Microphone system

Abstract

The invention provides a microphone system. The microphone position determination method is a method for determining the positions of a plurality of microphones (11) in a microphone array (1) having the plurality of microphones (11) arranged in a plurality of concentric circles. The microphone position determination method comprises: a constraint condition acquisition step for acquiring a constraint condition including the maximum number of the plurality of microphones (11); and a selection step for selecting, from among a plurality of combinations of the number of microphones (11) included in each of the plurality of concentric circles and the radius of each of the plurality of concentric circles, a combination indicating a directivity characteristic that has the smallest difference from a target value of the directivity characteristic of the microphone array (1), wherein the plurality of combinations satisfy the constraint condition.

Description

[0001] This application is a divisional application of the Chinese Invention Patent Application No. 202010830053.1, with the title of "Microphone position determination method and microphone system", filed on August 18, 2020. TECHNICAL FIELD

[0002] The present application relates to a method of determining positions of a plurality of microphones in a microphone array including the plurality of microphones and a microphone system including the microphone array. BACKGROUND

[0003] Conventionally, a microphone array installed in a conference room or the like is known. In the conventional microphone array disclosed in US Patent 9565493, a plurality of microphones are disposed on a plurality of concentric circles. SUMMARY

[0004] Problem to be solved by the invention

[0005] The configuration of the microphones in the conventional microphone array is determined by the experience and intuition of the designer. Therefore, the difference between the main lobe and the side lobe in the directivity characteristic of the microphone array is not enough, and improvement in directivity is required.

[0006] The present application focuses on this point, and the object of the present application is to improve the directivity of the microphone array.

[0007] Solution for solving the problem

[0008] The microphone position determination method according to the first aspect of the present application is a method for determining positions of a plurality of microphones in a microphone array having the plurality of microphones configured in a plurality of concentric circles.

[0009] The microphone position determination method includes a constraint condition acquisition step for acquiring a constraint condition including a maximum number of the plurality of microphones, and a selection step for selecting, from a plurality of combinations of (i) the number of microphones included in each of the plurality of concentric circles and (ii) the radius of each of the plurality of concentric circles, a combination representing a directivity characteristic having a minimum difference from a target value of a directivity characteristic of the microphone array, wherein the plurality of combinations satisfy the constraint condition.

[0010] The selection step can include selecting, by using a variable vector including the number of microphones included in each of the plurality of concentric circles and the radius of each of the plurality of concentric circles as a mutation vector used in a differential evolution algorithm, the combination of the number of microphones included in each of the plurality of concentric circles and the radius of each of the plurality of concentric circles representing the directivity characteristic having the minimum difference from the target value.

[0011] The constraint acquisition step can include acquiring the number of the plurality of sound source positioning microphones for specifying the direction of a sound source as one of the constraints. The constraint acquisition step can include acquiring the radius of an outermost one of the plurality of concentric circles as one of the constraints. The constraint acquisition step can include acquiring the number of microphones included in each of the plurality of concentric circles as three or more as one of the constraints.

[0012] The constraint acquisition step can include acquiring a target value of a directivity characteristic corresponding to a difference between the size of a main lobe and the size of a side lobe of sensitivity to an input sound signal as one of the constraints.

[0013] The selection step can include setting a vector including the number of the plurality of concentric circles configured with the plurality of microphones, the radius of each of the plurality of concentric circles, and the number of the microphones configured in each of the plurality of concentric circles as variables as an initial variable vector, calculating an initial objective function value which is a value indicating an error between an ideal value of a directivity characteristic of the microphone array and the directivity characteristic of the microphone array calculated using the initial variable vector, determining a plurality of update variable vectors different from the initial variable vector, calculating a plurality of update objective function values which are values indicating an error between an ideal value of a directivity characteristic of the microphone array and the directivity characteristic of the microphone array calculated using the plurality of update variable vectors, and selecting a combination of positions of the plurality of microphones corresponding to a minimum objective function value from among the initial objective function value and the plurality of update objective function values.

[0014] The microphone system according to the second aspect of the present application is a microphone array having a plurality of microphones configured on a plurality of concentric circles, wherein a variation amount of a difference between radii of two concentric circles adjacent to each other among the plurality of concentric circles does not monotonously increase according to a distance from a center position of the plurality of concentric circles, and an attenuation amount of a side lobe with respect to a main lobe in a directivity characteristic is equal to or greater than 10 dB.

[0015] The plurality of microphones can include a plurality of positioning microphones disposed at the center position and a plurality of positions on an innermost one of the plurality of concentric circles closest to the center position and for specifying a direction of a sound source, and a plurality of beamforming microphones disposed on the plurality of concentric circles and for collecting sound generated from a sound source specified by the plurality of positioning microphones.

[0016] Three or six of the plurality of microphones can be disposed equidistantly on the innermost concentric circle. A distance between two of the plurality of positioning microphones adjacent to each other can be less than or equal to half of a minimum wavelength of sound in a frequency band used to specify the direction of the sound source. The distance between the two positioning microphones can be less than or equal to 42.5 mm.

[0017] Some of the plurality of microphones can be disposed at intersections of at least one straight line passing through centers of the plurality of concentric circles and each of the plurality of concentric circles.

[0018] The microphone system described above can further include an audio processing section configured to process sound signals output from the microphone array, wherein the audio processing section can include a direction specifying section configured to specify a direction of a sound source based on a plurality of sound signals input from the plurality of positioning microphones, and a sound output section configured to output sound synthesized by weighting each of a plurality of sounds input to the plurality of beamforming microphones based on the direction of the sound source specified by the direction specifying section.

[0019] Effects of the invention

[0020] According to the present application, an effect of making it less likely for the microphone array to collect unnecessary sound is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1A and 1B Each shows an outline of a microphone system.

[0022] Figure 2 A structure of a microphone array is shown.

[0023] Figure 3 A structure of an audio processing section is shown.

[0024] Figure 4 is a flowchart showing an outline of a determination method of a configuration of a plurality of microphones.

[0025] Figure 5 A model used in the present search example is shown.

[0026] Figure 6 A directivity characteristic of a microphone array of the first search example is shown.

[0027] Figure 7 A directivity characteristic of a microphone array of the comparative example is shown.

[0028] Figure 8 A directivity characteristic of a microphone array of the second search example is shown.

[0029] Figure 9 The directivity characteristic of the microphone array in the third search example is shown. DETAILED DESCRIPTION

[0030] [Outline of the microphone system S]

[0031] Figure 1A and 1B The outline of the microphone system S is shown respectively. Figure 2 The structure of the microphone array 1 is shown. The microphone system S includes the microphone array 1 and the audio processing section 2, and is a system for collecting voices generated by a plurality of speakers H (H-1 to H-4 in Figure 1A and 1B in a space such as a conference room or a hall. The microphone system S need not include the audio processing section 2, and can be connected to a computer that performs audio processing.

[0032] As shown by the black circles in Figure 2 The microphone array 1 includes a plurality of microphones 11, and is installed on a ceiling, a wall surface, or a floor of a space where the speakers H stay. The microphone array 1 inputs a plurality of sound signals to the audio processing section 2 based on voices input to the plurality of microphones 11.

[0033] The audio processing section 2 is a device that processes sound signals output from the microphone array 1 (i.e., a plurality of sound signals output from the plurality of microphones 11). The audio processing section 2 specifies a direction toward a position where a speaker H (i.e., a sound source) who is speaking is located by analyzing sound signals input from the microphone array 1. Further, the audio processing section 2 performs a beamforming process by adjusting weight coefficients of a plurality of sound signals corresponding to the plurality of microphones 11 based on a direction toward the speaker H who is speaking, and makes the sensitivity to a voice generated by the speaker H higher than the sensitivity to sound from other directions than the direction toward the speaker H.

[0034] Figure 1A A state in which the speaker H-2 is speaking is shown. Figure 1B A state in which the speaker H-3 is speaking is shown. In the state shown in Figure 1A The audio processing section 2 performs a beamforming process so that a main lobe in the directivity characteristic of the microphone array 1 is directed toward the speaker H-2. In this case, the audio processing section 2 synthesizes a plurality of sound signals, for example, by assigning a larger weight to a sound signal output from a microphone 11 at a position near the speaker H-2 than a weight assigned to a sound signal output from the other microphones 11. In Figure 1BIn the state shown, the audio processing unit 2 performs beamforming processing so that the main lobe of the directional characteristic of the microphone array 1 points towards the speaker H-3. In this case, the audio processing unit 2 synthesizes multiple audio signals, for example, by assigning a greater weight to the audio signal output from the microphone 11 at a position near the speaker H-3 than to the audio signals output from other microphones 11.

[0035] In the microphone array 1, a plurality of microphones 11 are configured such that, due to the beamforming processing performed by the audio processing unit 2, the difference between the main lobe and the side lobe in the directivity characteristic is equal to or greater than 10 dB. Next, the structure of the microphone array 1 and the method for determining the configuration of the plurality of microphones 11 will be described in detail.

[0036] [Structure of Microphone Array 1]

[0037] like Figure 2 As shown by the black circle in the diagram, microphone array 1 includes multiple microphones 11 arranged on multiple (e.g., more than four) concentric circles. In microphone array 1, multiple microphones 11 are arranged for each of the four concentric circles C1, C2, C3, and C4. Concentric circle C1 is the innermost concentric circle, and three microphones 11 are arranged on concentric circle C1. The three microphones 11b (11b-1, 11b-2, and 11b-3) arranged on concentric circle C1 serve as: (i) a sound source localization microphone 11 for specifying the direction toward the location of the speaker H, which is the sound source; and (ii) a beamforming microphone 11 for collecting the speech produced by the speaker H.

[0038] Concentric circle C2 is the second concentric circle from the inside, and four microphones 11c are arranged on concentric circle C2. Concentric circle C3 is the third concentric circle from the inside, and seven microphones 11d are arranged on concentric circle C3. Concentric circle C4 is the outermost concentric circle. Seventeen microphones 11e are arranged on concentric circle C4. The microphones 11 arranged on concentric circles C2, C3, and C4 are used as beamforming microphones 11. It should be noted that in Figure 2 In the figure, among the multiple microphones 11c, 11d and 11e, only the microphone 11 arranged on the straight line L is marked with reference numerals.

[0039] As detailed below, the radii of the four concentric circles C1, C2, C3, and C4, as well as the number and position of the microphones 11 included in each concentric circle, are determined by searching for optimal pointing characteristics. As a result, the amount of variation in the difference between the radii of any two adjacent concentric circles in the four concentric circles C1, C2, C3, and C4 is determined such that this amount of variation does not monotonically increase with respect to the distance from the center positions of the multiple concentric circles.

[0040] Specifically, inFigure 2 In the illustrated microphone array 1, the radius of the concentric circle C1 is 0.03856 [m], the radius of the concentric circle C2 is 0.10660 [m], the radius of the concentric circle C3 is 0.14024 [m], and the radius of the concentric circle C4 is 0.21500 [m]. The difference between the radii of the concentric circles C1 and C2 is 0.06804 [m], the difference between the radii of the concentric circles C2 and C3 is 0.03364 [m], and the difference between the radii of the concentric circles C3 and C4 is 0.07476 [m], and these differences do not monotonously increase according to the distance from the center position of the concentric circles. In addition, the amount of attenuation of the side lobe with respect to the main lobe in the directivity characteristic of the microphone array 1 is -14.8 dB, and sufficient directivity is achieved. As described in detail below, since the configuration of the plurality of microphones 11 is determined by using an algorithm for searching for an optimal configuration of the plurality of microphones 11, the microphone array 1 has such a good directivity characteristic.

[0041] Among the plurality of microphones 11 included in the microphone array 1, (i) the microphone 11a configured at the center position of the plurality of concentric circles and (ii) the three microphones 11b (11b-1, 11b-2, and 11b-3) arranged at equal intervals on the innermost concentric circle C1 closest to the center position are used as a plurality of sound source positioning microphones 11 for specifying the position of a sound source. The other microphones 11 included in the microphone array 1 are used as a plurality of beamforming microphones 11 for collecting sound produced from a sound source at a position specified by the sound source positioning microphones 11. The microphone 11a and the microphones 11b-1 to 11b-3 can also be used as beamforming microphones 11. In other words, the microphone 11a and the microphones 11b-1 to 11b-3 can serve two purposes: sound source positioning and beamforming.

[0042] The distance between two sound source positioning microphones 11 adjacent to each other among the plurality of microphones 11 used as sound source positioning microphones 11 is less than or equal to half the minimum wavelength of sound in a frequency band for specifying the direction toward the position where the speaker H as a sound source is located. Since aliasing does not occur in the case where the distance between two sound source positioning microphones 11 is set in this way, the estimation accuracy in the direction toward the speaker H is improved.

[0043] In a case where the frequency range including the main frequency component of the voice of the assumed speaker H is equal to or higher than 500 Hz and equal to or lower than 4000 Hz, the distance D between the two sound source positioning microphones 11 adjacent to each other is preferably 42.5 mm or less because the wavelength of sound at a frequency of 4000 Hz is 85 mm. In a case where the frequency range including the main frequency component of the voice of the assumed speaker H is equal to or higher than 500 Hz and equal to or lower than 5000 Hz, the distance D is preferably 34 mm or less because the wavelength of sound at a frequency of 5000 Hz is 68 mm. It should be noted that if the distance D is too small, the difference of the sounds entering the respective sound source positioning microphones 11 becomes too small, for which reason the distance D is preferably, for example, 30 mm or more and 40 mm or less.

[0044] In addition, some of the microphones 11 are provided at a plurality of intersection points at which at least one straight line L passing through the centers of the plurality of concentric circles C1, C2, C3, and C4 intersects the respective concentric circles C1, C2, C3, and C4. Figure 2 In the example shown, the microphones 11a, 11b-1, 11c, 11d, and 11e are configured on the same straight line L. That is, one of the microphones 11 configured on the concentric circle C1, one of the microphones 11 configured on the concentric circle C2, one of the microphones 11 configured on the concentric circle C3, and one of the microphones 11 configured on the concentric circle C4 are configured on the same straight line L as one of the microphones 11 configured on the other concentric circles.

[0045] Since the microphone array 1 is constituted in this way, the accuracy of the audio processing to enhance the directivity toward the direction of the speaker H is improved, and the load of the audio processing is reduced. In addition, since the positional relationship of the plurality of microphones 11 becomes clearer, the accuracy of specifying the direction toward the speaker H is improved.

[0046] [Structure of the audio processing section 2]

[0047] Figure 3 The structure of the audio processing section 2 is shown. The audio processing section 2 includes an AD converter 21, an AD converter 22, a direction specifying section 23, and a sound output section 24.

[0048] The AD converter 21 converts a plurality of sound signals based on the sounds entering the plurality of sound source positioning microphones 11 into a plurality of sound source positioning digital data. The AD converter 21 inputs the converted sound source positioning digital data to the direction specifying section 23. The AD converter 22 converts a plurality of sound signals based on the sounds entering the plurality of beamforming microphones 11 Figure 3The AD converter 22 converts the plurality of sound signals of the sound of the "BF" in FIG. 1 into a plurality of beamforming digital data. The AD converter 22 inputs the converted beamforming digital data to the sound output section 24. The AD converter 21 and the AD converter 22 can be constituted by a plurality of devices, or can be constituted by a single device.

[0049] The direction specifying section 23 specifies a direction toward a position where the speaker H as a sound source is located on the basis of the plurality of sound signals input from the plurality of sound source positioning microphones 11. Specifically, the direction specifying section 23 specifies a direction toward the speaker H on the basis of the plurality of sound source positioning digital data input from the AD converter 21. The direction specifying section 23 specifies a direction toward the speaker H, for example, on the basis of a relationship between the loudness of the sound each of the plurality of sound source positioning digital data represents. The direction specifying section 23 notifies the sound output section 24 of the direction toward the speaker H specified.

[0050] The sound output section 24 outputs a sound synthesized by weighting each of the plurality of sounds input to the beamforming microphones 11 on the basis of the direction toward the speaker H specified by the direction specifying section 23. Specifically, the sound output section 24 generates a plurality of multiplied values by multiplying each of the plurality of beamforming digital data corresponding to each of the microphones 11 by a weight coefficient determined on the basis of the direction toward the position where the speaker H who is speaking is located, and adds the plurality of multiplied values generated, thereby outputting the synthesized sound. For example, the absolute value of the weight coefficient for the microphone 11 at the position corresponding to the direction toward the speaker H is set to a value larger than the absolute value of the weight coefficient for the microphone 11 at the other positions. Since the direction specifying section 23 and the sound output section 24 operate in this way, the reproducibility of the sound produced by the speaker H is improved regardless of the direction toward the position where the speaker H is located.

[0051] Since the directivity characteristic of the microphone array 1 differs depending on the configuration of the plurality of microphones 11, the quality of the sound synthesized by the sound output section 24 is affected by the configuration of the plurality of microphones 11. Next, a method of determining the configuration of the plurality of microphones 11 for improving the quality of the sound synthesized by the sound output section 24 will be described in detail.

[0052] [Outline of the method of determining the configuration of the plurality of microphones 11]

[0053] Figure 4 is a flowchart showing an outline of the method of determining the configuration of the plurality of microphones 11. As an example, the configuration search device has a computer, and determines the configuration of the plurality of microphones 11 by executing a program, utilizing the microphone position determination method shown in the flowchart of Figure 4 the plurality of microphones 11 by executing the program, utilizing the microphone position determination method shown in the flowchart of Figure 4The configuration search device determines the optimal configuration of the plurality of microphones 11 with the sound source in a certain direction, for example, by using a least squares method. The configuration search device determines the configuration of the plurality of microphones 11 that fits as many directions in which the sound sources are located as possible.

[0054] Hereinafter, the process in which the configuration search device determines the configuration of the plurality of microphones 11 will be described with reference to the flowchart shown in FIG. 6. The configuration search device determines the configuration of the plurality of microphones 11 by using, for example, a differential evolution (DE) method as a differential evolution algorithm or a JADE method as an improved DE method. Figure 4

[0055] To determine the configuration of the plurality of microphones 11, the configuration search device first acquires constraint conditions (step S1). For example, the configuration search device displays a screen for inputting the constraint conditions on a display and acquires the constraint conditions input on the screen.

[0056] The configuration search device acquires, for example, the maximum number of the plurality of microphones 11 as one of the constraint conditions. The configuration search device can acquire the number of the sound source positioning microphones 11 and the radius of the outermost one of the plurality of concentric circles as one of the constraint conditions. Since the configuration search device acquires these constraint conditions, it is possible to shorten the time for determining the configuration of the plurality of microphones 11 that satisfies the size and cost requirements of the microphone array 1. The configuration search device can acquire the number of the microphones 11 included in each of the plurality of concentric circles as one of the constraint conditions. By having three or more microphones 11 in one concentric circle, it is possible to reduce the change in the directivity characteristic due to the direction of the sound source.

[0057] Subsequently, the configuration search device acquires a target value of the directivity characteristic of the microphone array 1 (step S2). The directivity characteristic of the microphone array 1 is represented by a value corresponding to the difference between (i) the size of the main lobe of the sensitivity to the input sound signal and (ii) the size of the side lobe of the sensitivity to the input sound signal. For example, the directivity characteristic of the microphone array 1 is represented as the amount of attenuation of the side lobe with respect to the main lobe in the case where a predetermined sound is input to the microphone array 1. For example, the configuration search device displays a screen for inputting the target value on a display and acquires the target value input on the screen.

[0058] ​Next, the configuration search device determines an initial variable vector for starting the search for the optimal configuration of the plurality of microphones 11 by using the JADE method (step S3). For example, the configuration search device sets a vector including the number of the concentric circles in which the microphones 11 are arranged, the radius of each concentric circle, and the number of the microphones 11 in each concentric circle as variables to the initial variable vector.

[0059] Subsequently, the configuration search device calculates a value of the objective function in the case where the determined initial variable vector is used (i.e., an initial objective function value) (step S4), and temporarily stores the calculated value of the objective function in association with the initial variable vector as a reference function value (step S5). The value of the objective function is a value indicating the error between the ideal value of the directivity characteristic of the microphone array 1 and the directivity characteristic of the microphone array 1 calculated using the initial variable vector. The smaller the value of the objective function, the better the directivity characteristic.

[0060] Next, the configuration search device determines an update variable vector (step S6). The update variable vector is a variable vector that changes at least one of the variables included in the initial variable vector. The configuration search device determines the update variable vector by setting at least one of (i) the number of the concentric circles in which the microphones 11 are arranged, (ii) the radius of each concentric circle, and (iii) the number of the microphones 11 in each concentric circle to a value different from that of the initial variable vector. The configuration search device uses, for example, a differential evolution algorithm when determining the update variable vector.

[0061] The configuration search device uses, as the update variable vector, a variable vector including, for example, the number of the microphones 11 included in each of the plurality of concentric circles and the radius of each of the plurality of concentric circles, which is a mutant vector used in the differential evolution algorithm. The configuration search device selects, from a plurality of combinations of (i) the number of the microphones 11 included in each of the plurality of concentric circles and (ii) the radius of each of the plurality of concentric circles, a combination indicating the directivity characteristic having the smallest difference from the target value of the directivity characteristic, from among the plurality of combinations that satisfy the constraint condition.

[0062] Specifically, the configuration search device first calculates the objective function value in the case where the update variable vector is used (step S7). The configuration search device compares the calculated objective function value with the objective function value stored in step S5 (step S8). In the case where the calculated objective function value is equal to or greater than the stored reference function value (YES in step S8), the configuration search device causes the configuration determination processing to proceed to step S10. In the case where the calculated objective function value is smaller than the stored objective function value (NO in step S8), the configuration search device stores the calculated objective function value (i.e., the update objective function value) in association with the update variable vector as a new reference function value (step S9).

[0063] Next, the configuration search device determines whether the objective function value has been calculated a predetermined number of times (step S10). That is, the configuration search device determines whether the objective function value has been calculated for a predetermined number of variable vectors. The predetermined number of times is, for example, a number of times set by the designer of the microphone array 1. In the case where the objective function value has been calculated the predetermined number of times (YES in step S10), the configuration search device determines the configuration represented by the variable vector stored in association with the reference function value as the configuration of the plurality of microphones 11, and ends the processing.

[0064] In the case where the number of times of the objective function value calculation has not reached the predetermined number of times (NO in step S10), the configuration search device causes the configuration determination processing to return to step S6. By executing the selection steps of steps S7 to S10 in this way, the configuration search device selects the optimal combination of pointing characteristics representing the smallest difference from the target value of the pointing characteristics from among a plurality of combinations of positions of the microphones 11, which satisfy the constraint condition (step S11), from among the plurality of combinations. That is, the configuration search device selects the combination of positions of the plurality of microphones 11 corresponding to the smallest objective function value from among the initial objective function value and the plurality of update objective function values.

[0065] [Search example of optimal configuration using JADE method]

[0066] The following describes an example in which the optimal configuration of the plurality of microphones 11 is searched for using the JADE method. The following design processing is performed by executing a program by the configuration search device that executes the flowchart of FIG. 10. Figure 4 In the JADE method, an algorithm for enhancing the global searchability of the DE method is used for automatically adjusting the parameters for each problem. Therefore, even for a problem such as a problem in which there is a multi-peak objective function in determining the configuration of the plurality of microphones 11, the configuration search device can achieve good search by using the JADE method.

[0067] Figure 5 A model used in the present search example is shown. As shown in FIG. 11, the model is a rectangular parallelepiped having a length of 2 m, a width of 2 m, and a height of 2 m. Figure 5As shown, in a space where positions are defined by an x-axis, a y-axis, and a z-axis, a sound source that is a premise of searching for an optimal configuration of the plurality of microphones 11 is angled at θ from the x-axis in the xy plane, and is angled at Φ from the xy plane to the z-axis. That is, the configuration search device searches for a configuration of the plurality of microphones 11 in which directivity becomes optimal in a case where the microphone array 1 receives sound from a sound source that is located in the (θ, Φ) direction with respect to the origin.

[0068] Assume that the total number of the concentric circles is P, and the radius of each concentric circle is r p , and the number of the microphones 11 arranged in each concentric circle is M p (p = 1, 2,..., P). If the distance between the sound source and the microphone array 1 is sufficiently large with respect to the radius r P of the largest concentric circle, the sound signal generated by the sound source is considered to be a plane wave in the vicinity of the microphone array 1. In this case, the sound reception signal z pm (n) of the m-th microphone 11 on a certain concentric circle p can be based on the sound reception signals z p,xaxis (n) of the microphones 11 on the x-axis of each concentric circle, the time difference of arrival τ pm (θ, Φ) is expressed by the following equation.

[0069] [Equation 1]

[0070]

[0071] [Equation 2]

[0072]

[0073] [Equation 3]

[0074]

[0075] Here, c is the speed of sound. In this case, the directivity G(θ, Φ, ω k ) corresponding to the size of the main lobe of the microphone array 1 can be expressed by the following equation.

[0076] [Equation 4]

[0077]

[0078] The delay and the weight coefficient w * pm,k of the beamformer can be expressed by the following equation.

[0079] [Equation 5]

[0080]

[0081] The design problem related to the optimal configuration of multiple microphones 11 can be replaced by searching for the desired directivity D(θ,Φ,ω) that can be obtained and used as the target value. k The close directivity G(θ,Φ,ω) k The issue lies in the configuration of microphone 11. The error E(θ,Φ,ω) used during the search... k It can be expressed by the following formula.

[0082] [Formula 6]

[0083] E(θ, φ, ω) k )=|D(θ,φ,ω k )-G(θ,φ,ω k )|

[0084] The optimal configuration can be specified by obtaining a variable vector that minimizes the maximum error over the approximation band, as shown in the following equation.

[0085] [Formula 7]

[0086]

[0087] Here, in order to obtain the variable vector that minimizes the maximum error using the JADE method, the search device is configured to first initialize N solution groups X with uniformly random numbers over the domain of the search space. i (i = 1, 2, ..., N), and calculate the objective function value for each individual. Configure the search device to generate differentially mutated individuals, sub-individuals, and evolved individuals up to a maximum generation number I, and search for the minimum solution of the objective function.

[0088] To make the JADE method applicable to microphone configuration design problems, the variable vector x is defined as follows:

[0089] [Formula 8]

[0090] x = [M1, ..., M] P r1, ..., r P ] T Here, to ensure that the configuration is not determined to be impossible, the number of microphones 11 is kept at the maximum achievable number M. max The constraints within are defined as follows:

[0091] [Formula 9]

[0092]

[0093] In the microphone system S, sound source localization processing is performed before beamforming processing. Therefore, when determining the configuration of multiple microphones 11, the configuration of the sound source localization microphones 11 must also be considered. In order to... Figure 2One concentric circle is configured at the center position of the concentric circles and three or six sound source positioning microphones 11 are configured in the innermost concentric circle C1, and the following constraint condition is added:

[0094] [Formula 10]

[0095] M1 = 1, M2 = {3, 6}, v = {1, 2},

[0096] When the maximum radius of the outermost concentric circle is R max , the constraint condition for the radius r p of each concentric circle is expressed as follows:

[0097] [Formula 11]

[0098] r1 = 0, r P = R max , r p-1 < r p

[0099] In this case, the variable vector x' to be obtained is expressed as follows:

[0100] [Formula 12]

[0101] x' = [1, M2,..., M P , 0, r2,..., r p-1 , R max ] T

[0102] Therefore, as shown below, the design problem of configuring a plurality of microphones 11 is formulated as a mixed integer programming problem:

[0103] [Formula 13]

[0104] min δ, sub. to E(θ s , φ s , ω k ) ≤ δ

[0105] [Formula 14]

[0106] r p-1 < r p , M2 = {3, 6}, v = {1, 2}

[0107] [Formula 15]

[0108] v = {1, 2},

[0109] Here, θ s and Φs s = 1,..., S) denotes a discrete direction, and δ denotes a maximum error in the approximation band of Equation 6. In searching for the optimal configuration by the JADE method, the following enlarged objective function f(x') using this δ is utilized.

[0110] [Equation 16]

[0111]

[0112] Here, λ u (x') (u = 1,..., 4) denotes a penalty function. λ1(x') is a penalty function for limiting the maximum number of microphones 11.

[0113] [Equation 17]

[0114]

[0115] [Equation 18]

[0116]

[0117] λ2(x') is a penalty function for the number of sound source positioning microphones 11.

[0118] [Equation 19]

[0119]

[0120] λ3(x') is a penalty function for preventing the number of microphones 11 configured in each concentric circle from being 2 or less.

[0121] [Equation 20]

[0122]

[0123] λ4(x') is a penalty function for arranging the radii in ascending order. α > 0 is a constant for preventing the difference between the radii of adjacent concentric circles from being 0.

[0124] [Equation 21]

[0125]

[0126] [First Search Example]

[0127] In this search example, Φ L = 0 [rad] for simplicity. The desired directivity D(θ, ω k ) is set as shown in the following equation.

[0128] [Equation 22]

[0129]

[0130] Here, θ S1 and θ S2 It is the direction of the main lobe boundary. In this search example, θ S1 = -π / 3 [rad], θ S2 =π / 3 [rad], direction of sound source θ L =0 [rad], and the speed of sound c = 343 [m / s]. In the JADE method, μ F and μ CR The initial value of P is 0.5, and P best It is 0.05.

[0131] As a result of using a computer as a configuration search device and employing the JADE method to determine the configuration of multiple microphones 11 under the above conditions, a design is made. Figure 2 The microphone array 1 is shown. In the microphone array 1, the radius of each concentric circle and the number of microphones 11 in each concentric circle are shown in Table 1.

[0132] [Table 1]

[0133] Radius [m] Number of microphones 0 1 0.03856 3 0.10660 4 0.14024 7 0.21500 17

[0134] Figure 6 The microphone array 1 shown in the first search example (i.e., Figure 2 The pointing characteristics of the microphone array 1 shown. Figure 6 The directional characteristics of sound at the following frequencies are shown: 500Hz, 700Hz, 1000Hz, 2000Hz, and 4000Hz. Figure 6 In this context, the maximum value of the main lobe is represented as 0 dB.

[0135] As a comparative example, Table 2 shows the radius of each concentric circle of a microphone array with microphones 11 configured without using the JADE method, as well as the number of microphones 11 in each concentric circle. Figure 7 The directional characteristics of the microphone array in the comparative example are shown.

[0136] [Table 2]

[0137] Radius [m] Number of microphones 0 1 0.03 6 0.06 9 0.12 6 0.18 10

[0138] By comparison Figure 6 and Figure 7 Confirmed Figure 6 The pointing characteristics shown are Figure 7 The pointing characteristics shown have stronger pointing accuracy compared to the previous version. Specifically, in Figure 6 In the pointing characteristics shown, the minimum attenuation of the side lobes relative to the main lobe is 14.8 dB, while... Figure 7The minimum value of the amount of attenuation of the side lobe with respect to the main lobe in the directivity characteristic shown is 5 dB. Thus, it is confirmed that it is effective to determine the configuration of the plurality of microphones 11 using the JADE method.

[0139] [Second search example]

[0140] The radius of each of the concentric circles and the number of microphones 11 in each of the concentric circles determined using the JADE method under the condition that the number of microphones 11 is 48 and the maximum radius of the concentric circles is 0.215 [m] is shown in Table 3.

