JP3444611B2 - Noise control device - Google Patents

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 outputting a canceling sound of noise and anti-phase equal sound pressure from a speaker. In particular, the present invention relates to a frequency characteristic of residual sound of noise after cancellation. Controlling and adjusting tones.

[0002]

2. Description of the Related Art Conventionally, as a technique in such a field, a passive canceling sound device such as a muffler has been used to reduce noise generated from an internal combustion engine or the like.
Improvements have been made from the viewpoint of cancellation sound characteristics. On the other hand, there has been proposed an active noise control device that 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. By the way, the frequency characteristic or stability of the active noise control device itself is not sufficient, and its practical application has been delayed. However, as a result of the recent development of signal processing technology using digital circuits and expansion of the frequency range to be handled, many practical noise control devices have been proposed. As a technique in such a field, Japanese Patent Laid-Open No. 63-
There is one described in Japanese Patent No. 311396. What is described in this is that noise is detected by a noise source microphone installed upstream of the duct, and a signal processing circuit outputs a signal of opposite phase and equal sound pressure from the speaker installed downstream of the duct and is canceled. This is a so-called two-microphone / one-speaker type active noise control device in which a feedback system for detecting and feeding back the result with a canceling microphone is combined with a feedforward system.

By the way, this noise control device has a DSP (Digita) as a signal processing technique using a digital circuit.
Signal Processor) is used, and the DSP is provided with an adaptive filter (Adaptive Filfer). The adaptive filter forms a compensation sound for canceling noise.

[0004]

However, there is a problem in that the conventional noise control device cannot completely cancel the noise, there is a residual sound, and the residual sound cannot be reduced. This is because the residual noise of noise due to cancellation has a unique frequency characteristic, and there is a limit to noise cancellation with the adaptive filter alone.

Therefore, in view of the above problems, it is an object of the present invention to provide a noise control device capable of reducing the noise by considering the frequency characteristic of the residual sound and controlling the frequency of the residual sound to adjust the timbre of the noise. And

[0006]

In order to solve the above-mentioned problems, the present invention provides a noise control device having an adaptive filter for forming a canceling sound with respect to the noise of a noise source, a plurality of equalizers, and a residual sound frequency characteristic analysis. Section, frequency detection section,
A bandpass filter control unit and an equalizer control unit are provided.

The plurality of equalizers are connected in series to the input stage of the adaptive filter. The residual sound frequency characteristic analysis unit is provided with a plurality of band pass filters corresponding to the equalizer and a level detection unit connected to the band pass filters, and frequency analyzes the residual sound from which the noise is canceled.

The frequency detector is adapted to directly detect the fundamental frequency of the noise of the noise source. The bandpass filter control unit forms a harmonic frequency of the fundamental frequency based on the fundamental frequency and determines a center frequency of the bandpass filter. The equalizer control unit stores the frequency characteristic for adjusting the residual sound in advance, compares it with the frequency characteristic of the residual sound frequency characteristic analyzing unit, and determines the center frequency and gain of the plurality of equalizers so that they match. It is controlled.

Further, the high-speed Fourier transform unit may frequency analyze the residual sound from which the noise has been canceled.

[0010]

According to the noise control device of the present invention, the plurality of equalizers are connected in series to the input stage of the adaptive filter, whereby the adaptive filter controls the frequency characteristic of noise in accordance with the input signal. Therefore, the noise can be reduced and the timbre of the residual sound can be adjusted. The residual sound from which the noise is canceled is subjected to frequency analysis, the fundamental frequency of the noise of the noise source is directly detected, its harmonic frequency is formed based on the fundamental frequency, and the frequency analysis is controlled by this harmonic frequency. Is stored in advance the frequency characteristics for adjusting the residual sound, compared with the frequency characteristics, the center frequency of the plurality of equalizers so that they match,
By controlling the gain, the noise of the plurality of equalizers can be reduced and the tone color of the residual sound can be controlled.

Further, the high-speed Fourier transform unit performs frequency analysis on the residual sound with the noise canceled,
As described above, it is not necessary to detect the fundamental frequency directly from the noise source, and the configuration is simplified.

