JP2001056692A - Noise reducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To actualize stable sound elimination effect for a long time by reducing the margin that an arithmetic error is included and updating coefficients again as external situations change. SOLUTION: This device has its arithmetic processing part 40 composed of a sound elimination signal generation filter 31 which generates a sound elimination signal, adaptive control algorithm 32 which implements LMS algorithm, a transfer characteristic Gs filter 33 which represents characteristics of the space between a secondary sound source and a sensor microphone 11, a transfer characteristic Ge filter 34 which represents characteristics of the space between the secondary sound source and an error microphone 12, a subtracter 35, and an update decision part 41 which places the adaptive control algorithm 32 in operation to decides whether or not the sound elimination signal generation filter 31 is updated. Further, the device is equipped with a switching part 42 which switches whether or not the coefficient of the sound signal generation filter 31 is updated according to the decision made by the update decision part 41 and a switching part 43 which decides which of arithmetic parts 2 and 3 is put in operation and switches them.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device for silencing noise of an air-conditioning duct or the like, and more particularly to a noise reduction device which simultaneously emits sound waves having the same sound pressure and opposite phases to be canceled out of noise sound waves. The present invention relates to a noise reduction device that silences due to interference between both sound waves.

[0002]

2. Description of the Related Art In general, as a method of silencing noise propagating in an air-conditioning duct or the like, a passive silencing method such as a method of silencing by a sound absorbing material lined in a duct has been mainly used. There are problems such as loss and size when silencing low frequencies. Also, active silencing methods have been studied in which noise is emitted by radiating a sound having a phase opposite to that of the noise, but many problems remain.

A document showing an active noise reduction method is disclosed, for example, in Japanese Patent Application Laid-Open No. 7-334168 (active noise system).

FIG. 5 is a diagram showing the configuration of a conventional noise reduction device described in the above-mentioned publication, which is applied to an active noise type noise reduction device which actively cancels noise propagating in a duct.

In FIG. 5, reference numeral 10 denotes a duct through which noise propagates, 11 denotes a microphone provided in the duct 10 to detect a noise signal in the duct 10, 12 denotes a microphone provided in the duct 10 to detect a muffling state, Reference numeral 13 denotes a muffling speaker that emits sound waves having the same sound pressure and opposite phase to noise.

Reference numeral 14 denotes a microphone amplifier for amplifying the signal detected by the microphone 11, reference numeral 15 denotes a frequency cutoff filter for cutting off a signal in a frequency range which is not a target of silencing the amplified signal, and reference numeral 16 denotes an analog electric signal. A / D converter for converting a signal into a digital signal, 17
Is a microphone amplifier that amplifies the signal detected by the microphone 12, 18 is a frequency cutoff filter that cuts off a signal in a frequency range that is not a target of silencing the amplified signal, and 19 is a converter that converts an analog electric signal into a digital signal. A / D converter, 20 is the A / D converter 1
An arithmetic unit for generating a muffling signal from the outputs of 6, 6 and 19 by an adaptive filter and an adaptive control algorithm, 21 is a D / A converter for converting the digital muffling signal created by the arithmetic unit 20 into an analog signal, and 22 is a muffling unit. A frequency cutoff filter that cuts off a signal in a frequency region that is not a target of muffling in order to reproduce only a signal in a target frequency region.
(Hereinafter, sometimes referred to as a secondary sound source).

The arithmetic unit 20 performs adaptive control arithmetic for adaptively estimating the transfer characteristics of the sound in the space and generating a pseudo muffling signal. The arithmetic unit 20 includes a muffling signal generating filter 31 and an adaptive muffling filter. It comprises a control algorithm 32, a transfer characteristic Gs filter 33, a transfer characteristic Ge filter 34, and a subtractor 35.

In the above configuration, noise transmitted through the duct 10 is detected as an analog electric signal by a microphone 11 (hereinafter, referred to as a sensor microphone), and the signal is amplified by a microphone amplifier 14. The amplified analog signal is filtered by the frequency cutoff filter 15 to cut off a signal in a frequency region that is not a target of silencing. After that, the digital signal is converted into a digital signal through the A / D converter 16, and the obtained digital signal is input to the arithmetic unit 20.

An analog microphone detected by a microphone 12 (hereinafter referred to as an error microphone or an error sensor) for detecting a muffling state placed at a place where the user wants to mute the sound (here, downstream of the muffling speaker 13 as viewed from the noise source). The signal is also amplified by the microphone amplifier 17 and passed through the frequency cutoff filter 18 as in the case of the sensor microphone, and then the digital signal e is output by the A / D converter 19.
The result is converted to (n) and input to the arithmetic unit 20.

