JP2019161455A - Ambisonics signal generating device, sound field reproducing device, and ambisonics signal generating method - Google Patents

Abstract

To provide an Ambisonics signal generating device, a sound field reproducing device, and an Ambisonics signal generating method, capable of generating an appropriate Ambisonics signal even when applied to a scale model experiment.SOLUTION: An Ambisonics signal generating device 20 includes: a single microphone 22 for collecting sound in a predetermined target frequency band; a moving unit 24 for moving the microphone 22 to each of a plurality of positions separated by a distance d determined according to a value less than a half wavelength of sound having an upper limit frequency in the target frequency band; and an Ambisonics signal generating unit 28 for generating an Ambisonics signal on the basis of a signal of sound collected by the microphone 22 at each of the plurality of positions.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an ambisonics signal generation device, a sound field reproduction device, and an ambisonics signal generation method.

Conventionally, as a study tool used for acoustic design of a theater or a hall, there are computer simulation and scale model experiment. In the method using computer simulation as a study tool , the three-dimensional shape of a room is converted into a CAD (Computer Aided Design) model, and the sound propagation characteristics in the space are examined in accordance with geometric acoustics. In recent years, the computer's computing power has been improved, and architectural books have been converted to CAD so that room shape data can be shared with architectural designers. Therefore, it is becoming an economical and flexible tool.

  However, in the method using computer simulation, assumptions regarding signal reflection, analysis, and scattering may differ greatly from the actual sound field. In computer simulation, it is difficult to handle various irregular surfaces and design details such as two-dimensional curved surfaces and three-dimensional curved surfaces, which are important elements in actual buildings.

  On the other hand, in the method using the scale model experiment as a study tool, generally, a model of a real sound field with a scale of 1/10 to 1/20 of the actual scale is manufactured, and sound propagation is measured under a condition satisfying the similarity law. For example, an elaborate model can be produced by using NC (Numerically Controlled) machine tools based on architectural CAD data. In other words, the method using the scale model experiment can simulate the factor related to the room shape with considerable accuracy, and can consider the influence of curved surfaces and details for which no effective calculation method has been established. Therefore, the scale model experiment has become an important tool in projects that require high acoustic quality.

"Highly realistic acoustic technology and its theory" Ando, IEICE Fundamentals Review, Vol.3, No.4, pp33-46, 2010

  In the scale model experiment described above, for example, there are methods in which two monaural microphones are set apart at the sound receiving position of the scale model, or a small stereo microphone is used. Although this method can be easily measured, since the sound field that can be reproduced is limited to two dimensions, there is a problem that only a sound field equivalent to that of normal stereo reproduction can be reproduced.

  For example, there is a method of collecting sound using a small dummy head. This method simulates the head-related transfer function and can collect and reproduce a three-dimensional acoustic space. However, the shape of the head, auricle, shoulder, etc. of the small dummy head during sound collection and There is a problem that the same shape of the listener needs to completely satisfy the similar side, and if it is different, it cannot be accurately reproduced. Moreover, when the reproduced sound is presented with headphones, the above-described problems can be avoided, but it is technically difficult to perform out-of-head localization, and reproduction of a three-dimensional sound field is difficult.

  On the other hand, there is an ambisonics method as a method for collecting and reproducing a real sound field in three dimensions. Ambisonics is a method of hierarchically expanding the sound pressure at a sound receiving point with a spherical harmonic function, and the collection and reproduction of a three-dimensional sound field from monophonic is formulated (for example, see Non-Patent Document 1). .

  The first-order ambisonics is a method that uses expansion coefficients up to the first order of the spherical harmonic function, and there is no omnidirectionality (0th order) and directivity in the x, y, and z-axis directions. There are two types, A format and B format. In the A format, four cardioid microphones arranged at the vertices of a regular tetrahedron are used. In the B format, a microphone in which a bidirectional microphone is arranged near the center of the microphone unit, one for the x, y, and z directions and one omnidirectional microphone is used. And, it is a method of obtaining omnidirectional and bidirectional characteristics by calculation.

  Furthermore, in order to collect sound with high accuracy, a method of obtaining high-order directivity by a method using a multi-channel microphone installed on the sphere surface has been put into practical use.

  Therefore, it is desired to make the three-dimensional sound field audible by applying the ambisonics method to a scale model experiment. However, in this case, measurement in the ultrasonic band is required due to the similarity law, but there is no ambisonics microphone that satisfies this condition in a small size.

  As described above, when the conventional method is applied to the scale model experiment, the generation of the ambisonic signal by the sound collected in the scale model is not properly performed, and it is difficult to reproduce the sound field.

  The present invention has been made to solve the above problems, and even when applied to a scale model experiment, an ambisonic signal generator, a sound field reproducing device, and an ambisonics capable of generating an appropriate ambisonic signal. An object is to provide a signal generation method.

  In order to achieve the above object, an ambisonics signal generation device according to a first aspect includes a single microphone that collects sound in a predetermined target frequency band, and a half of the sound in the upper limit frequency of the target frequency band. A moving unit that moves the microphone to each of a plurality of positions separated by a distance determined according to a value less than a wavelength, and an ambience based on a sound signal collected by the microphone at each of the plurality of positions. A signal generation unit that generates a sonics signal.

  In the ambisonics signal generation device according to the first aspect, a single microphone is moved by the moving unit to each of a plurality of positions separated by a distance determined according to a value less than a half wavelength of the sound of the upper limit frequency of the target frequency band. Thus, an ambisonic signal is generated based on the sound signal collected by the microphone. Thereby, according to the ambisonics signal generation device of the first aspect, it is possible to generate an appropriate ambisonics signal even when applied to a scale model experiment.

  The ambisonic signal generator of the second aspect is the ambisonic signal generator of the first aspect, wherein the target frequency band is two or more of a plurality of bands divided according to the frequency, The distance is determined according to a value less than a half wavelength of the sound of the upper limit frequency of each of the two or more bands.

  In the ambisonics signal generation device of the second aspect, since the target frequency band is two or more bands among the plurality of bands divided according to the frequency, compared to one band (when not divided), The SN (signal-to-noise) ratio of the microphone can be improved.

  The ambisonics signal generation device according to a third aspect is the ambisonics signal generation device according to the first or second aspect, wherein the microphone collects sound in a scale model space created by reducing the actual sound field. To do.

  In the ambisonics signal generation device according to the third aspect, the ambisonic signal is generated by the sound collected in the scale model in order to collect the sound in the scale model space created by reducing the actual sound field by the microphone. can do.

The ambisonics signal generation device according to a fourth aspect is the ambisonic signal generation device according to any one of the first to third aspects, wherein the plurality of positions are generated by the signal generation unit. When the order of the sonic signal is n, it is determined at a position of (n + 1) ² or more.

In the ambisonics signal generation device according to the fourth aspect, when the order of the ambisonics signal is n, the sound is collected by the microphone at a position of (n + 1) ² or more, so that an ambisonics signal with high reproduction accuracy is generated. can do.

  The ambisonics signal generation device according to a fifth aspect is the ambisonics signal generation device according to any one of the first to fourth aspects, wherein the plurality of positions are assumed in a sound collection target space. A position corresponding to the origin of the three-dimensional space coordinates, and a position corresponding to each of a pair of points symmetrical with respect to the origin on each of the three axes of the three-dimensional space coordinates.

  In the ambisonics signal generation device according to the fifth aspect, the position corresponding to the origin of the three-dimensional spatial coordinates assumed in the sound collection target space and the origin on each of the three axes of the three-dimensional spatial coordinates are symmetrical. Sound is collected by a microphone at a position corresponding to each of the pair of points. Thus, according to the ambisonics signal generation device of the fifth aspect, since the sound is collected by the microphone at an appropriate position, it is possible to generate an ambisonic signal with high reproduction accuracy.

  The ambisonics signal generation device according to a sixth aspect is the ambisonics signal generation device according to any one of the first to fifth aspects, wherein the plurality of positions include positions where the distances are different.

