Transfer function measurement method and active noise reduction device

Abstract

To provide a measurement method of a transfer function, which can shorten total measurement time.SOLUTION: A measurement method of a transfer function includes: an output step S23 for simultaneously outputting sounds different in frequencies to a plurality of speakers by outputting a first signal to the plurality of speakers; and an acquisition step S25 for acquiring a second signal outputted from a microphone as an acquisition result of the sounds different in the frequencies; and a calculation step S26 for calculating the transfer functions of the sounds different in the frequencies on the basis of the first signal and the second signal.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present disclosure relates to a method for measuring a transfer function and an active noise reduction device. [Background technology]

[0002] Conventionally, there is known an active noise reduction device that actively reduces noise by outputting a cancellation sound for canceling the noise from a speaker using a reference signal that has a correlation with the noise and an error signal based on a residual sound resulting from interference between the noise and the cancellation sound in a specified space (see, for example, Patent Document 1). The active noise reduction device generates a cancellation signal for outputting the cancellation sound using an adaptive filter so that the sum of squares of the error signal is minimized. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 07-162986 Summary of the Invention [Problem to be solved by the invention]

[0004] The active noise reduction device generates a cancellation signal for outputting a cancellation sound by using a simulated transfer function that simulates the transfer function from the position of the speaker to the position of the microphone. The simulated transfer function is determined, for example, by actually measuring the transfer function, but when there are a large number of speakers, it becomes an issue to shorten the total measurement time of the transfer functions.

[0005] The present disclosure provides a method for measuring a transfer function that can reduce the total measurement time. [Means for solving the problem]

[0006] A method for measuring a transfer function according to one aspect of the present disclosure includes an output step of outputting a first signal to each of a plurality of speakers, thereby causing the plurality of speakers to simultaneously output sounds having different frequencies from each other, an acquisition step of acquiring a second signal output from a microphone as a result of acquiring the sounds having different frequencies from each other, and a calculation step of calculating a transfer function for each of the sounds having different frequencies based on the first signal and the second signal. Effect of the Invention

[0007] A transfer function measuring method according to an aspect of the present disclosure can reduce the total measurement time. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an overview of a noise reduction device according to an embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing the time waveform of noise heard at the microphone position. [Diagram 3] FIG. 3 is a schematic diagram of a vehicle equipped with a noise reduction device according to an embodiment. [Figure 4] FIG. 4 is a functional block diagram of a noise reduction device according to an embodiment. [Diagram 5] FIG. 5 is a flowchart of the basic operation of the noise reduction device according to the embodiment. [Figure 6] FIG. 6 is a diagram showing an outline of a method for measuring a transfer function according to a comparative example. [Figure 7] FIG. 7 is a diagram showing an outline of a method for measuring a transfer function according to an embodiment. [Figure 8] FIG. 8 is a block diagram illustrating a functional configuration of a transfer function measurement system according to the embodiment. [Figure 9] FIG. 9 is a flowchart of a method for measuring a transfer function according to the embodiment. [Figure 10] FIG. 10 is a first diagram showing an example of the relationship between the required component value and the measurement time, and the relationship between the error component value and the measurement time. [Figure 11] FIG. 11 is a diagram showing the gain of the transfer function obtained by the measurement method according to the comparative example and the measurement method according to the embodiment. [Figure 12] FIG. 12 is a diagram showing the phases of the transfer functions obtained by the measurement method according to the comparative example and the measurement method according to the embodiment. [Figure 13] FIG. 13 is a second diagram showing an example of the relationship between the required component value and the measurement time, and between the error component value and the measurement time. [Figure 14] FIG. 14 is a diagram showing a measurement result of the gain of the transfer function when the device 1 is applied to the measurement method according to the embodiment. [Figure 15] FIG. 15 is a diagram showing a measurement result of the phase of a transfer function when the device 1 is applied to the measurement method according to the embodiment. [Figure 16] FIG. 16 is a diagram showing an outline of a measurement method according to an embodiment to which the second solution is applied. [Figure 17] FIG. 17 is a diagram showing an example of frequency characteristics of a door speaker. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement and connection forms of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, components that are not described in the independent claims showing the highest concept are described as optional components.

[0010] In addition, each drawing is a schematic diagram and is not necessarily a precise illustration. In each drawing, the same reference numerals are used for substantially the same configurations, and duplicated explanations may be omitted or simplified.

[0011] (Embodiment) [overview] First, an outline of an active noise reduction device according to an embodiment will be described. Fig. 1 is a diagram showing an outline of an active noise reduction device according to an embodiment.

[0012] The active noise reduction device 10 shown in Fig. 1 is, for example, a device that is installed in a vehicle cabin and reduces noise generated while the vehicle is running. Noise caused by an engine 51 is momentarily a sound that is close to a sine wave of a single frequency. Therefore, the active noise reduction device 10 obtains a pulse signal indicating the frequency of the engine 51 from an engine control unit 52 that controls the engine 51, and outputs a cancellation sound for canceling the noise from a speaker SP1. An adaptive filter is used to generate the cancellation sound, and the cancellation sound is generated so as to reduce the residual sound obtained by a microphone M1 placed near the listener 30.

[0013] As shown in Fig. 1, the transfer function from the position of speaker SP1 (hereinafter also referred to as the sound output position) to the position of microphone M1 (hereinafter also referred to as the sound collection position) is represented by the symbol c1, and the output signal for outputting the cancellation sound is represented by the symbol out. In this case, the cancellation sound that reaches the position of microphone M1 (sound collection position) is represented as c1*out. Note that "*" means a convolution operator, c1 represents the impulse response of the transfer function, and C1 represents the simulated transfer function in the frequency domain.

[0014] Noise N at the position of microphone M1 m is expressed by the following (Equation 1), where R is the amplitude, ω is the angular frequency, and θ is the phase, and c1*out is expressed by the following (Equations 2-1) and 2-2. The active noise reduction device 10 is able to output a cancellation sound for canceling out the noise by calculating 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.