The digital signal e (n), which represents a mute state, is input to a calculation unit 20. The calculation unit 20 includes a secondary sound source simulating the transfer characteristic of the sound in the space and the sensor microphone 11
Between the secondary sound source and the error microphone 12
e, and a signal obtained by extracting only the sound from the upstream of the noise (the output of the subtractor 35) and an optimal filter such that the signal e (n) from the A / D converter 19 always approaches zero. The coefficient W is calculated by the adaptive algorithm 32, and a convolution operation is performed on the input signal from the sensor microphone 11 as a filter coefficient W of the muffling signal generation filter 31, thereby creating a muffling digital filter.

Here, the characteristic Gs between the secondary sound source and the sensor microphone and the characteristic Ge between the secondary sound source and the error microphone are determined before the sound is muted.

FIG. 6 is a diagram for explaining the operation of the arithmetic unit 20. When an adaptive filter is created, the muffling signal generating filter 31 can be expressed as shown in FIG.

In FIG. 6, 32 'is an adaptive control algorithm, 33 is a transfer characteristic Gs filter, and 34 is a transfer characteristic G.
e filter, 35 'is a subtractor, 36 is an M sequence (Maximum
Length Code: This is an M-sequence noise output unit that outputs random noise.

As shown in FIG. 6, the M-sequence noise output unit 3 created by the arithmetic unit 20 has almost the same system as that at the time of silencing.
6 is output from the secondary sound source, and the signals obtained from the sensor microphone and the error microphone through the paths of the respective transfer characteristics and the adaptive algorithm are made to correspond to the M-sequence random noise. Can be

Here, the Filtered-XLMS algorithm well known as the steepest descent method will be described as the adaptive algorithm 32. Signal e (n) indicating a mute state
Is a signal d (n) transmitted from the noise source through the duct 10.
Since the signal Y (n) output from the secondary sound source (mute speaker 13) passes through the duct 10 and enters the error sensor (microphone 12), the transfer function from the secondary sound source to the error sensor is represented by Ge. Then, it is shown as the following equation (1).

[0016]

(Equation 1) Further, the muffling signal generation filter 31 convolves the signal X (n) of the sensor microphone 11 with the filter coefficient W that can be updated, so that the signal Y output from the secondary sound source is obtained.
Since (n) is generated, it can be expressed as in the following equation (2).

[0017]

(Equation 2) That is, the signal e (n) indicating the mute state can be described as the following equation (3) from the above equations (1) and (2).

[0018]

(Equation 3) Next, if the evaluation function J = [e (n)] 2 is set to minimize the signal e (n) representing the mute state, the following equation (4) is obtained.
Can be expressed as

[0019]

(Equation 4) Since the evaluation function J is a quadratic function with respect to the filter coefficient W, when the minimum is minimized, the derivative ∇ (n) = ∂J / ∂W becomes zero when the derivative ゼ ロ (n) becomes zero as shown in the following equation (5). is there.

[0020]

(Equation 5) Therefore, since the control object changes with time, the filter coefficient W may be sequentially updated using the following equation (6), which is a method of the steepest descent method, so that the evaluation function J becomes minimum for that state.

[0021]

(Equation 6) The signal Y (n) output from the secondary sound source is generated according to the above equation (2) using the filter coefficient W obtained here. The signal Y (n) is converted into an analog signal by a D / A converter 21 and an analog signal for noise reduction is generated through a frequency cutoff filter 22 by analog signal processing. This silencing analog signal is transmitted to the speaker amplifier 2
The sound is amplified by 3 and drives a noise reduction speaker 13 which is a secondary sound source, and emits noise to be reduced. As a result, the noise and the sound wave for silencing collide with each other and cancel each other by causing interference, thereby performing silencing.

In FIG. 5, the filter-XLMS algorithm uses the spatial characteristic Gs between the secondary sound source and the sensor microphone and the signal Y (n) output from the secondary sound source to input the signal into the sensor microphone. The sound output from the next sound source is deleted.

As described above, according to the active noise type noise reduction device using the adaptive filter, the filter coefficient of the adaptive filter is sequentially updated so that the noise that cannot be completely eliminated in the duct to be controlled is minimized. , Mute.

The frequency cutoff filter 1 used above
Reference numerals 5, 18, and 22 are used to remove signals such as noise and to process only signals in a target frequency region to be silenced. In general, only signals in a target low frequency band are passed. A frequency cutoff filter having a frequency characteristic of passing only a signal having a frequency lower than a certain frequency fc with respect to an input as shown in FIG.

[0025]

However, in such a conventional noise reduction device, if the sound is repeatedly silenced for a long time, a calculation error due to a disturbance or a quantization error is accumulated in the adaptive filter coefficient. For this reason, there is a problem that the silencing effect is lost or diverges.

According to the present invention, there is provided a noise reduction apparatus capable of realizing a stable noise reduction effect over a long period of time by reducing the room for calculation errors and updating coefficients again in response to changes in external conditions. The purpose is to provide.

