JP2020086206A - Active noise reduction device, mobile device, and noise reduction method - Google Patents

Abstract

To provide an active noise reduction device capable of suppressing a degradation in a noise reduction effect when the temperature changes.SOLUTION: An active noise reduction device 10 includes a correction amount calculation unit 18 for calculating a first correction amount for reducing the influence of the temperature characteristic of a speaker SP0 used to correct the phase of the simulated transfer characteristic which simulates a transfer characteristic from a position of the speaker SP0 to a position of a microphone M based on temperature information, a correction unit 14 for generating a corrected reference signal by applying the simulated transfer characteristic corrected by the calculated first correction amount to a reference signal, and a filter coefficient updating unit 15 which sequentially updates a coefficient of the adaptive filter using an error signal and the generated corrected reference signal.SELECTED DRAWING: Figure 4

Description

The present disclosure relates to an active noise reduction device that actively reduces noise by interfering a cancellation sound with the noise, a mobile device using the same, and a noise reduction method.

Conventionally, noise is activated by outputting a cancel sound for canceling the noise from a speaker using a reference signal having a correlation with the noise and an error signal based on a residual sound in which the noise and the cancel sound in a predetermined space interfere with each other. There is a known active noise reduction device that reduces noise (for example, see Patent Document 1). The active noise reduction device uses an adaptive filter to generate a cancellation signal for outputting a cancellation sound so that the sum of squares of the error signal is minimized.

Japanese Patent Laid-Open No. 07-162986

The active noise reduction device generates a cancel signal for outputting a cancel sound by using a simulated transfer characteristic that simulates the transfer characteristic from the position of the speaker to the position of the microphone. The transfer characteristics change with temperature. Therefore, a sufficient noise reduction effect may not be obtained due to a change in temperature, or control may become unstable and a phenomenon such as sound increase may occur.

The present disclosure provides an active noise reduction device that can suppress a reduction in noise reduction effect when the temperature changes.

An active noise reduction device according to an aspect of the present disclosure is an active noise reduction device that reduces noise in a predetermined space, and a reference signal input unit to which a reference signal having a correlation with the noise is input, And a reference signal generator that generates a reference signal having a frequency specified based on the reference signal, and an output of a cancel sound for reducing the noise by applying an adaptive filter to the generated reference signal. An adaptive filter unit for generating a cancel signal used for the above, a cancel signal output unit for outputting the generated cancel signal to a speaker, the cancel sound, and an error signal corresponding to a residual sound due to interference of the noise. Is input from a microphone, an error signal input unit, a temperature information acquisition unit that acquires temperature information indicating the temperature of the predetermined space, and a position of the microphone from a position of the speaker based on the acquired temperature information. Correction amount calculation unit for calculating a first correction amount for reducing the influence of the temperature characteristic of the speaker, which is used for correcting the phase of the simulated transfer characteristic simulating the transfer characteristics up to and including the calculated first correction A coefficient of the adaptive filter using a correction unit that generates a corrected reference signal by applying the simulated transfer characteristic corrected by an amount to the reference signal, the error signal, and the generated corrected reference signal. And a filter coefficient updating unit that sequentially updates

The active noise reduction device according to one aspect of the present disclosure can suppress a decrease in noise reduction effect when the temperature changes.

FIG. 1 is a diagram showing an outline of a noise reduction device according to an embodiment. FIG. 2 is a schematic diagram showing a time waveform of noise heard at the position of the microphone. FIG. 3 is a schematic diagram of a vehicle including the noise reduction device according to the embodiment. FIG. 4 is a functional block diagram of the noise reduction device according to the embodiment. FIG. 5 is a flowchart of the basic operation of the noise reduction device according to the embodiment. FIG. 6 is a diagram showing the phase of the transfer characteristic of the speaker. FIG. 7 is a diagram showing the phase difference of the transfer characteristics of the speaker. FIG. 8 is a diagram showing an example of table information indicating the slope a and the intercept b at each temperature. FIG. 9 is a diagram showing a phase difference of transfer characteristics (with an inflection point) of the speaker. FIG. 10 is a flowchart of the first correction amount calculation operation including the table information (or correction formula) switching processing.

Hereinafter, embodiments will be specifically described with reference to the drawings. It should be noted that each of the embodiments described below shows a comprehensive or specific example. Numerical values, shapes, materials, components, arrangement positions and connection forms of components, steps, order of steps, and the like shown in the following embodiments are examples, and are not intended to limit the present disclosure. Further, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims showing the highest concept are described as arbitrary constituent elements.

In addition, each drawing is a schematic view and is not necessarily strictly illustrated. In each drawing, the same reference numerals are given to substantially the same configurations, and overlapping description may be omitted or simplified.

In the following embodiments, the absolute value of the phase of the simulated transfer characteristic (or transfer characteristic) is expressed as “phase”, and the phase of the transfer characteristic in the reference temperature environment and the transfer in the temperature environment in which the temperature changes from the reference temperature The difference between the characteristic and the phase is expressed as “phase difference”.

(Embodiment)
[Overview]
First, the outline of the active noise reduction device according to the embodiment will be described. First, FIG. 1 is a diagram showing an outline of an active noise reduction device according to an embodiment.

The active noise reduction device 10 shown in FIG. 1 is, for example, a device that is installed in a vehicle interior and reduces noise generated while the vehicle is running. The noise caused by the engine 51 is a sound that is instantaneously close to a sine wave having a single frequency. Therefore, the active noise reduction device 10 acquires a pulse signal indicating the frequency of the engine 51 from the engine control unit 52 that controls the engine 51, and outputs a cancel sound for canceling the noise from the speaker SP0. An adaptive filter is used to generate the cancel sound, and the cancel sound is generated so that the residual sound acquired by the microphone M arranged near the listener 30 becomes small.