[0012]

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 a first embodiment of the present invention. The noise control device shown in this figure is a first muffler 101 that reduces the noise level by coupling through a exhaust pipe of a noise source 100 such as a vehicle engine that is a noise source.
A speaker 50 that cancels noise with a second muffler 102 that is further coupled in series to the power amplifier, a power amplifier 51 that drives the speaker 50, and a noise compensation signal from a digital signal processing device 30 that will be described later and that is connected to the power amplifier 51. D / A that converts a digital signal that is an analog signal
A converter (Digital To Analog Converter) 52, a microphone 60 for capturing a residual sound in which noise in the muffler 102 is canceled by the speaker 50, and an amplifier 6 for amplifying a signal captured by the microphone 60.
1 and an A / D converter (Analog To Digital Converter) 62 for converting the analog signal amplified by the amplifier 61 into a digital signal so that the digital signal processing device 30 forms a reproduced sound in the speaker 50. It is equipped with.

The digital signal processor 30 has a DS
An adder 1 configured by a P (Digital Signal Processor), one of which inputs a signal from the A / D converter 62, and a plurality of equalizers 31 connected to the output of the adder 1 and connected in series with each other. , Equalizers 2, 3 and 4, for example. The number of the equalizers is set to 3 for the sake of simplification of the description and is not limited to this.

FIG. 2 is a diagram showing a configuration of an example of the equalizer shown in FIG. As shown in the figure, the equalizer is formed by a second-order digital filter, and the gain of a certain range is adjusted with respect to a specific center frequency. The center frequency and the gain can be changed by changing the value of the multiplication coefficient that constitutes such an equalizer. The frequency characteristics can be adjusted by connecting a plurality of such equalizers in series and forming three stages in the above example.

Next, the digital signal processing device 30 includes an adaptive filter 5 connected to the equalizer 4, and the adaptive filter 5 forms a compensation signal for canceling noise. The input signal of the adaptive filter 5 is adjusted by the equalizers 2, 3 and 4. FIG. 3 is a diagram showing the configuration of the adaptive filter of FIG. The adaptive filter 5 shown in this figure is a non-cyclic FIR (Finite Impulse Respon
se) type digital filter, in which the multiplication coefficient of the multiplier is made variable in order to cancel the periodic noise.

The adaptive filter 5 is provided with a filter coefficient updating unit 6. The filter coefficient updating unit 6 uses the signal of the residual sound detected by the microphone 60 as an error signal via the amplifier 61 and the A / D converter 62 so that the error signal is minimized. Set the filter coefficient of. Next, the adaptive filter 5 is provided with transfer characteristic simulation units 7 and 8. The transfer characteristic simulating unit 7 inputs the output signal of the adaptive filter 5, and its output is connected to the other input of the adding unit 1 to form a noise reproduction signal which is an input signal to the adaptive filter 5 by the added signal. To do. The transfer characteristic simulating section 8 receives the input signal of the adaptive filter 5 and outputs the output to the filter coefficient updating section 6 to adjust the update timing of the filter coefficient. The transfer characteristic simulation units 7 and 8 set the transfer characteristics from the adaptive filter 5 to the muffler and the microphone 60 to Hd, and
0, the amplifier 61, the A / D converter 62, and the transfer characteristic to the coefficient updating unit 6 are set to Hm, and the following transfer characteristic Hd1 is formed.

Hd1 = Hd · Hm (1) Next, the digital signal processing device 30 is provided with the frequency detecting section 10. The frequency detector 10 detects the rotation speed of the engine, which is the noise source 100, and obtains the rotation frequency of the engine from this rotation speed. A bandpass filter control unit 11 for controlling a frequency analyzed by a residual sound frequency characteristic analysis unit 32, which will be described later, is provided at a subsequent stage of the frequency detection unit 10. The hand-pass filter controller 11 forms this harmonic frequency by using the rotation frequency of the frequency detector 10 as a fundamental frequency.