[0027]

SUMMARY OF THE INVENTION A noise reduction device according to the present invention simultaneously emits sound waves having the same sound pressure and opposite phase to be canceled out from noise sound waves to the noise, thereby reducing the noise canceled by the interference between the sound waves. In the apparatus, a noise detecting means for detecting a noise sound wave, a muffling detecting means for detecting a muffling state, a sound emitting means for emitting a muffling sound wave to the noise sound wave, and a muffling signal to be supplied to the sound emitting means are generated. Muffling signal generating means, adaptive control means for updating or adaptively estimating or adaptively updating a filter coefficient for noise estimation from an output of the noise detecting means and an output of the muffling detecting means, and An update determining means for determining whether or not to update the coefficient of the muffling signal generating means, and a switching means for stopping the updating of the filter coefficient by the adaptive control means according to the determination of the update determining means. It is characterized in.

The update determining means may determine the coefficient update by storing the output from the silence detecting means in a predetermined array.

The update determining means stores the output from the silence detecting means in a predetermined array, and determines the coefficient update by comparing the average value of the absolute values of the elements of the array with a predetermined value. The update determination unit may store the output from the muffling detection unit in a predetermined half-wavelength array of the wavelength to be muffled, and store the maximum value of the absolute value of each element of the array. The determination of the coefficient update may be performed by comparing with a predetermined value.

The update judging means may judge the coefficient update based on the output of the silence detecting means at fixed time intervals, and the update judging means may observe the output level of the silence detecting means. However, the determination may be made so as to stop the coefficient update where the noise is stable.

The update judging means may be provided outside the silence processing operation unit by the adaptive control means and independently.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a block diagram showing a configuration of a noise reduction device according to a first embodiment of the present invention. This is an example in which the present invention is applied to an active noise type noise reduction device that actively cancels noise propagating in a duct. In the description of the noise reduction device according to the present embodiment, the same components as those in FIG. 5 are denoted by the same reference numerals.

FIG. 1 is a diagram showing the configuration of the mute process, showing the positional relationship between the sensor microphone, the error microphone, and the secondary sound source of the one-dimensional duct when the noise is transmitted from left to right through the duct, and the calculation unit. I have.

In FIG. 1, reference numeral 10 denotes a duct through which noise propagates, 11 denotes a microphone (noise detecting means) provided in the duct 10 and detects a noise signal in the duct 10, 12
Is a microphone (silence detecting means) provided in the duct 10 for detecting a muffling state, and 13 is a muffling speaker (sound emitting means) which radiates sound waves having the same sound pressure and opposite phase to noise.

Reference numeral 14 denotes a microphone amplifier for amplifying a signal detected by the microphone 11, reference numeral 15 denotes a frequency cutoff filter for cutting off a signal in a frequency range which is not a target of silencing the amplified signal, and reference numeral 16 denotes an analog electric signal. A / D converter for converting a signal into a digital signal, 17
Is a microphone amplifier that amplifies the signal detected by the microphone 12, 18 is a frequency cutoff filter that cuts off a signal in a frequency range that is not a target of silencing the amplified signal, and 19 is a converter that converts an analog electric signal into a digital signal. A / D converter, 40 is the A / D converter 1
An arithmetic processing unit for generating a muffling signal from the outputs of 6 and 19 by an adaptive filter and an adaptive control algorithm; 21, a D / A converter for converting the digital muffling signal created by the arithmetic processing unit 40 into an analog signal; A frequency cutoff filter that cuts off a signal in a frequency region that is not a target of silencing in order to reproduce only a signal in a frequency range that is a target of silencing. This is a speaker amplifier that outputs to a sound source.

The arithmetic processing unit 40 adaptively estimates the transfer characteristics of the sound in the space and performs an adaptive control operation for generating a pseudo muffling signal. The arithmetic processing unit 40 includes three arithmetic units 1, 2, and 3. . The processing of the operation units 1, 2, 3 is performed by one operation processing unit 40
It is done in. The arithmetic processing unit 40 includes a dedicated LSI, a microprocessor, or a DSP (digital signal process).
or). The DSP has an arithmetic unit mainly having a multiplication function, and performs signal processing by controlling the arithmetic function and data transfer by firmware.

The operation unit 1 includes a muffling signal generation filter 31
(Mute signal generating means) Secondary sound source (Mute speaker 1
3) and microphone (hereinafter referred to as sensor microphone) 11
Transfer characteristics Gs filter 3 representing the characteristics of the space between
3 and a subtractor 35.

The operation unit 2 is an LMS (Least Mean Square)
e) An adaptive control algorithm 32 (adaptive control means) for performing the algorithm, and a transfer characteristic Ge filter 34 representing the characteristics of the space between the secondary sound source (mute speaker 13) and the microphone (hereinafter referred to as an error microphone) 12. Have been.

