JP3405755B2 - Noise canceling 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 canceling device, and more particularly to a noise canceling device for canceling noise by adaptive prediction.

[0002]

2. Description of the Related Art As a measure against noise, a method (active control) of radiating a noise canceling sound having a phase opposite to that of noise from a speaker to reduce the noise (active control) has been spotlighted, and a part of an indoor space such as a factory or an office It is being put to practical use. Also, a method has been proposed in which noise is reduced by active control even in the passenger compartment of an automobile. In the method of canceling noise by active control, the coefficient of the adaptive filter is determined by adaptive signal processing using the reference signal that has a high correlation with the noise to be canceled, and the reference signal is input to the adaptive filter to generate the noise cancellation signal. And a method of detecting the current noise, predicting the noise after a predetermined time from the current noise by adaptive prediction processing, and generating a noise cancel signal so as to cancel the noise after the predetermined time.

The former noise canceling method controls so that only noise having a high correlation with the reference signal is canceled. When the noise source is an engine like a car, the noise generated by the engine rotation has a periodicity, and its frequency depends on the engine speed. For example, in a 4-cylinder engine, the periodic noise generated in the vehicle compartment is dominated by the second harmonic of the engine rotation speed, and the rotation speed is 600 rpm (1
0 rps), the frequency of noise generated in the passenger compartment is 2
When the frequency is 0 Hz and the rotation speed is 6000 rpm (100 rps), the frequency of noise generated in the vehicle interior is 200 Hz. Therefore, the engine speed is detected, and a sine wave signal having a constant amplitude and a frequency corresponding to the engine speed is generated as a reference signal to cancel the engine sound. As described above, the former method is effective when the noise to be canceled is known or can be easily predicted, but the unpredictable noise cannot be canceled. On the other hand, the latter method of noise cancellation by adaptive prediction controls so as to cancel all noise generated in a certain space.

FIG. 2 is a block diagram of a conventional noise canceling apparatus based on adaptive prediction. In the figure, 11 is a speaker which receives a noise cancel signal y (n) and outputs a cancel sound Sc so as to cancel noise at a noise cancel point (observation point), and 12 is noise Sn and the cancel sound Sc at the noise cancel point. A microphone that detects the synthesized sound of
Reference numeral 3 denotes a cancel sound propagation system characteristic imparting unit that convolves the noise cancel signal y (n) with the propagation characteristics of the cancel sound propagation system 14 from the speaker to the sensor. As shown in FIG. 3, the cancellation sound propagation system characteristic imparting unit 13 causes the M tap FIR
Type digital filter, for example, delay elements DL, DL for sequentially delaying the input signal by one sampling time Ts
... and, coefficients c ₁ to the delay element _{output, c 2, c 3 ··· c} M multiplies the multiplication section ML, ML, ... and, addition section AD which sequentially adds the multiplication unit output, Realized by AD ... Coefficients _{c 1, c 2, c 3} ··· c M is determined so as to simulate the propagation characteristics of the cancel sound propagation system 14. If the noise canceling signal at time n · Ts is y (n) and the output is s (n), the canceling sound propagation system characteristic imparting unit 13

[0005]

[Equation 1] The noise estimation signal s (n) used when estimating the noise is output. In this way, the cancel sound propagation system characteristic imparting unit 13 convolves the propagation characteristics of the cancel sound propagation system 14 with the noise cancel signal y (n), so that the output signal s (n) of the cancel sound propagation system characteristics is canceled at the noise cancel point. The sound Sc is simulated.

Reference numeral 15 subtracts the noise estimation signal s (n), which is the output of the cancel sound propagation system characteristic imparting unit 13, from the synthesized sound signal g (n) output from the microphone 12 and outputs the noise signal d (n). It is a noise signal generator. Since the synthesized sound signal g (n) is (Sn + Sc), the output d (n) of the noise signal generator 15 is d (n) = (Sn + Sc) -s (n) (2). Since Sc≈s (n), d (n) ≈Sn,
The output d (n) of the noise signal generator 15 becomes a noise signal according to the noise Sn. 16 is the FIR to which the noise signal d (n) is input
Type digital filter, and as shown in FIG. 4, it is configured by an N-tap FIR digital filter.
Delay the input signal by one sampling time (N-1)
N delay elements DL, DL ... And N multiplications for multiplying each delay element output by coefficients w ₁ (n), w ₂ (n), w ₃ (n) ... w _N (n) .. and addition units AD, AD, ... Which sequentially add the outputs of the respective multiplication units. That is, the noise signal at the current time n · Ts is d (n), and the coefficients of the respective multipliers at that time are w ₁ (n), w ₂ (n), w ₃ (n), ... W.
Assuming that _N (n) and the output noise canceling signal are y (n) ', the digital filter 16 is