Next, the residual sound frequency characteristic analysis unit 32 is provided with three band pass filters 12, 13 and 14 for branching and inputting the output signal of the A / D converter 62. Here, the number of bandpass filters is three in order to correspond to the number of equalizers. The bandpass filters 12, 13 and 14 are formed by digital filters (not shown). The bandpass filter 1
2, 13, and 14 are controlled by the bandpass filter control unit 11 so that the center frequency of the band changes. Further, behind the band pass filters 12, 13 and 14, there are provided level detection units 15, 16 and 17 for rectifying the respective output signals and averaging them to detect the levels.

An equalizer control unit 18 is provided in the digital signal processing device 30. The controller 18 receives the output signals of the level detectors 15, 16 and 17 and controls the equalizers 2, 3 and 4, and adjusts the center frequency and gain thereof. Here, if the noise transfer characteristic from the noise source 100 to the muffler is Hnoise, the noise signal at the noise source 100 is Sn, the output signal of the adaptive filter 5 is Sc, and the detection signal by the microphone 60 is Smo, The following formula is established.

Smo = Sn.Hnoise + Sc.Hd (2) Output signal of the adder 1 which is an input signal of the adaptive filter 5.
Se is as follows. Se = Smo-Hm-Sc-Hd1 (3) = (Sn-Hnoise + Sc-Hd) -Hm-Sc-Hd1 = Sn-Hnoise-Hm + Sc-Hd-Hm-Sc-Hd1 (Refer to equation (1)) = Sn Hnoise * Hm + Sc * Hd * Hm-Sc * Hd * Hm = Sn * Hnoise * Hm Therefore, a signal similar to the signal directly detected by the microphone 60 can be obtained. That is, with this configuration, an error signal for updating the filter coefficient of the adaptive filter 5 is formed by one microphone, and a signal to be input to the adaptive filter 5 is formed by this error signal.

Next, the control operation of the digital signal processing device 30 will be described. FIG. 4 is a diagram for explaining the operation of the bandpass filter controller 11 and the equalizer controller 18 of FIG. First, in the noise source 100, the rotation of the engine is periodic, and the frequency of rotation is used as the fundamental frequency of the noise, and a harmonic component that is an integral multiple of this is included. The frequency detector 10 detects the fundamental frequency of noise from the engine speed. The bandpass filter control unit 11 determines the harmonic component to be adjusted from the data of the fundamental frequency. For example, if the fundamental frequency is 100 Hz as shown in this figure (a), the frequency of the first harmonic is 200 Hz, and the second harmonic is
The harmonic frequency is 300 Hz. The bandpass filter control unit 11 sets the center frequencies of the bandpass filters 12, 13 and 14 corresponding to the fundamental frequency detected by the frequency detection unit 10 and the determined harmonic frequency.

In the equalizer control unit 18, as shown in FIG. 3A, the level detection units 15, 16 and 17 correspond to the frequencies (100, 200 and 300 Hz) from the bandpass filter control unit 11, respectively. When the detected levels A1, A2, A3 are input from the level detection unit ,
This is compared with pre-input levels B1, B2, B3 to form gains ΔG1, ΔG2, ΔG3 for adjusting the equalizers 2, 3 and 4 as shown in FIG.
That is, the equalizer control unit 18 controls the equalizers 2, 3
And 4 are the center frequencies (for example, 100 Hz, 200) obtained from the bandpass filter control unit 11.
Hz, 300 Hz), the gain (for example, ΔG1, ΔG2, ΔG3) is further set. The previously input levels B1, B2, B3 may be stored in the equalizer control unit 18 as a table with a function of frequency, for example.

Therefore, according to the present embodiment, FIG.
As shown in (a), the signal level input to the adaptive filter 5 is strengthened at 100 Hz, the input signal level is weakened at 200 Hz, and the input signal is strengthened at 300 Hz. , The levels of the signals detected by the microphone 60 are levels A1, A
It is corrected from 2, A3 to preset levels B1, B2, B3.