[0015]

number

[0016] Thus, the noise N m By outputting a cancellation sound having an opposite phase to the noise audible at the position of the microphone M1, the noise audible at the position of the microphone M1 becomes smaller, as shown in Fig. 2. Fig. 2 is a schematic diagram showing the time waveform of the noise audible at the position of the microphone M1.

[0017] [Overall configuration of a vehicle equipped with an active noise reduction device] The following describes in detail such an active noise reduction device 10. In the embodiment, the active noise reduction device 10 is mounted on a vehicle, as an example. Fig. 3 is a schematic diagram of a vehicle equipped with the active noise reduction device 10.

[0018] Vehicle 50 is an example of a moving body device, and includes active noise reduction device 10, engine 51, engine control unit 52, speakers SP1 to SP4, microphones M1 to M4, and a vehicle body 55. Specifically, vehicle 50 is an automobile, but is not particularly limited to this.

[0019] The engine 51 is a drive device that is a power source of the vehicle 50 and is also a noise source in the predetermined space 56. The engine 51 is disposed, for example, in a space separate from the predetermined space 56. Specifically, the engine 51 is installed in a space formed within the bonnet of the vehicle body 55.

[0020] The engine control unit 52 controls (drives) the engine 51 based on the accelerator operation of the driver of the vehicle 50, etc. The engine control unit 52 also outputs a pulse signal (engine pulse signal) according to the rotation speed (frequency) of the engine 51 as a reference signal. The frequency of the pulse signal is proportional to the rotation speed (frequency) of the engine 51, for example. Specifically, the pulse signal is an output signal of a TDC (Top Dead Center) sensor, or a so-called tachometer pulse. Note that the reference signal may be in any form as long as it has a correlation with noise.

[0021] The speakers SP1 to SP4 use the cancellation signal to output the cancellation sound to a predetermined space 56. The installation positions of the speakers SP1 to SP4 are not particularly limited.

[0022] The microphones M1 to M4 detect a residual sound resulting from interference between the noise and the cancellation sound in the predetermined space 56, and output an error signal based on the residual sound. The microphones M1 to M4 are installed, for example, on the headliner of each seat in the predetermined space 56, but the installation positions of the microphones M1 to M4 are not particularly limited.

[0023] The vehicle main body 55 is a structure constituted by the chassis and body of the vehicle 50. The vehicle main body 55 forms a predetermined space 56 (vehicle interior space) in which the speakers SP1 to SP4 and the microphones M1 to M4 are arranged.

[0024] [Configuration 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. For simplicity of explanation, the following describes the operation when reducing noise at the position where the microphone M1 is installed by using a cancellation sound output from the position where the speaker SP1 is installed. The active noise reduction device 10 can also output a cancellation sound from each of the speakers SP1 to SP4 to reduce noise at the positions where the microphones M1 to M4 are installed.

[0025] As shown in Fig. 4, the active noise reduction device 10 includes a reference signal input terminal 11a, a reference signal generating section 12, an adaptive filter section 13, a cancellation signal output terminal 11c, a correction section 14, an error signal input terminal 11b, a filter coefficient updating section 15, a storage section 16, a connection terminal 11d, and a measurement section 17. Each of the reference signal generating section 12, the adaptive filter section 13, the correction section 14, the filter coefficient updating section 15, and the measurement section 17 is realized by, for example, a processor such as a DSP (Digital Signal Processor) or a microcomputer executing a computer program stored in the storage section 16. Below, the relevant components will be described in detail for each step shown in the flowchart in Fig. 5.

[0026] [Reference signal generation] First, the reference signal generating unit 12 generates a reference signal based on the reference signal input to the reference signal input terminal 11a (S11 in FIG. 5).

[0027] 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.

[0028] More specifically, the reference signal generating unit 12 identifies the instantaneous frequency of the noise based on the reference signal input to the reference signal input terminal 11a, and generates a reference signal having the identified frequency. The reference signal generating unit 12 specifically includes a frequency detecting unit 12a, a sine wave generating unit 12b, and a cosine wave generating unit 12c.

[0029] The frequency detection unit 12a detects the frequency of the pulse signal, and outputs the detected frequency to the sine wave generation unit 12b and the cosine wave generation unit 12c. In other words, the frequency detection unit 12a identifies the instantaneous frequency of the noise.

[0030] The sine wave generating unit 12b outputs a sine wave of the frequency detected by the frequency detecting unit 12a as a first reference signal. The first reference signal is an example of a reference signal, and is a signal expressed as sin(2πft)=sin(ωt) when the frequency detected by the frequency detecting unit 12a is f. In other words, the first reference signal has a frequency (the same frequency as the noise) identified by the frequency detecting unit 12a. The first reference signal is output to a first filter 13a included in the adaptive filter unit 13 and a first correction signal generating unit 14b included in the correction unit 14.

[0031] The cosine wave generating unit 12c outputs a cosine wave of the frequency detected by the frequency detecting unit 12a as a second reference signal. The second reference signal is an example of a reference signal, and is a signal expressed as cos(2πft)=cos(ωt) when the frequency detected by the frequency detecting unit 12a is f. In other words, the second reference signal has a frequency (the same frequency as the noise) identified by the frequency detecting 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 generating unit 14c included in the correction unit 14.

[0032] [Canceling signal generation] The adaptive filter unit 13 generates a cancellation signal by applying (multiplying) a filter coefficient to the reference signal generated by the reference signal generation unit 12 (S12 in FIG. 5). In other words, the adaptive filter unit 13 applies a filter coefficient to a reference signal that is input to the reference signal input terminal 11a and converted into a reference signal. The cancellation signal is used to output a cancellation sound to reduce noise, and is output to the cancellation signal output terminal 11c. The adaptive filter unit 13 includes a first filter 13a, a second filter 13b, and an adder 13c. The adaptive filter unit 13 is a so-called adaptive notch filter.

[0033] The first filter 13a multiplies the first reference signal output from the sine wave generating unit 12b by a first filter coefficient. The first filter coefficient to be multiplied is a filter coefficient corresponding to A in the above (Equation 2), and is successively updated by the first updating unit 15a included in the filter coefficient updating unit 15. A first cancellation signal, which is the first reference signal multiplied by the first filter coefficient, is output to the adding unit 13c.