[0007]

[Equation 2] Then, the noise cancellation signal y (n) ′ is output. The coefficient of the digital filter 16 is determined by the adaptive predictor described later.

Reference numeral 17 denotes a sign inverting section which inverts the sign of the digital filter output y (n) 'and outputs a noise canceling signal y (n). 18 is the noise signal d (n) and the cancel sound propagation system 1
4 is a second cancel sound propagation system characteristic imparting section that convolves the propagation characteristic of No. 4 and has the same configuration as the cancel sound propagation system characteristic imparting section 13

[Equation 3] And outputs the signal r (n).

Reference numeral 19 denotes a cancel sound propagation system characteristic imparting section 18
Current output noise r (n) is used to predict the current noise, and the coefficients w ₁ (n), w ₂ (n), w of the digital filter 16 are predicted.
₃ (n) ... An adaptive predictor for determining w _N (n), 20 is a difference signal e (n) between the predicted noise signal d (n) ′ and the noise signal d (n) output from the adaptive predictor 19. ) Is a difference signal generator. As shown in FIG. 5, the adaptive predictor 19 includes an adaptive prediction processing unit 19a and an adaptive filter 19b having the same configuration as the digital filter 16. The adaptive prediction processing unit 19a
The output signal r (n) and the difference signal e (n) of the cancellation sound propagation system characteristic imparting unit 18 are input, and LMS (Least Mean Square)
Adaptive prediction is performed by an adaptive algorithm so that the difference signal e (n) becomes zero, and the coefficients w ₁ (n), w ₂ (n), w ₃ (n) of the adaptive filter 19b and the digital filter 16 are ...・ W
Determine _N (n). In the LMS adaptive algorithm,
Time (n +) one sampling time Ts after the current time n · Ts
1). Coefficients w ₁ (n + 1), w ₂ (n + 1), w ₃ (n + 1) ... w of the adaptive filter 19b and the digital filter 16 at Ts
_N (n + 1) is determined by the following coefficient updating formula. Incidentally, w
₁ (n), w ₂ (n), w ₃ (n) ... w _N (n) are coefficients at the current time n · Ts.

[0010]

[Equation 4] However, the j-th filter coefficient updating formula is given by w _j (n + 1) = w _j (n) + μ · r (n-j + 1) · en. In equation (4), (n) is the value at the current sampling time, (n + 1) is the value one sampling time later, and (n-1) is 1
The value before the sampling time, (n-2) means the value before the two sampling times, .... Also, μ determines the step of updating the coefficient of the adaptive filter or digital filter 1
It is the following constant (step size parameter).

The adaptive filter 19b is an adaptive prediction processing unit 19
The signal r (n) is digitally filtered according to the coefficient determined by a to output the predicted noise signal d (n) '. That is, the adaptive filter 19b is

[Equation 5] Then, the predicted noise signal d (n) 'is output.

A portion surrounded by a dotted line in FIG. 2 can be constituted by a DSP (digital signal processor), and a DA converter and an AD converter are provided at appropriate places. In noise cancellation by adaptive prediction, the noise cancellation signal y is calculated by performing the calculations of the above formulas (1) to (6) within one sampling time.
Output (n). That is, the cancel sound propagation system characteristic imparting unit 13 convolves the cancel sound propagation system characteristic into the noise cancel signal y (n) by the equation (1), and the noise signal generating unit 15
The noise signal d (n) is output by the equation (2). The cancel sound propagation system characteristic imparting unit 18 convolves the cancel sound propagation system characteristic with the noise signal d (n) by the equation (4) and outputs the signal r (n),
The difference signal generator 20 outputs the difference signal e (n). The adaptive prediction processing unit 19a executes the calculation of equation (5) to calculate the coefficients of the digital filter 16 and the adaptive filter 19b, and inputs these coefficients to the digital filter 16 and the adaptive filter 19b. The digital filter 16 performs the calculation of the equation (3), generates the noise cancellation signal y (n) via the sign inversion unit 17 and inputs it to the speaker 11, and the speaker outputs the noise cancellation sound Sc to cancel the noise. To do. Further, the adaptive filter 19b outputs the predicted noise signal d (n) 'according to the equation (6). After that, the above operation is repeated to cancel the noise.