As shown in FIG. 1, the transfer characteristic from the position of the speaker SP0 (hereinafter also referred to as a sound output position) to the position of the microphone M (hereinafter also referred to as a sound collection position) is c ₁ , and a cancel sound is generated. The output signal for outputting is represented by the symbol out. In this case, the cancel sound reaching the position of the microphone M (sound collection position) is expressed as c ₁ *out. Note that "*" means the convolution operator, c ₁ represents an impulse response of the transfer characteristics, C ₁ represents a simulated transfer characteristics in the frequency domain.

The noise N _{m at} the position of the microphone M is expressed by the following (Formula 1), where R is the amplitude, ω is the angular frequency, and θ is the phase, and c ₁ *out is the following (Formula 2-1), It is represented by (Equation 2-2). The active noise reduction device 10 calculates the first filter coefficient A and the second filter coefficient B in (Equation 2-1) and (Equation 2-2) by, for example, the LMS (Least Mean Square) method. , It is possible to output a cancel sound for canceling noise.

In this way, by outputting the cancel sound having the opposite phase to the noise N _m , the noise heard at the position of the microphone M becomes smaller as shown in FIG. FIG. 2 is a schematic diagram showing a time waveform of noise heard at the position of the microphone M.

[Overall Configuration of Vehicle Equipped with Active Noise Reduction Device]
Hereinafter, details of such an active noise reduction device 10 will be described. In the embodiment, active noise reduction device 10 is mounted in a vehicle as an example. FIG. 3 is a schematic diagram of a vehicle including the active noise reduction device 10.

The vehicle 50 is an example of a mobile device, and includes an active noise reduction device 10, an engine 51, an engine control unit 52, a speaker SP0, a microphone M, a temperature sensor 54, and a vehicle body 55. The vehicle 50 is specifically an automobile, but is not particularly limited.

The engine 51 is a drive device that is a power source of the vehicle 50 and a noise source of the predetermined space 56. The engine 51 is arranged, for example, in a space different from the predetermined space 56. The engine 51 is specifically installed in a space formed in the hood of the vehicle body 55.

The engine control unit 52 controls (drives) the engine 51 based on an accelerator operation of a driver of the vehicle 50 and the like. The engine control unit 52 also outputs a pulse signal (engine pulse signal) corresponding to the rotation speed (frequency) of the engine 51 as a reference signal. The frequency of the pulse signal is, for example, proportional to the rotation speed (frequency) of the engine 51. Specifically, the pulse signal is an output signal of a TDC (Top Dead Center) sensor, a so-called tacho pulse, or the like. The reference signal may have any form as long as it has a correlation with noise.

The speaker SP0 outputs a cancel sound to the predetermined space 56 using the cancel signal. The speaker SP0 is located near the door on the passenger seat side in the space 56, but the installation position of the speaker SP0 is not particularly limited. The vehicle 50 may include a plurality of speakers SP0.

The microphone M detects a residual sound in which the noise and the cancel sound in the predetermined space 56 interfere with each other, and outputs an error signal based on the residual sound. The microphone M is installed, for example, on a headliner or the like in the predetermined space 56, but the installation position of the microphone M is not particularly limited.

The temperature sensor 54 measures the temperature of the predetermined space 56 and outputs temperature information indicating the measured temperature. The temperature sensor 54 is realized by a temperature measuring element such as a thermocouple or a thermistor.

The vehicle body 55 is a structure body including a chassis and a body of the vehicle 50. The vehicle body 55 forms a predetermined space 56 (vehicle interior space) in which the speaker SP0, the microphone M, and the temperature sensor 54 are arranged.

[Structure and basic operation of active noise reduction device]
Next, the configuration and basic operation of the active noise reduction device 10 will be described. FIG. 4 is a functional block diagram of the active noise reduction device 10. FIG. 5 is a flowchart of the basic operation of the active noise reduction device 10.

The active noise reduction device 10 is an active type active noise reduction device that reduces noise at the second position where the microphone M is installed by the cancel sound output from the first position where the speaker SP0 is installed. Note that the active noise reduction device 10 can output the cancel sound from the speaker SP1 and the speaker SP2, but in the following embodiments, the case where the cancel sound is output from the speaker SP0 will be specifically described.

As shown in FIG. 4, the active noise reduction device 10 includes a reference signal input terminal 11a, a reference signal generation unit 12, an adaptive filter unit 13, a cancellation signal output terminal 11c, a correction unit 14, and an error signal input. A terminal 11b, a filter coefficient updating unit 15, a storage unit 16, a temperature information input terminal 11d, and a temperature information acquisition unit 17 are provided. Each of the reference signal generation unit 12, the adaptive filter unit 13, the correction unit 14, the filter coefficient update unit 15, and the temperature information acquisition unit 17, which is realized by, for example, a microcomputer, is a DSP (Digital Signal Processor) or the like. It may be realized by a processor or a dedicated circuit. Hereinafter, related components will be described in detail for each step shown in the flowchart of FIG.

[Generation of reference signal]
First, the reference signal generation unit 12 generates a reference signal based on the reference signal input to the reference signal input terminal 11a (S11 in FIG. 5).

A reference signal having a correlation with noise is input to the reference signal input terminal 11a. The reference signal is, for example, a pulse signal output by the engine control unit 52.

More specifically, the reference signal generation unit 12 specifies the instantaneous frequency of noise based on the reference signal input to the reference signal input terminal 11a, and generates the reference signal having the specified frequency. Specifically, the reference signal generation unit 12 includes a frequency detection unit 12a, a sine wave generation unit 12b, and a cosine wave generation unit 12c.

The frequency detection unit 12a detects the frequency of the pulse signal and outputs the detected frequency to the sine wave generation unit 12b, the cosine wave generation unit 12c, and the correction amount calculation unit 18 included in the correction unit 14. In other words, the frequency detection unit 12a specifies the instantaneous frequency of noise.

The sine wave generation unit 12b outputs the sine wave having the frequency detected by the frequency detection unit 12a as the first reference signal. The first reference signal is an example of the reference signal, and is a signal represented by sin(2πft)=sin(ωt) when the frequency detected by the frequency detection unit 12a is f. That is, the first reference signal has the frequency (the same frequency as noise) specified by the frequency detection unit 12a. The first reference signal is output to the first filter 13a included in the adaptive filter unit 13 and the first correction signal generation unit 14b included in the correction unit 14.

The cosine wave generation unit 12c outputs the cosine wave of the frequency detected by the frequency detection unit 12a as the second reference signal. The second reference signal is an example of the reference signal, and is a signal represented by cos(2πft)=cos(ωt) when the frequency detected by the frequency detection unit 12a is f. That is, the second reference signal has the frequency (the same frequency as the noise) specified by the frequency detection unit 12a. The second reference signal is output to the second filter 13b included in the adaptive filter unit 13 and the second correction signal generation unit 14c included in the correction unit 14.

[Generation of cancellation signal]
The adaptive filter unit 13 generates a cancel signal by applying (multiplying) the filter coefficient to the reference signal generated by the reference signal generating unit 12 (S12 in FIG. 5). In other words, the adaptive filter unit 13 applies the filter coefficient to the reference signal that is the reference signal input to the reference signal input terminal 11a and that has been converted into the reference signal. The cancel signal is used to output a cancel sound for reducing noise, and is output to the cancel signal output terminal 11c. The adaptive filter unit 13 includes a first filter 13a, a second filter 13b, and an addition unit 13c. The adaptive filter unit 13 is a so-called adaptive notch filter.

The first filter 13a multiplies the first reference signal output from the sine wave generation unit 12b by the first filter coefficient. The first filter coefficient to be multiplied is a filter coefficient corresponding to A in the above (Equation 2), and is sequentially updated by the first updating unit 15a included in the filter coefficient updating unit 15. The first cancel signal, which is the first reference signal multiplied by the first filter coefficient, is output to the adder 13c.

The second filter 13b multiplies the second reference signal output from the cosine wave generation unit 12c by the second filter coefficient. The second filter coefficient to be multiplied is a filter coefficient corresponding to B in (Equation 2) above, and is sequentially updated by the second updating unit 15b included in the filter coefficient updating unit 15. The second cancellation signal, which is the second reference signal multiplied by the second filter coefficient, is output to the adder 13c.

The adder 13c adds the first cancel signal output from the first filter 13a and the second cancel signal output from the second filter 13b. The adder 13c outputs a cancel signal obtained by adding the first cancel signal and the second cancel signal to the cancel signal output terminal 11c.

The cancel signal output terminal 11c is a terminal formed of metal or the like. The cancel signal generated by the adaptive filter unit 13 is output to the cancel signal output terminal 11c. The speaker SP0 is connected to the cancel signal output terminal 11c. Therefore, the cancel signal is output to the speaker SP0 via the cancel signal output terminal 11c. The speaker SP0 outputs a cancel sound based on the cancel signal.

[Correction of simulated transfer characteristics]
The temperature information input terminal 11d receives the temperature information output from the temperature sensor 54 and indicating the temperature around the speaker SP0. The temperature information acquisition unit 17 acquires the temperature information output by the temperature sensor 54 via the temperature information input terminal 11d.

The correction amount calculation unit 18 calculates the correction amount used to correct the phase of the simulated transfer characteristic that simulates the transfer characteristic from the position of the speaker SP0 to the position of the microphone microphone 53 based on the acquired temperature information ( S13 of FIG. 5). In other words, the transfer characteristic is a transfer function. The simulated transfer characteristic to be corrected is a simulated transfer characteristic simulating the transfer characteristic in a reference temperature environment (for example, 20° C. environment) (hereinafter, also simply referred to as simulated transfer characteristic in 20° C. environment). Details of the method of calculating the correction amount will be described later.

[Correction of reference signal]
The correction unit 14 generates a corrected reference signal in which the simulated transfer characteristic corrected by the correction amount calculated by the correction amount calculation unit 18 is applied to the reference signal. That is, the correction unit 14 generates a corrected reference signal obtained by correcting the reference signal (S14 in FIG. 5). The correction unit 14 includes a control unit 14a, a first correction signal generation unit 14b, and a second correction signal generation unit 14c.

The simulated transfer characteristic C ₁ is a transfer characteristic that simulates a path from the position of the speaker SP0 to the position of the microphone M. The simulated transfer characteristic is specifically a gain and a phase (phase delay) for each frequency. The simulated transfer characteristic is measured in advance in the space 56 for each frequency and stored in the storage unit 16, for example. That is, the storage unit 16 stores the frequency and the gain and phase for correcting the signal of the frequency.

The control unit 14a acquires the frequency output by the frequency detection unit 12a and reads the gain and phase corresponding to the acquired frequency from the storage unit 16. Further, the control unit 14a corrects the read phase according to the correction amount calculated by the correction amount calculation unit 18. Then, the control unit 14a outputs the read gain and the corrected phase.

The first correction signal generation unit 14b generates a first corrected reference signal obtained by correcting the first reference signal based on the gain and phase output by the control unit 14a. The first corrected reference signal is an example of the corrected reference signal. When the gain output by the control unit 14a is α and the corrected phase is φα, the first corrected reference signal is expressed as α·sin(ωt+φα). The generated first corrected reference signal is output to the first updating unit 15a included in the filter coefficient updating unit 15.

The second correction signal generation unit 14c generates a second post-correction reference signal obtained by correcting the second reference signal based on the gain and the phase output by the control unit 14a. The second corrected reference signal is an example of the corrected reference signal. When the gain output by the control unit 14a is β and the corrected phase is φβ, the second corrected reference signal is expressed as β·cos(ωt+φβ). The generated second corrected reference signal is output to the second updating unit 15b included in the filter coefficient updating unit 15.

The storage unit 16 is a storage device that stores simulated transfer characteristics at the reference temperature. The storage unit 16 also stores a predetermined table or a predetermined correction formula for calculating the correction amount, a coefficient of the adaptive filter, and the like. The storage unit 16 is specifically realized by a semiconductor memory or the like. When the active noise reduction device 10 is realized by a processor such as a DSP, the storage unit 16 also stores a control program executed by the processor. The storage unit 16 may store other parameters used for signal processing performed by the active noise reduction device 10.

[Update Filter Coefficient]
The filter coefficient updating unit 15 sequentially updates the filter coefficient based on the error signal input to the error signal input terminal 11b and the generated corrected reference signal (S15 in FIG. 5).

The error signal input terminal 11b is a terminal formed of metal or the like. An error signal based on the residual sound generated at the second position of the microphone M due to the interference of the canceling sound and the noise is input to the error signal input terminal 11b. The error signal is output by the microphone M.

The filter coefficient updating unit 15 specifically includes a first updating unit 15a and a second updating unit 15b.

The first updating unit 15a calculates the first filter coefficient based on the first corrected reference signal acquired from the first correction signal generating unit 14b and the error signal acquired from the microphone M. Specifically, the first update unit 15a uses the LMS method to calculate the first filter coefficient so that the error signal is minimized, and outputs the calculated first filter coefficient to the first filter 13a. .. Further, the first updating unit 15a sequentially updates the first filter coefficient. When the first corrected reference signal is represented by r ₁ and the error signal is represented by e, the first filter coefficient A (corresponding to A in (Equation 2) above) is represented by the following (Equation 3). In addition, n is a natural number and is a variable (in other words, a variable indicating the number of updates) corresponding to how many updates are performed. That is, A(n) indicates the state at the nth update. μ is a scalar amount, which is a step size parameter that determines the update amount of the filter coefficient per sampling.

The second updating unit 15b calculates the second filter coefficient based on the second corrected reference signal acquired from the second correction signal generating unit 14c and the error signal acquired from the microphone M. Specifically, the second update unit 15b uses the LMS method to calculate the second filter coefficient so that the error signal is minimized, and outputs the calculated second filter coefficient to the second filter 13b. .. Further, the second updating unit 15b sequentially updates the second filter coefficient. When the second corrected reference signal is represented by r ₂ and the error signal is represented by e, the second filter coefficient B (corresponding to B in (Equation 2) above) is represented by the following (Equation 4).

[Calculation method of the first correction amount]
The phase of the transfer characteristic from the position of the speaker SP0 to the position of the microphone M changes depending on the temperature. If only the simulated transfer characteristic in the 20° C. environment is stored in the storage unit 16, and if the simulated transfer characteristic in the 20° C. environment is always used regardless of the actual environmental temperature, a sufficient noise reduction effect cannot be obtained. There are cases.

Therefore, the active noise reduction device 10 corrects the phase of the simulated transfer characteristic in the environment of 20° C. according to the measured value of the temperature. The simulated transfer characteristic may be a simulated transfer characteristic in a temperature environment other than 20°C.

The transfer characteristic from the position of the speaker SP0 to the position of the microphone M is a combination of the transfer characteristic of the speaker SP0 itself and the transfer characteristic of the propagation path (in other words, the speed of sound). Therefore, two main factors that cause the phase of the transfer characteristic to change with temperature are the temperature characteristic of the speaker and the temperature characteristic of the propagation path. First, a method of calculating the first correction amount corresponding to the variation in the phase of the transfer characteristic due to the temperature characteristic of the speaker will be described.

The phase of the transfer characteristic from the position of the speaker SP0 to the position of the microphone M fluctuates as the lowest resonance frequency f0 of the speaker SP0 changes according to the temperature. FIG. 6 is a diagram showing the phase of the transfer characteristic of the speaker SP0 when the temperature changes from −30° C. to +60° C. in steps of 5° C. FIG. 7 is a diagram showing a phase difference of the transfer characteristic in the environment of 20° C. of the phase of the transfer characteristic of the speaker SP0 when the temperature changes from −30° C. to +60° C. in steps of 5° C. The horizontal axis of FIGS. 6 and 7 represents frequency. FIG. 6 shows the transfer characteristics of a certain speaker, and the transfer characteristics differ from speaker to speaker.

The phase difference indicates the difference between the phase of the transfer characteristic of the speaker SP0 in a 20° C. environment and the phase of the transfer characteristic of the speaker SP0 at each temperature from −30° C. to +60° C. That is, the phase difference Δphase1 (hereinafter, abbreviated as Δp1) is the phase phase (20° C.) of the transfer characteristic of the speaker SP0 in the environment of 20° C. and each temperature (T° C.) from −30° C. to +60° C. ), the phase of the transfer characteristic of the speaker SP0 is represented as phase (T°C), and the expression is Δp1=phase (20°C)-phase (T°C).

The phase difference Δp1 at each temperature shown in FIG. 7 can be approximated to a linear expression having the frequency f as a variable. That is, if the slope of this linear expression is a and the intercept is b, then Δp1=a·f+b. FIG. 8 shows the slope a and the intercept b in the form of table information. FIG. 8 is a diagram showing an example of table information indicating the slope a and the intercept b at each temperature.

The phase difference Δp1 corresponds to the first correction amount for correcting the phase of the simulated transfer characteristic in the environment of 20°C. Therefore, if the table information of FIG. 8 is stored in the storage unit 16, the correction amount calculation unit 18 calculates the first correction amount (that is, the phase difference Δp1) by referring to the stored table information. be able to. Specifically, the correction amount calculation unit 18 refers to the table information and obtains the slope a and the intercept b associated with the temperature closest to the current temperature indicated by the temperature information acquired by the temperature information acquisition unit 17. By specifying, the first correction amount can be calculated.

