Microphone device

Abstract

A microphone device is provided with a plurality of microphones (20), where d is the interval between two microphones among the plurality of microphones, MicSNR is the SN ratio of the single microphones, c is the sound velocity, f is the frequency of a processing object, theta is the azimuth angle of an operation seat with respect to the plurality of microphones, and delta theta is the minimum azimuth angle of a detection object, d is the interval between two microphones among the plurality of microphones, c is the sound velocity, f is the frequency of the processing object, theta is the azimuth angle of the operation seat with respect to the plurality of microphones, and delta theta is the minimum azimuth angle of the detection object. When the voltage amplitude of the output signal of the microphone based on the output voltage when 94dBA sound is received is A, [Delta] [tau] = d / c {sin (theta + [Delta] [theta])-sin [theta]}, and the differential voltage effective rate EDER is defined by the mathematical formula, the interval d is set to a value satisfying d < c / 2f and EDER > 0.7.

Description

Technical Field

[0001] The present disclosure relates to a microphone device. Background Art

[0002] A technology related to a voice recognition operation that allows a driver to operate an air conditioner or the like in a car cabin without taking his eyes off the direction of travel of the car has been proposed. Various noises are generated during driving. In order to improve the SN ratio, that is, the strength of the operator's voice signal relative to the noise so as to easily recognize the operator's speech content, a voice enhancement technology based on a microphone array using a plurality of microphones has been proposed (for example, see Patent Document 1).

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-149612 Summary of the invention

[0006] When the microphone device is mounted on a vehicle, the size of the mounting space is limited, so the device needs to be miniaturized. On the other hand, if the microphones are arranged closely, the time difference and amplitude difference of the signals between the microphones become smaller relative to the electrical noise generated by the microphones themselves, so there is a possibility that the performance as a microphone array cannot be maintained.

[0007] Therefore, it is desirable to set the interval between the microphones to a value that can achieve miniaturization while ensuring the performance of the device. However, Patent Document 1 does not study the minimum value of the interval between the microphones that can ensure the performance of the device.

[0008] The present disclosure has been made in view of the above-mentioned points, and an object of the present disclosure is to provide a microphone device that can be reduced in size.

[0009] In order to achieve the above-mentioned purpose, according to one viewpoint of the present disclosure, the microphone device includes multiple microphones, the interval between two microphones among the multiple microphones is set to d, the SN ratio of a single microphone is set to MicSNR, the sound speed is set to c, the frequency of the processing object is set to f, the azimuth angle of the operating seat relative to the multiple microphones is set to θ, the minimum azimuth angle as the detection object is set to Δθ, the voltage amplitude of the output signal of the microphone based on the output voltage when a sound of 94dBA is received is set to A, Δτ=d / c{sin(θ+Δθ)-sinθ}, the differential voltage efficiency EDER is defined by mathematical formula 1, and the interval d is set to a value that satisfies d<c / 2f and EDER>0.7.

[0010] [Formula 1]

[0011]

[0012] By setting the interval d so as to satisfy EDER>0.7, it is possible to suppress the difference between the output signals of the plurality of microphones from being buried in the self-noise.

[0013] Therefore, by reducing the distance d within a range satisfying EDER>0.7, the microphone device can be miniaturized while ensuring the voice recognition performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a front view of the microphone device according to the first embodiment.

[0015] Figure 2 It is a diagram for explaining a method of detecting an azimuth angle.

[0016] Figure 3 This is a diagram showing the relationship between the azimuth angle and the angular resolution.

[0017] Figure 4 It is a diagram for explaining a method of detecting an azimuth angle.

[0018] Figure 5 This is a diagram showing the relationship between the azimuth angle and the angular resolution.

[0019] Figure 6 is a graph showing the output signal of a microphone.

[0020] Figure 7 This is a graph showing the voltage difference of the output signal of the microphone.

[0021] Figure 8 This is a diagram showing the relationship between frequency and differential voltage efficiency.

[0022] Fig. 9 It is a diagram for explaining the required angular resolution.

[0023] Fig.10 This is a diagram showing the relationship between the microphone interval and the differential voltage efficiency.

[0024] Fig.11 This is a diagram showing the relationship between the microphone interval and the differential voltage efficiency.

[0025] Fig.12 This is a diagram showing the relationship between the microphone interval and the differential voltage efficiency. DETAILED DESCRIPTION

[0026] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals for description.