[0141] [Table 3]

[0142] Radius [m] Number of microphones 0 1 0.04070 3 0.09592 8 0.17148 16 0.21500 20

[0143] Figure 8 The directivity characteristic of the microphone array 1 of the second search example is shown. In the directivity characteristic shown, the minimum value of the amount of attenuation of the side lobe with respect to the main lobe is 16.1 dB. It is also confirmed that the directivity characteristic shown has stronger directivity than the directivity characteristic shown in Figure 8 Figure 8 Figure 7

[0144] [Third search example]

[0145] The radius of each of the concentric circles and the number of microphones 11 in each of the concentric circles determined using the JADE method under the condition that the number of microphones 11 is 64 and the maximum radius of the concentric circles is 0.215 [m] is shown in Table 4.

[0146] [Table 4]

[0147] Radius [m] Number of microphones 0 1 0.04718 3 0.08322 5 0.10001 9 0.15456 8 0.21500 38

[0148] Figure 9 The directivity characteristic of the microphone array 1 of the third search example is shown. In the directivity characteristic shown, the minimum value of the amount of attenuation of the side lobe with respect to the main lobe is 17.4 dB. It is also confirmed that the directivity characteristic shown has stronger directivity than the directivity characteristic shown in Figure 9 Figure 9 Figure 7

[0149] The microphone array 1 designed by using the JADE method has the following common features:

[0150] (1) The amount of change in the difference between the radii of two concentric circles adjacent to each other among the plurality of concentric circles does not monotonously increase according to the distance from the center position of the plurality of concentric circles; and

[0151] ​​​​​​(2) The attenuation amount of a side lobe with respect to a main lobe in a directivity characteristic is greater than or equal to 10 dB. When the microphone array 1 has these characteristics, the microphone array 1 preferentially collects sound generated by a sound source from which sound should be collected, and makes it difficult to collect unnecessary sound.

[0152] [Modified example]

[0153] The above shows an example in which three sound source positioning microphones 11 are arranged at equal intervals on the innermost concentric circle C1, but six sound source positioning microphones 11 can be arranged at equal intervals on the innermost concentric circle C1.

[0154] The present application is described based on typical embodiments. The technical scope of the present application is not limited to the scope described in the above embodiments, and various changes and modifications can be made within the scope of the present application. For example, the specific embodiments of the distribution and integration of the devices are not limited to the above embodiments, and all or a part of these embodiments can be constituted with any unit that is functionally or physically distributed or integrated. Furthermore, new typical embodiments generated by any combination of the above embodiments are included in the typical embodiments of the present application. Furthermore, the effects of the new typical embodiments brought about by these combinations also have the effects of the original typical embodiments.

[0155] Reference signs

[0156] 1 microphone array

[0157] 2 audio processing section

[0158] 11 microphone

[0159] 21 AD converter

[0160] 22 AD converter

[0161] 23 direction specifying section

[0162] 23 sound output section

Claims

1. A microphone system comprising a microphone array having a plurality of microphones arranged in a plurality of concentric circles, wherein, The microphone system comprises a plurality of concentric circles in which the difference between the radii of any two adjacent concentric circles does not increase monotonically with respect to the distance from the center of the plurality of concentric circles. Multiple positioning microphones are positioned at the central location and at multiple locations on the innermost concentric circle closest to the central location, and are used to specify the direction of the sound source; and Multiple beamforming microphones are positioned on the multiple concentric circles and are used to collect sound generated from sound sources specified by the multiple positioning microphones.

2. The microphone system according to claim 1, wherein, Three or six positioning microphones are arranged at equal intervals on the innermost concentric circles.

3. The microphone system according to claim 1, wherein, The distance between any two adjacent positioning microphones in the plurality of positioning microphones is less than or equal to half the minimum wavelength of the sound in the frequency band used to specify the direction of the sound source.

4. The microphone system according to claim 3, wherein, The distance between the two positioning microphones is less than or equal to 42.5 mm.

5. The microphone system according to claim 1, wherein, Some of the microphones are located at multiple intersection points where at least one straight line passing through the center of the plurality of concentric circles intersects each of the plurality of concentric circles.

6. The microphone system according to claim 1, further comprising: An audio processing unit is used to process the sound signals output from the microphone array, wherein, The audio processing unit includes: A direction-designating unit is used to specify the direction of a sound source based on multiple sound signals input from the plurality of positioning microphones; and The sound output unit is used to output a sound synthesized by weighting each of the multiple sounds input to the plurality of beamforming microphones based on the direction of the sound source specified by the direction specification unit.

7. The microphone system according to claim 1, wherein, The attenuation of the side lobes relative to the main lobe in the pointing characteristics is equal to or greater than 10 dB.

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