The operation section 3 is constituted by an update judgment section 41 (update judgment means) for judging whether or not to update the muffling signal generation filter 31 by operating the adaptive control algorithm 32.

The operation units 1 and 2 are connected to a switching unit 42
The operation unit 2 and the operation unit 3 are selected by the switching unit 43 and connected to the A / D converter 19.

The switching unit 42 controls the adaptive control algorithm 32
Is operated to determine whether to update the coefficient of the muffling signal generation filter 31.
The path for updating the coefficient of the muffling signal generation filter 31 is switched according to the result of the determination.

The switching unit 43 is a switch that determines which of the operation unit 2 and the operation unit 3 is to be moved at a predetermined time interval and switches the operation.

The sounds collected by the sensor microphone 11 and the error microphone 12 are transmitted to the microphone amplifiers 14 and 1 respectively.
7. After passing through frequency cutoff filters 15 and 18 and being converted into digital signals by A / D converters 16 and 19,
It is input to each operation unit.

Hereinafter, the operation of the noise reduction device configured as described above will be described. The basic operation of the noise reduction device is the same as that of the conventional example shown in FIG.

The noise transmitted through the duct 10 is detected by the sensor microphone 11, passes through the microphone amplifier 14 and the frequency cutoff filter 15, is converted into a digital signal by the A / D converter 16, and is input to the arithmetic unit 1. The arithmetic unit 1 performs the following processing.

The noise signal is a characteristic G between the secondary sound source simulating the sound transfer characteristic of the space and the sensor microphone 11, which is a sound output from the secondary sound source (muffling speaker 13) as a muffling signal.
By subtracting the difference between the signal filtered using s (the output of the transfer characteristic Gs filter 33) and the subtractor 35, a signal obtained by extracting only the noise from the upstream of the noise is obtained. The signal from which only the noise is extracted is filtered by the muffling signal generation filter 31 and the D / A converter 2
1. The signal is output from the silencing speaker 13, which is a secondary sound source, through the frequency cutoff filter 22 and the speaker amplifier 23. The coefficient W of the muffling signal generating filter 31 is
It is updated by the adaptive control algorithm 32 of the arithmetic unit 2.

Whether or not to update the coefficient of the muffling signal generating filter 31 is switched by the switching unit 42, and the determination is made by the update determining unit 41 of the arithmetic unit 3.

The arithmetic unit 2 is configured to filter the signal input to the muffling signal generating filter 31 using a transfer characteristic Ge filter 34 between the secondary sound source simulating the sound transfer characteristic and the error microphone 12, The adaptive algorithm 32 calculates an optimal filter coefficient W such that the difference from the signal e (n) input from the input signal 12 always approaches zero, and updates the filter coefficient W of the muffling signal generation filter 31.

The switching between the arithmetic unit 2 for updating the coefficient using the adaptive control algorithm 32 and the arithmetic unit 3 having the update judging unit 41 for judging the update of the coefficient is performed by a switching unit 43.
Done by

The switching by the switching unit 43 is performed at regular intervals, and whether or not the determination operation is performed is switched by the switching unit 42. When it is determined that the coefficient is not updated, the switching unit 42 is turned off, and the coefficient of the muffling signal generation filter 31 is not updated. Also, when the calculation unit 3 is performing the update determination, the switching unit 42
F, so that the coefficient of the muffling signal generation filter 31 is not updated.

The operation of the update judging section 41 of the arithmetic section 3 will be described.

The update judging section 41 has an array Z having a number of taps enough to receive a predetermined half-wave of the silencing frequency.
When the switching unit 43 is switched to the arithmetic unit 3, the signal e (n) coming from the error microphone 12 and collected for each sample time is collected by the number of taps in the array Z.

The array Z that has been collected takes the absolute values of all its elements and takes the average value Zh of the absolute values. The average value Zh is compared with a predetermined constant Zt, and when Zh is smaller than Zt, the switching unit 42 is turned off so that the coefficient is not updated, and when Zh is equal to or greater than Zt, the switching unit 42 is turned on and the coefficient is turned on. Make an update. That is, when the condition that “the average value Zh is smaller than the constant Zt” is satisfied, the coefficient update is stopped, and when the condition is not satisfied, the coefficient update is performed.

The flow of the switching units 42 and 43 and the operation units 1, 2 and 3 will be described with reference to FIG.

FIG. 2 shows the switching units 42 and 43 and the operation units 1 and 2,
6 is a timing chart showing the flow of the processing of No. 3;

As shown in FIG. 2, the operation unit 2 and the operation unit 3 are switched by the switching unit 43 at regular intervals, and when the switching unit 43 is switched to the operation unit 3, the update determination unit 41 generates a mute signal. It is determined whether or not the coefficient of the filter 31 is to be updated.
2 is switched. This makes it possible to determine whether to update the coefficient at regular intervals. In FIG. 2, when the calculation unit 3 makes the determination at the (n + 2) -th time, the condition is met, so that the coefficient is not updated. When the determination is made at the (n + 4) -th time, the condition is not satisfied. I'm starting to do it again.