[0027] (First Embodiment)

[0028] A first embodiment is described. The microphone device of this embodiment is mounted on a vehicle and used for voice recognition operation. Figure 1 As shown, the microphone device includes a substrate 10 , a microphone 20 , and a signal processing unit 30 .

[0029] The substrate 10 is a rectangular plate-shaped member made of resin, etc. The microphone device is mounted on a vehicle by fixing the substrate 10 to an instrument panel, an overhead console, or the like.

[0030] The microphone 20 receives a sound wave and outputs a signal corresponding to the sound pressure of the received sound wave. As the microphone 20, a MEMS (Micro Electro Mechanical Systems) microphone or the like is used.

[0031] The microphone 20 is set to a microphone with a high SN ratio. Specifically, if the ratio of the output signal to the self-noise at 94 dBA and 1 kHz of the microphone 20 is defined in dB as the SN ratio MicSNR, the SN ratio MicSNR is set to be 70 dB or more, for example, 78 dB. In addition, the voltage corresponding to the LSB (least significant bit) of the ADC (analog-to-digital converter) 31 described later (hereinafter referred to as the LSB voltage) is set to be smaller than the output voltage generated by the self-noise of the microphone 20.

[0032] The microphone device includes a plurality of microphones 20. Specifically, if n is a natural number, the number of microphones 20 is 2. n Furthermore, the plurality of microphones 20 are arranged in an array along two directions or three directions that are inclined with respect to each other.

[0033] In this embodiment, eight microphones 20 are arranged on the substrate 10. Four of the eight microphones 20 are arranged at the corners of the substrate 10. The remaining four are arranged between the microphones 20 arranged at the corners of the substrate 10. That is, the eight microphones 20 are arranged in a rectangular shape.

[0034] The signal processing unit 30 processes the output signal of the microphone 20, and includes an ADC 31, a microcomputer 32, and an interface 33. The signal processing unit 30 is disposed in the center of the plurality of microphones 20 disposed in a rectangular shape.

[0035] The ADC 31 is used to convert the analog voltage signal outputted from the microphone 20 into a digital signal. The ADC 31 performs AD conversion on the output signal of the microphone 20. The digital signal generated by the ADC 31 is inputted to the microcomputer 32.

[0036] The microcomputer 32 performs sound enhancement processing or noise reduction processing based on the digital signal generated by the ADC 31 .

[0037] The interface 33 is used to connect the microphone device to other devices. The signal generated by the sound enhancement processing of the microcomputer 32 is transmitted to other devices via the interface 33.

[0038] The effect obtained by configuring the microphone 20 in a rectangular shape will be described. Figure 2 As shown, two adjacent microphones 20 among the eight microphones 20 are set as microphones 21 and 22. The interval between the microphones 21 and 22 is set as d. The azimuth angle of the arrival direction of the sound wave relative to the normal line of the surface of the substrate 10 is set as θ. Specifically, the azimuth angle θ is the azimuth angle of the operating seat relative to the substrate 10 and the plurality of microphones 20. c is set as the speed of sound. If the time difference of the signals detected by the microphones 21 and 22 is set as τ, then τ=(d / c)sinθ.

[0039] The change in the time difference of the output signals of the microphones 21 and 22 when the azimuth angle of the sound wave changes by Δθ relative to the azimuth angle θ is denoted as Δτ. According to τ+Δτ=1 / c·{dsin(θ+Δθ)}, Δτ=(d / c)·sin(θ+Δθ)-τ=(d / c){sin(θ+Δθ)-sinθ}.

[0040] For example, when Δθ=5°, the relationship between the azimuth angle θ and |Δτ| is as follows: Figure 3 As shown in . If Δθ is set as the minimum azimuth angle that the microphone device wants to detect, then Δτ becomes the quantity that expresses the angular resolution in the time domain. Figure 3 As shown, when θ=90°, Δτ≈0, that is, the angular resolution becomes approximately 0.

[0041] In the car cabin, the operator's voice is reflected by the interior walls of the car cabin and reaches the microphone device from various directions. Therefore, in order to determine the direction of the sound source to separate the operator's voice from noise and perform sound enhancement, it is necessary to make the angle resolution greater than 0.

[0042] In this embodiment, some of the plurality of microphones 20 are as follows: Figure 4 Shown along with Figure 2 The microphones 21 and 22 are arranged in different directions. Specifically, if the arrangement direction of the microphones 21 and 22 is set as a first direction, a part of the microphones 20 is arranged along a second direction perpendicular to the first direction.