[0034] The second filter 13b multiplies the second reference signal output from the cosine wave generating unit 12c by a second filter coefficient. The second filter coefficient to be multiplied is a filter coefficient corresponding to B in the above (Equation 2), and is successively updated by the second updating unit 15b included in the filter coefficient updating unit 15. A second cancellation signal, which is the second reference signal multiplied by the second filter coefficient, is output to the adding unit 13c.

[0035] The adder 13c adds the first cancellation signal output from the first filter 13a and the second cancellation signal output from the second filter 13b, and outputs the cancellation signal obtained by adding the first cancellation signal and the second cancellation signal to the cancellation signal output terminal 11c.

[0036] The cancellation signal output terminal 11c is a terminal made of metal or the like. A cancellation signal generated by the adaptive filter unit 13 is output to the cancellation signal output terminal 11c. A speaker SP1 is connected to the cancellation signal output terminal 11c. Therefore, a cancellation signal is output to the speaker SP1 via the cancellation signal output terminal 11c. The speaker SP1 outputs a cancellation sound based on the cancellation signal.

[0037] [Reference signal correction] The correction unit 14 generates a corrected reference signal by applying the simulated transfer function to the reference signal. That is, the correction unit 14 generates a corrected reference signal by correcting the reference signal (S13 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.

[0038] The simulated transfer function is a transfer function that simulates a path from the position of the speaker SP1 to the position of the microphone M1. Specifically, the simulated transfer function is a gain and a phase (phase delay) for each frequency. The simulated transfer function is, for example, actually measured in advance for each frequency in the space 56 and stored in the storage unit 16. That is, the storage unit 16 stores the frequency and the gain and phase for correcting the signal of that frequency.

[0039] The control unit 14a acquires the frequency output by the frequency detection unit 12a, and reads out the gain and phase corresponding to the acquired frequency from the storage unit 16. Then, the control unit 14a outputs the read-out gain and phase.

[0040] The first correction signal generating unit 14b generates a first corrected reference signal 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 a corrected reference signal. If the gain output by the control unit 14a is α and the phase after correction is φα, the first corrected reference signal is expressed as α·sin(ωt+φα). The generated first corrected reference signal is output to a first updating unit 15a included in the filter coefficient updating unit 15.

[0041] The second correction signal generating unit 14c generates a second corrected reference signal by correcting the second reference signal based on the gain and phase output by the control unit 14a. The second corrected reference signal is an example of a corrected reference signal. If the gain output by the control unit 14a is β and the phase after correction 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.

[0042] The memory unit 16 is a storage device in which the simulated transfer function is stored. The memory unit 16 also stores coefficients of an adaptive filter and the like. Specifically, the memory unit 16 is 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 memory unit 16 also stores a control program executed by the processor. The memory unit 16 may also store other parameters used in the signal processing performed by the active noise reduction device 10.

[0043] [Update filter coefficients] The filter coefficient update unit 15 sequentially updates the filter coefficients based on the error signal input to the error signal input terminal 11b and the generated corrected reference signal (S14 in FIG. 5).

[0044] The error signal input terminal 11b is a terminal made of metal or the like. An error signal based on a residual sound generated at the second position of the microphone M1 due to interference between the canceling sound and the noise is input to the error signal input terminal 11b. The error signal is output by the microphone M1.

[0045] Specifically, the filter coefficient update unit 15 includes a first update unit 15a and a second update unit 15b.

[0046] The first update unit 15a calculates a first filter coefficient based on the first corrected reference signal acquired from the first correction signal generation unit 14b and the error signal acquired from the microphone M1. Specifically, the first update unit 15a calculates a first filter coefficient using the LMS method so that the error signal is minimized, and outputs the calculated first filter coefficient to the first filter 13a. The first update unit 15a also sequentially updates the first filter coefficient. If the first corrected reference signal is expressed as r1 and the error signal is expressed as e, the first filter coefficient A (corresponding to A in the above (Equation 2)) is expressed by the following (Equation 3). Note that n is a natural number and is a variable that indicates how many updates have been made (in other words, a variable that indicates the number of updates). That is, A(n) indicates the state at the nth update. μ is a scalar quantity and is a step size parameter that determines the amount of update of the filter coefficient per sampling.

[0047]

number

[0048] The second update unit 15b calculates a second filter coefficient based on the second corrected reference signal acquired from the second correction signal generation unit 14c and the error signal acquired from the microphone M1. Specifically, the second update unit 15b calculates the second filter coefficient using the LMS method so that the error signal is minimized, and outputs the calculated second filter coefficient to the second filter 13b. In addition, the second update unit 15b sequentially updates the second filter coefficient. If the second corrected reference signal is expressed as r2 and the error signal is expressed as e, the second filter coefficient B (corresponding to B in the above (Equation 2)) is expressed by the following (Equation 4).

[0049]

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[0050] [Transfer function measurement method] As described above, the storage unit 16 of the active noise reduction device 10 stores a simulated transfer function (hereinafter, simply referred to as a transfer function) that has been measured in advance. Here, when measuring the transfer function in the space 56 in which the four speakers SP1 to SP4 and the four microphones M1 to M4 are installed, a measurement method can be considered in which the acquisition of a sound (more specifically, a sound of a single frequency, a sine wave) output from one speaker by the four microphones M1 to M4 is repeated four times, the number of times being the number of speakers SP1 to SP4. In other words, a method can be considered in which the number of speakers that simultaneously output sound is limited to one and the transfer function is measured. FIG. 6 is a diagram showing an outline of a measurement method of a transfer function according to such a comparative example. In the example of FIG. 6, the sound output from one speaker changes in 1 Hz increments in the range of 21 to 300 Hz. In other words, the transfer function (gain and phase) is measured every 1 Hz.