As described above, the noise reduction device according to the first embodiment includes a sensor microphone 11 for detecting a noise signal in a duct 10 and an error microphone 1 for detecting a mute state.
2. A silencing speaker (secondary sound source) 13 which emits sound waves having the same sound pressure and opposite phase to noise, A / D converters 16 and 1
9, an arithmetic processing unit 40 for generating a muffling signal by an adaptive filter and an adaptive control algorithm from the output of C.9. The arithmetic processing unit 40 includes a muffling signal generating filter 31 for generating a muffling signal, and an adaptive control algorithm 32 for performing an LMS algorithm. A transfer characteristic Gs filter 33 representing the space characteristic between the secondary sound source and the sensor microphone 11; a transfer characteristic Ge filter 34 representing the space characteristic between the secondary sound source and the error microphone 12; 35, an update determination unit 41 that determines whether or not to update the muffling signal generation filter 31, a switching unit 42 that switches a path for updating a coefficient of the muffling signal generation filter 31 according to the determination from the update determination unit 41, A switching unit 43 configured to determine which of the operation unit 2 and the operation unit 3 is to be moved at a predetermined time interval and to switch the operation unit; In, the update determination unit 4 in the silencing process
By observing the muffling level at the position of the error microphone 12 at regular time intervals, it is possible to stop updating the coefficient of the muffling signal generating filter 31 in a stable state.

Therefore, compared with the adaptive algorithm that always performs noise reduction, by eliminating the updating of the coefficients of the noise reduction signal generation filter, it is possible to reduce the room for calculation errors due to disturbances and quantization errors. Even when the update determination is being performed, the sound is muted, and the coefficient can be updated again in response to a change in the external situation, so that a stable silencing effect can be realized for a long time.

In this embodiment, since the coefficient update determination processing is divided from the filter coefficient update processing at time intervals, the adaptive algorithm that has been operating so far can be used without changing to an arithmetic unit having a high processing capability. By using the above device, it can be added by a simple modification of software. In other words, an arithmetic device having a high processing capability is expensive, but the present embodiment can use a conventional arithmetic device having a relatively low processing capability as it is, and can be implemented easily at low cost. . Second Embodiment FIG. 3 is a block diagram illustrating a configuration of a noise reduction device according to a second embodiment of the present invention. In the description of the noise reduction device according to the present embodiment, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description of the overlapping portions will be omitted.

FIG. 3 is a block diagram of the mute process, showing the positional relationship between the sensor microphone, the error microphone, and the secondary sound source of the one-dimensional duct when the noise is transmitted from left to right through the duct, and the calculation unit. I have.

In FIG. 3, reference numeral 50 denotes the A / D converter 1
This is an arithmetic processing unit that creates a muffling signal from the outputs of Nos. 6 and 19 using an adaptive filter and an adaptive control algorithm.

The arithmetic processing unit 50 adaptively estimates the transfer characteristic of the sound in the space and performs an adaptive control operation for generating a pseudo muffling signal, and a sub-operation unit 5 provided outside. Consists of

The main operation unit 4 includes a muffling signal generation filter 31, an adaptive control algorithm 32 for performing an LMS algorithm, and a transfer characteristic Gs filter representing the space characteristics between the secondary sound source (muffling speaker 13) and the sensor microphone 11. 33, a transfer characteristic Ge filter 34 representing the characteristics of the space between the secondary sound source and the error microphone 12, and a subtractor 35.

The sub operation unit 5 is an operation unit provided outside the main operation unit 4, and operates the adaptive control algorithm 32 from a signal input from the error microphone 12,
An update determination unit 41 determines whether or not to update the coefficient of the muffling signal generation filter 31. The sub-operation unit 5 is a circuit (or a software processing unit using a CPU) that performs an operation process independently of the operation of the main operation unit 4 when the main operation unit 4 is configured by, for example, a DSP or the like. In this case, the sub-processing unit 5 may be one that is processed by a control unit that controls the entire noise reduction device, or may be one that is performed by another device connected to the noise reduction device by a communication line.

The subtraction unit 35 of the main operation unit 4 and the transfer characteristic Ge filter 34 are connected via the switching unit 42. The switching unit 42 is a switch that operates the adaptive control algorithm 32 and determines whether to update the coefficient of the muffling signal generation filter 31.

The sounds collected by the sensor microphone 11 and the error microphone 12 are transmitted to the microphone amplifiers 14 and 1 respectively.
7. After passing through frequency cutoff filters 15 and 18 and being converted into digital signals by A / D converters 16 and 19,
It is input to each operation unit.

Hereinafter, the operation of the noise reduction device configured as described above will be described. Note that the basic operation of the noise reduction device is the same as that of the first embodiment, and a description of the operation of this portion will be omitted.