[0043] Therefore, the characteristic of Δτ becomes Figure 5 That is, near θ = 90°, where the angular resolution of microphones 21 and 22 becomes 0, Figure 4 The angle resolution of the two microphones 20 shown is the largest, and the two Δτ characteristics are in a form that compensates for each other's angle resolution. Figure 5 In the figure, the solid line represents the Δτ in microphones 21 and 22, and the dotted line represents Figure 4 Δτ of microphone 20 is shown.

[0044] By arranging the plurality of microphones 20 along two axes inclined to each other in this manner, it is possible to obtain a characteristic in which the angular resolutions are compensated for each other, and it is possible to prevent the angular resolution of the entire microphone device from becoming zero.

[0045] Furthermore, by arranging the plurality of microphones 20 in a rectangular shape and arranging them along two orthogonal axes, it is possible to suppress the azimuth angle at which the angular resolution becomes extremely small and the effect of sound enhancement or noise suppression is reduced in all directions of 360°.

[0046] As described above, in the present embodiment, eight microphones 20 are arranged on the substrate 10. However, by providing at least three microphones 20 and arranging one microphone 20 at a position away from the straight line connecting the other two microphones 20, it is possible to suppress a decrease in angular resolution. Furthermore, by arranging the plurality of microphones 20 so that the straight line connecting the two microphones 20 is orthogonal to the straight line connecting the two microphones 20 including the other microphone 20, it is possible to suppress a decrease in angular resolution in all directions.

[0047] In addition, by providing at least four microphones 20, it is possible to arrange the plurality of microphones 20 in a rectangular shape, thereby suppressing the reduction in angular resolution. In addition, it is also possible to arrange the plurality of microphones 20 in three dimensions. For example, it is also possible to provide at least four microphones 20 and arrange one of the four microphones 20 at a position away from the plane passing through the other three microphones. When the microphones 20 are arranged in this way, it is also possible to suppress the reduction in angular resolution. In addition, when the microphones 20 are arranged in this way, it is possible to improve the detection capability.

[0048] The lower limit of the interval d is explained. Figure 6 As shown, the voltages of the output signals of the two microphones 20 generate a voltage difference ΔE corresponding to the time difference Δτ. If there is no noise in the output signal, the time difference Δτ can be detected based on the voltage difference ΔE. However, in reality, due to the electrical noise of the microphone 20 itself, noise is superimposed on the output signal. The inventors of the present invention have studied the relationship between the magnitude of the electrical noise of the microphone 20 and whether Δτ can be detected.

[0049] Assumption Figure 6 The two output signals shown are sinusoidal waves with amplitude A and frequency f. In this case, if the initial phase is ignored, the voltage difference ΔE becomes ΔE = Asin(2πft) - Asin{2πf(t-Δτ)} = 2Asin(πfΔτ)·cos{πf(2t-Δτ)} when time is set to t and pi is set to π. That is, the voltage difference ΔE is represented by a cosine function with an amplitude of 2Asin(πfΔτ).

[0050] When d = 6 mm, θ = 0°, Δθ = 3°, f = 1 kHz, and A = 1, Δτ = 0.91 μs. The voltage difference ΔE at this time is as follows Figure 7 In addition, regarding the amplitude, the decibel display is performed with the amplitude A being set to 0 dB as the reference.

[0051] Figure 7 The waveform shown is an ideal waveform without electrical noise. In the actual circuit, Figure 7 A certain amount of electrical noise is superimposed on the waveform shown. For example, when using a microphone 20 with an SN ratio of 60 dB, electrical noise with an effective amplitude of 0.001, i.e. -60 dB, is superimposed on the reference amplitude of the input signal input to the microphone 20, i.e. 1.00, i.e. 94 dBA. At this time, it is considered that Figure 7 In the waveform shown, the signal with an amplitude of -60 dB or less is buried in the electrical noise, and the time difference cannot be detected.

[0052] Here, the amplitude of the electrical noise that will serve as the reference is defined as the reference amplitude Ath, and the ratio of the time that the voltage difference ΔE becomes an amplitude greater than the reference amplitude Ath to the time of the entire signal is defined as the effective voltage difference EDER (Effective Delta-E Ratio). That is, when the period of the voltage difference ΔE is set to T1 and the length of time that ΔE becomes greater than the reference amplitude Ath in one period is set to T2, EDER = T2 / T1. For example, if the reference amplitude Ath is set to -60dB, T2 becomes Figure 7 EDER=100% indicates that the voltage difference ΔE can be fully detected, and EDER=0% indicates that the voltage difference ΔE is buried in noise and cannot be detected.

[0053] EDER becomes a function of frequency f, amplitude A, and SN ratio MicSNR. The lower the frequency f, and the larger the amplitude of the electrical noise, the smaller the EDER. For example, when d = 6 mm, θ = 0°, and Δθ = 3°, EDER becomes Figure 8 As shown.

[0054] In order to make EDER equal to or greater than 0, the amplitude must not be buried in the electrical noise of the microphone 20. In other words, 2Asin(πfΔτ)≥10^(-MicSNR / 20) must be satisfied. Here, the amplitude A is set to the relative effective voltage amplitude of the output signal of the microphone 20 when the voltage when receiving a sound of 94 dBA is set to 0 dB, that is, when the reference amplitude is 1.0.

[0055] Since EDER is represented by a cosine function, which is a periodic function, in order to find the ratio of the time when the amplitude is equal to or greater than a certain value, it is sufficient to find the ratio of the time in the interval from 0 to π / 2, for example. Let Amp>0, let Amp=|2Asin(πfΔτ)|, and let the phase angle at which |ΔE| becomes a certain voltage value Const be φ. Since Amp·cosφ=Const, φ=cos －1 (Const / Amp), so in the range of 0 to π / 2, EDER = cos －1 (Const / Amp) / (π / 2). Where, Const=10^(-MicSNR / 20), Amp≥Const. That is, EDER is defined by Mathematical Formula 1.

[0056] [Formula 1]

[0057]

[0058] In the experiment conducted by the present inventors, good performance was obtained when EDER>0.7. Therefore, the interval d that can achieve small specifications of the microphone device while obtaining good performance is a value that satisfies EDER>0.7.

[0059] In mathematical formula 1, frequency f is the lowest frequency of the frequency band that is the object of signal processing in the signal processing unit 30, and is set to f≥100 Hz, for example. When the vehicle is running, the low-frequency component of the noise entering the microphone 20 is very large, so in the voice recognition device, a filter for reducing the volume of the low-frequency band is provided to reduce the consumption of the dynamic range of the ADC. The lowest frequency f is the cutoff frequency of the filter. In mathematical formula 1, amplitude A is the relative effective voltage amplitude of the output signal of the microphone 20 when the amplitude of the signal output by the microphone 20 when receiving a sound of 94 dBA is set to 0 dB, that is, to the reference amplitude of 1.0. The effective voltage amplitude is calculated by 1 / √2×voltage amplitude.

[0060] It is desirable that the dynamic range of ADC31 is larger than the dynamic range of microphone 20. If the sound pressure at the rated maximum output of microphone 20 is set to MicMAX, the dynamic range of microphone 20 is (MicMAX-94)+MicSNR. In addition, if the number of conversion bits of ADC31 is set to m, the dynamic range of ADC31 is 20×log 10 (2 m-1). In addition, the dynamic range of ADC31 may also be smaller than the dynamic range of microphone 20. In this case, the MicSNR of mathematical formula 1 is replaced by the pseudo SN ratio of ADC31 calculated based on the dynamic range of ADC31. In addition, the dynamic range of ADC31 may also be equal to the dynamic range of microphone 20. The meaning that the dynamic range of ADC31 is larger than the dynamic range of microphone 20 is the same as the meaning that the LSB voltage of ADC31 is smaller than the self-noise of microphone 20. As mentioned above, in the present embodiment, the LSB voltage of ADC31 is smaller than the self-noise of microphone 20, but the LSB voltage of ADC31 may also be larger than the self-noise of microphone 20. In addition, the LSB voltage of ADC31 may also be equal to the self-noise of microphone 20.

[0061] Conventionally, microphones for voice recognition are arranged near the steering column, but in recent years they are arranged near the overhead console, the headliner, or other locations close to the mouths of passengers in the driver's seat or the front passenger seat.

[0062] Regarding Δθ, it is believed that if the size of a human face can be distinguished, the sound source can be separated and recognized. The distance between the substrate 10 and the operating seat, more specifically, the distance between the microphone 20 arranged on the substrate 10 and the operator's mouth is set to L [m]. The horizontal width of a human face is about 156 mm, so it is believed that when θ = 0°, if Δθ such as Δθ = arctan (0.078 / L) can be distinguished, noise can be reduced.

[0063] For example Fig. 9 As shown, when the distance L is about 0.3m, according to arctan (0.078 / 0.3) ≈ 13°, it is believed that if the direct sound of about ±13° can be distinguished, the noise can be reduced. In addition, when the distance L is about 0.4m, according to arctan (0.078 / 0.4) ≈ 11°, it is believed that if the direct sound of about ±11° can be distinguished, the noise can be reduced.

[0064] The relationship between the frequency f, the SN ratio MicSNR, and the lower limit of the interval d is, for example, Figure 10 to Figure 12 As shown. Figure 10 to Figure 12 These are graphs of EDER when f=400 Hz, 200 Hz, and 100 Hz, and θ=0° and Δθ=14°, respectively.

[0065] like Fig.10 As shown, in the case of f=400 Hz, EDER>0.7 is when MicSNR=54 dB, d>2.6 mm, and when MicSNR=44 dB, d>8.2 mm.

[0066] like Fig.11As shown, in the case of f=200 Hz, EDER>0.7 is when MicSNR=44 dB, d>17 mm, when MicSNR=54 dB, d>5.0 mm, and when MicSNR=64 dB, d>1.7 mm.

[0067] like Fig.12 As shown, in the case of f=100 Hz, EDER>0.7 is when MicSNR=44dB, d>33mm, when MicSNR=54dB, d>10mm, and when MicSNR=64dB, d>3.2mm.

[0068] Thus, EDER is defined by frequency f, SN ratio MicSNR, azimuth angle θ, minimum azimuth angle Δθ, and amplitude A. Furthermore, by finding the condition of interval d that satisfies EDER>0.7, the interval d can be reduced within a range that ensures the performance of the microphone device, thereby miniaturizing the microphone device.

[0069] The upper limit of the interval d is explained. The larger the interval d is, the more the directivity of the microphone device can be improved. On the other hand, when the interval d exceeds 1 / 2 of the wavelength of the sound of the frequency f, spatial aliasing occurs. That is, if the wavelength of the sound of the frequency f input to the microphone 20 is set to λ, spatial aliasing occurs when d>λ / 2=(c / f)·(1 / 2). Therefore, it is desirable to set the interval d to a value that satisfies d<c / 2f.

[0070] Humans can hear sounds at around 20Hz to 20kHz, but the ITU-T (International Telecommunication Union-Telecommunication sector) stipulates that the frequency band for telephones is 300Hz to 3.4kHz. Therefore, in order to maintain voice recognition performance, it is desirable to set the upper limit of the frequency f to 3.4kHz and within the range of the frequency f, d < c / 2f.

[0071] If Celsius temperature is deg_c, c=331.5+0.61×deg_c, and c≈347 m / s at room temperature, for example, 25° C. At this time, the maximum value of the interval d that can suppress spatial aliasing at a frequency f up to 3.4 kHz is 347 [m / s] / 3.4 [kHz]×1 / 2≈51 [mm].

[0072] In addition, in reality, sound includes a wide frequency band, and the direction of arrival of the sound is determined not by using a single frequency but by using the frequency bands above and below it. Therefore, the interval d may not satisfy d<λ / 2. However, it is desirable to suppress the occurrence of spatial aliasing in the frequency band containing a large amount of sound information.

[0073] In order to achieve miniaturization while maintaining the performance of the microphone device, it is desirable to make EDER close to 0.7. For example, it is desirable to set the interval d so that 0.8>EDER.

[0074] Regarding the upper and lower limits of the interval d, the interval d between at least one pair of adjacent microphones 20 may satisfy the above conditions. That is, in some microphones 20, the interval d may not satisfy the above conditions.

[0075] As described above, in this embodiment, by setting the interval d so as to satisfy EDER>0.7, it is possible to suppress the difference between the output signals of the plurality of microphones from being buried in the self-noise. Therefore, by reducing the interval d within the range satisfying EDER>0.7, it is possible to miniaturize the microphone device while ensuring the voice recognition performance.

[0076] Furthermore, according to the above-described embodiment, the following effects can be obtained.

[0077] (1) At least three microphones 20 are provided, and one microphone 20 is disposed at a position away from a straight line connecting the other two microphones 20. This can suppress a decrease in angular resolution.

[0078] (2) The straight line connecting the two microphones 20 is perpendicular to the straight line connecting the two microphones 20 including the other microphone 20. This can suppress a decrease in angular resolution.

[0079] (3) The signal processing unit 30 is disposed in the center of the plurality of microphones 20 arranged in a rectangular shape. This can prevent the substrate 10 from becoming larger.

[0080] (4) The number of microphones 20 is 2 n In the case of digital processing, if the number of data is set to a power of 2, there will be no wasted bits when expressing it in binary, and processing can be performed efficiently using the same storage capacity and communication bandwidth resources.

[0081] (5) The microphone 20 is a MEMS microphone. This allows the microphone 20 to be small, inexpensive, and have less variation in characteristics than when the microphone 20 is a dynamic microphone, a condenser microphone, an ECM (Electret Condenser Microphone), or the like.

[0082] (Other Embodiments)

[0083] In addition, the present disclosure is not limited to the above-mentioned embodiments and can be appropriately changed. In addition, in the above-mentioned embodiments, the elements constituting the embodiments are not necessarily necessary elements, except for the cases where it is specifically stated that they are necessary and the cases where it is considered to be obviously necessary in principle. In addition, in the above-mentioned embodiments, when referring to the number, value, amount, range and other numerical values ​​of the constituent elements of the embodiments, except for the cases where it is specifically stated that they are necessary and the cases where it is considered to be obviously limited to a specific number in principle, it is not limited to the specific number. In addition, in the above-mentioned embodiments, when referring to the shape, positional relationship, etc. of the constituent elements, etc., except for the cases where it is specifically stated that they are necessary and the cases where it is considered to be obviously limited to a specific shape, positional relationship, etc. in principle, it is not limited to the shape, positional relationship, etc.

Claims

1. A microphone device, characterized in that: The microphone device includes a plurality of microphones. The interval between two microphones among the plurality of microphones is set to d, The SN ratio of the microphone is set to MicSNR. Let the speed of sound be c, Set the frequency of the processing object to f, The azimuth angle of the operating seat relative to the plurality of microphones is set to θ, The minimum azimuth angle to be detected is set to Δθ. The voltage amplitude of the output signal of the microphone is set to A, based on the output voltage when receiving a sound of 94 dBA. Let Δτ=d / c{sin(θ+Δθ)-sinθ}, The differential voltage efficiency EDER is defined by equation 1: At this time, the interval d is set to a value satisfying d<c / 2f and EDER>0.7: [Formula 1] 2. The microphone device according to claim 1, characterized in that: The interval d is set to a value satisfying d<c / 2f and EDER>0.7 when f≤3.4 kHz.

3. The microphone device according to claim 1, characterized in that: The distance between the microphone and the operating seat is set to L [m], The interval d is set to a value satisfying d<c / 2f and EDER>0.7 when θ=0° and Δθ=arctan(0.078 / L).

4. The microphone device according to claim 3, characterized in that: The interval d is set to a value satisfying d<c / 2f and EDER>0.7 when L=0.3 m.

5. The microphone device according to claim 1, characterized in that: The interval d is set to a value satisfying d<c / 2f and EDER>0.7 when MicSNR≥70 dB.

6. The microphone device according to claim 1, characterized in that: The microphone device is mounted on a vehicle for voice recognition. The interval d is set to a value satisfying d<c / 2f and EDER>0.7 when f≥100 Hz.

7. The microphone device according to any one of claims 1 to 6, characterized in that: The microphone device comprises at least three microphones. One of the microphones is disposed at a position away from a straight line connecting the other two microphones.

8. The microphone device according to claim 7, characterized in that: A straight line connecting the two microphones is perpendicular to a straight line connecting the two microphones including another one of the microphones.

9. The microphone device according to claim 8, characterized in that: The microphone device comprises at least four microphones. The plurality of microphones are arranged in a rectangular shape.

10. The microphone device according to claim 9, characterized in that: The microphone device includes a signal processing unit disposed in the center of the plurality of microphones arranged in the rectangular shape.

11. The microphone device according to any one of claims 1 to 6, characterized in that: Let n be a natural number, The number of microphones is 2 n .

12. The microphone device according to claim 11, characterized in that The microphone device includes eight microphones.

13. The microphone device according to any one of claims 1 to 6, characterized in that: The microphone device comprises at least four microphones. One of the four microphones is disposed at a position away from a plane passing through the other three microphones.

14. The microphone device according to any one of claims 1 to 6, characterized in that: The microphone is a MEMS microphone.

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