described as an example. Multiplier 9
In 2-0, the output of the multiplier 91 and the transfer characteristic compensator 8
Is multiplied by the output value C (n). Adder 93-
At 0, t = t_nTap value at _OMultiply from (n)
The output value is subtracted from the unit 92-0, and the result is set to the next t
= T_{n + 1}Tap value at_OTap as (n + 1)
Update the value.

That is, the tap value is updated as W _O (n + 1) = W _O (n) -αC (n) e (n) (3). Also other taps _Wi
Also for W _i (n + 1) = W _i (n) −αC (n−i) e (n) (4), the tap value is updated.

As described above, when the tap value is updated, the sound wave sent from the speaker 14 has the same amplitude as the noise from the noise source 10 at the input of the microphone 15, but the opposite phase, and the vicinity of the microphone. Reduce noise in. It should be noted that the above description of the operation is applied to the noise in the range where the characteristic of converting the electric signal from the speaker 14 into the sound wave is good.

That is, a sound wave signal is obtained from the electric signal of the speaker.
The conversion loss characteristic of the signal is shown in FIG. 4 (A), for example.
Then the frequency in the frequency band where the loss characteristic is flat is
Number f ₃For the above, the operation described above reduces noise.
Let However, the conversion loss of the speaker is large.
F of (A)₁For the noise indicated by, the adaptive filter 7
f₁The signal generated to cancel the noise of
The output of the microphone 15 is not converted into sound waves by the peaker
From f₁The error signal of the frequency component is output.

Therefore, due to this error signal, the tap value of the adaptive filter 7 gradually increases as the error accumulates, as described in equation (4). Saturate and generate distortion,
In some cases, the control system diverges beyond the value that can be recorded in the memory that records the tap value.

For the noise of the frequency component of f ₂ shown in FIG. 4 (A), the noise can be reduced by overdriving the amplifier or the speaker. In order to solve the problems described above, the present invention includes a stabilizing filter 1, an adder 2 and a stabilizing filter compensator 3.

As shown in FIG. 4B, the loss frequency characteristic of the stabilizing filter 1 is as shown in FIG.
(A)) has the opposite characteristic. That is, the loss of the stabilizing filter is infinite in the frequency band where there is no loss in the speaker, and conversely, the loss of the stabilizing filter is 0 if the loss of the speaker is infinite.

The stabilizing filter 1 having such characteristics
When the signal output from the adaptive filter 7 is passed through,
The speaker 14 outputs a signal of a frequency component that has not been converted into a sound wave. The output of the stabilizing filter 1 is added to the signal output from the microphone 15 by the adder 2 to cancel the signal of the frequency component not converted by the speaker 14. That is, the error e (n) input to the tap value updating unit 9 is eliminated, and stable operation is achieved.

In this case, the error e (n) is eliminated and the system operates stably, but it goes without saying that the noise is not reduced with respect to the noise of the frequency bypassed by the stabilizing filter. Then, if it is desired to reduce the noise of such a frequency, a speaker having a wide band may be used.

The stabilizing filter 1 can be constituted by a delay line with taps, a specific example of which is shown in FIG. 3, and its operation is as described in the transfer characteristic compensating section 8. In this case, the tap value C of the stabilizing filter is recorded as a plurality of characteristic values, and the characteristic value corresponding to the type of the installed speaker is selected and recorded in the tap value memory 81. By doing so, the change of the speaker can be dealt with immediately.

The stabilizing filter compensator 3 compensates the transfer characteristic for the signal component passing through the stabilizing filter 1. In other words, the stabilizing filter 1 is compensated so that the passing signal has a phase opposite to that of the signal picked up by the microphone 15.

The stabilizing filter compensator 3 is composed of a delay line with taps, as shown in FIG. 3, similarly to the transfer characteristic compensator 8. The operation is as described in the transfer characteristic compensator. Tap value C of the stabilizing filter compensator 3
Is related to the characteristic of the stabilizing filter 1, and a value that is a transfer characteristic corresponding to the set stabilizing filter is set.

In the embodiment described above, the characteristic of the stabilizing filter is set to be the opposite characteristic of the speaker, but by setting the characteristic of the stabilizing filter in this way,
Noise in any frequency band operates at a similar level and can operate stably. However, the characteristic of the stabilizing filter does not have to match the inverse characteristic of the speaker characteristic, and may be a characteristic of passing a signal in a frequency band blocked by the speaker.

That is, for example, even if the signal of frequency f ₂ shown in FIG. 4A is cut by the stabilizing filter, a signal larger than the signal for frequency f ₃ is generated by the adaptive filter as described above. Reduce noise. Therefore, the characteristic of the stabilizing filter may be the characteristic indicated by the dotted line in FIG. 4 (B), which is a loss that does not saturate the control system.

In the embodiment, the stabilizing filter passes both the low frequency region and the high frequency region. However, for example, in the case of reducing the noise in the interior of the automobile, the engine of the automobile is reduced. The noise generated by rotation is mainly in the low frequency region, has few components in the high frequency region, and is less persistent.

Therefore, in such a case, the characteristics of the stabilizing filter may be limited to the low frequency region, and stable operation results are obtained in the actual operation result. Although one embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and various modifications can be made according to the gist of the invention.

[0038]

As described above, according to the present invention, the following effects can be obtained. Since the frequency component cut by the speaker is extracted and added to the output from the microphone, the low frequency component picked up by the microphone from the noise source is canceled out and there is no error in adaptive control and it is stable. It can be operated.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a specific example of an adaptive filter and a tap value updating unit of the same embodiment.

FIG. 3 is a configuration diagram of a stabilizing filter, a stabilizing filter compensating unit, and a transfer characteristic compensating unit of the embodiment.

FIG. 4 is an explanatory diagram of filter characteristics.

[Explanation of symbols]

 1 Stabilizing filter 2 Adder 3 Stabilizing filter compensator 7 Adaptive filter 8 Transfer characteristic compensator 9 Tap value updating unit 10 Noise source 11 Pickup circuit 12, 16 Analog-digital converter (A / D) 13 Digital-analog converter ( D / A) 14 Speaker 15 Microphone

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H03H 21/00 8842-5J (72) Inventor Eiji Shibata 1-7-2 Nishishinjuku, Shinjuku-ku, Tokyo Fuji Heavy Industries Incorporated (72) Inventor Atsumi Kaneshiro 25 Nishimachi, Yamada, Kawagoe, Saitama Prefecture, 1 Pioneer Co., Ltd. Kawagoe Factory (72) Manabu Nohara 25 25 Nishimachi, Kawagoe, Saitama, Japan 1 Pioneer Co., Ltd. Kawagoe Factory

Claims (1)

[Claims] 1. A transmission of a tap value of an adaptive filter for generating a signal for reducing noise input to a microphone until the output from the microphone and the signal generated by the adaptive filter reach the microphone. In a noise reduction device adapted to reduce a noise signal from the microphone by adaptively controlling it with a signal from a transfer characteristic compensator for compensating for the characteristic, at least a speaker for converting the noise reducing signal into a sound wave. A stabilizing filter that passes a signal in a frequency band that is cut in the frequency domain, and a signal that is output from the adaptive filter is branched and input to the stabilizing filter, and a signal that is output from the stabilizing filter is input to the microphone. A noise reduction device comprising: