Patent Translate Powered by EPO and Google Notice This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate, complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or financial decisions, should not be based on machine-translation output. DESCRIPTION JPH11298988 [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling a microphone provided in a speech recognition apparatus used in a car. [0002] 2. Description of the Related Art A speech recognition device is for recognizing words and sentences uttered by a speaker, and a microphone of a headset is used to input a speech to the speech recognition device in order to improve the recognition rate. In recent years, voice recognition devices have been installed in automobiles, and various developments have been made for use in, for example, voice dials and the like. In this hands-free telephone system, when the driver puts on a headset, driving is hindered, so a microphone fixed in a certain place is used. [0003] However, since there is a fixed distance between the speaker and the fixed microphone in the fixed microphone, the noise in the passenger compartment, which is generated when the vehicle is traveling, comes in, and the voice recognition device is realized. There is a problem that it is difficult to improve the recognition rate of A microphone with directional characteristics is used as a solution to this problem, but the required directivity can not always be obtained. In 03-05-2019 1 particular, the sensitivity for the speaker peaks and the sensitivity for noise in the passenger compartment is It is impossible to obtain a microphone under the following conditions. [0004] Furthermore, there is also a method of removing noise by digital signal processing of signals input from a plurality of microphones, but since a high-performance CPU (central processing unit) is required, it can be realized at a cost stage I have a problem. Therefore, in view of the above problems, the present invention realizes low cost while improving S / N by controlling directivity characteristics so that the sensitivity dips in the noise incoming direction and the sensitivity peaks in the speaker direction. It is an object of the present invention to provide a method and an apparatus for controlling microphone directivity characteristics. [0005] SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is an apparatus for controlling the directional characteristics of a microphone for extracting the speech of a speaker under noise, which are arranged at equal intervals and at equal intervals. And, the sensitivity is peaked in the direction of the speaker based on the difference in the phase of the plurality of microphones for inputting the plane sound wave and the phase sound of the plane sound input to each microphone by processing the output signals of the plurality of microphones And a microphone circuit for controlling the directional characteristic of the microphone so that the sensitivity is dipted in the direction. Specifically, the microphone circuit has a figure eight positive and negative electrodes at the central symmetry axis between the two left and right microphones by taking the difference between the output signals of the two left and right microphones of the three microphones. A differential amplifier that forms an 8-shaped directivity, an integrator that integrates the result obtained by the differential amplifier, and recovers the degradation of directivity at a low frequency obtained by the differential amplifier; The output signal of the integrator and the output signal of one of the three microphones are added together to eliminate one pole of the directivity characteristic of the figure-8 positive and negative electrodes obtained by the differential amplifier And an adder for emphasizing the poles of R to sharpen the directivity characteristics. By this means, it has become possible to sharpen the directivity in the range of frequencies used for speech recognition. The mounting position of a plurality of microphones and gain control of each microphone enable control of directivity characteristics such that sensitivity is peaked to the speaker and sensitivity to noise is dip. As a result, the S / N is improved and the speech recognition rate is improved. 03-05-2019 2 [0006] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The control method and apparatus for controlling the microphone directivity according to the embodiment of the present invention is applied to a speech recognition apparatus used in an automobile as described above, for example, in a frequency range of 300 Hz to 5 kHz. For sound emission of a plurality of microphones, for example, two or three microphones arranged at equal intervals in a straight line, the sensitivity is peaked in the speaker direction and dips in the floor direction of the car Having the characteristics improves the S / N as follows, as compared to the use of one microphone. [0007] Directional Characteristics of Two Microphone Pairs FIG. 1 is a diagram for explaining an example of the directional characteristics of the linear arrangement of two microphones according to the present invention. As shown in the figure, it is assumed that two microphones MIC1 and MIC2 separated by a distance d are disposed on a straight line, and a plane wave arrives from the direction of angle θ. The center position O between the two microphones MIC1 and MIC2 is a reference point (attention point), and the sound pressure of each of the microphones MIC1 and MIC2 is represented by the following equation (1). R is the distance, and k = (ω / c) is the wavelength constant (c is the speed of sound). [0009] Sum of Outputs of Two Microphones Suppose that the sum of the outputs of the microphones MIC1 and MIC2 is used as the entire output as in the following equation (2). Here, the magnitudes of the sensitivity of the microphones MIC1 and MIC2 are not particularly specified, and both are equal. [0011] Accordingly, the directivity function D is as shown in the following equation (3). 03-05-2019 3 [0013] FIG. 2 is a diagram for explaining the outline of the directivity characteristic of the equation (3). Assuming that d = 4 cm and c = 340 m / s, kd shown in the figure is expressed by the following equation (4). [0015] From the above equation (4), the values of kd of the respective frequencies are as shown in Table 1 below. [0017] Therefore, as can be seen from Table 1 above, in the case of simple addition, the directivity characteristic becomes a strong ellipse at frequency f = 1500 Hz or more, but the directivity characteristic in one direction is weak at low frequency less than frequency f = 1500 Hz. It is difficult to make a circle and strengthen the directional characteristics in one direction. A case is considered in which the difference between the output of the microphone MC1 and the output of the difference microphone MC2 of the outputs of the two microphones is taken as the entire output. The directivity function D in this case is given by the following equation (5). [0019] FIG. 3 is a diagram for explaining the outline of the directivity characteristic of the equation (5). As shown in the figure, although the above equation (5) has a figure of eight shape and has positive and negative directivity characteristics with respect to the symmetry axis, the magnitude of the directivity characteristics decreases in proportion to the frequency in the low frequency range . Therefore, in the method of taking the output difference between the two microphones, the integrator is essential thereafter. Using an integrator with a gain of 1 / jωτ, the directivity function D is given by the following equation (6). 03-05-2019 4 [0021] Beamforming The two directivity functions D of the equations (3) and (6) above can be said to be basic elements when considering a beamformer below. Summation of outputs of two microphones to which a phaser is added on the other hand Fig. 4 is a block diagram 1 of directivity formation, showing a configuration example in which a phaser is added to a method of summing the outputs of two microphones It is. As shown in the figure, in the microphone circuit 10, an All Pass (all pass) delay circuit is added to the output of the microphone MIC2, and the output thereof is summed with the output of the microphone MIC1. The directivity characteristic function D in this case is expressed by the following equations (7) and (8). [0023] FIGS. 5 and 6 are diagrams for explaining examples of numerical calculation results of each frequency of equation (8) with d = 4 cm and τ = 135 μsec for the directivity characteristics of FIG. As shown in FIGS. 5 and 6, in the present method, directivity in a specific direction can not be realized at low frequencies. Although the configuration is simple, since it is in the form of ¦ D ¦ = 2cos {(kd / 2) cos θ + tan−1ωτ}, there is a drawback that the directivity characteristic in a specific direction at a low frequency can not be largely obtained. In order to realize the directivity as shown in FIG. 5D in a wide frequency range by this method, it is necessary to provide appropriate phase shift to each frequency instead of the phase shift by AllPass. [0024] Adding the integrator to the difference between the outputs of the two microphones with a phase shifter added on the other hand Figure 7 is a block diagram 2 of directivity formation, and adds phase shift based on equation (6) in Figs. It is a figure which shows the example of a structure. The directivity characteristic D obtained from the microphone circuit 10 of this figure is shown by the following equations (9) and (10). [0026] Here, τ used in FIG. 4 and equations (7) and (8) is indicated as τ = CR. 8 and 9 are diagrams for 03-05-2019 5 explaining examples of numerical calculation results at each frequency of equation (10) with d = 6 cm, CR = 63 μsec, and τ = 87 μsec for the directional characteristics of FIG. 7. The value of CR is set to θ = 45 ° and D has a dip. [0027] The form of (1 / ωτ) sin [(kd / 2) cos θ − tan −1 ω CR] is easier to obtain good directivity at a lower frequency than cos [(kd / 2) cos θ + tan −1 ω τ]. Adding a positive value to the characteristic of the difference between the outputs of the two microphones. FIG. 10 shows a block diagram 3 of directivity formation. Equation (6), as shown in FIG. 3, has directivity of FIG. 8 with respect to the symmetry axis centered on the origin, so that the diagram of FIG. In the microphone circuit 10 shown, a beamformer in which the minus (negative) side of the figure of eight is canceled by a positive value and the plus (positive) side is emphasized can be considered. [0028] In FIG. 10, D is the following equation (11). [0030] FIGS. 11 and 12 are diagrams for explaining examples of numerical calculation results at each frequency of equation (11) with d = 6 cm and τ = 120 μsec for the directivity characteristics of FIG. The value of τ is set such that D has a dip at θ = 45 °. According to this figure, among the three methods of FIG. 4 and FIG. 7 including the present method, the present method of FIG. 10 can realize the best directivity from a low frequency to a considerably high frequency. Recognize. [0031] Three-microphone linear arrangement integration method Since the three-microphone integration method shown in FIG. 10 can obtain excellent directivity characteristics in a wide 03-05-2019 6 range from low frequencies to fairly high frequencies, this will be examined in detail below. FIG. 13 is a diagram for explaining a basic configuration adopting the three microphone linear arrangement integration method. As shown in the figure, three microphones are linearly arranged at equal intervals, and in the microphone circuit 10, respective outputs are combined using an integrator and an adder to obtain a desired output. As described later, by appropriately adjusting the gain, the dip point of the sensitivity can be set arbitrarily. The LPF (low pass filter) compensates for the deterioration of the directivity at a high frequency, as described later. The case where the LPF is not used for convenience of explanation will be described again in detail. The directivity function D in the case where the LPF is not used in FIG. 13 is expressed by the following equation (12). [0033] At kd / 2 << 1, that is, at low frequencies, the directivity function D is given by the following equation (13). [0035] FIG. 14 is a diagram for explaining the outline of the equation (13). Assuming that τ = c / d, the distribution of the directivity function ¦ D ¦ of equation (13) with respect to θ is as shown in the figure. FIG. 15 is a diagram for explaining the change of 2 sin [(kd / 2) cos θ] / ω τ with respect to ω. When the change of 2 sin [(kd / 2) cosθ] / ωτ with respect to ω is examined at each θ, it becomes as shown in the figure. However, here, the value of τ is set such that ¦ D ¦ becomes zero at θ = 0 °. [0036] In 1) d = 4 cm in FIG. 15, 2 sin [(kd / 2) cos θ] / ω τ is 1 and θ in equation (12) is 0 at θ = 0 °. Then, since the value for each θ is almost the same as when f = 0 until the frequency is less than 1 kHz, the directivity characteristic is as shown in FIG. FIG. 16 is a diagram for explaining the outline of the deterioration of the directivity characteristic. However, further, when the frequency is higher than 1 kHz, the distribution of ¦ D ¦ is roughly degraded as shown in FIG. 16 (a). 03-05-2019 7 [0037] When the frequency becomes 4 kHz or more at 3) d = 8 cm in FIG. 15, the directivity characteristic is further degraded as shown in FIG. Therefore, as the d is increased, the directivity characteristics at high frequencies are more likely to be deteriorated. Next, it is considered to compensate for the directivity at high frequency using the LPF. In order to realize the target directivity characteristic of FIG. 14 at a high frequency, it is necessary to make the value of 2 sin [(kd / 2) cos θ] / ωτ at each θ equal to the value when θ = 0. Therefore, here, the idea of providing an LPF as shown in FIG. 13 to compensate for the reduction in the magnitude of the value of 2 sin [(kd / 2) cos θ] / ωτ at high frequencies by peaking due to the resonance characteristic of the LPF take. [0038] The transfer function of the above LPF is given by the following equation (14). [0040] Therefore, the compensation of the directivity is performed by using the enlargement of the magnitude from the lower frequency to f0. However, in the case of 3) d = 8 cm in Fig. 14, compensation is impossible even with this method at a frequency of about 4 kHz or more. FIG. 17 is a diagram for explaining the amplitude characteristic of equation (14). When the LPF is used, the directivity function D is expressed by the following equation (15) as shown in the figure. [0042] At the original low frequency, (c: sound velocity) as in the following equation (16) [0044] 【００４４】とすればよい。 03-05-2019 8 Numerical Calculation Example of Directional Characteristics The result of calculating the directional characteristics for d = 6 cm when the LPF is not used is shown in FIGS. 11 and 12 described above. However, in order to give a dip at θ = 45 °, τ = 120 μsec. [0045] FIG. 18 and FIG. 19 are diagrams for explaining an example of calculation results in which characteristics are improved at frequency using an LPF at d = 6 cm. From the results of FIGS. 6A to 6G, the characteristic improvement by the LPF can be clearly understood. Here, in the LPF, f0 = 6,800 Hz, Q = 20, d = 6 cm, and τ = 120 μsec. Next, the case where dip is applied at θ = 0 ° will be taken as d = 4 cm. From equation (16), it can be found that τ 求 120 μsec. High frequency compensation was performed using the LPF in this case. [0046] FIGS. 20 and 21 are diagrams for explaining examples of numerical calculation results of the directivity function D of FIG. As shown in the figure, by changing d = 6 cm to d = 4 cm, good directivity characteristics are obtained up to a considerably high frequency. FIG. 22 is a diagram showing a configuration example of the microphone circuit 10 in which the basic configuration of FIG. 13 is embodied in the case of d = 6 cm, θ = 45 ° dip or d = 4 cm, θ = 0 ° dip. However, each route of the basic configuration of FIG. 13 is multiplied by -1. The microphone circuit 10 shown in the figure is provided with a differential amplifier 11 which receives output signals from the microphones MC2 and MC3 to form a difference between them and an LPF 12 which is connected to the output of the differential amplifier 11 to perform high frequency compensation. , An integrator 13 connected to the LPF 12 for integration, and an adder 14 for adding the output of the integration 13 and the output of the microphone MC1. The values of the types of transistors, operational amplifiers, resistors, capacitors, etc. forming the differential amplifier 11, the LPF 12, the integrator 13 and the adder 14 shown in FIG. 22 are an example. Here, assuming that dip is given at d = 6 cm and θ = 45 °, τ = 120 μsec (d = 4 cm, the present circuit configuration is also obtained in the case of dip at θ = 0 °). [0047] Next, when the conventional integrator is used as it is as the integrator 13, there are two problems in its configuration. The feedback resistor for taking the offset of the operational 03-05-2019 9 amplifier (OP) that constitutes the integrator 13 gives a high resistance value for realizing an integration characteristic close to an ideal one. However, even at low frequencies (about 300 Hz or less), it is quite difficult to actually obtain the ideal integral characteristic. On the other hand, the feedback resistance is large. [0048] Therefore, a large DC error is generated in the output of the integrator 13 also by a slight offset error in the previous stage (DC differential error when the integration characteristic is provided to OP1 constituting the differential amplifier 11). As a solution to the above problems, as shown in the circuit diagram of FIG. 22, the middle point of the feedback resistance of the integrator 13 and the ground are short-circuited to an AC point. However, it is necessary to make the short circuit capacity (impedance) sufficiently smaller than RC2 and RC3. [0049] Next, the operation of each circuit of the microphone circuit of FIG. 22 will be described. FIG. 23 is a diagram for explaining the differential amplifier circuit 11 of FIG. The following equations (17) and (18) hold at point P in the figure. [0051] In the above equation, the following equation (19): [0053] If the following condition is satisfied, the following equation (20) holds. [0055] Here, if RA1 = RA2 RA3 = RA4, the following equation (21) holds. [0057] FIG. 24 is a view for explaining the high Q LPF 12 of FIG. 03-05-2019 10 This figure shows a multiple feedback LPF that can be expected to operate stably. Here, by using the capacitance division circuit of CB4 and CB5, it is possible to realize the high Q of Q, which was conventionally difficult. In the case of this configuration, the influence of the finite GB product can not be ignored. In FIG. 24, the following equation (22) is established. [0059] Further, at point P in FIG. 24, the following equation (23) is established. [0061] Therefore, the transfer function of the present LPF 12 is given by the following equation (24). [0063] Then, if the frequency range is in a range where the third term of the denominator can be neglected, the following equation (25) is simplified. [0065] However, there is a relation of equation (26). [0067] FIG. 25 is a diagram for explaining the integration circuit 13 operable up to the low frequency range of FIG. In the integrating circuit 13 of this figure, C 'originally uses a large capacity of the electric field capacitor, and in the alternating current, it aims at zero impedance. 03-05-2019 11 However, here the influence of this capacity C 'is investigated below. If the continuity of the current of the point P is obtained, ignoring the finite GB product, the following equations (27) and (28) hold. [0069] Therefore, the following equation (29): [0071] The sufficient condition for obtaining the ideal integral characteristic of the following equation (30): [0073] 【００７３】となる。 FIG. 26 is a diagram for explaining the addition circuit 14 of FIG. The following equations (31) and (32) hold at point P in the figure. [0075] Therefore, the following equations (33) and (34) hold. [0077] Equations (35) and (36) hold in FIG. 22 in which the above circuits are combined. [0079] However, ω 0 and Q are shown in equation (26). 03-05-2019 12 Thus, by using a plurality of microphones and analog circuits, it is possible to obtain desired microphone directivity characteristics at low cost. Sharpening of Beam Former FIG. 27 shows an example of a 3-microphone linear arrangement integration method as a multi-microphone system having directivity characteristics in half in free space. In the microphone circuit 10 shown in this figure, a multi-microphone system having directivity in half of free space, for example, multiplies the directivity of FIG. 13 (represented in FIG. 27) In some cases, it was considered to make the beam sharper. At low frequencies, the value of sin (kd cos θ) decreases, so the directivity characteristic decreases. Therefore, it is then necessary to use an integrator for amplification. [0080] In this case, the directivity function D is expressed by the following equation (37). [0082] FIGS. 28 and 29 show the directivity characteristics of the equation (37). As shown in the figure, the directivity characteristic of equation (37) is shown. Further expanding the equation (37) gives the following equation (38). [0084] Considering a microphone arrangement in which the value of the real part is zero and the value of this expression becomes the value of the imaginary part, the following expression (39) based on this result is shown. [0086] FIG. 30 is a view showing the arrangement of microphones for realizing the directivity 03-05-2019 13 characteristic of the equation (39). As shown in the figure, a series arrangement of five microphones is performed to fully satisfy equation (39). Three Microphone Implementation of a Sharpened Beam However, it is not desirable to use as many as five microphones as in FIG. Therefore, [1] microphones MIC2 and MIC3 are moved right by d to realize 3 microphones; [2] microphones MIC2 and MIC3 are moved left to d to realize 3 microphones; [3] microphone MIC5 is We decided to move 3 mics to the right by moving the MIC 4 d to the right by d to the right; [0087] FIG. 31 is a view for realizing the directivity characteristic sharpened by the microphone arrangement of [1]. The directivity characteristic obtained by the microphone circuit 10 shown in this figure is expressed by the following equation (40). [0089] In the case of [2], the directivity characteristic is given by the following equation (41). [0091] The absolute value of the directivity characteristic is the same as in [1]. FIG. 32 is a diagram for realizing the directivity characteristic sharpened by the microphone arrangement of [3]. The directivity characteristic obtained by the microphone circuit 10 shown in this figure is expressed by the following equation (42). [0093] Further transforming equation (42) yields equation (43) below. [0095] 03-05-2019 14 It can be seen that the form is quite similar to the formula (37). As mentioned above, although 3 types of 3 microphones were considered, the case of [3] is further examined among them. In practice, the output of FIG. 32 requires a further integration circuit. FIGS. 33 and 34 are diagrams showing the directivity characteristics in the case of [3]. However, it is assumed that d = 2.5 cm and τ = 30 μsec. As shown in the figure, the sharpness of the directivity characteristic starts to decrease from f = 2000 Hz or more. Therefore, paying attention to equation (43), changes with frequency of cos (kd / 2 cos θ) and 1 / ωτ sin (kd / 2) cos θ are examined. [0096] FIG. 35 is a diagram showing the results of numerical calculation of cos (kd / 2) cos θ and 1 / ωτ sin (kd / 2 cos θ) in equation (43). From (b) of FIG. 35, it can be understood that when the frequency is low, the directivity characteristic becomes sharp according to 1 / ωτ sin (kd / 2 cos θ) of Expression (43). Moreover, the reduction with respect to the frequency of each magnitude ¦ size of FIG.35 (b) is small to about f = 4000 Hz. However, at frequencies higher than that, it causes the directivity characteristics to be degraded. [0097] However, as shown in FIG. 35A, cos (kd / 2 cos θ) in [] of equation (43) starts to decrease from a fairly low frequency. In addition, at high frequencies, the directional characteristic begins to appear on the left side, because cos (kd / 2 cos θ) decreases. FIGS. 36 and 37 are diagrams showing the directivity characteristic changed from d = 2.5 cm to 2 cm in FIG. As shown in the figure, good directivity characteristic sharpness is maintained up to f = 5000 Hz, and sharpening is realized to a considerably high frequency. However, τ = 30 μsec. [0098] FIG. 38 is a diagram showing an example of a configuration in which 1 / jωτ ′ is added to the output of FIG. 32 to sharpen the beam. Referring to equation (43), the directivity function D obtained by the microphone circuit 10 shown in FIG. 38 is expressed as the following equation (44). 03-05-2019 15 [0100] Therefore, the following equation (45) is established. [0102] FIG. 39 is a diagram showing an example of the configuration of a specific microphone circuit 10 based on FIG. 32 and FIG. The circuit element values shown in this figure are set as an approximate reference in FIG. In the drawing, the following condition (46) is required between the circuit elements. [0104] Here, in the circuit of FIG. 39, the following equation (47) holds as an ideal form of the operational amplifier (op). [0106] Then, when the condition of the equation (46) is satisfied, the equation (47) becomes as the following equations (48) and (49). [0108] FIGS. 40, 41 and 42 show simulation results of the magnitudes of the transmissions ¦ V 0 / Vi M ¦, ¦ V 0 / Vi L ¦ and ¦ V 0 / Vi R ¦ for the respective inputs of the circuit of FIG. 39. なお、オペアンプはＴＬ−０６１である。 Near f = 300 Hz, almost target characteristics are obtained. In practice, the circuit element values may be set to lower the gain level by 20 to 30 dB. 03-05-2019 16 [0109] The degradation of the integration characteristic in the low frequency band of 300 Hz or less in FIGS. 40, 41 and 42 is due to the impedance of the electric field capacitor of the integration circuit. However, it does not matter in particular. Sharpening of Beams by Five Microphones If 1cos (kd cos θ) is multiplied by the directional characteristic having sensitivity to half of the free space described above, the directional characteristic becomes sharper as described below. However, in this case, five microphones are input. [0110] The directivity function D obtained by multiplying the equation (12) by 1-cos (kd cos θ) is given by the following equation (50). [0112] The equation (50) is transformed to the following equation (51). [0114] FIG. 43 is a diagram showing a linear arrangement of five microphones satisfying the directivity characteristic of equation (51). As shown in the figure, five microphones are arranged at equal intervals in a straight line, and the configuration of the microphone circuit 10 is formed. FIG. 44 and FIG. 45 show directivity characteristics in FIG. 43 with d = 2 cm and τ = 120 μsec. As shown in the figure, the directivity characteristic is sharpened more than three microphones. [0115] Further, the directivity function D obtained by multiplying the above-mentioned equation (10) by 1-cos (kd cos θ) becomes as in the following equation (52). [0117] 03-05-2019 17 The equation (52) is transformed to the following equation (53). [0119] FIG. 46 is a diagram showing a linear arrangement of five microphones satisfying the directivity characteristic of the equation (53). As shown in the figure, five microphones are arranged at equal intervals in a straight line, and the configuration of the microphone circuit 10 is formed. 47 and 48 show the directivity characteristics in FIG. 46 where d = 2 cm, τ = 50 μsec, and CR = 30 μsec. As shown in the figure, the directivity characteristic is sharpened more than three microphones. [0120] FIG. 49 is a view showing an example in which the linear arrangement multi microphones according to the present invention are arranged in a car. As shown in the figure, in the case where a plurality of (multi) microphones in a linear arrangement are attached to an A pillar (a front pillar) which is located in front of a speaker in an automobile and makes an angle of 45.degree. The height of the microphones is matched to the height of the mouth of the speaker, the peak of the directivity of the multimicrophone is 135 °, and the dip of the directivity of the multimicrophone is 45 ° toward the floor of the car. It will be the direction. By optimizing the directional characteristics of the microphone for each car, the S / N of the voice input to the voice recognition device can be secured. [0121] FIG. 50 is a diagram showing an example of controlling the dip of the directivity by controlling the gain of the microphone, taking the configuration of FIG. 13 as an example. As shown in FIG. 6A, the microphones 1, 2 and 3 are linearly arranged, and initial values of gains G1, G2 and G3 are respectively set, and dips downward in the left side of FIG. Is facing. In this case, when the gain G2 is smaller than the initial value, as shown on the right side of the figure (b), the dip 03-05-2019 18 direction moves upward. In this way, by changing the dip position of the microphone directivity according to the position of the speaker's mouth, even if the speaker changes, the S / N level of the speech input to the speech recognition device can be maintained. Stable voice recognition processing. [0122] FIG. 51 is a diagram showing another example of the arrangement of a plurality of (multi) microphones. As shown in the figure, a plurality of microphones may be attached to the back of a rearview mirror used for driving a car. In this way, the limitations of the mounting space of multiple microphones can be expanded. In addition, it can reduce the design impact on the interior due to the installation of the microphone when viewed from the inside of the car. [0123] Note that each of the plurality of microphones may have a non-directional characteristic. [0124] According to the present invention, according to the present invention, it is possible to sharpen the directivity of the microphone in the range of frequencies used for speech recognition, and furthermore, the sensitivity is peaked for the speaker. It became possible to control the directional characteristics so that the sensitivity to noise would be dip. 03-05-2019 19

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