Whether the coefficient of the muffling signal generating filter 31 is updated or not is switched by the switching unit 42.
Switching by the switching unit 42 is performed by the update determination unit 4 of the sub-operation unit 5.
Determined by 1.

When the switching section 42 is ON, the signal input to the muffling signal generation filter 31 is filtered using the transfer characteristic Ge filter 34 between the secondary sound source simulating the sound transfer characteristic and the error microphone 12. The adaptive algorithm 32 calculates an optimal filter coefficient W such that the difference between the signal and the signal e (n) input from the error microphone 12 always approaches zero, and updates the filter coefficient W of the muffling signal generation filter 31. To go.

The determination of the coefficient update by the sub-operation unit 5 is performed at certain time intervals. The update determination unit 41 determines whether or not to perform the coefficient update, and the switching unit 42 switches. When it is determined that the coefficient update is not performed, the coefficient of the muffling signal generation filter 31 is not updated.

The operation of the update judging section 41 of the sub arithmetic section 5 is as follows.
This is the same as described for the update determination unit 41 in FIG.

The array Z that has been collected takes the absolute values of all its elements and finds the average value Zh of the absolute values.
The average value Zh is compared with a predetermined constant Zt. When Zh is smaller than Zt, the switching unit 42 is turned off so that the coefficient is not updated, and when Zh is larger than Zt, the switching unit 42 is turned on. Update the coefficient. That is, when the condition that “the average Zh of the absolute value of the signal input from the error sensor 12 is smaller than the constant Zt” is satisfied, the coefficient update is stopped, and when the condition is not satisfied, the coefficient update is performed. Here, the constant Zt is a value that changes depending on the sound to be silenced or the setting condition of the silence, and is set in advance.

FIG. 4 shows the flow of the switching section 42 and the main calculation section 4.
This will be described with reference to FIG.

FIG. 4 is a timing chart showing the processing flow of the switching section 42 and the main processing section 4.

As shown in FIG. 4, the update determination section 41 of the sub-operation section 5 makes a determination at regular intervals, and determines whether or not to perform the coefficient update of the muffling signal generation filter 31. The switching unit 42 is switched according to the result. This makes it possible to determine whether to update the coefficient at regular intervals. In FIG. 4, when the sub-operation unit 5 makes the determination at the (n + 2) -th time, the condition is met, so that the coefficient is not updated. When the determination is made at the (n + 4) -th time, the condition is deviated from the condition. Coefficient updating has begun again. The meaning of the processing of the main operation unit 4 in FIG.
N + 1 to n + 2 times when coefficient updating is performed, and n + 4
Since the silencing process is performed while updating the coefficient after the first time, it indicates that much of the processing capacity of the arithmetic unit is used, and the silencing process without performing the coefficient updating is performed from n + 2 to n + 4. This indicates that there is room in the processing capacity of the arithmetic unit.

As described above, in the noise reduction device according to the second embodiment, as in the first embodiment, in the noise reduction processing, compared with the case of the adaptive algorithm in which the noise reduction is always performed, the error microphone is reduced. The noise reduction level at the position is observed at regular time intervals, and the coefficient update of the noise reduction signal generation filter is stopped at a stable place to reduce the room for calculation errors, and the coefficient update is performed again in response to changes in external conditions. As a result, a stable silencing effect can be realized for a long time.

In particular, in the present embodiment, the configuration in which the coefficient update determination unit 41 for the silencing process is installed in the external sub-operation unit 5 is employed, so that the processing of the main operation unit 4 can be performed for a long time without imposing a large load. Silence processing can be performed. As a result, the coefficient can always be updated in the same manner as in the conventional silencing process of the adaptive algorithm, so that the muting can be quickly followed and muted when the situation changes.

Since the number of processes for which the coefficient is not updated is reduced, the main arithmetic unit 4
Resting is also effective in reducing power consumption. Third Embodiment In the first and second embodiments, whether or not to perform coefficient update is determined depending on whether or not the average value Zh of absolute values of all elements of the array Z is smaller than a predetermined value Zt. However, instead, it may be determined whether or not to perform the coefficient update depending on whether or not the maximum value Zp of the absolute values of all the elements of the array Z is smaller than a predetermined value Zt.

The third embodiment of the present invention has the same overall configuration as the first embodiment. However, the update determination unit is different. The update determination unit 41 in FIG. 1 is replaced with an update determination unit 61 in the present embodiment.

Hereinafter, the operation of the noise reduction device configured as described above will be described. Since the basic operation of the noise reduction device is the same as that of the first embodiment, the description of the operation of this portion will be omitted.

The switching unit 43 switches between the arithmetic unit 2 that updates the coefficient using the adaptive control algorithm 32 and the arithmetic unit 3 that has an update determining unit 61 that determines the update of the coefficient.