Assuming that the noise-canceling sound propagation system 14 is a system that has only signal delay and no attenuation (delay time is τ), the adaptive predictor 19 causes the noise before the cancellation sound propagation system characteristic imparting section 18 to be τ. The signal d (n-τ) is input as the signal r (n). The adaptive predictor 19 determines the noise signal d (n
-[tau]) is used to perform adaptive prediction processing so that the predicted noise signal d (n) 'matches the current noise signal d (n), and the coefficient of the digital filter 16 is determined. Therefore, when the current noise signal d (n) is input to the digital filter 16, the noise signal d (n + τ) after τ is output as the signal y (n) ′. The noise signal d (n + τ) after τ is sign-inverted to be a noise cancellation signal y (n) (= −d (n + τ)), which is input to the speaker 11 and is transmitted via the cancellation sound propagation system 14. The noise cancellation point is reached. In this case, since the cancellation sound propagation system 14 causes a delay of τ time, the noise cancellation sound Sc at the noise cancellation point corresponds to −d (n), and the noise Sn (= d (n)) can be canceled. The above is the case of only the signal delay, but the same can be considered for a system in which the amplitude is attenuated in addition to the signal delay.

[0014]

By the way, the noise signal d
The noise estimation signal s (n) required to generate (n) is
The cancellation sound propagation system characteristic imparting unit 13 creates the noise cancellation signal y (n) by convolving the propagation system characteristic. However, since the cancellation sound propagation system characteristic imparting unit 13 is composed of a FIR digital filter having a finite length, the accuracy deteriorates as the frequency becomes lower, and in particular, the DC component has a value even though it is originally zero. The so-called offset occurs. Thus, if the noise estimation signal s (n) has a DC component,
The DC component is gradually accumulated by the positive feedback loop PFL, which causes a phenomenon in which the coefficient and the predicted noise signal cannot be correctly output from the adaptive predictor 19, and noise cannot be effectively canceled. From the above, it is an object of the present invention to provide a noise canceling device capable of removing an offset, correctly outputting a coefficient and a predicted noise signal from an adaptive predictor, and effectively canceling noise.

[0015]

According to the present invention, there is provided a speaker for receiving a noise cancel signal and outputting a cancel sound, a sensor (microphone) for detecting a synthesized sound of noise and the cancel sound, and a noise cancel signal. From the speaker to the sensor, the first cancel sound propagation system characteristic imparting section that imparts the propagation characteristic of the cancel sound propagating system, the high-pass filter that is provided after the first cancel sound propagating system characteristic imparting section, and the synthesized sound signal A noise signal generator that subtracts the output of the high-pass filter and outputs a noise signal, a digital filter that inputs the noise signal and outputs a noise cancellation signal, and a second cancellation sound that imparts the propagation characteristics of the cancellation sound propagation system to the noise signal. Propagation system characteristic imparting section, with difference signal between predicted noise signal and said noise signal, and with said second canceled sound propagation system characteristic The output signal of the section are input,
This is achieved by an adaptive prediction unit that performs adaptive prediction processing so as to match the predicted noise signal with the noise signal and determines the coefficient of the digital filter.

