Estimation device, restoration device, estimation method, and program

Abstract

To provide an estimation device for estimating an expansion coefficient to be used when restoring an acoustic field from optical measurement data when an acoustic source exists inside an acoustic field restoration area.SOLUTION: An estimation device represents an expansion of an acoustic field itself by the spherical harmonics expansion, and estimates an expansion coefficient of the acoustic field based on the spherical harmonics expansion using a measurement value measured by an optical acoustic field measurement system and the information representing the laser optical path.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to sound field measurement using light. [Background technology]

[0002] Optical sound field measurement is used as a method for measuring and visualizing sound fields non-contactly. When trying to obtain the sound pressure distribution on a certain plane from the line integral values ​​measured by optical measurement, a process called sound field restoration or sound field reconstruction is required to estimate the value of each point from the projection data.

[0003] So far, methods for restoring sound fields based on the wave equation have been proposed. Sound field restoration based on the wave equation can be divided into an internal sound field problem, which restores the sound field in a region inside a virtual boundary under the condition that a sound source exists outside the virtual boundary, and an external sound field problem, which restores the sound field outside a virtual boundary under the condition that a sound source exists inside the virtual boundary. Regarding the external sound field problem, a conventional technique has proposed a method for restoring the radiation sound field from a sound source existing inside a restoration region by expanding a two-dimensional sound field into circular harmonic functions (see Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Phuc Duc Nguyen, Kenji Ishikawa, Noboru Harada, Takehiro Moriya, "Acousto-optic reconstruction of exterior sound field based on concentric circle sampling with circular harmonic expansions", arXiv:2311.01715, 2023. Summary of the Invention [Problem to be solved by the invention]

[0005] However, no method has been proposed for reconstructing a three-dimensional external sound field based on the wave equation from optical line integral measurements.

[0006] The present invention aims to provide a restoration device that can restore a three-dimensional sound field with high accuracy, and an estimation device, estimation method, and program for estimating expansion coefficients used in sound field restoration, regarding the problem of restoring an external sound field from measurement of line integral values ​​using light. [Means for solving the problem]

[0007] In order to solve the above problems, according to one aspect of the present invention, an estimation device represents the expansion of a sound field itself using a spherical harmonic expansion, and estimates the expansion coefficients of the sound field based on the spherical harmonic expansion using measurements taken by an optical sound field measurement system and information representing the laser optical path. [Effects of the Invention]

[0008] According to the present invention, by using a spherical harmonic expansion of a three-dimensional sound field, it is possible to achieve the effect of accurately restoring a sound field in an external sound field problem in which a sound source exists inside the sound field restoration area. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a functional block diagram of a restoration system according to a first embodiment. [Figure 2] FIG. 2 is a diagram showing an example of a processing flow of the restoration system according to the first embodiment. [Figure 3] FIG. 1 is a diagram showing an example of the configuration of a computer to which the present technique is applied. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described. In the drawings used in the following description, components having the same functions and steps performing the same processes will be denoted by the same reference numerals, and duplicated explanations will be omitted. In the following description, the symbols "~" and " -" etc. should normally be written directly above the character immediately following it, but due to limitations in text notation, they are written immediately before the character in question. In formulas, these symbols are written in their original positions. Furthermore, unless otherwise specified, processing performed on each element of a vector or matrix is ​​assumed to apply to all elements of that vector or matrix.

[0011] <Key Points of the First Embodiment> This embodiment uses spherical harmonic expansion of the sound field for reconstructing a three-dimensional sound field from optical measurement data.

[0012] The sound source is placed inside the measurement area, and laser measurements are taken of line integrals from various directions and distances surrounding the sound source.The coefficients of spherical harmonics are calculated from the measured line integrals, and the sound field is reconstructed using these coefficients.

[0013] By using spherical harmonic functions, it is possible to reconstruct a three-dimensional sound field with high accuracy under the condition that a sound source is located inside the reconstruction target area. Such a condition occurs, for example, when measuring the sound emitted from a speaker. By using this embodiment, it is possible to measure the three-dimensional directivity of the sound source and perform a highly accurate simulation of the sound field created by the sound source. First, the line integral value d i This section briefly explains the sound field measurement system that measures the above.

[0014] <Sound field measurement system> The sound field measurement system includes a device for optical acoustic measurement and a speaker as a sound source. The device for optical acoustic measurement can be any optical acoustic measurement technology, such as a laser Doppler velocimeter (LDV), a polarization high-velocity interferometer, or digital holography.

[0015] In measuring a sound field, for example, the following methods (i) to (iv) can be used. (i) Simultaneous measurement from various directions of the sound source to be measured (ii) Fix the sound source to be measured and move or rotate the measurement beam to measure from various directions sequentially. (iii) Fix the measurement beam and move or rotate the sound source to measure the sound source at various positions and angles. (iv) Measurements are taken sequentially at various positions by moving and rotating both the sound source and the measurement beam.