FIG. 5 is a diagram showing a noise control device according to a second embodiment of the present invention, and FIG. 6 is a diagram for explaining the operation of the equalizer control section 18 in FIG. 5 is different from the noise control device according to the first embodiment of FIG. 1 in that the frequency detection unit 10, the bandpass filter control unit 11, the bandpass filters 12, 13 and 14 and the level detection in the first embodiment are different. Instead of the units 15, 16 and 17, a fast Fourier transformation unit 20 is provided. The high-speed Fourier transform unit 20 can analyze the frequency of the residual sound from the microphone 60, and controls the equalizers 2, 3 and 4 through the equalizer control unit 18 based on the obtained frequency spectrum in the same manner as described above. Thus, according to this embodiment, as in the first embodiment, the noise source 1
Since it is not necessary to detect the rotation frequency from the rotation speed of 00, the configuration becomes simple.

Further, the equalizers 2-1, 2-2, ..., 2
By providing a large number of −n, the gains of the equalizers 2-1, 2-2, ..., 2-n can be continuously changed with respect to frequency, as shown in FIG. 6B. As shown, the residual sound from the microphone 60 can be continuously controlled.

[0026]

As described above, according to the present invention, since a plurality of equalizers are connected in series to the input stage of the adaptive filter, the adaptive filter has a noise frequency characteristic in accordance with a desired input signal. Is controlled, the residual sound can be reduced and the timbre can be adjusted. Further, the high-speed Fourier transforming unit, based on the result of frequency analysis of the residual sound in which the noise is canceled, based on the center frequencies of a plurality of equalizers,
Since the gain is adjusted, the configuration can be simplified.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a configuration of an example of the equalizer of FIG.

FIG. 3 is a diagram showing a configuration of an adaptive filter of FIG.

4 is a diagram illustrating operations of a bandpass filter control unit 11 and an equalizer control unit 18 of FIG.

FIG. 5 is a diagram showing a noise control device according to a second embodiment of the present invention.

6 is a diagram illustrating an operation of the equalizer control unit 18 in FIG.

[Explanation of symbols]

2, 3, 4, ... Equalizer 5 ... Adaptive filter 10 ... Frequency detector 11 ... Handpass filter controller 12, 13, 14 ... Multiple bandpass filters 15, 16, 17 ... Level detector 18 ... Equalizer controller 20 ... High-speed Fourier transform unit 30 ... Digital signal processing device 31 ... A plurality of equalizers 32 ... Residual sound frequency characteristic analysis unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Osamu Ishikawa               1-2-2 Goshodori, Hyogo-ku, Kobe-shi, Hyogo               Issue within Fujitsu Ten Limited (72) Inventor Toshitaka Yamato               1-2-2 Goshodori, Hyogo-ku, Kobe-shi, Hyogo               Issue within Fujitsu Ten Limited                (56) Reference JP-A-2-306845 (JP, A)                 JP-A-5-216485 (JP, A)                 JP-A 1-248797 (JP, A)

Claims (2)

(57) [Claims] 1. A noise control device having an adaptive filter (5) for forming a cancellation sound for noise of a noise source (100), comprising a plurality of noise filters connected in series to an input stage of the adaptive filter (5). Of the equalizer (31), a plurality of bandpass filters corresponding to the equalizer (31), and a level detector connected to the bandpass filters, and a residual sound frequency characteristic analyzing unit (32) for frequency-analyzing the residual sound from which the noise is canceled. ), A frequency detector (10) for directly detecting the fundamental frequency of the noise of the noise source (100), and forming a harmonic frequency thereof based on the fundamental frequency to determine the center frequency of the bandpass filter. And a frequency characteristic of the residual sound frequency characteristic analysis unit (32) for storing the frequency characteristic for adjusting the residual sound in advance. Compared with gender, the plurality of equalizers as they are approximations (3
A noise control device comprising: an equalizer control unit (18) for controlling the center frequency and the gain of 1). 2. A noise control device having an adaptive filter (5) for forming a cancellation sound for noise of a noise source (100), comprising a plurality of noise filters connected in series to an input stage of the adaptive filter (5). An equalizer (31), a high-speed Fourier transform unit (20) for frequency-analyzing the residual sound from which the noise has been canceled, and a frequency characteristic for adjusting the residual sound in advance, which is stored in the high-speed Fourier transform unit (20). Compared with the frequency characteristics of
The equalizers (31) so that they match
Equalizer control unit (1 that controls the center frequency and gain of the
8) A noise control device comprising: