Acoustic controller, acoustic control system, program, and method

Abstract

To provide an acoustic controller, acoustic control system, program, and method for making it easy to transmit sound only in a specific direction.SOLUTION: An acoustic controller comprises an acoustic filter coefficient calculation unit. The acoustic filter coefficient calculation unit calculates, on the basis of a sound pressure multiplication factor at a sound increase control point at which sound increase is performed by sounds reproduced from a main sound source and two or more additional sound sources and transfer functions between the sound increase control point and the main sound source and the additional sound sources, a first relational expression between acoustic filter coefficients that are applied to a voice signal including information on sound to be reproduced and are determined to be equal to volume speed of sound reproduced from the main sound source and the respective additional sound sources; calculates a second relational expression among acoustic filter coefficients of the main sound source and the respective additional sound sources under a condition that a sum of a total sum of volume speed of sound reproduced from the respective additional sound sources and a volume speed of sound reproduced from the main sound source is not zero; and calculates the respective acoustic filter coefficients on the basis of the first relational expression and the second relational expression.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to an audio control device, an audio control system, a program, and a method. [Background technology]

[0002] Various voice-based services are currently in use, such as voice guidance in public spaces, voice guidance in car navigation systems, and voice conversations in online conference systems. While the voices used in these types of services are useful for people who need guidance and want to have conversations, they can be merely a distraction for people who do not need guidance and do not want to have conversations. In other words, the areas where voices should or should not be conveyed vary depending on the location and time of use. Therefore, there is a demand for sound field control technology that can easily convey sound in only specific directions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-048468 Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments provide an audio control device, an audio control system, a program, and a method that facilitate transmission of sound only in a specific direction. [Means for solving the problem]

[0005] An acoustic control device according to one embodiment includes an acoustic filter coefficient calculation unit that calculates a first relational expression between acoustic filter coefficients that are to be applied to an audio signal containing information about sounds to be reproduced and are determined to be equal to the volumetric velocities of sounds reproduced from the main sound source and the additional sound source, based on a sound pressure multiplication factor at a sound increase control point that is increased by sounds reproduced from a main sound source and two or more additional sound sources, and a transfer function between the main sound source and the additional sound source and the sound increase control point, calculates a second relational expression between the acoustic filter coefficients of the main sound source and the additional sound source under the condition that the sum of the volumetric velocities of the sounds reproduced from each of the additional sound sources and the volumetric velocity of the sound reproduced from the main sound source is not zero, and calculates each acoustic filter coefficient based on the first relational expression and the second relational expression. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of an acoustic control device according to an embodiment. [Figure 2] FIG. 2 is an external view showing an example of the configuration of a speaker. [Figure 3] FIG. 3 is a block diagram showing elements included in the control device. [Figure 4] FIG. 4 is a conceptual diagram of an acoustic power control law for explaining the condition of equation (2). [Figure 5] FIG. 5 is a diagram showing an example of a sound increase area that is set when the conditions of the sound power minimization control law are satisfied. [Figure 6] FIG. 6 is a diagram showing sound pressure nodes formed when the conditions of the acoustic power reduction control law are satisfied. [Figure 7] FIG. 7 is a diagram showing an example of a sound increase area that is set when the conditions of the sound power reduction control law are satisfied. [Figure 8] FIG. 8 is a diagram showing the gain characteristics of the acoustic filter coefficients qL, qC, and qR obtained from equation (1) when αi=−βi=−1 and αr+βr=1 in the example of FIG. [Figure 9]FIG. 9 is a diagram showing the phase characteristics of the acoustic filter coefficients qL, qC, and qR obtained from equation (1) when αi=−βi=−1 and αr+βr=1 in the example of FIG. [Figure 10] FIG. 10 is a diagram showing the sound pressure level around a speaker when a sound convoluted with the acoustic filters having the characteristics of FIGS. 8 and 9 is emitted. [Figure 11] FIG. 11 is a diagram showing evaluation points in the calculation results described in FIGS. [Figure 12] FIG. 12 is a diagram showing the calculation results of the frequency characteristics of sound pressure at evaluation points A and B. [Figure 13] FIG. 13 is a diagram showing frequency characteristics of the sound pressure difference between evaluation points A and B before and after the combined control of sound increase control and sound power reduction control is performed. [Figure 14] FIG. 14 is a diagram showing changes in sound pressure distribution when the frequency of the audio signal and the speaker interval are variously changed. [Figure 15] FIG. 15 shows the experimental results for noise in the 400 Hz-1250 Hz band, which is the applicable frequency band. [Figure 16] FIG. 16 shows the results of an experiment using noise up to 20,000 Hz, including frequencies outside the applicable frequency band. [Figure 17] FIG. 17 is a diagram showing evaluation points in the experimental results described with reference to FIGS. [Figure 18] FIG. 18 shows the results of increasing the volume of noise in the left direction caused by a noise source in the 400 Hz-1250 Hz band, which is the applied frequency band. [Figure 19] FIG. 19 is a conceptual diagram illustrating a case where the acoustic control device according to the embodiment is used in a voice guidance system. [Figure 20] FIG. 20 is a conceptual diagram of a voice guidance system as an application example of the sound control system according to the embodiment. [Figure 21] FIG. 21 is a conceptual diagram of a case where the sound control system according to the embodiment is used in a digital signage system. [Figure 22]FIG. 22 is a conceptual diagram of a case where the sound control system according to the embodiment is used in a digital signage system. [Figure 23] FIG. 23 is a diagram showing an example of an acoustic control device in which the main sound source C and the additional sound sources S1, . . . , Si are not arranged side by side. [Figure 24] FIG. 24 is a diagram showing the positional relationship between the sound source and the sound increase control point that allows a sufficient sound pressure gradient to be obtained. [Figure 25] FIG. 25 is a diagram illustrating an example of a hardware configuration of an acoustic control device. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of an acoustic control device according to an embodiment. The acoustic control device 100 has an audio signal input unit 101, an audio signal processing device 102, a control device 103, and speakers 104L, 104C, and 104R. In the embodiment, the speakers 104L, 104C, and 104R are arranged side by side in a horizontally long housing, for example, as shown in FIG. 2. FIG. 2 shows the arrangement of the speakers 104L, 104C, and 104R as viewed from the front. The speaker 104C is located between the speakers 104L and 104R. FIG. 2 shows an example in which the speakers 104L, 104C, and 104R are housed together in a straight line. The angle formed by the two directions from speaker 104C toward speakers 104L and 104R is preferably 150 degrees or more and 180 degrees or less, and more preferably 170 degrees or more and 180 degrees or less. The angle formed by the front direction of speaker 104C and the direction from speaker 104C toward speaker 104L, and the angle formed by the front direction of speaker 104C and the direction from speaker 104C toward speaker 104R are, for example, 85 degrees or more and 95 degrees or less. FIG. 2 shows an example in which the front directions of speakers 104L, 104C, and 104R are parallel to one another. The front directions of speakers 104L, 104C, and 104R are parallel to one another or form an angle of 5 degrees or less with respect to one another. The positional relationship between each speaker can be determined, for example, based on the center of the front of the speaker. The vertical direction and the depth direction are directions along the front direction of speaker 104C. The horizontal direction is a direction perpendicular to the front direction of speaker 104C. Unless otherwise specified, a straight line hereinafter refers to a line that passes through speakers 104L and 104R.

[0008] The acoustic control device 100 combines sound increase control using multiple speakers with sound power reduction control to make it easier for sound to be transmitted only to the area directly in front of the speakers arranged side by side. Sound increase control is a control that increases the sound pressure in a specific direction by controlling the amplitude of sound emitted from multiple speakers. On the other hand, sound power reduction control is a control that reduces the sound power of multiple speakers as if they were a single speaker by controlling the amplitude and phase of the sound emitted from the multiple speakers so as not to minimize it.

[0009] The audio signal input unit 101 inputs an audio signal to the audio signal processing device 102. The audio signal input unit 101 may also input the audio signal to the control device 103. The audio signal is a signal that includes sound information. The audio signal is prepared in advance for playback, for example. The audio signal may be generated sequentially for each playback, or may be input by the user or the control device 103, for example.

[0010] The audio signal processing device 102 performs signal processing on an audio signal and includes an amplifier 1021 and acoustic filters 1022L, 1022C, and 1022R.

[0011] The amplifier 1021 amplifies the audio signal input from the audio signal input unit 101 with a gain G. The gain G may be a fixed value, for example, 1, or may be specified by the control device 103.

[0012] The acoustic filter 1022L filters the audio signal output from the amplifier 1021 using an acoustic filter coefficient q designated by the control device 103. L Then, the acoustic filter 1022L outputs the filtered audio signal to the speaker 104L. Also, the acoustic filter 1022C filters the audio signal output from the amplifier 1021 according to the acoustic filter coefficient q C Then, the acoustic filter 1022C outputs the filtered audio signal to the speaker 104C. Also, the acoustic filter 1022R filters the audio signal output from the amplifier 1021 according to the acoustic filter coefficient q R Then, the acoustic filter 1022R outputs the filtered audio signal to the speaker 104R. These acoustic filters are designed to pass only sounds in a specific band of the audio signal. L , q C , q Rmay be set equal to the complex volume velocity of the speakers 104L, 104C, 104R.

[0013] The control device 103 determines acoustic filter coefficients q to be given to the acoustic filters 1022L, 1022C, and 1022R based on the frequency of the audio signal and the respective intervals between the speakers 104L, 104C, and 104R. L , q C , q R The control device 103 may also set a gain G. The control device 103 will be described in detail later.

[0014] The speakers 104L, 104C, and 104R are sound sources that emit sounds corresponding to filtered audio signals output from the corresponding acoustic filters. For example, when viewed from the front of the speaker 104C, the speaker 104L operates as the left speaker, the speaker 104C operates as the center speaker, and the speaker 104R operates as the right speaker. The functions and configurations of the speakers 104L and 104R are interchangeable. The speaker 104C is the main sound source. The speakers 104L and 104R, which are arranged symmetrically with respect to the speaker 104C, are additional sound sources. In the configuration of FIG. 2, the spacing between the speakers 104L, 104C, and 104R is a fixed value. Here, the speakers 104L, 104C, and 104R do not necessarily have to be configured as an integrated unit. On the other hand, for the purpose of acoustic power reduction control and acoustic power increase control, it is desirable that speakers 104L, 104C, and 104R be arranged relatively close to each other. Furthermore, the housing shown in FIG. 2 may also house audio signal input unit 101, audio signal processing device 102, and control device 103. The distance d between speakers 104L, 104C, and 104R is determined according to the frequency band in which a sound pressure gradient is generated by acoustic power increase control and acoustic power reduction control. For example, distance d is between 0.05 m and 2 m.

[0015] Next, we will explain the control device 103. Fig. 3 is a block diagram showing elements included in the control device 103. The control device 103 has an acquisition unit 1031, an acoustic filter coefficient calculation unit 1032, an acoustic filter coefficient storage unit 1033, and an acoustic filter setting unit 1034.

[0016] The acquisition unit 1031 acquires various pieces of information necessary for calculating acoustic filter coefficients. Then, the acquisition unit 1031 inputs the acquired information to the acoustic filter coefficient calculation unit 1032. The information acquired by the acquisition unit 1031 includes, for example, information on frequency, speaker spacing, and transfer function.

[0017] The frequency is the frequency of the audio signal input from the audio signal input unit 101. The acquisition unit 1031 acquires, for example, frequency information from the audio signal input unit 101. Note that if the speed of sound c is known, the frequency can be converted into a wave number. The acquisition unit 1031 may acquire the wave number information from the audio signal input unit 101. Furthermore, if the frequency of the audio signal is a fixed value, the acquisition unit 1031 may input pre-stored information on the fixed value of the frequency to the acoustic filter coefficient calculation unit 1032.

[0018] The speaker spacing is the spacing between each of a plurality of speakers. The acquisition unit 1031 acquires the speaker spacing based on, for example, an input from a user. The speaker spacing may be equal or different. Note that if the speakers are fixed, the speaker spacing may be treated as a fixed value. In this case, the acquisition unit 1031 may input information about the fixed speaker spacing stored in advance to the acoustic filter coefficient calculation unit 1032.

[0019] The transfer function is a function that represents the transfer characteristics of sound between each of the speakers 104L, 104C, and 104R and the volume increase control point, and is determined by the positional relationship between the speakers 104L, 104C, and 104R and the volume increase control point. The volume increase control point is the control target position for volume increase control. The transfer function represents the spatial transfer characteristics C of the sound transferred from the speaker 104L to the volume increase control point. L , the spatial transmission characteristic C of the sound transmitted from the speaker 104C to the sound increase control pointC , spatial transmission characteristic C of the sound transmitted from the speaker 104R to the sound increase control point R The spatial transfer characteristics are expressed as a matrix with elements . Each spatial transfer characteristic can be measured from a microphone-acquired signal obtained by emitting a sound based on a random signal or a sound based on a TSP (Time Stretched Pulse) signal from the speakers 104L, 104C, and 104R in an anechoic room or listening room with little sound reflection, and collecting this sound with a microphone placed at the position of the volume increase control point. The acquisition unit 1031 acquires the transfer function measured in this manner. Note that if the positions of the speakers 104L, 104C, and 104R and the positions of the volume increase control points are fixed, the transfer function can be treated as a fixed transfer function. In this case, the acquisition unit 1031 may input a pre-stored fixed transfer function to the acoustic filter coefficient calculation unit 1032.

[0020] The acoustic filter coefficient calculation unit 1032 receives various information from the acquisition unit 1031, and also receives acoustic filter coefficients for at least one speaker from the acoustic filter coefficient storage unit 1033, and calculates acoustic filter coefficients for the remaining speakers. The acoustic filter coefficient calculation unit 1032 then inputs the acoustic filter coefficients to the acoustic filter setting unit 1034.

[0021] The acoustic filter coefficient storage unit 1033 stores the acoustic filter coefficient q for the speaker 104C. C I remember.

[0022] The acoustic filter setting unit 1034 sets the acoustic filter coefficient q L is set to the acoustic filter 1022L, and the acoustic filter coefficient q C is set to the acoustic filter 1021C, and the acoustic filter coefficient q R is set as the acoustic filter 1022R.

[0023] The acoustic filter coefficients in the embodiment will be described below. The acoustic filter coefficients are calculated from a first relational expression and a second relational expression which are determined based on the sound increase control law and the sound power control law, respectively. The first relational expression determined from the sound increase control law when there are M sound increase control points and N sound sources is expressed by the following formula (1), and the second relational expression determined from the sound power control law is expressed by the following formula (2). Here, one of the N sound sources is the main sound source and the rest are additional sound sources.

number

[0024] The condition of equation (2) will be explained below. Fig. 4 is a conceptual diagram of the acoustic power control law for explaining the condition of equation (2). Fig. 4 shows an acoustic power control law using three speakers 104L, 104C, and 104R arranged side by side. For simplicity of explanation, the distance between speaker 104L and speaker 104C and the distance between speaker 104C and speaker 104R are assumed to be equal.

[0025] In FIG. 4, when the speakers 104L, 104C, and 104R are viewed as one speaker, the acoustic power W is expressed by the following equation (3).

number

[0026] Here, in equation (3), q L =α q C , q R =β q C α and β are the α in equation (2) si In this case, equation (3) can be expressed as equation (4).

number

[0027] As shown in equation (4), the acoustic power W is a function of the product kd of the wave number and the speaker spacing. Therefore, the amount of reduction in acoustic power W is determined by the kd value. When the value of kd, i.e., the frequency of the sound emitted from the speaker and the speaker spacing, is appropriately determined, the values ​​of sinc(kd) and sinc(2kd) in equation (4) can both be approximated to 1. In this case, equation (4) is approximated as in equation (5). To minimize the acoustic power W in equation (5), it is sufficient that the first or second term in the parentheses in equation (5) is zero.

number

[0028] As mentioned above, both α and β are complex functions. r +jα i , β=β r +jβ i After separating the real part and the imaginary part, the parentheses in equation (5) are rearranged, and the parentheses in equation (5) are expressed as equation (6).

number

[0029] From equation (6), the approximate solution that minimizes the acoustic power W is α r +β r =-1, and α i +β i = 0. As shown in FIG. 4, when the speakers 104L and 104R as two additional sound sources are arranged symmetrically with respect to the speaker 104C as the main sound source, and the point in front of the speaker is set as the sound increase control point, q L =q R , i.e., α=β(α r =β r , and α i =β i ) is established. At this time, from equation (6), α i =β i = 0 and α r =β r= -1 / 2, W is minimized. Finally, from equations (1) and (2), the acoustic filter coefficient q L , q C , q R , q L =-1 / 2, q C =1, q R In Figure 4, the acoustic filter coefficients q applied to each speaker can be set as L , q C , q R When sound is emitted from the speakers 104L, 104C, and 104R with these acoustic filter coefficients, a sound pressure gradient occurs around the speakers 104L, 104C, and 104R, making it possible for the sound to reach only the areas around the sound increase control points.

[0030] Here, since the speakers 104L and 104R are located symmetrically with respect to the speaker 104C, the acoustic filter coefficient is set to q L =-1 / 2, q C =1, q R =-1 / 2, and when sound is emitted from speakers 104L, 104C, and 104R, area A to the right of speaker 104R shown in Fig. 5 becomes a sound-boosting area where sound pressure increases. The same is true for the area to the left of speaker 104L, which is not shown. On the other hand, in front of speaker 104C, a node n of sound pressure is formed due to interference between the sounds from speakers 104L and 104R, which are out-of-phase sounds. As a result, the sound-boosting effect is reduced in the area in front of speaker 104C.

[0031] In this way, when the sound from speaker 104L and the sound from speaker 104R are in an anti-phase relationship at a position directly in front of speaker C, the acoustic power W is minimized, but the sound amplification effect in front of speaker 104C is also reduced. If speakers 104L, 104C, and 104R are arranged vertically in the depth direction so that area A to the right of speaker 104R faces directly forward, a sufficient sound amplification effect in the front direction can be expected. However, arranging speakers 104L, 104C, and 104R vertically means an increase in size in the depth direction. Depending on the application of the acoustic control device, it may be difficult to arrange the speakers side by side in the depth direction.

[0032] The reason why a sound pressure node is formed in the front direction of speaker 104C is that the sounds radiated from speakers 104L and 104R, which are additional sound sources arranged symmetrically with respect to speaker 104C, which is the main sound source, are in an anti-phase relationship at the position in front of speaker 104C. Therefore, if the sounds radiated from speakers 104L and 104R, which are arranged symmetrically with respect to speaker 104C, are not in anti-phase at the position in front of speaker 104C, the acoustic power W will not be minimized, but the sound will also be increased in the front direction of speaker 104C.

[0033] Therefore, in the embodiment, in formula (6), α i =β i = 0, and α i =-β i It is assumed that, and α r +β r =X (X ≠ -1). For example, when X is 1, α = α r +jα i , β=β r +jβ i Therefore, the condition of the following equation (7) is obtained. α+β=1 (7)

[0034] From equations (2) and (7), the acoustic filter coefficient q L , q C , q R , q L = α, q C =1, qR = (1-α). From this equation and equation (1), the final acoustic filter coefficient q L , q C , q R Figure 6 shows the acoustic filter coefficients q applied to each speaker. L , q C , q R Here, the value of X may be any value other than -1. From the perspective of reducing the acoustic power W, the value of X is close to -1. However, the closer the value of X is to -1, the smaller the effect of increasing the sound in the front direction of the speaker becomes. For this reason, it is desirable to determine the value of X by taking into consideration the effect of reducing the acoustic power W and the effect of increasing the sound in the front direction. Note that, in experiments conducted by the applicant, it has been confirmed that when X is set to 0, 1, or 2, the effect of reducing the acoustic power W and the effect of increasing the sound in the front direction are both achieved.

[0035] For example, q L =1, q C =1, q R When ρ = -1, the node n of the sound pressure is formed biased toward the speaker 104R side, as shown in Fig. 6. Therefore, the reduction in the sound boost effect is suppressed in front of the speaker 104C. Therefore, as shown in Fig. 7, the area A in front of the speaker 104C can become a sound boost area.

[0036] The acoustic filter coefficients calculated as described above are an example of a case where the sound source is composed of a main sound source and two additional sound sources arranged symmetrically with respect to the main sound source. Generally, when composed of N additional sound sources, the acoustic filter coefficients should be determined so that the condition shown in the following equation (8) is satisfied. That is, the sum of the complex volume velocity of the main sound source and the sum of the complex volume velocities of the additional sound sources should not be 0. In this case, the sounds radiated from at least two of the additional sound sources will be in antiphase.

number

[0037] 8 and 9 show the example of FIG. 4 with αi =-β i =-1, and α r +β r = 1, and the acoustic filter coefficient q obtained from equation (1) L , q C , q R The gain and phase characteristics of the signal are shown. The product of the gain and phase characteristics is subjected to an inverse Fourier transform to calculate an FIR (finite impulse response) filter as an acoustic filter to be convolved with the audio signal.

[0038] As shown in Figure 8, the acoustic filter coefficient q C The convolved speech signal and the acoustic filter coefficients q L The gain of the speech signal convolved with q is almost the same in the range of 500Hz-3000Hz. As shown in Figure 9, the gain of the acoustic filter coefficient q C The convolved speech signal and the acoustic filter coefficients q L The phase of the convolved speech signal is also almost the same in the range of about 500Hz-3000Hz. On the other hand, the acoustic filter coefficient q R The gain of the convolved audio signal is the acoustic filter coefficient q in the range of 500Hz-3000Hz. C The speech signal convolved with and the acoustic filter q L is lower than the gain of the convoluted audio signal. Also, the acoustic filter coefficient q R The sign of the phase of the convolved speech signal is the acoustic filter coefficient q L is inverted with respect to the sign of the phase of the convolved speech signal, while the acoustic filter coefficients q R The convolved speech signal and the acoustic filter coefficients q L is not in antiphase with the convolved audio signal.

[0039] Fig. 10 shows the sound pressure level around the speaker when sound convoluted with the acoustic filters having the characteristics shown in Figs. 8 and 9 is emitted. Fig. 10 shows an example in which the speaker spacing is 0.1 m and the frequency of the emitted sound is 1500 Hz. The x-axis and y-axis in Fig. 10 represent the distance from the origin, for example, when the origin is the position of speaker 104C. The vertical axis in Fig. 10 represents the sound pressure level. In other words, Fig. 10 shows the distribution of sound pressure levels in the area in front of speaker 104C.

[0040] 10 is a diagram showing the calculation results for the relationship between the frequency and the sound pressure level when radiated as shown in FIG. 10. The horizontal axis of FIG. 10 is the frequency of the audio signal. The vertical axis of FIG. 10 is the sound pressure level. As shown in FIGS. 8 and 9, the acoustic filter coefficient q L The convolved speech signal and the acoustic filter coefficients q R 10, there is no sound pressure node that would cause a drop in sound pressure level in the front direction of speaker 104C. Also, a sound pressure gradient occurs in the front left direction.

[0041] The combined control of sound increase control and acoustic power reduction control for three speakers will be further described below. Fig. 11 is a diagram showing evaluation points in the calculation results described in Figs. 12 and 13. Points L, C, and R in Fig. 11 indicate the positions of speakers 104L, 104C, and 104R, respectively. That is, speaker 104C is located at the origin. The distance between speakers 104L and 104C, and the distance between speakers 104C and 104R are d, respectively. The sound increase control point P is located at position (-dL, -R). Figs. 12 and 13 show the results when d = 0.1 m, L = 0.2 m, R = 0.5 m, and U = 0.2 m.

[0042] Also, the acoustic filter coefficients q convolved with the audio signals input to the speakers 104L, 104C, and 104R are L , q C , q Ris calculated from equations (1), (2), and (8) as shown in the following equation (9). Here, n in equation (9) is the multiplication factor of the sound pressure energy at the sound increase control point P. D c is the transfer function between the increase control point P and the loudspeaker 104C. L is the transfer function between the loudspeaker control point P and the loudspeaker 104L. R is the transfer function between the increase control point P and the speaker 104R.

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[0043] In this setting, evaluation point A is set at the position (-d, -U), and evaluation point B is set at the position (+d, -U). As shown in Fig. 10, evaluation point A is a point that is expected to be louder than evaluation point B.

[0044] FIG. 12 shows the calculation results of the frequency characteristics of sound pressure at evaluation points A and B. As shown in FIG. 12, the sound pressure at evaluation point A is higher than the sound pressure at evaluation point B until the frequency of the audio signal reaches approximately 3000 Hz. The difference between the sound pressure at evaluation point A and the sound pressure at evaluation point B is approximately 10 dB-12 dB. As shown, for audio signals up to 3000 Hz, a sufficient sound pressure gradient is ensured between evaluation points A and B. In other words, the sound becomes difficult to hear at evaluation point B, while the sound is easy to hear at evaluation point A. On the other hand, once the frequency exceeds 3000 Hz, the difference in sound pressure between evaluation point A and evaluation point B begins to disappear, and thereafter the sound pressure at evaluation point B becomes higher than the sound pressure at evaluation point A. This is due to the effect of side lobes occurring at higher frequencies.

[0045] FIG. 13 is a diagram showing the frequency characteristics of the sound pressure difference between evaluation points A and B before and after the implementation of combined control of sound increase control and acoustic power reduction control. OFF:AB in FIG. 13 shows the calculation results of the frequency characteristics of the sound pressure difference between evaluation points A and B before the implementation of combined control. Before the implementation of combined control, sound is radiated only from speaker 104C, which is the main sound source. On the other hand, ON:AB in FIG. 13 shows the frequency characteristics of the sound pressure difference between evaluation points A and B after the implementation of combined control. After the implementation of combined control, sound is radiated from speaker 104C, which is the main sound source, and speakers 104L and 104R, which are additional sound sources. As shown in FIG. 13, there is no sound pressure difference between evaluation points A and B before the implementation of combined control. In other words, the sound is heard equally at both evaluation points A and B. On the other hand, after the implementation of combined control, a sound pressure difference occurs between evaluation points A and B.

[0046] FIG. 14 shows how the sound pressure distribution changes when the frequency of the audio signal and the speaker spacing are varied. As shown in FIG. 14, if the frequency, i.e., the product kd of the wave number and the speaker spacing, is the same, the sound pressure distributions match. It can also be seen that the side lobes are suppressed more effectively at lower frequencies with the same speaker spacing, and at narrower speaker spacing with the same frequency. From this relationship between frequency and speaker spacing, the effect of control using the designed acoustic filter coefficients can be estimated. For example, if the frequency of the audio signal to be reproduced is known, an appropriate speaker spacing can be determined accordingly. Conversely, if the speaker spacing is fixed, the applicable frequency band that provides a sufficient sound pressure gradient can be determined accordingly.

[0047] Figure 15 shows the experimental results for noise in the 400 Hz-1250 Hz band, which is the target frequency band. As mentioned above, the target frequency band is the frequency band of the audio signal where a sufficient sound pressure gradient is expected, determined by the speaker spacing. In Figure 15, the speaker spacing d is 0.1 m. Figure 16 shows the experimental results for noise up to 20,000 Hz, including noise outside the target frequency band. The experiment was conducted by arranging three speakers 104L, 104C, and 104R side by side as shown in Figure 17, and measuring the sound pressure at evaluation points A, B, C, D, and E in the front direction of speaker 104C. Evaluation point B is located directly in front of speaker 104L, separated by a distance R. Evaluation point C is located directly in front of speaker 104C, separated by a distance R. Evaluation point D is located directly in front of speaker 104L, separated by a distance R. Evaluation point A is located at a distance L to the left of evaluation point B. Evaluation point E is located at a distance L to the right of evaluation point D. L is 0.2 m. The distance R in the front direction from evaluation points A, B, C, D, and E is 0.25 m. The horizontal axis in Figures 15 and 16 represents the center frequency of the 1 / 3 octave band. The vertical axis in Figures 15 and 16 represents the 1 / 3 octave band level.

[0048] As shown in Fig. 15, when the acoustic filter coefficients obtained according to equation (8) are used, a sound pressure gradient of approximately 12 dB is realized at any of the evaluation points AE in the front direction of speaker 104C in the applicable frequency band of 400 Hz to 1250 Hz. Also, as shown in Fig. 16, when the acoustic filter coefficients obtained according to equation (8) are used, a sound pressure gradient of approximately 12 dB is realized at any of the evaluation points AE in the front direction of speaker 104C, even in frequency bands higher than the applicable frequency band. This is because the acoustic filter coefficients are designed to prevent the generation of sound pressure nodes in the front direction of the speaker.

[0049] FIG. 18 shows the results of boosting the sound level in the left direction due to a noise source in the 400 Hz-1250 Hz band, which is the target frequency band. The speaker spacing d used to obtain the results in FIG. 18 was 0.1 m. In other words, with the position of speaker 104C as the origin, speaker 104L is located at (-0.1, 0), and speaker 104R is located at (0.1, 0). The boost control point is located at (-0.3, -1). The distance R to the evaluation point is 0.25 m from the speaker position. In FIG. 18, the sound pressure drops sharply when the evaluation point changes from directly in front of speaker 104L to directly in front of speaker 104R, i.e., when the evaluation point changes from (-0.1, 0.25) to (0.1, 0.25). Thus, in this embodiment, a sharp sound pressure gradient can be formed by a change in spacing as short as 0.2 m.

[0050] Fig. 19 is a conceptual diagram of a case where a sound control device according to an embodiment is used in a voice guidance system. Fig. 19 shows a schematic diagram of the distribution of sound pressure in the vicinity of a user listening to voice guidance from the voice guidance system. Sound pressure distribution G1 in Fig. 19 is the distribution of sound pressure caused by sound emitted from the sound control device, and sound pressure distribution G2 is the distribution of sound pressure due to natural attenuation that is not subject to control by the sound control device.

[0051] By emitting sound based on the acoustic filter coefficients described in the embodiment, as shown in FIG. 19 , the speakers 104L, 104C, and 104R can be arranged side by side, with the front direction of the speaker 104C being the sound-increased area A. That is, as shown by the sound pressure distribution G1 in FIG. 19 , the sound pressure is high in the sound-increased area A, but the sound pressure drops sharply outside the sound-increased area A. Furthermore, as shown by the sound pressure distribution G2, the sound pressure also drops due to natural attenuation depending on the distance from the sound control device. Therefore, a user u1 in the sound-increased area A can hear the guidance voice radiated from the sound control device. On the other hand, a user u2 outside the sound-increased area A has difficulty hearing the guidance voice radiated from the sound control device. Background noise is particularly common in public spaces. Therefore, in the area where user u2 is located, the sound pressure of the guidance voice radiated from the sound control device drops sharply, and this voice is further masked by background noise. Therefore, it is expected that user u2 will have even more difficulty hearing the guidance voice in public spaces. Therefore, the technology of the embodiment is also suitable for use in audio guidance in public spaces.

[0052] Furthermore, by utilizing the characteristic that sound pressure rapidly attenuates within a narrow range described in the embodiment, the technology of the embodiment can also be applied to a sound control system configured with multiple sound control devices arranged in a straight line. FIG. 20 is a conceptual diagram of a voice guidance system as an application example of the sound control system according to the embodiment. In FIG. 20, a first sound control device consisting of horizontally arranged speakers 104L1, 104C1, and 104R1 and a second sound control device consisting of horizontally arranged speakers 104L2, 104C2, and 104R2 are arranged in a straight line. FIG. 20 also shows a schematic view of the sound pressure distribution around a user listening to the voice guidance of the voice guidance system. Sound pressure distribution G1 in FIG. 20 is the distribution of sound pressure generated by the sound emitted from the first sound control device, and sound pressure distribution G2 is the distribution of sound pressure due to natural attenuation, which is not subject to control by the first sound control device. Also, sound pressure distribution G3 in FIG. 20 is the distribution of sound pressure caused by sound radiated from the second acoustic control device, and sound pressure distribution G4 is the distribution of sound pressure due to natural attenuation that is not subject to control by the second acoustic control device.

[0053] In this arrangement, for the first acoustic control device on the left, a volume increase control point is set on the front left side of speaker 104C1, thereby setting a volume increase area A1 on the front left side of speaker 104C1. On the other hand, for the second acoustic control device on the right, a volume increase control point is set on the front right side of speaker 104C2, thereby setting a volume increase area A2 on the front right side of speaker 104C2.

[0054] As a result, as shown by sound pressure distribution G1 in FIG. 20 , the sound pressure is high in the increased volume area A1, but drops sharply outside the increased volume area A1. Furthermore, as shown by sound pressure distribution G2, a drop in sound pressure also occurs due to natural attenuation depending on the distance from the first sound control device. Therefore, user u1 in the increased volume area A1 can hear the guidance audio emitted from the first sound control device. On the other hand, user u2 outside the increased volume area A1 has difficulty hearing the guidance audio emitted from the first sound control device. Furthermore, as shown by sound pressure distribution G3 in FIG. 20 , the sound pressure is high in the increased volume area A2, but drops sharply outside the increased volume area A2. Furthermore, as shown by sound pressure distribution G4, a drop in sound pressure also occurs due to natural attenuation depending on the distance from the second sound control device. Therefore, user u2 in the increased volume area A2 can hear the guidance audio emitted from the second sound control device. On the other hand, a user u1 outside the sound-increased area A1 has difficulty hearing the guidance voice emitted from the second sound control device.

[0055] In this way, even in a voice guidance system in which multiple sound control devices are arranged in a straight line, it is possible to prevent a user from hearing the sound from the adjacent sound control device where the user is actually listening to the guidance. This also contributes to protecting the privacy of individual users. Conventionally, ultrasonic speakers have been used to generate such directional sounds. However, because ultrasonic speakers have such good directivity, secondary sounds can be heard due to reflections from the wall or floor behind them. The technology of the embodiment does not require the use of ultrasonic speakers, so such secondary sounds are not heard.

[0056] In Fig. 20, the volume increase control points are set in different directions for the first and second sound control devices. However, because there is natural attenuation of sound pressure depending on the distance from the sound control device as shown by sound pressure distributions G2 and G4 in Fig. 20, it is not necessarily necessary to set the volume increase control points in different directions for the first and second sound control devices as long as there is a certain amount of distance between the first and second sound control devices.

[0057] 21 and 22 are conceptual diagrams of a case where the acoustic control system according to the embodiment is used in a digital signage system. Figures 21 and 22 are top views of the digital signage system. In the digital signage system of Figure 21, a first acoustic control device consisting of horizontally arranged speakers 104L1, 104C1, and 104R1 is arranged facing the front, and a second acoustic control device consisting of horizontally arranged speakers 104L2, 104C2, and 104R2 is arranged facing the rear. In the digital signage system of Figure 22, a first sound control device consisting of speakers 104L1, 104C1, and 104R1 arranged side by side is arranged facing forward, a second sound control device consisting of speakers 104L2, 104C2, and 104R2 arranged side by side is arranged facing backward, a third sound control device consisting of speakers 104L3, 104C3, and 104R3 arranged side by side is arranged facing right, and a fourth sound control device consisting of speakers 104L4, 104C4, and 104R4 arranged side by side is arranged facing left.

[0058] 21 and 22, similar to the voice guidance system, high sound pressure is only present within the volume-increased area of ​​each voice control device, and the sound pressure drops sharply outside the volume-increased area. Therefore, users within each volume-increased area can only hear the sound emitted from the corresponding sound control device.

[0059] As described above, according to the embodiment, the acoustic filter coefficients are designed so that the acoustic power when multiple sound sources are viewed as one sound source is reduced but not minimized. By implementing such acoustic control that combines acoustic power reduction control and sound increase control, the position of the sound pressure node is shifted from the front direction of the main sound source, so that the sound in the front direction of the main sound source can be increased while the sound sources are arranged side by side.

[0060] (Variation) In the above-described embodiment, a combination of sound increase control and sound power reduction control using three sound sources arranged side by side has been mainly described. As shown in equations (2) and (8), the technology of the embodiment can be applied to a case where the number of sound sources is four or more. Here, one of the sound sources is a main sound source, and the rest are additional sound sources. Furthermore, the technology of the embodiment can be applied to a case where a main sound source C and additional sound sources S1, ..., S are combined as shown in FIG. 23 . i The above may be applied even if they are not arranged side by side.

[0061] For example, as shown in FIG. 23, when the sound increase control point P is one point, the additional sound source S i The acoustic filter coefficient q si The first and second relational expressions for the sound increase control law and the sound power control law are expressed as equations (10) and (11). si must satisfy the condition of equation (12).

number

[0062] In addition, in the embodiment, the volume increase control point P can be set at any position in front of the sound source. However, as described above, the longer the distance between the sound sources, the more likely the sound pressure at positions farther from the sound source is to decrease due to the influence of side lobes. Furthermore, the further away from the sound source, the greater the decrease in sound pressure due to natural attenuation. Therefore, in order to obtain a sufficient sound pressure gradient at the volume increase control point P, it is desirable to set the volume increase control point P within a certain range from the sound source. FIG. 24 is a diagram showing the positional relationship between the sound source and the volume increase control point P that can obtain a sufficient sound pressure gradient. FIG. 24 shows a main sound source C and two additional sound sources S arranged symmetrically with respect to the main sound source C. The distance between the main sound source C and the additional sound sources S is d. The applicant's experiments have confirmed that a sufficient sound pressure gradient can be obtained at the volume increase control point P if the volume increase control point P is arranged within the range of −3d≦x≦3d in the x direction, which coincides with the direction of the line along which the sound sources are arranged in the arrangement shown in FIG. 24 .

[0063] Next, an example of the hardware configuration of the acoustic control device 100 described in each of the above-mentioned embodiments will be described with reference to Fig. 25. Fig. 25 is a diagram showing an example of the hardware configuration of the acoustic control device 100.

[0064] As shown in FIG. 25, the acoustic control device includes a computer to which a control unit 209, a memory unit 210, a power supply unit 211, a timing device 212, a communication interface (I / F) 205, an input unit 206, an output device 207, and an external interface (I / F) 208 are electrically connected.

[0065] The control unit 209 includes a CPU (Central Processing Unit), RAM (Random Access Memory), and / or ROM (Read Only Memory), and controls each component in accordance with information processing. The control unit 209 can operate as the audio signal input unit 101, the audio signal processing device 102, and the control device 103. The control unit 209 can call up an execution program stored in the storage unit 210 and execute processing.

[0066] The storage unit 210 is a medium that stores information such as programs so that it can be read by a computer, machine, etc. The storage unit 210 can also store speaker spacing information, audio signal frequency information, and transfer function information. The storage unit 210 can be, for example, an auxiliary storage device such as a hard disk drive or a solid state drive. The storage unit 210 may also include a drive. A drive is a device for reading data stored in another auxiliary storage device, a recording medium, etc., and includes, for example, a semiconductor memory drive (flash memory drive), a CD (Compact Disk) drive, a DVD (Digital Versatile Disk) drive, etc. The type of drive may be selected appropriately depending on the type of storage medium.

[0067] The power supply unit 211 supplies power to each element of the audio control device 100. The power supply unit 211 may further supply power to each element of a device that includes the audio control device 100. The power supply unit 211 may include, for example, a secondary battery or an AC power supply.

[0068] The timing device 212 is a device that measures time. For example, the timing device 212 may be a clock including a calendar, and transmits information on the current year, month, and / or date and time to the control unit 209. The timing device 212 may be used to add a date and time to the audio signal to be played back.

[0069] The communication interface 205 is, for example, a short-range wireless communication (e.g., Bluetooth (registered trademark)) module, a wired LAN (Local Area Network) module, a wireless LAN module, etc., and is an interface for performing wired or wireless communication via a network. This communication via the network may be either wireless or wired. The network may be an internetwork including the Internet, or another type of network such as an in-house LAN. Furthermore, the communication interface 205 may perform one-to-one communication using a USB (Universal Serial Bus) cable or the like. Furthermore, the communication interface 205 may include a micro USB connector. The communication interface 205 is an interface for connecting the acoustic control device to external devices such as automobiles, trains, household electrical appliances, and various communication devices. The communication interface 205 is controlled by the control unit 209 and receives various types of information from external devices via a network or the like. The various types of information include, for example, information on speaker spacing, audio signal frequency, and transfer function information set in the external device.

[0070] The input unit 206 is a device that accepts input, and may be, for example, a touch panel, physical buttons, a mouse, a keyboard, etc. The output device 207 is a device that performs output, and may be, for example, a display, a speaker, etc. that outputs information by display, audio, etc. Information on speaker spacing, information on the frequency of audio signals, and information on transfer functions may be input via the input unit 206.

[0071] The external interface 208 is used to connect the main body of the audio control device with external devices, such as a printer, a memory, and a communication device.

[0072] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0073] 100 Acoustic control device, 101 Audio signal input unit, 102 Audio signal processing device, 103 Control device, 104L, 104C, 104L Speaker, 205 Communication interface, 206 Input unit, 207 Output device, 208 External interface, 209 Control unit, 210 Memory unit, 211 Power supply unit, 212 Timing device, 1021 Amplifier, 1022L, 1022C, 1022R Acoustic filter, 1031 Acquisition unit, 1032 Acoustic filter coefficient calculation unit, 1033 Acoustic filter coefficient memory unit, 1034 Acoustic filter setting unit.

Claims

1. calculate a first relational expression between acoustic filter coefficients to be applied to the audio signal containing information of the reproduced sound, the acoustic filter coefficients being determined so as to be equal to the volume velocities of the sounds reproduced from the main sound source and the two or more additional sound sources, based on a sound pressure multiplication factor at a sound increase control point that is increased by sounds reproduced from the main sound source and two or more additional sound sources, a transfer function between the main sound source and the sound increase control point, and a transfer function between each of the additional sound sources and the sound increase control point; calculating a second relational expression between the acoustic filter coefficients of the main sound source and the additional sound source on the condition that the sum of the volume velocities of the sounds reproduced from each of the additional sound sources and the volume velocity of the sound reproduced from the main sound source is not zero; calculating each of the acoustic filter coefficients based on the first relational expression and the second relational expression; An acoustic control device comprising an acoustic filter coefficient calculation unit.

2. the main sound source and each of the additional sound sources are arranged in a straight line, In the direction along the straight line, the volume increase control point is set within a range three times the distance between the main sound source and the additional sound source. The acoustic control device according to claim 1 .

3. A plurality of the acoustic control devices according to claim 1 or 2 are arranged, The positions of the sound increase control points for each of the acoustic control devices are different. Sound control system.

4. Calculating a first relational expression between acoustic filter coefficients to be applied to the audio signal containing information of the reproduced sound, the acoustic filter coefficients being determined so as to be equal to the volume velocities of the sounds reproduced from the main sound source and the two or more additional sound sources, based on a sound pressure multiplication factor at a sound increase control point that is increased by sounds reproduced from the main sound source and two or more additional sound sources, a transfer function between the main sound source and the sound increase control point, and a transfer function between each of the additional sound sources and the sound increase control point; Calculating a second relational expression between the acoustic filter coefficients of the main sound source and the additional sound source, on the condition that the sum of the volume velocities of the sounds reproduced from each of the additional sound sources and the volume velocity of the sound reproduced from the main sound source is not zero; calculating each of the acoustic filter coefficients based on the first relational expression and the second relational expression; An acoustic control program that causes a computer to execute the above.

5. Calculating a first relational expression between acoustic filter coefficients to be applied to the audio signal containing information of the reproduced sound, the acoustic filter coefficients being determined so as to be equal to the volume velocities of the sounds reproduced from the main sound source and the two or more additional sound sources, based on a sound pressure multiplication factor at a sound increase control point that is increased by sounds reproduced from the main sound source and two or more additional sound sources, a transfer function between the main sound source and the sound increase control point, and a transfer function between each of the additional sound sources and the sound increase control point; Calculating a second relational expression between the acoustic filter coefficients of the main sound source and the additional sound source, on the condition that the sum of the volume velocities of the sounds reproduced from each of the additional sound sources and the volume velocity of the sound reproduced from the main sound source is not zero; calculating each of the acoustic filter coefficients based on the first relational expression and the second relational expression; An acoustic control method comprising:

6. the main sound source and each of the additional sound sources are arranged side by side in a direction intersecting a front direction of the main sound source, The main sound source is located between at least two of the additional sound sources. The acoustic control device according to claim 1 .

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