  In the ambisonics signal generation device according to the sixth aspect, it is possible to include sounds collected by the microphones at positions with different distances, so that the degree of freedom in positioning during sound collection can be increased.

  In order to achieve the above object, a sound field reproduction device according to a seventh aspect includes the ambisonics signal generation device according to any one of the first to sixth aspects, and the ambisonics signal generation device. And a drive unit that generates a drive signal for driving the speaker using the generated ambisonics signal.

  In the sound field reproduction device according to the seventh aspect, the driving unit can drive the speaker by the drive signal generated from the ambisonic signal generated by the ambisonic signal generator of the present disclosure. As described above, according to the sound field reproducing device of the seventh aspect, even when applied to the scale model experiment, it is possible to generate an appropriate ambisonic signal and appropriately reproduce the sound field.

  In order to achieve the above object, an ambisonics signal generation method according to an eighth aspect includes a step of a single microphone collecting sound in a predetermined target frequency band, and a moving unit including the target frequency band. Moving the microphone to each of a plurality of positions separated by a distance determined according to a value less than a half wavelength of the sound of the upper limit frequency of the sound, and a signal generator is collected by the microphone at each of the plurality of positions. Generating an ambisonics signal based on the signal of the sound that has been sounded.

  According to the present disclosure, even when applied to a scale model experiment, it is possible to generate an appropriate ambisonic signal.

It is a block diagram which shows an example of a structure of the sound field reproduction | regeneration system of embodiment. It is a figure which shows an example of the sound source of embodiment. It is a figure which shows an example of the microphone and moving part of embodiment. It is a block diagram which shows an example of a structure of the control system of the sound field reproducing | regenerating apparatus (ambisonics signal generation apparatus) of embodiment. It is a flowchart which shows an example of the flow of the ambisonics signal generation process of embodiment. It is a figure explaining the position example of the sound collection position of the microphone for obtaining a primary ambisonics signal. It is a flowchart which shows an example of the flow of the ambisonics signal reproduction | regeneration processing of embodiment. It is a figure explaining the position example of the sound collection position of the microphone for obtaining a secondary ambisonics signal.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, this embodiment does not limit this invention.

  First, an example of the overall configuration of a sound field reproduction system 1 to which the present invention is applied will be described with reference to FIG.

  As shown in FIG. 1, the sound field reproduction system 1 of this embodiment includes a sound field reproduction device 10, a scale model 12, a sound source 14, and a speaker 18. As shown in FIG. 1, the sound field reproduction device 10 according to the present embodiment includes an ambisonic signal generation device 20 and an ambisonic decoder 30. Furthermore, the ambisonics signal generation device 20 includes a microphone 22, a moving unit 24, a control unit 26, and an ambisonics signal generation unit 28.

  The scale model 12 of this embodiment is a model in which the actual sound field is reduced to 1/10 as an example. Needless to say, the reduction ratio of the model is not limited to this embodiment. Inside the scale model 12, a sound source 14, a microphone 22, and a moving unit 24 are arranged.

  The sound source 14 is a sound source for the scale model 12. The sound source 14 of the present embodiment has sufficient acoustic power, a wide and flat frequency characteristic, a reproducibility of a radiation waveform (no hysteresis) required as a sound source used for a scale model experiment, and a lifetime.・ Performs such as good durability. The sound source 14 satisfies the similarity to the ISO3882 dodecahedron sound source when measuring physical quantities. An example of the sound source 14 of the present embodiment is shown in FIG.

  The sound source 14 shown in FIG. 2 uses a vibration body that is fixed around a vibration film to which a PVDF (PolyVinylidene DiFluoride) film, which is a piezoelectric vibration body, is bonded and held in a waveform. The size of one unit of the vibrating body was 22.8 mm × 11.8 mm × 3.8 mm, and the width and depth of the tack were 3 mm to 6 mm, and 0.5 mm to 1 mm. This vibrating body was attached to each surface of the dodecahedron as a vibrating portion 14A, and the sound source 14 was produced as a 1/10 scale dodecahedron speaker.