In addition, it is not essential that the table information is stored in the storage unit 16. Each of the slope a and the intercept b of the table information shown in FIG. 8 can be approximated to a linear expression with the environmental temperature T as a variable. For example, the slope a and the intercept b are approximated by the following linear expression.

a(T)=0.0097T-0.1926
b(T)=-1.3427T+29.57

Then, instead of the table information of FIG. 8, if the correction formula Δp1=a(T)·f+b(T) is stored in the storage unit 16, the correction amount calculation unit 18 uses the stored correction formula. , The first correction amount (that is, the phase difference Δp1) can be calculated. Specifically, the correction amount calculation unit 18 can calculate the first correction amount by substituting the current temperature indicated by the temperature information acquired by the temperature information acquisition unit 17 into the correction formula.

[Calculation method of second correction amount]
Next, a method of calculating the second correction amount corresponding to the variation in the phase of the transfer characteristic due to the temperature characteristic of the propagation path (in other words, the speed of sound) will be described.

When the distance from the position of the speaker SP0 to the position of the microphone M (that is, the length of the propagation path) is L, the arrival time t of the sound at the environmental temperature T and the environmental temperature T0 (for example, 20° C.) The difference Δt(T) in the arrival time t0 of is expressed by the following equation.

Therefore, the phase difference (that is, the second correction amount) Δphase2 (hereinafter, abbreviated as Δp2) due to the temperature characteristic of the propagation path is Δp2=Δt(T)·f·360. The correction amount calculation unit 18 can calculate the second correction amount using such an equation.

From the above, if the first correction amount is Δp1 and the second correction amount is Δp2, the total correction amount is Δp1+Δp2. When the phase of the simulated transfer characteristic is pb, the phase pc of the corrected simulated transfer characteristic is pc=pb−Δp1−Δp2. That is, the correction unit 14 can correct the simulated transfer characteristic by the first correction amount calculated by the correction amount calculation unit 18 and the second correction amount calculated by the correction amount calculation unit 18. The correction amount calculation unit 18 may calculate at least one of the first correction amount and the second correction amount.

[Modified Example of Calculation Method of First Correction Amount]
Since the temperature characteristics of the speaker SP0 are different for each speaker SP0, the table information for calculating the first correction amount and the correction formula are determined for each speaker SP0. In other words, the table information for calculating the first correction amount and the correction formula are customized for each speaker SP0. Here, depending on the speaker SP0, the phase difference Δp1 may not be approximated by one linear expression. FIG. 9 is a diagram showing the phase difference of the transfer characteristics of the speaker SP0. In FIG. 9, the solid line indicates the phase difference of the transfer characteristics, and the broken line indicates the approximate expression.

The phase difference of the transfer characteristics shown in FIG. 9 has an inflection point near 220 Hz. When the frequency of the reference signal is 220 Hz or higher, the transfer characteristic can be approximated by a linear expression having a positive slope with the frequency of the reference signal as a variable. On the other hand, when the frequency of the reference signal is less than 220 Hz, the phase difference of the transfer characteristic can be approximated by a linear expression having a negative slope with the frequency of the reference signal as a variable.

When two types of linear expressions are required to approximate the phase difference of the transfer characteristics in this way, the storage unit 16 stores the first table information and the first table information corresponding to the two types of linear expressions. Two kinds of table information of different second table information may be stored, and the two kinds of table information may be switched according to the frequency of the reference signal. Similarly, the storage unit 16 stores two types of correction formulas corresponding to the two types of primary formulas, that is, a first correction formula and a second correction formula different from the first correction formula. The equation may be switched depending on the frequency of the reference signal. FIG. 10 is a flowchart of the first correction amount calculation operation including the table information (or correction formula) switching processing.

The correction amount calculator 18 acquires the frequency of the reference signal from the frequency detector 12a (S21), and determines whether the frequency of the reference signal is equal to or higher than a predetermined value (S22). In the example of FIG. 9, the predetermined value is 220 Hz, but this value is not particularly limited because it changes depending on what kind of speaker is used as the speaker SP0.

When the correction amount calculation unit 18 determines that the frequency of the reference signal is equal to or higher than the predetermined value (Yes in S22), the first correction amount is calculated using the first table information (or the first correction formula) (S23). ). On the other hand, when the correction amount calculation unit 18 determines that the frequency of the reference signal is less than the predetermined value (No in S22), the correction amount calculation unit 18 calculates the first correction amount using the second table information (or the second correction formula). (S24).

In this way, the correction amount calculation unit 18 can appropriately correct the simulated transfer characteristic having the inflection point by performing the switching process of the table information (or the correction formula).

[Effect of reducing required storage capacity]
As described above, if one simulated transfer characteristic is corrected according to the temperature, a plurality of simulated transfer characteristics are prepared for each temperature and the simulated transfer characteristic is switched (hereinafter, also referred to as a comparative example method). The effect of being able to reduce the storage capacity required for storing information than that described) is obtained. Hereinafter, such effects will be described. In the following, four speakers SP0 and four microphones M are used, the transfer characteristic phase data size is 2 bytes/Hz, and the frequency range is 30 Hz to 300 Hz (that is, the number of data is 271). Under the condition that the number of temperature switching is 18 (5° C. interval between −30° C. and 60° C.), the necessary storage capacity is compared.

In the method of the comparative example, the number of tables of the phase of the simulated transfer characteristic is 16 when the number of speakers SP0×the number 4 of microphones M is 4. Then, in the method of the comparative example, a storage capacity of 2 (byte)×16 (the number of tables)×271 (the number of data)×18 (the number of temperature switching)=156 Kbytes is required.

On the other hand, in order to realize the correction method using the table information, two pieces of information of the slope a and the intercept b (each 2 bytes) are 4 (the number of speakers SP0)×18 (the number of temperature switching)× Only two types (note: the two types of meanings necessary when there is an inflection point) are stored in the storage unit 16. That is, in the correction method using the table information, 2 (bytes)×2 (slope a and intercept b)×4 (number of speakers SP0)×18 (temperature switching number)×2 (type)=576 bytes of storage Needs capacity.

