JPH05127679A - Noise controller - Google Patents

Abstract

PURPOSE:To improve the precision of the generation of an erasure sound, specially, for a noise which greatly varies. CONSTITUTION:The noise controller which performs adaptive control to generate characteristics inverse to characteristics of a noise and minimize an error signal is provided with an FIR filter 70 which takes an output signal out of an optional filter tap, adjusts the output signal, and varies the filter tap length, an operation state change detector 16 which detects a change in the operation state of a noise source and adjusts the output signal from the filter tap of the FIR filter 70, and a minimization part 79 which updates only the coefficient of the FIR filter 70 required to adjust the output signal according to the operation state change signal of the operation state change detector 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise control device for canceling noise by using a speaker, and an object thereof is to improve the accuracy of forming a canceling sound for a noise which changes greatly.

[0002]

2. Description of the Related Art Conventionally, a passive muffler such as a muffler has been used to reduce noise generated from an internal combustion engine, etc., but improvement has been desired from the viewpoint of size, muffling characteristics and the like. On the other hand, conventionally, there has been proposed an active noise control device which cancels noise by outputting from a speaker a compensating sound having an opposite phase and equal sound pressure to the noise generated from a sound source. However, the frequency characteristics, stability, etc. of the active noise control device itself are not sufficient, and its practical application has been delayed. As a result of the recent development of signal processing technology using digital circuits and expansion of the frequency range that can be handled, many practical noise control devices have been proposed (for example, Japanese Patent Laid-Open No. 63-3).
11396 publication). This is a feedforward system that detects noise with a noise source supplement microphone installed upstream of the duct and outputs a signal of opposite phase and equal sound pressure to the noise with a signal processing circuit from a speaker installed downstream of the duct, and muffling. This is a so-called two-microphone / one-speaker type active noise control device that combines a feedback system that detects the generated result with a microphone for a muffling point and minimizes the muffling result. In this device, an adaptive filter that forms a compensating sound of opposite phase and equal sound pressure is a DSP (Digit).
al SignalProcessor), FI
R (Finite Impulse Response)
It consists of filters.

[0003]

However, since the filter tap length is fixed in the conventional adaptive filter, a certain convergence time is always required to obtain a certain effect. For this reason, when the target noise changes drastically, there is a problem in that the above-mentioned constant convergence time cannot be obtained, a complete convergence state cannot be obtained, and a sufficient noise control effect cannot be obtained.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise control device capable of ensuring a predetermined convergence time and improving responsiveness even if the noise changes drastically.

[0005]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a noise control device that performs adaptive control to form a characteristic opposite to the characteristic of noise and minimize its error signal. A filter, a noise source operating state change detector, and a minimization unit are provided. The FIR filter takes an output signal from an arbitrary filter tap and adjusts the output signal to make the filter tap length variable. The operating state change detector detects a change in engine speed as an operating state of noise source, and adjusts an output signal from the filter tap of the FIR filter. The minimization unit uses the F required for adjusting the output signal from the operation state change signal of the operation state change detector.
The coefficient of the IR filter is updated.

[0006]

According to the noise control device of the present invention, the FIR filter extracts an output signal from an arbitrary filter tap and adjusts the output signal to make the filter tap length variable. Further, the operating state change detector detects, for example, a change in the engine speed and adjusts an output signal from the filter tap of the FIR filter, whereby the filter tap length can be changed by the change in the engine speed.
Further, since the minimization unit updates only the coefficient of the FIR filter necessary for adjusting the output signal from the operation state change signal (rotation speed change signal) of the operation state change detector, the convergence time of the calculation for obtaining the coefficient Is shortened and responsiveness is improved with respect to a drastic change in the rotation speed.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a noise control device according to an embodiment of the present invention, which is an example in which an engine speed is used as a signal indicating a driving state of an engine noise source such as an automobile as a noise source. The overall configuration of the present invention will be described with reference to this figure. The device includes an engine 1 of an automobile or the like, an exhaust gas pipe 2 for releasing exhaust gas of the engine 1 to the atmosphere, and an exhaust gas pipe 2 on the way to the atmosphere for suppressing noise generation. A sub muffler 3 that gradually reduces the pressure of the exhaust gas and interferes with the noise generated by the pressure reduction due to the reflection of the wall, and a main muffler 4 provided after the sub muffler 3 for the same purpose as above. A tail pipe 5 connected to the main muffler 4 for discharging exhaust gas to the atmosphere, an engine control unit 6 for controlling the engine 1 based on a rotation speed signal (Sr) of the engine 1, and self-forming And a compensation signal forming section 7 for forming a controlled signal for noise from the compensated compensation signal and an error signal of a feedback system which will be described later, and forming a compensated signal using the controlled signal. Digital / analog converter 8 for converting the digital output signal from the 7 into an analog signal
A low-pass filter 9 connected to the digital / analog converter 8 for removing harmonics, a power amplifier 10 connected to the low-pass filter 9, and a sound wave driven by a signal from the power amplifier 10. Connected to the microphone 12, and a speaker 11 for emitting noise to cancel the noise from the tail pipe 5, a microphone 12 for supplementing the result of the noise from the tail pipe 5 being canceled by the speaker 11, and converting the result into an electric signal. Amplifier 13, a low pass filter 14 connected to the amplifier 13, an analog signal connected to the low pass filter 14 to convert an analog signal into a digital signal, and the converted signal is feedback controlled by the compensation signal forming section 7. The analog / digital converter 15 used as a signal or as a part of the controlled signal and the rotational speed of the engine 1 are directly detected. The output signal of the analog / digital converter 15 or indirectly changes the rotational speed of the output signal of the analog / digital converter 15 to switch the filter tap length of the compensation signal forming unit 7, and the compensation signal forming unit 7 and the digital / analog converter 8 And a rotation speed change detector 16 for switching the cycle of the sampling signal used in the analog / digital converter 15. The analog / digital converter 15
The cut-off frequency of is to match the sampling period when the rotation speed is the slowest for the purpose of preventing the digital signal from being folded back.

FIG. 2 is a diagram showing the configuration of the compensation signal forming section of FIG. As shown in the figure, the compensation signal forming unit 7 has 0
No. 1 to F having filter tap lengths from No. 256 to No. 256
An IR filter 71, a second FIR filter 72 connected in series with the first FIR filter 71 and having a filter tap length of 257 to 512, and the second FIR filter 72.
A third FIR filter 7 connected in series with the filter 72 and having filter tap lengths from 513 to 1024
3 and variable multipliers 74, 75 and 76 which are respectively connected to the first FIR filter 71, the second FIR filter 72 and the third FIR filter 73 and change the multiplication coefficient thereof to 0 or 1. An adder 77 that adds the outputs of the variable multipliers 74 and 75, an output of the adder 77 and an output of the third FIR filter 73, and outputs the addition signal to the digital / analog converter 8. FIR filter 70 including an adder 78 for
The multiplication coefficients of the variable multipliers 74, 75 and 76 of the first FIR filter 71, the second FIR filter 72 and the third FIR filter 73 so that the miscalculation signal from the digital converter 15 is minimized. Minimizing section 79 for updating
A transfer characteristic forming section 80 for simulating a transfer characteristic of a feedback system described later, an inverted signal from the transfer characteristic forming section 80, and a signal from the analog / digital converter 15 via the microphone 12 described later. And an adder 81 for reproducing a noise signal and using it as an input signal of the first FIR filter 71.

FIG. 3 is a diagram showing the configuration of each FIR filter in FIG. The FIR filter shown in the figure has an input signal of 1
A plurality of delay devices 721 that delay each sampling period
A plurality of variable multipliers 722 connected to the input signal and the output signal of each delay device 721, and each variable multiplier 72.
2 and a plurality of adders 723 connected to each other. The coefficients a0, a1, a2, ... Am of each variable multiplier 722 are variable by the supply from the minimization unit 79.

Here, when the sampling frequency is fs, the sampling period T is T = 1 / fs, and when the input signal is x (t) = exp (jωt), the output signal y
(T) can be expressed as follows. y (t) = a0 · exp (jωt) + a1 · expjω
(T−T) + a2 · expjω (t−2T) + ... +
am · expjω (t−mT) = exp (jωt) · (a0 + a1 · exp (−jω)
T) + a2 · exp (−j2ωT) + ... + am · e
xp (−jmωT)) Next, the minimizing unit 79 that updates the coefficient will be described. When the input signal is expressed as x (n) = exp (jnωt) and the coefficient ak (n) in the above equation, each coefficient ak (n) is obtained by converging by the following equation.

[0011]

[Equation 1]

In this equation, e (n) (represented as SE in FIG. 1) is an output signal of the analog / digital converter 15 and represents an error signal. Α is a convergence constant and a coefficient ak (n).
It takes a predetermined time to converge to a constant value. Therefore, if the change in the number of revolutions of the engine 1 is large, there is a possibility that processing within this convergence time may become difficult. Next, a series of operations of this embodiment will be described. The noise signal generated by the engine 1 is SN, the output signal of the compensation signal forming unit 7 is SC, the output signal of the microphone 12 is SM, and the output signal of the adder 81 is SR. Further, the transfer characteristic from the engine 1 to the microphone 12 is HNOISE, and the transfer characteristic from the compensation signal forming unit 7 to the microphone 12 is Hd.
1. If the transfer characteristic from the microphone 12 to the adder 81 is HM and Hd = Hd1 · HM, the output signal of the microphone 12 is SM = SN · HNOIS.
E + SC · Hd1 and output signal S from the adder 81
R = SM ・ HM-SC ・ Hd = (SN ・ HNOISE +
SC ・ Hd1-SC ・ Hd1) ・ HM = SN ・ HNOI
The signal becomes SE / HM, and a signal when only noise is detected by the microphone 12 is calculated.

Next, the minimizing section 79 of the compensation signal forming section 7
The output signal SE of the analog / digital converter 15 is given as a control signal for changing the coefficient by. The compensation signal forming unit 7 changes the coefficient so that the control signal becomes zero. Since SE = SMHM, when SE = 0, SM = 0. Therefore, by inputting the output signal SR from the adder 81 to the compensation signal forming unit 7 as a controlled signal and inputting the output signal SE to the analog / digital converter 15 as a control signal, the compensation signal forming unit 7 The compensation signal SC is calculated and output so that SE = 0.

FIG. 4 shows the FI as the engine speed changes.
It is a figure explaining switching of an R filter etc. The rotation speed change detector 16 shown in FIG. 1 converts the frequency of noise from the rotation speed of the engine 1 by a predetermined method to obtain a frequency change rate Δf / Δt of noise, and a constant k1 having the following relationship.
As shown in FIG. 4A, the engine speed change is small as compared with ≦ k2 ≦ k3, and if Δf / Δt ≦ k1, the operation mode III is determined, and the engine speed change increases and k1 ≦
If Δf / Δt ≦ k2, it is determined to be the operation mode II, and if the rotation speed change further increases and k3 ≦ Δf / Δt, it is determined to be the operation mode I. Thus, the rotation speed change detector 16
Is judged by the variable multiplier 7 as shown in FIG.
The multiplication factors of 4, 75 and 76 and the sampling period are switched. In addition, the FIR selected in the above operation mode
Only the multiplication coefficient of the filter is calculated, and the multiplication coefficient that is not selected is not calculated.

FIG. 5 is a diagram showing the operation timing of the FIR filter in each operation. As shown in the figure, at the rising edge of the sampling signal, the analog signal is taken into the analog / digital converter 15 and DSP processing is performed, and coefficient updating processing is further performed. Then, the result is output to the digital / analog converter 8 at the next rising signal, and the analog signal is input to the analog / digital converter 15 in the same manner as above, and the operation is repeated. In this operation, as shown in the figure, the FIR filter tap length becomes smaller and the sampling period becomes smaller as the number of revolutions increases. Therefore, as the number of rotations increases, the filter tap length to be controlled becomes shorter, so that the number of calculations for convergence increases as shown in [Equation 1], and the number of calculations of multiplication coefficients that require convergence time decreases. Can be shortened.

FIG. 6 is a diagram showing the response of each FIR filter. By making the FIR filter tap length variable as described above in accordance with the change in the rotation speed, the convergence time is shortened as the FIR filter tap length is shortened as shown in FIG. 6, so that the effect amount rises faster. Note that the sampling cycle is made variable by using an ordinary frequency divider in order to adjust as the change in the number of revolutions increases.

FIG. 7 is a diagram showing a comparison of the noise control effect between the embodiment of the present invention and the conventional example. Regarding the effect of the embodiment shown by the broken line in this figure, there is no portion where the effect is significantly reduced when the change in the rotational speed is large, and the effect amount as a whole can be improved. In the above description, the total length of the FIR filter tap length is 1024 in the compensation signal forming section 7, but the invention is not limited to this, and the FIR filter is switched to three, but the invention is not limited to this.

[0018]

As described above, according to the present invention, an output signal is taken out from an arbitrary filter tap and the output signal is adjusted to make the filter tap length variable to detect a change in the operating state of the noise source. FIR filter Since the output signal from the filter tap is adjusted and the coefficient of the FIR filter necessary for adjusting the output signal is updated from the rotation speed change signal, the coefficient is adjusted even if the noise source state changes rapidly. The convergence time for updating is shortened and the response of noise control is improved. The noise source is not limited to an engine such as an automobile, but may be a motor, an air conditioner, or any other machine, and the signal indicating the change in the operating state of the noise source is not limited to the rotation speed signal, and for example, ignition timing. A signal, a signal indicating a change in negative pressure on the intake side of the engine, or noise itself may be taken out by a microphone or a vibration pickup sensor, and a signal (fundamental wave) having a frequency showing a noise peak may be used.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration of a compensation signal forming unit in FIG.

FIG. 3 is a diagram showing a configuration of each FIR filter of FIG.

FIG. 4 is a diagram illustrating switching of FIR filters and the like due to a change in engine speed.

FIG. 5 is a diagram showing the operation timing of the FIR filter in each operation.

FIG. 6 is a diagram showing the response of each FIR filter.

FIG. 7 is a diagram showing a comparison of noise control effects between an example of the present invention and a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Engine 2 ... Exhaust gas pipe 3 ... Sub muffler 4 ... Main muffler 5 ... Tail pipe 7 ... Compensation signal forming unit 16 ... Rotational speed change detector 70 ... FIR filter 71 ... First FIR filter 72 ... Second FIR filter 73 ... Third FIR filter 74, 75, 76 ... Variable multiplier 77, 78 ... Adder 79 ... Minimization section

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Sakiyama 1-2-2 Goshodori, Hyogo-ku, Kobe, Hyogo Prefecture Inside Fujitsu Ten Limited

Claims (1)

[Claims] 1. A noise control device for performing an adaptive control for forming a characteristic opposite to a characteristic of noise and minimizing an error signal thereof, extracting an output signal from an arbitrary filter tap, and adjusting the output signal FIR with variable filter tap length
The FIR filter (70) detects the change in the operating state of the noise source and the FIR filter (7).
0) of the operating state change detector (16) for adjusting the output signal from the filter tap, and the FIR filter (70) necessary for adjusting the output signal from the operating state change signal of the operating state change detector 16. A noise control device comprising: a minimization unit (79) for updating the coefficient.