[0016]

The speaker receives the noise cancel signal and outputs the cancel sound, and the microphone detects the synthesized sound of the noise and the cancel sound at the observation point. The first cancel sound propagation system characteristic imparting unit convolves the noise cancel signal with the propagation characteristic of the cancel sound propagation system from the speaker to the microphone, and outputs a signal corresponding to the noise cancel sound at the observation point. Remove the low frequency components contained in. The noise signal generation unit generates a noise signal by subtracting the output of the high-pass filter from the synthesized sound signal, and the second cancel sound propagation system characteristic imparting unit convolves the cancel sound propagation system characteristic into the noise signal. The adaptive prediction unit receives the output of the second cancel sound propagation system characteristic imparting unit, performs adaptive prediction processing so that the difference between the predicted noise signal predicted by itself and the noise signal becomes zero, and the coefficient of the digital filter is set. Then, the digital filter performs filtering processing on the noise signal using the determined coefficient to generate a noise cancellation signal and inputs it to the speaker.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Overall Structure FIG. 1 is a block diagram of a noise canceling device by adaptive prediction according to the present invention. The same parts as those of the conventional device of FIG. Reference numeral 11 is a speaker which receives the noise cancellation signal y (n) and outputs a cancellation sound Sc so as to cancel the noise at the noise cancellation point (observation point),
Reference numeral 12 is a microphone that detects a synthesized sound of the noise Sn and the cancel sound Sc at the noise cancel point, and 13 is a cancel sound propagation system characteristic that convolves the propagation characteristics of the cancel sound propagation system 14 from the speaker to the sensor with the noise cancellation signal y (n). It is an application unit. Reference numeral 21 denotes a high-pass filter that is provided after the first cancel sound propagation system characteristic imparting unit 13 and removes a direct current component included in the noise estimation signal s (n) output from the characteristic imparting unit 13, and 15 denotes the microphone 12 Output s (n) 'of the high-pass filter 21 from the synthesized sound signal g (n)
Is a noise signal generator that outputs the noise signal d (n). Reference numeral 22 indicates the total frequency characteristic of the path from the input section of the cancel sound propagation system characteristic imparting section 13 to the input section of the noise signal generating section 15 via the high-pass filter 21, and the input section of the cancel sound propagation system characteristic imparting section 13. It is a high-pass filter inserted so that the total frequency characteristic reaching the observation point via the speaker 11 matches, and has the same frequency characteristic as the high-pass filter 21.

The synthetic sound signal g output from the microphone 12
Since (n) is (Sn + Sc), the noise signal generator 15
The output d (n) of the above becomes d (n) = (Sn + Sc) -s (n) '(2)'. Since Sc≈s (n) ′, d (n) ≈Sn, and the output d (n) of the noise signal generator 15 becomes a noise signal corresponding to the noise Sn. Further, the noise signal d (n) does not include a DC component because the high-pass filter 21 is inserted. Reference numeral 16 is a FIR type digital filter to which the noise signal d (n) is input, and 17 is a sign inverting section which inverts the sign of the digital filter output y (n) 'to cancel the noise signal y (n).
Is output. Reference numeral 18 denotes a second cancel sound propagation system characteristic imparting unit for convoluting the noise signal d (n) with the propagation characteristic of the cancel sound propagating system 14, and 19 denotes the cancel sound propagating system characteristic imparting unit 18.
The current noise is predicted from the output signal r (n) of the digital filter 16 and the coefficients w ₁ (n), w ₂ (n), w ₃ (n) of the digital filter 16 are ...
An adaptive predictor for determining w _N (n), 20 is an adaptive predictor 1
Predicted noise signal d (n) 'and noise signal d (n) output from 9
Is a difference signal generation unit for generating the difference signal e (n). The portion surrounded by a dotted line in FIG. 1 can be configured by a DSP (digital signal processor), and a DA converter and an AD are provided at appropriate places.
A converter is provided.

The entire operation speaker 11 receives the noise cancel signal y (n) through the high-pass filter 22 and outputs a noise cancel sound, and the microphone 12 detects a synthesized sound of the noise Sc and the cancel sound Sn at the observation point. To do. The cancellation sound propagation system addition unit 13 receives the noise cancellation signal y (n) and convolves the cancellation sound propagation system characteristic with the noise cancellation signal y (n) according to the equation (1), and the high-pass filter 21 uses the cancellation sound propagation system characteristic addition unit. The DC component contained in the noise estimation signal s (n) which is the output of 13 is removed. The noise signal generator 15 generates the noise signal d (n) according to the equation (2) ', and the digital filter 1
6, the second cancel sound propagation system characteristic imparting unit 18, and the difference signal generating unit 20. The cancel sound propagation system characteristic imparting unit 18 convolves the cancel sound propagation system characteristic with the noise signal d (n) according to the equation (4) and outputs the signal r (n).
0 is the difference signal e between the predicted noise signal d (n) 'and the noise signal d (n)
Output (n).

The adaptive prediction processing unit 19a executes the calculation of equation (5) to calculate the coefficients of the digital filter 16 and the adaptive filter 19b, and inputs these coefficients to the digital filter 16 and the adaptive filter 19b. The digital filter 16
Equation (3) is calculated, and the noise cancellation signal y (n) is input to the high-pass filter 22 and the first cancellation sound propagation system characteristic imparting unit 13 via the sign inverting unit 17. Further, the adaptive filter 19b outputs the predicted noise signal d (n) 'according to the equation (6). After that, the above operation is repeated to cancel the noise. As described above, the cancel sound propagation system characteristic imparting unit 13
Since the high-pass filter 21 is inserted on the output side of, the direct current component included in the output of the characteristic imparting unit 13 can be removed, the coefficient and the predicted noise signal can be correctly output from the adaptive predictor 19, and the noise can be effectively reduced. You can cancel. It should be noted that, although the above description is for a single microphone, a plurality of microphones can be dealt with by performing the same processing on the signals from each microphone. Although the present invention has been described above with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention described in the claims, and the present invention does not exclude these.

[0021]

As described above, according to the present invention, since the first high-pass filter is inserted on the output side of the first cancel sound propagation system characteristic imparting section, the output of the first cancel sound propagation system characteristic imparting section is improved. The included DC component can be removed, the coefficient and the predicted noise signal can be correctly output by the adaptive predictor, and the noise can be effectively canceled. In addition, a second high frequency filter having the same frequency characteristic as the first high pass filter
Since the high-pass filter of 1 is provided in the front stage of the speaker, the noise signal can be correctly estimated and output by the noise signal generator, and the noise canceling effect can be improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a noise canceling device of the present invention.

FIG. 2 is a configuration diagram of a conventional noise canceling device based on adaptive prediction.

FIG. 3 is a configuration diagram of a cancel sound propagation system characteristic imparting unit.

FIG. 4 is a configuration diagram of a digital filter.

FIG. 5 is a configuration diagram of an adaptive predictor.

[Explanation of symbols]

11 ... Speaker 12 ... Sensor (microphone) 13 ... First cancel sound propagation system characteristic imparting unit 14 ... Cancellation sound propagation system 15..Noise signal generator 16 ... Digital filter 18 ... Second cancel sound propagation system characteristic imparting unit 19 ... Adaptive prediction unit 21,22 ... High-pass filter

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G10K 11/178 F01N 1/00 H03H 17/02 601 H03H 17/04 641 H03H 21/00

Claims (2)

(57) [Claims] 1. A speaker which receives a noise cancellation signal and outputs a cancellation sound so as to cancel the noise at the noise cancellation point, a sensor which detects a noise at the noise cancellation point and a synthesized sound of the cancellation sound, and a speaker for the noise cancellation signal. To a sensor, a first cancel sound propagation system characteristic imparting section that imparts a characteristic of a cancel sound propagation system characteristic, a high-pass filter provided after the first cancel sound propagation system characteristic imparting section, and a high-pass filter that is higher than the synthesized sound signal. Noise signal generator that outputs the noise signal by subtracting the noise output, a digital filter that inputs the noise signal and outputs the noise cancellation signal, and a second cancellation sound propagation system characteristic that adds the characteristics of the cancellation sound propagation system to the noise signal Providing unit, a difference signal between the predicted noise signal and the noise signal, and the second signal A noise canceling device including an adaptive prediction unit that receives the output signals of the cancel sound propagation system characteristic imparting unit and performs adaptive prediction processing so that the predicted noise signal and the noise signal match to determine the coefficient of the digital filter. . 2. The noise canceling device according to claim 1, wherein another high-pass filter having the same frequency characteristic as that of the high-pass filter is provided in the front stage of the speaker.