As described above, the method of correcting using the table information can significantly reduce the required storage capacity as compared with the method of the comparative example.

Further, in order to realize the correction method using the correction formula, four pieces of information of the inclination and intercept of a(T) and the inclination and intercept of b(T) (each 2 bytes) are 4 (speaker). Only the number of SP0)×2 types (note: the two types of meanings required when there is an inflection point) may be stored in the storage unit 16. That is, in the correction method using the correction formula, 2 (byte)×4 (slope and intercept of a(T), and slope and intercept of b(T))×4 (number of speakers SP0)×2 A storage capacity of (type)=64 bytes is required.

As described above, the correction method using the correction formula can significantly reduce the required storage capacity as compared with the comparative example method, and further reduces the required storage capacity as compared with the correction method using the table information. can do.

[Effect of reducing the number of parameter designs]
Further, the method of correcting using the table information and the method of correcting using the correction formula can reduce the number of parameter designs as compared with the method of the comparative example.

The method of the comparative example requires the design of 16 (number of tables)×271 (number of data)×18 (number of temperature switching)=78048 parameters.

On the other hand, in order to realize the correction method using the table information, it is only necessary to design four frequency ranges and prepare two sets of the inclination a and the intercept b (the number of temperature switching). That is, the method of correction using the table information requires the design of 4 (frequency range)+2 (slope a and intercept b)×18 (temperature switching number)=40 parameters.

As described above, the method of correcting using the table information can significantly reduce the number of required parameter designs as compared with the method of the comparative example.

Further, in order to realize a method of correcting using a correction formula, four frequency ranges are designed, and four slopes and intercepts of a(T) and slopes and intercepts of b(T) are set. Just prepare. That is, the method of correcting using the correction formula requires designing 4 (frequency range)+4 (a(T) slope and intercept, and b(T) slope and intercept)=8 parameters.

As described above, the method of correcting using the correction formula can significantly reduce the number of required parameters to be designed as compared with the method of the comparative example, and the method of correcting the required parameters more than the method of correcting using the table information. The number of designs can be reduced.

[Effect of reducing the amount of information processing]
Further, the correction method using the table information and the correction method using the correction formula can reduce the amount of information processing as compared with the method of the comparative example.

In the method of the comparative example, the correction amount calculation unit 18 acquires 16 (the number of tables)×271 in order to acquire the simulated transfer characteristic corresponding to the temperature indicated by the temperature information acquired by the temperature information acquisition unit 17 from the storage unit 16. (Number of data)=4336 times of load processing needs to be performed.

On the other hand, in the method of correcting using the table information, the correction amount calculation unit 18 can read the inclination a and the intercept b corresponding to the temperature indicated by the temperature information acquired by the temperature information acquisition unit 17 from the storage unit 16. Good. That is, the required load process is twice. After that, it is necessary to repeat three scalar operations 16 times as an operation for correcting the simulated transfer characteristic. That is, a total of 48 scalar operations are required.

As described above, the method of using the table information for correction can significantly reduce the number of load processes as compared with the method of the comparative example.

Further, in the method of correcting using the correction formula, the correction amount calculation unit 18 corresponds to the temperature indicated by the temperature information acquired by the temperature information acquisition unit 17, the slope and intercept of a(T), and b( The inclination and intercept of T) may be read from the storage unit 16. That is, the required load processing is four times. After that, two scalar operations are required to calculate a(T), two scalar operations are required to calculate b(T), and three scalar operations are performed to correct the simulated transfer characteristic. It is necessary to repeat the calculation 16 times. That is, a total of 52 scalar operations are required.

As described above, the method of correcting using the correction formula can significantly reduce the number of load processes as compared with the method of the comparative example.

[Summary]
As described above, the active noise reduction device 10 is an active noise reduction device that reduces noise in the predetermined space 56. The active noise reduction device 10 includes a reference signal input terminal 11a to which a reference signal having a correlation with noise is input, and a reference signal generation unit 12 that generates a reference signal having a frequency specified based on the input reference signal. , An adaptive filter unit 13 for generating a cancel signal used to output a cancel sound for reducing noise by applying an adaptive filter to the generated reference signal, and for outputting the generated cancel signal to a speaker. Of the cancel signal output terminal 11c, the cancel signal and the error signal input terminal 11b to which the error signal corresponding to the residual sound due to the interference with the noise is input from the microphone M, and the temperature information indicating the temperature of the predetermined space 56 is acquired. Of the temperature characteristics of the speaker SP0 used to correct the phase of the simulated transfer characteristic that simulates the transfer characteristic from the position of the speaker SP0 to the position of the microphone M based on the acquired temperature information. A correction amount calculation unit 18 for calculating a first correction amount for reducing the influence, and a correction unit 14 for generating a corrected reference signal in which the simulated transfer characteristic corrected by the calculated first correction amount is applied to the reference signal. And a filter coefficient updating unit 15 that sequentially updates the coefficients of the adaptive filter using the error signal and the generated corrected reference signal. The reference signal input terminal 11a is an example of a reference signal input section, the cancel signal output terminal 11c is an example of a cancel signal output section, and the error signal input terminal 11b is an example of an error signal input section.

Such an active noise reduction device 10 can correct the suspicious transfer characteristic in consideration of the temperature characteristic of the speaker SP0. Therefore, the active noise reduction device 10 can suppress the reduction of the noise reduction effect when the temperature changes.

Further, for example, the correction amount calculation unit 18 calculates the first correction amount based on the acquired temperature information and a predetermined correction formula. The predetermined correction formula is, for example, Δp1=a(T)·f+b(T).

Such an active noise reduction device 10 can correct the simulated transfer characteristic while reducing the amount of information required for correction stored in the storage unit 16.

Further, for example, the predetermined correction formula is a linear function having a frequency as a variable, and each of the slope a(T) and the intercept b(T) of the linear function is a linear function having a temperature as a variable.

Such an active noise reduction device 10 calculates the first correction amount if the storage unit 16 stores four pieces of information of the inclination and intercept of a(T) and the inclination and intercept of b(T). can do.

Further, for example, when the frequency of the reference signal is equal to or higher than the predetermined value, the correction amount calculation unit 18 calculates the first correction amount using the first correction formula as the predetermined correction formula, and the frequency of the reference signal is If it is less than the predetermined value, the first correction amount is calculated using a second correction formula different from the first correction formula as the predetermined correction formula.

Such an active noise reduction device 10 can appropriately correct the simulated transfer characteristic having the inflection point by performing the correction type switching process. If the transfer characteristic has two or more inflection points, three or more correction equation switching processes may be performed.

Further, for example, the correction amount calculation unit 18 calculates the first correction amount based on the acquired temperature information and the predetermined table information. The predetermined table information is, for example, table information as shown in FIG.

Such an active noise reduction device 10 can correct the transfer characteristic by reducing the amount of information required for correction stored in the storage unit 16.

Further, for example, when the frequency of the reference signal is equal to or higher than a predetermined value, the correction amount calculation unit 18 calculates the first correction amount by using the first table information as the predetermined table information, and calculates the frequency of the reference signal. Is less than the predetermined value, the first correction amount is calculated using the second table information different from the first table information as the predetermined table information.

The active noise reduction device 10 as described above can appropriately correct the simulated transfer characteristic having the inflection point by performing the table information switching process. When the transfer characteristic has two or more inflection points, switching processing of three or more pieces of table information may be performed.

Further, for example, the correction amount calculation unit 18 further uses the second correction amount for reducing the influence of the change in the sound velocity depending on the temperature, which is used for the correction of the phase of the transfer characteristic based on the acquired temperature information. To calculate. The correction unit 14 generates a corrected reference signal in which the transfer characteristic corrected by the calculated first correction amount and the calculated second correction amount is applied to the reference signal.

The active noise reduction device 10 as described above can correct the transfer characteristic in consideration of both the temperature characteristic of the speaker SP0 and the temperature change of the sound velocity. Therefore, the active noise reduction device 10 can suppress the reduction of the noise reduction effect when the temperature changes.

A noise reduction method executed by a computer such as the active noise reduction device 10 is a noise reduction method that reduces noise in the predetermined space 56. The noise reduction method generates a reference signal having a frequency specified on the basis of a reference signal having a correlation with the noise, and applies an adaptive filter to the generated reference signal, thereby canceling the noise. A cancel signal used for output is generated, the generated cancel signal is output to the speaker, and the transfer characteristic from the position of the speaker SP0 to the position of the microphone M is simulated based on the temperature information indicating the temperature of the predetermined space 56. A first correction amount for reducing the influence of the temperature characteristic of the speaker SP0 used for correcting the phase of the simulated transfer characteristic is calculated, and the simulated transfer characteristic corrected by the calculated first correction amount is used as a reference signal. The applied corrected reference signal is generated, and the error signal output from the microphone M, which is the error signal corresponding to the residual sound due to the interference of the cancel sound and the noise, and the generated corrected reference signal are used for adaptation. The coefficient of the filter is updated sequentially.

In such a noise reduction method, the pseudo transmission characteristic can be corrected in consideration of the temperature characteristic of the speaker SP0. Therefore, the noise reduction method can suppress the reduction of the noise reduction effect when the temperature changes.

(Other embodiments)
Although the embodiments have been described above, the present disclosure is not limited to the above embodiments.

The active noise reduction device according to the above embodiment may be mounted on a mobile device other than a vehicle. The mobile device may be, for example, an aircraft or a ship. Further, the present disclosure may be realized as a mobile device other than such a vehicle.

Further, the configuration of the active noise reduction device according to the above embodiment is an example. For example, the active noise reduction device may include components such as a D/A converter, a filter, a power amplifier, or an A/D converter.

Further, the processing performed by the active noise reduction device according to the above embodiment is an example. For example, part of the digital signal processing described in the above embodiment may be realized by analog signal processing.

Further, for example, in the above-described embodiment, another processing unit may execute the process executed by the specific processing unit. Further, the order of the plurality of processes may be changed, or the plurality of processes may be executed in parallel.

Further, in the above-described embodiment, each component may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or a processor reading and executing a software program recorded in a recording medium such as a hard disk or a semiconductor memory.

Further, each component may be realized by hardware. For example, each component may be a circuit (or integrated circuit). These circuits may form one circuit as a whole or may be separate circuits. Further, each of these circuits may be a general-purpose circuit or a dedicated circuit.

In addition, the general or specific aspects of the present disclosure may be realized by a non-transitory recording medium such as a system, an apparatus, a method, an integrated circuit, a computer program, or a computer-readable CD-ROM. Further, the system, the device, the method, the integrated circuit, the computer program, and the computer-readable non-transitory recording medium may be implemented in any combination.

For example, the present disclosure may be realized as a noise reduction method executed by an active noise reduction device (computer or DSP), or may be realized as a program for causing the computer or DSP to execute the noise reduction method. Further, the present disclosure may be realized as a mobile device or a noise reduction system including the active noise reduction device according to the above-described embodiment, a speaker, and a microphone.

In addition, it is realized by making various modifications to those embodiments by those skilled in the art, or by arbitrarily combining the components and functions of the embodiments without departing from the spirit of the present disclosure. The present disclosure also includes the forms.

The noise reduction device of the present disclosure is useful, for example, as a device that can reduce noise in the vehicle interior.