The switching by the switching unit 43 is performed at regular intervals, and the updating determination unit 61 determines whether or not the coefficient updating is performed by the switching unit 42. When it is determined that the coefficient update is not performed, the coefficient of the muffling signal generation filter 31 is not updated. Also, even when the calculation unit 3 is performing the update determination, the coefficient update of the muffling signal generation filter 31 is not performed.

The operation of the update judging section 61 of the arithmetic section 3 will be described. The present embodiment is characterized in that the update determining unit 61 determines the coefficient update.

The update judging section 61 has an array Z having the number of taps enough to receive a half wavelength of the predetermined silencing frequency.
And when it is switched to the arithmetic unit 3,
The signal e (n) input from the error microphone 12 collected for each sample time is collected for the number of taps in the array Z.

The array Z that has been collected takes absolute values for all elements and extracts the maximum value Zp among them.
The maximum value Zp is compared with a predetermined constant Zt, and when Zp is smaller than Zt, the switching unit 42 is turned off so that the coefficient is not updated, and when Zp is larger than Zt, the switching unit 42 is turned on. Update the coefficient. That is, when the condition that “the maximum value Zp is smaller than the constant Zt” is satisfied, the coefficient update is stopped, and when not, the coefficient update is performed.

The processing flow of the switching units 42, 43 and the processing units 1, 2, 3 is the same as that of FIG.

As described above, the noise reduction apparatus according to the third embodiment performs the coefficient update adaptively by observing the signal from the error microphone 12 at fixed time intervals, and the update determination unit 61 The value input from the error microphone 12 is stored in a predetermined half-wavelength array of the wavelength to be silenced, and the maximum value Zp of the absolute value of each element of the array is
Since the coefficient update is determined by comparing with a value defined from the beginning, similar to the first embodiment,
In the silencing process, by observing the silencing level at the position of the error microphone 12 at regular intervals, the updating of the coefficient of the silencing signal generation filter is stopped at a stable location compared to the adaptive algorithm that always silences. As a result, there is less room for calculation errors to enter, and the coefficient can be updated again in response to changes in external conditions, so that a stable noise reduction effect can be realized for a long time.

Further, since the coefficient update determination processing is divided at a time interval from the main processing, the software of the adaptive algorithm that has been running can be simplified without changing to an arithmetic unit having a high processing capability. It can be added with minor modifications.

In particular, in the present embodiment, the maximum value Zp of the absolute value of each element of the array is compared with the predetermined value Zt. Therefore, as in the first and second embodiments, the average value of the absolute value is used. As compared with the case where Zh is used, the amount of calculation can be reduced, and the responsiveness is also high. However, when there is an influence of disturbance such as noise, it is better to use the average value Zh of the absolute values as in the first and second embodiments. Fourth Embodiment In the present embodiment, the coefficient update determination unit 41 of the external sub-operation unit 5 in FIG. 3 is replaced by the update determination unit 61 of the third embodiment, and the overall configuration is the second configuration. This is the same as the embodiment.

The basic operation of this noise reduction device is described in the second section.
The operation of the update determination unit 61 is the same as that of the third embodiment.
The description of the operation is omitted because it is the same as that of the first embodiment. The processing flow of the switching unit 42 and the main calculation unit 4 is the same as that of FIG.

As described above, in the noise reduction device according to the fourth embodiment, as in the third embodiment, the noise reduction processing is performed at the error microphone position in the noise reduction processing as compared with the adaptive algorithm in which the noise reduction is always performed. By observing the muffling level of the muffler at regular time intervals and stopping updating the coefficient of the muffling signal generation filter at a stable point, there is less room for calculation error, and the coefficient can be updated again in response to changes in external conditions. , And a stable silencing effect can be realized for a long time.

Further, as in the second embodiment, the external sub-operation unit 5 is provided with the coefficient update determination unit 61 for silencing processing, so that the processing of the main operation unit 4 is not greatly burdened. This enables long-term silence processing. As a result, the coefficient can always be updated in the same manner as in the conventional silencing process of the adaptive algorithm, so that the muting can be quickly followed and muted when the situation changes. Furthermore, since the processing is not performed for the processing in which the coefficient is not updated, the main operation unit 4 is rested at that time.
It is also effective in reducing power consumption.

In each of the above embodiments, the noise reduction system for the noise in the duct has been described as an example. However, it is needless to say that the present invention can be applied to a noise reduction device in another propagation path or shape.

In each of the above embodiments, the LMS adaptive algorithm has been described. However, with respect to a filter having a filter coefficient in the adaptive algorithm and performing a coefficient update for the silencing process, another adaptive algorithm may obtain the same effect. be able to.

In each of the above embodiments, the signal e (n) from the error sensor is put in the array Z for the determination.
There is no particular limitation, and the method may be performed in any form, and the size of the array Z is not particularly limited.

In the first and third embodiments,
Although the switching unit 43 is described to perform switching at a fixed time interval, the switching is not particularly limited, and the same effect can be obtained even if the switching is performed irregularly.

In each of the above embodiments, the condition is determined by extracting the state once in the updating unit. However, the same state continues twice or several times depending on the noise and the state of the apparatus. In some cases, it may be better to change according to the condition status, such as changing the update status.

Further, the processing section and the switching timing of the calculation unit described in each of the above embodiments are merely examples, and the same effect can be obtained even if the value is changed or changed depending on the noise transmission path.

Further, the type, number, connection method, and the like of the respective circuit units constituting the noise reduction device, for example, filters, etc., are not limited to the above-described embodiments.

[0100]

According to the noise reduction apparatus of the present invention, adaptive control means for updating or adaptively estimating the filter coefficient for noise estimation and updating the filter coefficient of the muffling signal generating means for generating a muffling signal. And updating means for determining whether to update the coefficient of the muffling signal generating means, and switching means for stopping updating of the filter coefficient by the adaptive control means in accordance with the determination of the updating determining means. By reducing the room for an error and updating the coefficient again in response to a change in the external situation, a stable noise reduction effect can be realized for a long time.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a noise reduction device according to a first embodiment to which the present invention has been applied.

FIG. 2 is a timing chart showing a processing flow of a switching unit and a calculation unit of the noise reduction device.

FIG. 3 is a block diagram illustrating a configuration of a noise reduction device according to a second embodiment to which the present invention has been applied.

FIG. 4 is a timing chart showing a processing flow of a switching unit and a calculation unit of the noise reduction device.

FIG. 5 is a block diagram illustrating a configuration of a conventional noise reduction device.

FIG. 6 is a diagram for explaining an operation of a calculation unit of the conventional noise reduction device.

FIG. 7 is a characteristic diagram of a frequency cutoff filter.

[Explanation of symbols]

1, 2, 3 arithmetic unit, 4 main arithmetic unit, 5 sub arithmetic unit (external arithmetic unit), 10 ducts, 11 microphones (noise detection means), 12 microphones (silence detection means), 13 mute speaker (sound emission) Means), 14, 17
Microphone amplifier, 15, 18, 22 frequency cutoff filter, 16, 19 A / D converter, 23 speaker amplifier, 31 silence signal generation filter (silence signal generation means), 32 adaptive control algorithm 32 (adaptive control means), 33 transfer characteristics Gs filter, 35 subtractor,
40, 50 arithmetic processing unit, 41, 61 update determination unit (update determination unit), 42, 43 switching unit (switching unit)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F16L 55/04 F16L 55/04 (72) Inventor Takashi Ichikawa 1-7-12 Toranomon, Minato-ku, Tokyo Offshore F-term (reference) in Denki Kogyo Co., Ltd. 3G004 CA12 DA25 EA01 3H025 CA01 CB41 5D061 FF02

Claims (7)

[Claims] 1. A noise reduction device for simultaneously radiating sound waves having the same sound pressure and opposite phase to be canceled out from noise sound waves to noises to thereby mute the sound waves by interference between the sound waves. Muffling detection means for detecting a muffling state, sound emission means for emitting muffling sound waves to noise sound waves, muffling signal generation means for generating muffling signals to be supplied to the sound emission means, output of the noise detection means Adaptive control means for updating or adaptively estimating a filter coefficient for noise estimation from the output of the muffling detection means and updating the filter coefficient of the muffling signal generation means; and updating the coefficient of the muffling signal generation means. Update determination means for determining whether or not to perform, and switching means for stopping the update of the filter coefficient by the adaptive control means according to the determination of the update determination means. Noise reduction device to. 2. The noise reduction apparatus according to claim 1, wherein the update determination unit stores the output from the silence detection unit in a predetermined array and determines the update of the coefficient. 3. The update determining means stores the output from the muffling detecting means in a predetermined array, and compares the average value of the absolute values of each element of the array with a predetermined value to update the coefficient. The noise reduction device according to claim 1, wherein the determination is performed. 4. The update judging means stores the output from the silence detecting means in a predetermined half-wavelength array of the wavelength to be silenced, and sets the maximum absolute value of each element of the array to a predetermined value. 2. The noise reduction device according to claim 1, wherein a coefficient update determination is made by comparing. 5. The noise reduction apparatus according to claim 1, wherein the update determination unit determines a coefficient update based on an output of the muffling detection unit at regular time intervals. 6. The apparatus according to claim 1, wherein the update determining unit observes an output level of the silence detecting unit and determines to stop the coefficient update when the silencing is stable. A noise reduction device according to any one of the claims. 7. The noise reduction apparatus according to claim 1, wherein the update determination unit is provided outside the noise reduction processing operation unit by the adaptive control unit.