  Note that the sound source 14 of the present embodiment is a target frequency for collecting a sound source 14 for a low frequency range corresponding to a frequency up to 40 kHz and a sound source 14 for a high frequency range corresponding to a frequency of 14 kHz to 300 kHz. It is used properly according to the bandwidth.

  On the other hand, as the microphone 22 of the present embodiment, a single microphone that collects an ambisonic signal is used. As a specific example, in the present embodiment, as the microphone 22, a 4138 type, external polarization type sound pressure sound field microphone manufactured by B & K Co., Ltd. is used as a single unit. The microphone 22 of the present embodiment collects the sound output from the sound source 14 and outputs the collected sound signal to the ambisonic signal generator 28.

  The microphone 22 of this embodiment is attached to a moving unit 24, and can be moved to each of a plurality of predetermined positions (details will be described later) by the moving unit 24. An example of the microphone 22 and the moving unit 24 of the present embodiment is shown in FIG. The moving unit 24 of the present embodiment includes an automatic stage 24A, a holding unit 24B attached to the automatic stage 24A, and a holding unit 24C attached to the tip of the holding unit 24B. A microphone 22 is held at the tip of the holding portion 24C.

  The automatic stage 24A is connected to the control unit 26, and automatically moves the microphone 22 held by the holding unit 24C in a three-dimensional direction (x, y, z) according to an instruction from the control unit 26. . The exterior of the automatic stage 24A is covered with a sound absorbing material so that the sound from the sound source 14 does not reverberate (reflect).

  In this embodiment, as a specific example, positioning is performed by combining a high-grade XY stage, ALD-4011-G0M, manufactured by Chuo Seiki, and a high-grade Z lift stage, LV-4042-1, manufactured by Chuo Seiki. An automatic stage having an accuracy of 0.01 mm, a stage size of 40 mm × 40 mm, and a height of 90 mm was produced and used as the moving unit 24. The length of the holding portion 24B was 280 mm, and the length of the holding portion 24C was 50 mm.

  The control unit 26 of the present embodiment has a function of performing control to output sound in a predetermined target frequency band from the sound source 14. Further, the control unit 26 has a function of outputting an instruction for moving the microphone 22 to a plurality of predetermined positions (details will be described later) to the moving unit 24.

  The ambisonic signal generator 28 generates an ambisonic signal based on the sound signal output from the microphone 22. The ambisonics signal generation unit 28 of the present embodiment is an example of the signal generation unit of the present disclosure.

  The ambisonics decoder 30 decodes the ambisonic signal generated by the ambisonic signal generator 28 and generates a drive signal for driving each of the plurality of speakers 18 for reproducing the sound field. The ambisonics decoder 30 of the present embodiment is an example of a drive unit of the present disclosure.

  The control unit 26, the ambisonics signal generation unit 28, and the ambisonics decoder 30 of the present embodiment can be realized by a server computer or the like. With reference to FIG. 4, the configuration of the sound field reproduction device 10 (the ambisonics signal generation device 20) will be described. As shown in FIG. 4, the sound field reproduction apparatus 10 of this embodiment includes a CPU (Central Processing Unit) 40, a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 44, and an I / F (Interface). Part 46 is provided. The CPU 40 controls the overall operation of the sound field reproduction device 10. The ROM 42 stores in advance various programs including an ambisonic signal generation processing program, which will be described later, and an ambisonic signal reproduction process, which are executed by the CPU 40. The RAM 44 temporarily stores various data. The I / F unit 46 communicates with each of the sound source 14, the speaker 18, and the microphone 22 by at least one of wireless communication and wired communication. Although not shown, the I / F unit 46 transmits / receives various signals to / from an external device of the sound field reproduction device 10 by at least one of wireless communication and wired communication. The moving unit 24, the CPU 40, the ROM 42, the RAM 44, and the I / F unit 46 are connected to each other via a bus 49 such as a system bus or a control bus.

  Next, the operation of the sound field reproduction device 10 in the sound field reproduction system 1 of the present embodiment will be described.