10 Active Noise Reduction Device 11a Reference Signal Input Terminal 11b Error Signal Input Terminal 11c Cancel Signal Output Terminal 11d Temperature Information Input Terminal 12 Reference Signal Generator 12a Frequency Detector 12b Sine Wave Generator 12c Cosine Wave Generator 13 Adaptive Filter 13a No. 1 filter 13b 2nd filter 13c addition part 14 correction part 14a control part 14b 1st correction signal generation part 14c 2nd correction signal generation part 15 filter coefficient update part 15a 1st update part 15b 2nd update part 16 storage part 17 temperature information Acquisition unit 18 Correction amount calculation unit 30 Listener 50 Vehicle 51 Engine 52 Engine control unit 54 Temperature sensor 55 Vehicle body 56 Space M Microphone SP0 Speaker

Claims (15)

An active noise reduction device for reducing noise in a predetermined space,
A reference signal input unit to which a reference signal having a correlation with the noise is input,
A reference signal generation unit that generates a reference signal having a frequency specified based on the input reference signal;
By applying an adaptive filter to the generated reference signal, an adaptive filter unit that generates a cancellation signal used to output a cancellation sound for reducing the noise,
A cancel signal output unit for outputting the generated cancel signal to a speaker,
An error signal input unit in which an error signal corresponding to a residual sound caused by interference between the cancel sound and the noise is input from a microphone,
A temperature information acquisition unit that acquires temperature information indicating the temperature of the predetermined space,
Based on the acquired temperature information, used for correcting the phase of the simulated transfer characteristic that simulates the transfer characteristic from the position of the speaker to the position of the microphone, for reducing the influence of the temperature characteristic of the speaker. A correction amount calculation unit for calculating one correction amount;
A correction unit that generates a corrected reference signal by applying the simulated transfer characteristic corrected by the calculated first correction amount to the reference signal;
An active noise reduction device comprising: a filter coefficient updating unit that sequentially updates the coefficient of the adaptive filter using the error signal and the generated corrected reference signal. The active noise reduction device according to claim 1, wherein the correction amount calculation unit calculates the first correction amount based on the acquired temperature information and a predetermined correction formula. The predetermined correction formula is a linear function with frequency as a variable,
The active noise reduction device according to claim 2, wherein each of the slope and the intercept of the linear function is a linear function having temperature as a variable. The correction amount calculation unit,
When the frequency of the reference signal is equal to or higher than a predetermined value, the first correction amount is calculated using the first correction formula as the predetermined correction formula,
The first correction amount is calculated using a second correction formula different from the first correction formula as the predetermined correction formula when the frequency of the reference signal is less than a predetermined value. Active noise reduction device. The active noise reduction device according to claim 1, wherein the correction amount calculation unit calculates the first correction amount based on the acquired temperature information and predetermined table information. The correction amount calculation unit,
When the frequency of the reference signal is equal to or higher than a predetermined value, the first correction amount is calculated using the first table information as the predetermined table information,
The active amount according to claim 5, wherein when the frequency of the reference signal is less than a predetermined value, second table information different from the first table information is used as the predetermined table information. Noise reduction device. The correction amount calculation unit further uses, based on the acquired temperature information, a second correction amount for reducing the influence of a change in sound velocity depending on temperature, which is used for correcting the phase of the simulated transfer characteristic. Calculate,
The correction unit generates the corrected reference signal by applying the simulated transfer characteristic corrected by the calculated first correction amount and the calculated second correction amount to the reference signal. The active noise reduction device according to claim 1. An active noise reduction device according to any one of claims 1 to 7,
The speaker,
A mobile device comprising the microphone. A noise reduction method for reducing noise in a predetermined space,
Generating a reference signal having a frequency specified based on a reference signal having a correlation with the noise;
By applying an adaptive filter to the generated reference signal, to generate a cancellation signal used to output a cancellation sound to reduce the noise,
Output the generated cancellation signal to the speaker,
Based on temperature information indicating the temperature of the predetermined space, the influence of the temperature characteristic of the speaker, which is used for correcting the phase of the simulated transfer characteristic that simulates the transfer characteristic from the position of the speaker to the position of the microphone, is reduced. Calculate the first correction amount for
Generating a corrected reference signal by applying the simulated transfer characteristic corrected by the calculated first correction amount to the reference signal,
The coefficient of the adaptive filter is sequentially updated using an error signal output from the microphone and corresponding to a residual sound due to the interference of the cancel sound and the noise, and the generated corrected reference signal. How to reduce noise. The noise reduction method according to claim 9, wherein in the calculation of the first correction amount, the first correction amount is calculated based on the acquired temperature information and a predetermined correction formula. The predetermined correction formula is a linear function with frequency as a variable,
The noise reduction method according to claim 10, wherein each of the slope and the intercept of the linear function is a linear function having temperature as a variable. In the calculation of the first correction amount,
When the frequency of the reference signal is equal to or higher than a predetermined value, the first correction amount is calculated using a first correction formula as the predetermined correction formula,
When the frequency of the reference signal is less than a predetermined value, the first correction amount is calculated using a second correction formula different from the first correction formula as the predetermined correction formula. Described noise reduction method. The noise reduction method according to claim 9, wherein in the calculation of the first correction amount, the first correction amount is calculated based on the acquired temperature information and predetermined table information. In the calculation of the first correction amount,
When the frequency of the reference signal is equal to or higher than a predetermined value, the first correction amount is calculated using the first table information as the predetermined table information,
The first correction amount is calculated using second table information different from the first table information as the predetermined table information when the frequency of the reference signal is less than a predetermined value. Noise reduction method. The noise reduction method further calculates a second correction amount for reducing the influence of a change in sound velocity according to temperature, which is used for correcting the phase of the simulated transfer characteristic, based on the acquired temperature information. Then
In the generation of the corrected reference signal, the corrected reference signal is generated by applying the simulated transfer characteristic corrected by the calculated first correction amount and the calculated second correction amount to the reference signal. The noise reduction method according to any one of claims 9 to 14.

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