[0016] The measurement system may be a method that measures only one point at a time, such as a laser Doppler vibrometer, or a method that measures multiple points at once using a camera, such as a polarization high-speed interferometer or digital holography. During the measurement, the relative position and angle of the sound source and the measurement beam as seen from the sound source are recorded.

[0017] The restoration area can be set to any area regardless of the measurement area. From the line integral value data measured in this way, the expansion coefficients of the sound field based on spherical harmonic expansion are derived, and the sound field is restored using the expansion coefficients.

[0018] First, the spherical harmonic expansion of the sound field will be explained.

[0019] <Spherical harmonic expansion of sound field> According to Reference 1, for any three-dimensional sound field in which sound sources exist only inside the region of interest, the sound field expansion itself can be expressed as follows using a spherical harmonic expansion:

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[0020]

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[0021] According to equation (1), the expansion coefficients a of the spherical harmonics of the sound field lm If we know the expansion coefficients a, we can reconstruct any three-dimensional sound field in which the sound source exists only inside the region. lm Estimate.

[0022] (Reference 1) Earl G. Williams, "Fourier Acoustics: Sound Radiation and Nearfield Acoustical Holography", Academic Press, 1999.

[0023] <Derivation of expansion coefficients of spherical harmonics from optical measurement data> In optical acoustic measurements, the line integral of the sound pressure along the laser beam path, d i is measured. Therefore, the line integral value d i can be written as follows:

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[0024] where d i is the i-th measurement data, r s,i and r e,iare the coordinates of the start and end points of the line integral value of the i-th measurement ray. Note that if the total number of laser optical paths is H, then i = 1, 2, ..., H. H is an integer equal to or greater than 1. The larger H is, the higher the accuracy of the sound field reconstruction, but the measurement and calculation costs also increase. Therefore, H should be set appropriately taking into account the required accuracy, measurement costs, and calculation costs. Since the measurement area includes the start and end points of the laser optical paths, for example, by setting laser optical paths to evenly surround the sound source, sound field reconstruction can be performed with uniform accuracy. However, if the accuracy of sound field reconstruction at a specific position or direction is to be increased, it is possible to set many laser optical paths that pass through that position and direction.

[0025] By truncating the spherical harmonic expansion to a finite order M and substituting it into equation (3), the line integral value d i can be written as follows:

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[0026] This can be rewritten in matrix form as follows:

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[0027] Here, each element of the matrix Υ is - Y l,m,iThis corresponds to, and can be calculated using equation (5) from the positional relationship between the sound source and the measurement light beam during measurement and the sound frequency. Also, since the vector d is a measurement value using light, it is possible to estimate the expansion coefficient a from it.

[0028] The expansion coefficient a can be estimated by any method, such as a method using a pseudoinverse matrix, a method using truncated singular value decomposition, a method of solving a regularized least squares problem, etc. For example, the estimated value ~a of the expansion coefficient a is calculated by the regularized least squares method using the following equation.

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[0029] <Sound field reconstruction from expansion coefficients based on spherical harmonic expansion> Using the estimated values ​​a~ of the expansion coefficients of the sound field based on the spherical harmonic expansion obtained by equation (6), it is possible to reconstruct the sound field at any position using equation (1).

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[0030] <Restoration system according to the first embodiment> FIG. 1 shows an example of the configuration of a restoration system according to the first embodiment, and FIG. 2 shows the processing flow thereof.

[0031] The reconstruction system includes an estimator 100 and a reconstruction unit 200 .

[0032] The restoration system takes the measurement value d measured by the above-mentioned sound field measurement system as input, estimates the expansion coefficients of the sound field based on spherical harmonic expansion, performs sound field restoration using the estimated value ~a, and outputs the restoration result.

[0033] Each part will be explained below.

[0034] <Estimation part 100> The estimation unit 100 estimates the measured values ​​d=[d1, d2, ..., d i ,…,d H ] T and the laser path L=[L1,L2,…,L i ,…,L H ] is input, and using these values, the expansion coefficients a of the sound field based on spherical harmonic expansion are estimated (S100), and the estimated values ​​a~ are output.

[0035] As mentioned above,

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[0036]

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[0037]

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[0038] <Restoration unit 200> The restoration unit 200 receives as input the estimated values ​​a~ of the expansion coefficients of the sound field based on the spherical harmonic function expansion and the restoration point coordinates, performs sound field restoration using the spherical harmonic function expansion (S200), and outputs the restoration result. For example, the restoration unit 200 may perform the restoration of a certain restoration point coordinate (ζ u ,θ u ,φ u ) is calculated using equation (11) and output as the restoration result.

[0039]

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[0040] The above process is performed for a certain angular frequency ω s In the case of data containing two or more frequencies, it is assumed that processing is performed for S angular frequencies ω1, ω2, ..., ω s ,…,ω S For each angular frequency ω s The estimation process S100 and the restoration process S200 may be performed independently, and S restored sound pressures ~p(1), ~p(2), ..., ~p(s), ..., ~p(S) may be output, or a superposition of Q restored sound pressures ~p(1), ~p(2), ..., ~p(s), ..., ~p(S) may be output.

[0041] <Effects> With the above configuration, when a sound source is present inside the sound field restoration area, it is possible to restore the sound field from the optical measurement data with higher accuracy than before.

[0042] <Modification> The estimation unit 100 and the reconstruction unit 200 may be configured as an estimation device and a reconstruction device, respectively, which are separate devices.

[0043] <Other variations> The present invention is not limited to the above-described embodiments and modifications. For example, the various processes described above may not only be executed in chronological order as described, but may also be executed in parallel or individually depending on the processing capabilities of the devices that execute the processes or as needed. Other modifications are possible within the scope of the present invention.

[0044] [Processor, program, recording medium] The functions performed by the components described herein may be implemented in circuitry or processing circuitry, including general-purpose processors, application-specific processors, integrated circuits, ASICs (Application Specific Integrated Circuits), a CPU (a Central Processing Unit), conventional circuits, and / or combinations thereof, programmed to perform the described functions. A processor includes transistors and other circuits and is considered to be circuitry or processing circuitry. A processor may also be a programmed processor that executes programs stored in memory.

[0045] In this specification, a circuitry, unit, or means is hardware that is programmed to realize or performs the described functions, which may be any hardware disclosed herein or any hardware known to be programmed to realize or perform the described functions.

[0046] If the hardware is a processor considered to be a type of circuitry, the circuitry, means, or unit is a combination of the hardware and software used to configure the hardware and / or processor.

[0047] The various processes described above can be implemented by loading a program that executes each step of the above method into the recording unit 2020 of the computer 2000 shown in Figure 3, and operating the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc.

[0048] The program describing the processing contents can be recorded on a computer-readable recording medium, which may be, for example, a magnetic recording device, an optical disk, a magneto-optical recording medium, a semiconductor memory, or any other suitable recording medium.

[0049] The program may be distributed, for example, by selling, transferring, lending, etc. a portable recording medium such as a DVD or CD-ROM on which the program is recorded. Furthermore, the program may be stored in a storage device of a server computer, and then transferred from the server computer to another computer via a network, thereby distributing the program.

[0050] A computer that executes such a program may first temporarily store the program recorded on a portable recording medium or transferred from a server computer in its own storage device. Then, when executing a process, the computer reads the program stored on its own recording medium and executes the process in accordance with the read program. Alternatively, the computer may read the program directly from a portable recording medium and execute the process in accordance with the program. Furthermore, the computer may execute the process in accordance with the program each time a program is transferred from a server computer to the computer. The server computer may not transfer the program to the computer, but may instead execute the process through a so-called ASP (Application Service Provider) service, which realizes the processing function by issuing an execution instruction and obtaining the results. Furthermore, the server computer may execute the process on a terminal using a so-called SaaS (Software as a Service) service, which allows users to use part of the server computer along with the program. In this embodiment, the program includes information used for computer processing that is equivalent to a program (such as data that is not a direct instruction to the computer but has properties that define computer processing).

[0051] Furthermore, in this embodiment, the device is configured by executing a predetermined program on a computer, but at least a part of the processing contents may be realized by hardware.

Claims

1. The sound field expansion itself is expressed by a spherical harmonic expansion, and the expansion coefficients of the sound field based on the spherical harmonic expansion are estimated using the measurements taken by the optical sound field measurement system and information representing the laser light path. Estimation device.

2. 2. The estimation device of claim 1, estimating a matrix having elements of the expansion coefficients using a matrix having elements of line integral values ​​along one or more laser optical paths and a vector having elements of the measurement values; Estimation device.

3. A restoration device that uses the estimated values ​​of expansion coefficients estimated by the estimation device of claim 1, A sound field is restored using spherical harmonic function expansion from the estimated value and the restoration point coordinates. Restoration device.

4. The sound field expansion itself is expressed by a spherical harmonic expansion, and the expansion coefficients of the sound field based on the spherical harmonic expansion are estimated using the measurements taken by the optical sound field measurement system and information representing the laser light path. Estimation method.

5. A program for causing a computer to function as the estimation device of claim 1.

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