Example 1
In the present embodiment, a description will be given of a form in which a primary ambisonic signal is generated and reproduced by the sound field reproducing apparatus 10.

  First, the ambisonic signal generation processing by the ambisonic signal generation device 20 in the present embodiment will be described.

  In the ambisonics signal generation device 20 of the present embodiment, as an example, when an instruction to start a scale model experiment performed by an external device is received, the CPU 40 executes an ambisonics signal generation processing program stored in the ROM 42. As a result, the CPU 40 functions as the control unit 26 and the ambisonics signal generation unit 28 and executes the ambisonics signal generation process shown in FIG.

  In step S100 illustrated in FIG. 5, the control unit 26 causes the sound source 14 to output sound in the target frequency band. In the present embodiment, as an example, the correspondence between the target frequency band and the distance d (hereinafter also referred to as “the distance of the microphone 22”) where the microphone 22 is arranged when collecting sound and the sound source 14 used. The relationship was determined as shown in Table 1 according to the similarity rule. As shown in Table 1, in this embodiment, as an example, considering the characteristics of the sound source 14 and the S / N ratio of the microphone 22, the band is divided into two, a low sound range and a high sound range as shown in Table 1 below. Each of the bands was set as a target frequency band, and sound output and sound collection were performed for each target frequency band.

  The distance d of the microphone 22 is preferably large (separated) in consideration of the sensitivity (SN ratio) of the differential signal of the impulse response signal (hereinafter referred to as “IR”), but spatial aliasing From the viewpoint of suppressing the occurrence, the upper limit frequency of the sound to be collected (target frequency band) is less than the half wavelength (λ / 2).

  In the next step S102, the control unit 26 sets a variable m for managing sound collection by the microphone 22 to “1” (m = 1). In step S104, the control unit 26 moves the microphone 22 to the Nth position.

  In the present embodiment, sound is collected by the microphone 22 at each of a plurality of positions away from the center w (see FIG. 6) from the sound source 14 and ± d / 2 from the center w in the x, y, and z axis directions. . As an example, in the present embodiment, the microphone 22 is sequentially arranged at each of the seven positions r1 to r7 shown in FIG. In the example shown in FIG. 6, the position r1 corresponds to the center w of the sound receiving point, and each of the positions r2 to r7 is separated from the center w by d / 2. Note that the center w of the present embodiment corresponds to an example of the origin of the three-dimensional spatial coordinates of the present disclosure.

  Thus, in this embodiment, since the sound is collected seven times, the above “N” representing the number of times of sound collection is set to 7. Note that the position of the microphone 22 is not limited to the positions r1 to r7 illustrated in FIG. 6 and may be any position where the distance d satisfies less than λ / 2.

  In the next step S <b> 106, sound is collected by the microphone 22, and the control unit 26 acquires the sound collected by the microphone 22.

  In next step S108, the control unit 26 determines whether or not the variable m is equal to the number N of times of sound collection (m = N). That is, it is determined whether or not sound collection has been performed at all sound collection positions. If the variable m is not equal to the number N of sound collection times, the determination in step S108 is negative and the process proceeds to step S110. In step S110, the control unit 26 adds “1” to the variable m (m = m + 1), returns to step S104, and repeats the above processing.

  On the other hand, if the variable m is equal to the number N of times of sound collection (m = N), the determination in step S108 is affirmative, and the process proceeds to step S112.

  In step S112, the ambisonic signal generation unit 28 generates an ambisonic signal from the sound signal collected at each sound collection position, and ends the present ambisonic signal generation process. In the present embodiment, as an example, the ambisonic signal generator 28 generates an ambisonic signal by deriving a bi-directional IR by taking a difference for each direction of the IR of each sound signal.

  Next, the reproduction of the sound field by the primary ambisonic signal generated in this way will be described.

  In the sound field reproduction device 10 of the present embodiment, as an example, when the reproduction of the sound field is instructed from an external device, the CPU 40 executes the ambisonics signal reproduction processing program stored in the ROM 42 so that the CPU 40 It functions as the ambisonics decoder 30 and executes the ambisonics signal reproduction process shown in FIG.

  In step S <b> 150 shown in FIG. 7, the ambisonics decoder 30 generates a drive signal for driving the speaker 18 by decoding the ambisonic signal output from the ambisonic signal generator 28. Note that the decoding method (driving signal generation method) can be a method similar to a general decoding method of an ambisonic signal generated by collecting sound in a real sound field, and thus description thereof is omitted.

  In the next step S152, the ambisonics decoder 30 outputs the drive signal generated in the above step S150 to each of the speakers 18, and ends the ambisonics signal reproduction process.

  The speaker 18 is driven according to the drive signal generated in this way, and the sound is reproduced, so that the sound field using the primary ambisonics signal in the scale model experiment can be reproduced.

(Example 2)
In the present embodiment, in order to further improve the accuracy of sound collection, a description will be given of a mode in which the sound field reproduction device 10 generates and reproduces an nth-order ambisonics signal. When the method of the first embodiment is applied to the generation / reproduction of the n-th order ambisonics signal, it is necessary to measure IR at a large number of positions (sound collection by the microphone 22), and as the order increases, The load for derivation becomes large, and realization becomes difficult. Therefore, in the present embodiment, a description will be given of an example for enabling sound collection at fewer positions when generating an n-th order ambisonics signal.

  First, the ambisonic signal generation processing by the ambisonic signal generation device 20 in the present embodiment will be described. The overall flow of the ambisonic signal generation process performed by the ambisonic signal generation apparatus 20 of the present embodiment is the same as the ambisonic signal generation process (see FIG. 5) of the first embodiment, so refer to FIG. explain.

  In step S100 illustrated in FIG. 5, the control unit 26 causes the sound source 14 to output sound in the target frequency band. As described above, the distance d of the microphone 22 is less than the half wavelength (λ / 2) of the upper limit frequency of the sound to be collected (target frequency band). In this embodiment, as an example, the correspondence relationship between the target frequency band, the distance d of the microphone 22 and the sound source 14 used is determined as shown in Table 2 according to the similarity rule. As shown in Table 2, in this embodiment, as an example, the characteristics of the sound source 14 and the S / N ratio of the microphone 22 are taken into consideration. As shown in Table 2 below, there are three bands of low, medium and high frequencies. Each of the divided bands was set as a target frequency band, and sound output and sound collection were performed for each target frequency band.

  In the next steps S102 to S110, the control unit 26 moves the microphone 22 to the N different positions by the moving unit 24 as in the processes of steps S102 to S110 of the ambisonics signal generation process of the first embodiment. Collect sound at each position.

The minimum number of signals necessary for obtaining the nth-order ambisonics signal is (n + 1) ² . Therefore, for example, when acquiring a primary ambisonics signal, the minimum number of signals is 4, and it is necessary to collect the sound by arranging the microphones 22 at at least four different positions. For example, when acquiring a secondary ambisonics signal, the minimum number of signals is 9, and it is necessary to arrange the microphones 22 at nine different positions at least to collect sound. As an example, in this embodiment, when acquiring a secondary ambisonics signal, the microphones 22 are sequentially arranged at each of the 11 positions r1 to r11 shown in FIG. In the example shown in FIG. 8, positions r8 to r11 are further added to the positions r1 to r7 of the first embodiment. The positions r8 to r11 are the same as the position r6 in the height direction (z-axis direction). Thus, when acquiring a secondary ambisonics signal, in the example shown in FIG. 8, since the sound is collected 11 times, the above “N” representing the number of times of sound collection is set to 11. Note that the position of the microphone 22 is not limited to the positions r1 to r11 illustrated in FIG. 8 and may be any position where the distance d satisfies less than λ / 2.

  In the next step S112, the ambisonic signal generation unit 28 generates an ambisonic signal from the sound signal collected at each sound collection position, and ends the present ambisonic signal generation process. A method for generating an ambisonic signal in the present embodiment will be described in detail.

When a plane wave with an amplitude Q comes from the ψ and φ directions (ψ is an azimuth angle, φ is an elevation angle with 0 ° directly above),

When the sound pressure p generated by the plane wave is expanded in a spherical harmonic, the sound pressure p is expressed by the following equation (1).