[0051] The measurement method shown in Fig. 6 has an issue in that it takes a long time to measure the transfer function. As a result of intensive research, the inventors have found a measurement method as shown in Fig. 7 in which sounds of different frequencies are output simultaneously (in other words, in parallel) from the speakers SP1 to SP4. Fig. 7 is a diagram showing an overview of the measurement method of the transfer function according to the embodiment. Note that the transfer function (gain and phase) is measured every 1 Hz, similarly to the comparative example. The measurement method as shown in Fig. 7 will be specifically described below. Fig. 8 is a block diagram showing the functional configuration of a measurement system of the transfer function according to the embodiment.

[0052] Measurement system 40 shown in Fig. 8 includes active noise reduction device 10, speakers SP1-SP4, microphones M1-M4, and information terminal 60. Active noise reduction device 10 has a normal operation mode (an example of a first operation mode) for performing the operation shown in Fig. 5 (i.e., for reducing noise in space 56), as well as a measurement mode (an example of a second operation mode) for executing the method for measuring a transfer function according to the embodiment shown in Fig. 7. In the measurement mode, measurement unit 17 mainly performs processing.

[0053] The information terminal 60 is an information terminal that functions as a user interface in the measurement mode, and is connected to the connection terminal 11d of the active noise reduction device 10 via a cable or the like. The information terminal 60 is, for example, a personal computer. It is not essential that the measurement system 40 includes the information terminal 60, and measurement of the transfer function may be realized only by the active noise reduction device 10 without using the information terminal 60.

[0054] 9 is a flowchart of a method for measuring a transfer function according to an embodiment. Note that, although the formulas used in the following description of the method for measuring a transfer function are continuous system formulas, the measurement unit 17 may actually perform processing based on a discrete system formula that is an approximation of the continuous system formula. First, the active noise reduction device 10 (measurement unit 17) acquires, via the connection terminal 11d, a mode transition command output by the information terminal 60 (S21). The active noise reduction device 10 transitions to the measurement mode based on the acquired mode transition command (S22).

[0055] During the operation of the measurement mode, the measurement unit 17 outputs the first signal to each of the speakers SP1 to SP4, thereby causing the speakers SP1 to SP4 to simultaneously output sounds (sine waves) of different frequencies (S23). For example, as shown in FIG. 7, when the speaker SP1 outputs a sound of 21 Hz, the speaker SP2 outputs a sound of 91 Hz, the speaker SP3 outputs a sound of 161 Hz, and the speaker SP4 outputs a sound of 231 Hz. When the speaker SP1 outputs a sound of 22 Hz, the speaker SP2 outputs a sound of 92 Hz, the speaker SP3 outputs a sound of 162 Hz, and the speaker SP4 outputs a sound of 232 Hz. When the frequencies measured simultaneously are close to each other, there is a high possibility that interference will affect the measurement results. For this reason, the difference between the frequencies measured simultaneously is set to, for example, 30 Hz or more.

[0056] The microphones M1 to M4 simultaneously pick up sounds of different frequencies and output second signals as the acquisition results (S24). The measurement unit 17 acquires the second signals output from the microphones M1 to M4 (S25).

[0057] Next, the measurement unit 17 calculates a transfer function based on the first signal output in step S23 and the second signal acquired in step S25 (S26). The measurement unit 17 can calculate the transfer function from the position of the speaker SP1 to the position of the microphone M1, for example, based on the first signal output to the speaker SP1 and the second signal acquired from the microphone M1. Hereinafter, a method for calculating the transfer function in step S26 will be specifically described.

[0058] If the first signal output to the speaker SP1 is y(t)=γsinωt and the second signal acquired from the microphone M1 is x(t)=αsinωt+βcosωt, the gain and phase of the transfer function can be calculated by the following equations: Note that atan2 indicates the arctangent of two arguments.

[0059]

number

[0060] In order to calculate the gain and phase of such a transfer function, the measurement unit 17 measures the transfer function from the speaker SP1 to the microphone M1 at a certain frequency over a period T m (Hereinafter, measurement time T m The following parameters A, B, and C are calculated using the first signal y(t) and the second signal x(t).

[0061]

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[0062] In addition, y(t)×sinωt is an example of a first function based on the first signal y(t) and has time as a variable, and the parameter C is an example of a first parameter obtained by integrating the first function with respect to time. Each of x(t)×sinωt and x(t)×cosωt is an example of a second function based on the second signal x(t) and has time as a variable, and the parameter A and parameters B Each of these is an example of a second parameter obtained by time-integrating a second function. m is the time corresponding to the integral interval. When the parameters A, B, and C are expanded, they become as follows.

[0063]

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[0064] As shown by the parameters A, B, and C after these expansions, T m =(n / ω)π, then

number

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[0065] In addition, T m If ≠(n / ω)π, the underlined dashed lines among the parameters A, B, and C after expansion remain as error components. Here, the components required to calculate the transfer function (αT m Term, βT of parameter B m Term, γT of parameter C m (section) is T mThe value of the required component increases in proportion to the measurement time T m 10 is a graph showing an example of the relationship between the required component and the error component when α=β=γ=1 and ω=200π (100 Hz).

[0066] As shown in FIG. 10, the measurement unit 17 measures T m =(n / ω)π, T m By setting T to a sufficiently long time, the influence of the error component can be reduced. m =(n / ω)π, T m The influence of the error component can also be reduced by setting the time to a sufficiently long time. Note that the sufficiently long time is, for example, 500 ms, but is not limited thereto.

[0067] As described above, the measurement unit 17 of the active noise reduction device 10 executes the method of measuring a transfer function according to the embodiment shown in Fig. 7. Specifically, the measurement unit 17 outputs a first signal to each of the multiple speakers SP1 to SP4, thereby causing the multiple speakers SP1 to SP4 to simultaneously output sounds having different frequencies from each other, acquires a second signal output from the microphone M1 as a result of acquiring the sounds having different frequencies from each other, and calculates the transfer function of each of the sounds having different frequencies from each other based on the first signal and the second signal. Since such a method of measuring a transfer function can perform processing in parallel, it is possible to shorten the total measurement time compared to the method of measuring a transfer function according to the comparative example shown in Fig. 6.

[0068] When the measurement of the transfer functions from the speakers SP1 to SP4 to the microphones M1 to M4 in the range of 21 Hz to 300 Hz (i.e., all transfer functions) is completed, the measurement unit 17 transmits the measurement results to the information terminal 60. As a result, 16 transfer functions from the four speakers SP1 to SP4 to the four microphones M1 to M4, each of which includes data in the range of 21 Hz to 300 Hz, are stored in the storage unit of the information terminal 60. In practice, the transfer functions are measured multiple times by changing the conditions of the vehicle 50 (such as the temperature of the space 56, the open / closed state of the windows of the vehicle 50, etc.), and a final simulated transfer function is determined. The determined final simulated transfer function is stored in the storage unit of the active noise reduction device (mass-produced product) in the manufacturing process.

[0069] [Improving the transfer function measurement method 1] Measurement time T m If the measurement time T is set to a sufficiently long time (for example, 500 ms), it is considered that there is no significant difference between the transfer function obtained by the measurement method according to the comparative example (FIG. 6) and the transfer function obtained by the measurement method according to the embodiment (FIG. 7). Here, the inventors have set the measurement time T m is set to 10 periods of the frequency to be measured, and a comparison is made between the transfer function obtained by the measurement method according to the comparative example and the transfer function obtained by the measurement method according to the embodiment.

[0070] FIG. 11 is a diagram showing the gain of the transfer function obtained by the measurement method according to the comparative example and the measurement method according to the embodiment (comparison example: dashed line, embodiment: solid line). FIG. 12 is a diagram showing the phase of the transfer function obtained by the measurement method according to the comparative example and the measurement method according to the embodiment (comparison example: dashed line, embodiment: solid line). Note that in the measurement method according to the embodiment, m was set to 10 periods of the smallest frequency among the multiple frequencies that are the target of simultaneous transfer function measurement. For example, when the transfer function of 50 Hz and the transfer function of 100 Hz are measured simultaneously, 10 periods of 50 Hz are 200 ms and 10 periods of 100 Hz are 100 ms, so the measurement time T mis set to 200ms.

[0071] 11 and 12, there is a difference between the transfer function obtained by the measurement method according to the comparative example and the transfer function obtained by the measurement method according to the embodiment. Hereinafter, a method for reducing this difference (a method for bringing the transfer function obtained by the measurement method according to the embodiment closer to the transfer function obtained by the measurement method according to the comparative example) will be described.

[0072] In the measurement method according to the embodiment, when the transfer function of a sound of a certain frequency is measured, the sound of another frequency output simultaneously with the sound of the certain frequency becomes a disturbance. That is, the disturbance is included in the second signal. It is considered that this disturbance is the cause of the above difference. For example, when the transfer function of a sound with an angular velocity of ω0 and the transfer function of a sound with an angular velocity of ω1 are measured simultaneously using two speakers, if the sound with an angular velocity of ω0 is the measurement target, the sound with an angular velocity of ω1 becomes the disturbance, and if the sound with an angular velocity of ω1 is the measurement target, the sound with an angular velocity of ω0 becomes the disturbance. If the angular velocity to be measured is ω and the angular velocity that becomes the disturbance is ω', the second signal including the disturbance can be expressed as x(t)=αsinωt+βcosωt+α'sinω't+β'cosω't. The third and fourth terms on the right side are disturbance components. Among the above-mentioned parameters A, B, and C, the parameters A and B based on the second signal are expressed as follows.

[0073]

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[0074] The parameter A is expanded as follows:

[0075]

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[0076] The parameter A can be further rearranged as follows:

[0077]

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[0078] The first solid underlined part in this formula is a required component. 1 Second If we define the dashed underlined part as error component A1, the next solid underlined part as error component A2, and the next dashed underlined part as error component A3, in order to make all error components A1 to A3 zero, we need to set the measurement time T so that the following formula is satisfied, where n0, n1, and n2 are any positive integers (natural numbers). m should be set.

[0079]

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[0080] However, the measurement time T m becomes a relatively long time. Here, the value of the required component and the values ​​of the error components A1 to A3 change as shown in FIG. 13. FIG. 13 shows the relationship between the value of the required component and the values ​​of the error components A1 to A3 and the measurement time T m 13 is a diagram showing an example of the relationship between the error components A1 and A3. As shown in FIG. 13, it can be seen that the influence of the error component A3 is dominant among the error components A1 to A3. The condition for simultaneously measuring two frequencies is |ω+ω'|>2|ω-ω'|. In other words, if the condition is that the sum of the simultaneously measured frequencies is greater than twice the difference between the simultaneously measured frequencies, then under this condition, ω'-ω<2ω<ω'+ω, and therefore the error component A3 is dominant.

[0081] Similarly to parameter A, parameter B can be expanded and rearranged as follows:

[0082]

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[0083] Although not shown, the error components B1 to B3 behave similarly to the error components A1 to A3. That is, among the error components B1 to B3, the influence of the error component B3 is dominant.

[0084] In order to make the error components A3 and B3 zero, the measurement time T is set so that the following formula is satisfied, where n is an arbitrary positive integer. m should be set.

[0085]

number

[0086] Since ω = 2πf, the difference in frequency f´-f at which the transfer function is measured is kept constant, and the measurement time T m =n / (f´-f) (i.e., measurement time T m to the time obtained by dividing the natural number n by the frequency difference), it is possible to shorten the total measurement time and reduce errors at the same time. For example, if the frequency difference at which the transfer functions are simultaneously measured is 50 Hz, the measurement unit 17 can shorten the total measurement time and reduce errors at the same time by setting the measurement time to n × (1 / 50) = n × 20 ms.

[0087] A transfer function measured using the measurement method to which such ingenuity 1 is applied will be specifically described below. FIG. 14 is a diagram showing the measurement results of the gain of the transfer function. The dashed line in FIG. 14 indicates the gain of the transfer function when the transfer function of a sound with a frequency of 80 Hz to 90 Hz is measured using the measurement method according to the comparative example. The solid line in FIG. 14 indicates the gain of the transfer function when ingenuity 1 is further applied to the measurement method according to the embodiment (the transfer function of a sound with a frequency of 80 Hz to 90 Hz is measured simultaneously with the transfer function of a sound with a frequency of 130 Hz to 140 Hz). m 14 shows the gain of the transfer function when T = 140 ms (that is, n = 7 in the above formula). m The figure shows the gain of the transfer function when the delay time is set to 130 ms.

[0088] 15 is a diagram showing the measurement results of the phase of the transfer function. The dashed line in FIG. 15 shows the phase of the transfer function when the transfer function of a sound with a frequency of 80 Hz to 90 Hz is measured using the measurement method according to the comparative example. The solid line in FIG. 15 shows the phase of the transfer function when the measure 1 is further applied to the measurement method according to the embodiment. m The dashed line in FIG. 15 shows the phase of the transfer function when T m = 130 ms.

[0089] 14 and 15, by applying the technique 1 to the measurement method according to the embodiment, the transfer function measured by the measurement method according to the embodiment can be made to approach the transfer function measured by the measurement method according to the comparative example. In other words, the technique 1 can achieve both a reduction in the total measurement time and a reduction in errors.

[0090] [Technique 2] To further reduce the error, it is necessary to take into consideration the distortion components of the speakers SP1 to SP4. For example, when the speaker SP1 outputs a 30 Hz sound, a 60 Hz sound corresponding to a second-order distortion component and a 90 Hz sound corresponding to a third-order distortion component are also output. In the measurement method according to the embodiment, when sounds of different frequencies are output simultaneously, the distortion components are also output simultaneously from the speakers SP1 to SP4, which causes an error.

[0091] Therefore, the measurement unit 17 may use the measurement method according to the comparative example (outputting sound from only one speaker) when the frequency of the measurement target belongs to a frequency band where the influence of the distortion component is large, and may execute the measurement method according to the embodiment when the frequency of the measurement target belongs to a frequency band where the influence of the distortion component is small. For example, in order to keep the error within 5%, the measurement unit 17 executes the measurement method according to the embodiment when the difference between the sound pressure of the signal to be measured and the sound pressure of the distortion component is 26 dB or more. In this way, the measurement unit 17 may switch between the measurement method according to the comparative example and the measurement method according to the embodiment. FIG. 16 is a diagram showing an outline of the measurement method according to the embodiment to which such a device 2 is applied. As in FIG. 6 and FIG. 7, the difference in color (density of hatching) of the arrows shown in FIG. 16 indicates the difference in the speakers.

[0092] 16, when the frequency of the measurement target is less than a threshold (e.g., 100 Hz), the number of speakers that simultaneously output sound is limited to one, and sound is output from the four speakers SP1 to SP4 sequentially. When the frequency of the measurement target is equal to or greater than the threshold, sound is output from the four speakers SP1 to SP4 in parallel at the same time.

[0093] The threshold value is set to, for example, the lowest resonance frequency of the speakers SP1 to SP4. When the active noise reduction device 10 is mounted on a vehicle 50, door speakers with a speaker diameter of, for example, 16 cm are used as the speakers SP1 to SP4. Fig. 17 is a diagram showing an example of the frequency characteristics of a door speaker, and mainly shows the frequency characteristics of the sound pressure SPL (Sound Pressure Level) of the sound output from the door speaker and the frequency characteristics of the total harmonic distortion THD (Total Harmonic Distortion). Note that total harmonic distortion = second order distortion + third order distortion + ·.

[0094] Generally, the lowest resonance frequency F0 of a door speaker is around 70 to 90 Hz, and the total harmonic distortion THD is relatively large below F0. As mentioned above, in order to set the error within 5%, that is, to set the difference between the sound pressure of the signal to be measured and the sound pressure of its distortion component to 26 dB or more, it is reasonable to set the value of F0 as the threshold.

[0095] When the minimum resonance frequencies of the speakers SP1 to SP4 are different, for example, the minimum resonance frequency with the largest value is adopted. Since it is expected that distortion components will increase in the frequency band below the minimum resonance frequency, if the minimum resonance frequency is used as the threshold, the influence of the distortion components can be suppressed while shortening the total measurement time. Note that the threshold may be determined empirically or experimentally, and it is not essential that the minimum resonance frequency of the speakers SP1 to SP4 is adopted as the threshold.

[0096] [Ingenuity 3] In addition, in the measurement method according to the embodiment, when measuring the transfer function of a sound of a certain frequency, another method for reducing the influence of sounds of other frequencies output simultaneously with the sound of the certain frequency can be to apply a Hanning window to each of the first signal and the second signal. By applying such a Hanning window, it is expected that the influence of sounds of other frequencies can be further reduced.

[0097] [Variations] The measurement method according to the embodiment is executed by the active noise reduction device 10 (measurement unit 17), but may be executed by a device other than the active noise reduction device 10. The measurement method according to the embodiment may be executed by, for example, a dedicated device for measuring a transfer function or a personal computer.

[0098] Furthermore, the space for which the transfer function is measured is the space 56 inside the vehicle 50, but it may be another space. There is also no particular limitation on the use of the measured transfer function. The measured transfer function may be used for purposes other than the active noise reduction device 10.

[0099] Moreover, two or more of the above-mentioned ideas 1 to 3 may be combined and applied to the measurement method according to the embodiment.

[0100] [summary] As described above, the method for measuring the transfer function includes an output step S23 of causing the multiple speakers SP1 to SP4 to simultaneously output sounds of different frequencies by outputting a first signal to each of the multiple speakers SP1 to SP4, an acquisition step S25 of acquiring a second signal output from the microphone M1 as a result of acquiring the sounds of different frequencies, and a calculation step S26 of calculating the transfer function of each of the sounds of different frequencies based on the first signal and the second signal.

[0101] Such a method of measuring a transfer function can shorten the total measurement time compared to a measurement method in which sounds are serially output from the multiple speakers SP1 to SP4.

[0102] Also, for example, in the calculation step S26, the transfer functions of the sounds having different frequencies are calculated based on a parameter C obtained by integrating a first function based on a first signal and with time as a variable, and parameters A and B obtained by time-integrating a second function based on a second signal and with time as a variable, and the integral interval of the first function and the measurement time T corresponding to the integral interval of the second function are calculated. m is set based on the difference between the frequencies of sounds having different frequencies. The parameter C is an example of a first parameter, and the parameters A and B are examples of second parameters.

[0103] Such a transfer function measurement method is performed over a measurement time T m By setting an appropriate value, it is possible to shorten the total measurement time and reduce errors at the same time.

[0104] Also, for example, in the calculation step S26, the measurement time T m is set to the time obtained by dividing the natural number n by the difference.

[0105] Such a method for measuring a transfer function can achieve both a reduction in the total measurement time and a reduction in errors.

[0106] Also, for example, the method of measuring the transfer function further includes a first measurement step of measuring the transfer function by limiting the speakers that simultaneously output sound to one of the multiple speakers SP1 to SP4, and switching between the first measurement step and a second measurement step including an output step S23, an acquisition step S25, and a calculation step S26 depending on the frequency of the measurement target.

[0107] In such a method of measuring a transfer function, when a frequency at which errors are likely to occur is the measurement target, the first measurement step is executed instead of the second measurement step, thereby making it possible to reduce errors.

[0108] Also, for example, the method of measuring the transfer function executes a first measurement step when a frequency that is less than the lowest resonant frequency of one of the multiple speakers SP1 to SP4 is to be measured, and executes a second measurement step when a frequency that is equal to or greater than the lowest resonant frequency of one of the multiple speakers SP1 to SP4 is to be measured.

[0109] Such a method of measuring a transfer function can reduce errors by performing the first measurement step instead of the second measurement step when a frequency lower than the lowest resonant frequency of one of the multiple speakers SP1 to SP4 is to be measured.

[0110] Also, for example, in the calculation step S26, the transfer functions of the sounds having different frequencies are calculated based on a parameter C obtained by integrating a first function based on a first signal and with time as a variable, and parameters A and B obtained by time-integrating a second function based on a second signal and with time as a variable, and the measurement time corresponding to the integration interval of the first function and the integration interval of the second function is set based on the difference in frequency between the sounds having different frequencies. The measurement method of the transfer functions further includes a first measurement step of measuring the transfer function by limiting the speaker that simultaneously outputs sounds to one of the multiple speakers SP1 to SP4, and switching between the first measurement step and a second measurement step including an output step S23, an acquisition step S25, and a calculation step S26.

[0111] Such a method for measuring a transfer function can achieve both a reduction in the total measurement time and a reduction in errors.

[0112] Further, the multiple speakers SP1 to SP4 and the microphones M1 to M4 are installed in a space 56 within the vehicle 50, for example.

[0113] Such a method for measuring a transfer function can shorten the total measurement time when measuring a transfer function targeting the space 56 inside the vehicle 50 .

[0114] Also for example, the transfer function measurement method is performed by an active noise reduction device 10 that reduces noise in a space 56 .

[0115] In this manner, the method for measuring the transfer function can be implemented by the active noise reduction device 10.

[0116] Also, for example, the active noise reduction device 10 has a normal operation mode for reducing noise in a space and a measurement mode for executing a transfer function measurement method, and transitions to the measurement mode upon receiving a mode transition command from the information terminal 60. The normal operation mode is an example of a first operation mode, and the measurement mode is an example of a second operation mode.

[0117] In this way, the method for measuring the transfer function can be realized by transitioning the operation modes of the active noise reduction device 10.

[0118] The active noise reduction device 10 also includes a reference signal input terminal 11a to which a reference signal correlated with the noise is input, 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 that generates a cancellation signal used to output a cancellation sound to reduce the noise by applying an adaptive filter to the generated reference signal, a cancellation signal output terminal 11c for outputting the generated cancellation signal to a speaker, an error signal input terminal 11b to which an error signal corresponding to the cancellation sound and residual sound due to interference with the noise is input from microphone M1, a correction unit 14 that generates a corrected reference signal by applying simulated transfer characteristics that simulate the transfer characteristics from the position of speaker SP1 to the position of microphone M1 to the reference signal, a filter coefficient update unit 15 that sequentially updates the coefficients of the adaptive filter using the error signal and the generated corrected reference signal, and a measurement unit 17. The measurement unit 17 outputs a first signal to each of the multiple speakers SP1 to SP4 including the speaker SP1, thereby causing the multiple speakers SP1 to SP4 to simultaneously output sounds having different frequencies from each other, acquires a second signal output from the microphone M1 as a result of acquiring the sounds having different frequencies from each other, and calculates a transfer function for each of the sounds having different frequencies from each other based on the first signal and the second signal. The reference signal input terminal 11a is an example of a reference signal input section, the cancellation signal output terminal 11c is an example of a cancellation signal output section, and the error signal input terminal 11b is an example of an error signal input section.

[0119] The method of measuring the transfer function executed by such active noise reduction device 10 can shorten the total measurement time in measuring the transfer function, compared to a measurement method in which sounds are output serially to the multiple speakers SP1 to SP4.

[0120] (Other embodiments) Although the embodiments have been described above, the present disclosure is not limited to the above-described embodiments.

[0121] The active noise reduction device according to the above embodiment may be mounted on a moving body device other than a vehicle. The moving body device may be, for example, an aircraft or a ship. Furthermore, the present disclosure may be realized as such a moving body device other than a vehicle.

[0122] The configuration of the active noise reduction device according to the above embodiment is merely 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.

[0123] Furthermore, the processes performed by the active noise reduction devices according to the above-described embodiments are merely examples. For example, part of the digital signal processing described in the above-described embodiments may be realized by analog signal processing.

[0124] In addition, for example, in the above embodiment, the process executed by a specific processing unit may be executed by another processing unit. Furthermore, the order of multiple processes may be changed, or multiple processes may be executed in parallel.

[0125] In the above 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 on a recording medium such as a hard disk or a semiconductor memory.

[0126] Furthermore, each component may be realized by hardware. For example, each component may be a circuit (or an integrated circuit). These circuits may form a single circuit as a whole, or each may be a separate circuit. Furthermore, each of these circuits may be a general-purpose circuit, or a dedicated circuit.

[0127] In addition, the general or specific aspects of the present disclosure may be realized in a system, an apparatus, a method, an integrated circuit, a computer program, or a non-transitory recording medium such as a computer-readable CD-ROM, or in any combination of a system, an apparatus, a method, an integrated circuit, a computer program, and a computer-readable non-transitory recording medium.

[0128] For example, the present disclosure may be realized as a program for causing a computer or a DSP to execute the method for measuring a transfer function, or as a computer-readable non-transitory recording medium storing such a program. Furthermore, the present disclosure may be realized as the measurement system according to the above-described embodiment.

[0129] In addition, the present disclosure also includes forms obtained by applying various modifications to each embodiment that a person skilled in the art may conceive, or forms realized by arbitrarily combining the components and functions of each embodiment within the scope that does not deviate from the spirit of the present disclosure. [Industrial Applicability]

[0130] The method for measuring a transfer function disclosed herein can reduce the total measurement time, and the transfer function measured by such a method can be used, for example, in an active noise reduction device for reducing noise inside a vehicle cabin. [Explanation of symbols]

[0131] 10. Active noise reduction devices 11a Reference signal input terminal 11b Error signal input terminal 11c Cancellation signal output terminal 11d Connection terminal 12 Reference signal generation section 12a Frequency detection section 12b Sine wave generator 12c Cosine wave generator 13 Adaptive filter section 13a First Filter 13b Second Filter 13c Addition section 14 Correction section 14a Control section 14b First correction signal generation section 14c Second correction signal generation section 15 Filter coefficient update section 15a First update part 15b Second update part 16 Memory section 17 Measurement section 30 listeners 40 Measurement System 50 vehicles 51 Engine 52 Engine control unit 55 Vehicle body 56 Space 60 Information terminal M1, M2, M3, M4 Microphones SP1, SP2, SP3, SP4 speakers

Claims

1. an output step of outputting a first signal to each of a plurality of speakers to cause the plurality of speakers to simultaneously output sounds having different frequencies from each other; an acquisition step of acquiring a second signal output from one microphone as a result of acquiring the sounds having different frequencies, the second signal including components of the sounds having different frequencies; a calculation step of calculating a transfer function of each of the sounds having different frequencies from each other based on the first signal and the second signal, the transfer function being from each of the positions of the plurality of speakers to the position of the one microphone; In the calculation step, Calculating a transfer function for each of the sounds having different frequencies based on a first parameter obtained by integrating a first function based on the first signal and having time as a variable, and a second parameter obtained by time-integrating a second function based on the second signal and having time as a variable, A measurement time corresponding to an integral interval of the first function and an integral interval of the second function is set based on a difference between the frequencies of the sounds having different frequencies. How to measure transfer functions.

2. In the calculation step, the measured time is set to a time obtained by dividing a natural number n by the difference. The method for measuring a transfer function according to claim 1 .

3. The method for measuring the transfer function includes the steps of: The method further includes a first measurement step of measuring a transfer function by limiting the number of speakers that simultaneously output sound to one of the plurality of speakers, The first measurement step and the second measurement step including the output step, the acquisition step, and the calculation step are switched according to a frequency of the measurement target. The method for measuring a transfer function according to claim 1 .

4. The method for measuring the transfer function includes the steps of: When a frequency that is lower than a lowest resonance frequency of one of the plurality of speakers is to be measured, the first measurement step is performed; When a frequency equal to or higher than the lowest resonance frequency of one of the plurality of speakers is to be measured, the second measurement step is executed. The method for measuring a transfer function according to claim 3.

5. The method for measuring the transfer function comprises: The method further includes a first measurement step of measuring a transfer function by limiting the number of speakers that simultaneously output sound to one of the plurality of speakers, Switching between the first measurement step and a second measurement step including the output step, the acquisition step, and the calculation step The method for measuring a transfer function according to claim 1 .

6. The plurality of speakers and the one microphone are installed in a space within a vehicle. The method for measuring a transfer function according to any one of claims 1 to 5.

7. The method for measuring the transfer function is performed by an active noise reduction device that reduces noise in the space. The method for measuring a transfer function according to claim 6.

8. The active noise reduction device comprises: a first mode of operation for reducing noise in the space and a second mode of operation for performing the method for measuring the transfer function; Transitioning to the second operation mode by receiving a mode transition command from an information terminal. The method for measuring a transfer function according to claim 7.

9. a reference signal input unit to which a reference signal having a correlation with noise is input; a reference signal generating unit that generates a reference signal having a frequency determined based on the input reference signal; an adaptive filter unit that generates a cancellation signal used to output a cancellation sound for reducing the noise by applying an adaptive filter to the generated reference signal; a cancellation signal output unit for outputting the generated cancellation signal to a speaker; an error signal input unit to which an error signal corresponding to the cancellation sound and a residual sound caused by interference with the noise is input from one microphone; a correction unit that generates a corrected reference signal by applying a simulated transfer function that simulates a transfer function from the position of the speaker to the position of the one microphone to the reference signal; a filter coefficient update unit that sequentially updates coefficients of the adaptive filter by using the error signal and the generated corrected reference signal; A measuring unit, The measurement unit is outputting a first signal to each of a plurality of speakers including the speaker, thereby causing the plurality of speakers to simultaneously output sounds having different frequencies from each other; acquiring a second signal output from one of the microphones as a result of acquiring the sounds having different frequencies, the second signal including components of the sounds having different frequencies; Calculating a transfer function for each of the sounds having different frequencies, the transfer function being from each of the positions of the plurality of speakers to the position of the one microphone, based on the first signal and the second signal; In calculating the transfer function, Calculating a transfer function for each of the sounds having different frequencies based on a first parameter obtained by integrating a first function based on the first signal and having time as a variable, and a second parameter obtained by time-integrating a second function based on the second signal and having time as a variable, A measurement time corresponding to an integral interval of the first function and an integral interval of the second function is set based on a difference between the frequencies of the sounds having different frequencies. Active noise reduction devices.

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