In the above equation (1),

It is.

When the above equation (1) is truncated at the n-th order, expressed in a matrix, and the plane wave of the sound source 14 is multiplied by the spherical harmonic function, the following equation (2) is obtained.

Both sides of the above equation (2), the following equation (3) is obtained when applying a pseudo-inverse of X · Y _r from the left.

The left side in the above equation (3) represents the directivity of the sound field of a plane wave, and the middle side is an arbitrary

Of microphone 22 in

Represents the directivity of the sound field that can be derived from. The bold letter B on the right side is called a plane wave ambisonics signal and corresponds to a B signal in primary ambisonics.

  As described above, the ambisonics signal generation device 20 according to the present embodiment can generate the B signal from the sound signal collected by the microphone 22 at an arbitrary position.

  Next, the reproduction of the sound field by the n-th order ambisonic signal generated in this way will be described. The overall flow of the ambisonic signal reproduction process performed by the sound field reproduction apparatus 10 of the present embodiment is the same as that of the ambisonic signal reproduction process (see FIG. 7) of the first embodiment, and will be described with reference to FIG. To do.

  In step S150 shown in FIG. 7, the ambisonics decoder 30 decodes the ambisonic signal to generate a drive signal. A method for decoding the ambisonics signal in this embodiment will be described in detail.

When L speakers 18 are installed on the same spherical surface at the same distance from the center, and the sound wave radiated from these speakers 18 is a plane wave, and the sound pressure generated by these is spherically developed, the following (4 ) Formula is obtained.

In the above equation (4), (θ _l , φ _l ) is the direction of the speaker 18 viewed from the origin, and a _l is a drive signal for each speaker 18.

Here, the sound pressure produced by the plane wave and the sound pressure produced by the L speakers 18 are equal (equation (1) = equation (4)), and the expansion is expressed by a truncation matrix in the nth order, and the orthogonality of the spherical harmonic functions Is used, the following equation (5) is obtained.

  Therefore, a drive signal for driving the speaker 18 is derived from the above equation (5).

  In the next step S152, the ambisonics decoder 30 outputs the drive signal derived by the above equation (5) to each of the speakers 18 and ends the present ambisonics signal reproduction process.

  The speaker 18 is driven in accordance with the drive signal generated in this way, and the sound is reproduced, so that the sound field can be reproduced using the nth-order ambisonics signal in the scale model experiment.

  As described above, the ambisonics signal generation device 20 of the present embodiment includes a single microphone 22 that collects sound in a predetermined target frequency band, and less than a half wavelength of the sound in the upper limit frequency of the target frequency band. The ambisonics is based on a moving unit 24 that moves the microphone 22 to each of a plurality of positions that are separated by a distance d determined according to the value of, and a sound signal collected by the microphone 22 at each of the plurality of positions. And an ambisonics signal generator 28 for generating a signal.

  Thereby, according to the ambisonics signal generation device 20 (sound field reproduction device 10) of the present embodiment, even when applied to a scale model experiment, an appropriate ambisonic signal can be generated, and the sound field of the scale model 12 can be generated. Can be auditioned in a three-dimensional sound field.

  Therefore, according to the ambisonics signal generation device 20 (sound field reproduction device 10) of the present embodiment, it is possible to dramatically improve the presentation technology and to evaluate the spatial impression with high acoustic quality. It is possible to greatly contribute to accuracy improvement.

  Moreover, according to the ambisonics signal generation device 20 (sound field reproduction device 10) of the present embodiment, it is possible to generate an appropriate ambisonic signal even when applied to a scale model experiment with a simpler configuration than the conventional one. It becomes.

  In the present embodiment, the sound field reproduction device 10 (the ambisonics signal generation device 20) has been described in the form of the sound collection target space as the scale model 12 space, but the present invention is not limited to this form, and the real sound field Needless to say, (actual sound field) may be used as a sound collection target space.

  Further, in the present embodiment, the form in which the distance d is the same at all the positions (sound collection positions) of the microphone 22 has been described. However, the present invention is not limited to this form, and if the distance d satisfies less than λ / 2, The distance d may be different depending on the position.

  In addition, various processors other than the CPU 40 may execute at least one of the ambisonic signal generation processing and the ambisonic signal reproduction processing executed by the CPU 40 executing software (program) in the present embodiment. As a processor in this case, in order to execute specific processing such as PLD (Programmable Logic Device) and ASIC (Application Specific Integrated Circuit) whose circuit configuration can be changed after manufacturing a field-programmable gate array (FPGA) or the like. A dedicated electric circuit, which is a processor having a circuit configuration designed exclusively, is exemplified. Further, at least one of the ambisonic signal generation process and the ambisonic signal reproduction process may be executed by one of these various processors, or a combination of two or more processors of the same type or different types (for example, It may be executed by a plurality of FPGAs and a combination of a CPU and an FPGA. Further, the hardware structure of these various processors is more specifically an electric circuit in which circuit elements such as semiconductor elements are combined.

  Moreover, although this embodiment demonstrated the aspect by which various programs were previously memorize | stored (installed) in ROM42 of the sound field reproducing | regenerating apparatus 10, it is not limited to this. At least one of the ambisonics signal generation processing program and the ambisonics signal reproduction processing program is a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), a USB (Universal Serial Bus) memory, etc. It may be provided in a form recorded on the recording medium. Further, at least one of the ambisonics signal generation processing program and the ambisonics signal reproduction processing program may be downloaded from an external device via a network.

  In addition, the configurations and operations of the sound field reproduction system 1, the sound field reproduction device 10, the ambisonic signal generation device 20, and the like described in the present embodiment are examples, and the situation is within the scope that does not depart from the gist of the present invention. Needless to say, it can be changed accordingly.

DESCRIPTION OF SYMBOLS 1 Sound field reproduction | regeneration system 10 Sound field reproduction | regeneration apparatus 12 Scale model 14 Sound source 18 Speaker 20 Ambisonics signal generation apparatus 22 Microphone 24 Moving part 28 Ambisonics signal generation part 30 Ambisonics decoder

Claims (8)

A single microphone that collects sound in a predetermined target frequency band;
A moving unit that moves the microphone to each of a plurality of positions separated by a distance determined according to a value less than a half wavelength of the sound of the upper limit frequency of the target frequency band;
A signal generation unit that generates an ambisonics signal based on a sound signal collected by the microphone at each of the plurality of positions;
Ambisonics signal generator including The target frequency band is two or more bands among a plurality of bands divided according to frequency,
The ambisonic signal generation device according to claim 1, wherein the distance is determined according to a value less than a half wavelength of a sound having an upper limit frequency in each of the two or more bands. The ambisonics signal generation device according to claim 1, wherein the microphone collects sound in a scale model space created by reducing a real sound field. The plurality of positions are determined to be (n + 1) ² or more, where n is the order of the ambisonic signal generated by the signal generation unit. Ambisonics signal generator. The plurality of positions are positions corresponding to the origin of the three-dimensional space coordinates assumed in the sound collection target space, each of a pair of points symmetrical with respect to the origin on each of the three axes of the three-dimensional space coordinates. The ambisonics signal generation device according to any one of claims 1 to 4, wherein the ambisonics signal generation device includes a position corresponding to. The plurality of positions include positions where the distances are different.
The ambisonic signal generation device according to any one of claims 1 to 5. The ambisonics signal generation device according to any one of claims 1 to 6,
A drive unit for generating a drive signal for driving a speaker using the ambisonics signal generated by the ambisonics signal generation device;
A sound field reproduction apparatus including: A single microphone collects sound of a predetermined target frequency band; and
A moving unit moving the microphone to each of a plurality of positions separated by a distance determined according to a value less than a half wavelength of the sound of the upper limit frequency of the target frequency band; and
A step of generating an ambisonic signal based on a sound signal collected by the microphone at each of the plurality of positions;
An ambisonics signal generation method including: