JP2013167607A - Acoustic field diffusible indicator calculation device, method therefor, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an acoustic field diffusible indicator calculation device capable of calculating an acoustic field diffusible indicator value, with information of energy components of reflection sound and time changes thereof taken into consideration therein.SOLUTION: An arrival direction of a vector quantity I(nΔt) of an acoustic intensity is converted into an azimuth angle φ and an elevation angle θ with acoustic intensities I(nΔt), I(nΔt), and I(nΔt) used as inputs, the acoustic intensities being set for every sample n in each axial direction of the X axis, the Y axis and the Z axis that orthogonally cross using an original point that is defined as any position in the acoustic field as a reference. The interior of the acoustic field is divided into virtual cells obtained by dividing the elevation angle direction and the azimuth angle direction by a predetermined angular resolution, under conditions that the elevation angle direction is defined using the Z axis as a reference and an X axis-Y axis plane direction is defined as the azimuth angle direction, vector quantities I(nΔt) are accumulated in the time direction for every cell, and an acoustic field diffusible indicator representing a dispersion degree of a cumulative value of the acoustic intensity of each cell is calculated.

Description

  The present invention relates to a sound field diffusibility index calculating apparatus, method and program for calculating an index representing the degree of sound diffusion in a sound field in the field of acoustic measurement.

  Conventionally, in order to measure the degree of sound diffusion in a sound field, a spatial correlation between two points has often been used. It is clear that this theoretically results in a Sinc function, and there is an advantage that the degree of sound diffusion can be evaluated quantitatively to some extent by comparison with this theoretical value. In addition, in the past, there has also been known a method of using a directional microphone such as a parabola microphone and, more recently, using a sound intensity measurement to grasp the direction of arrival of reflected sound from time to time and quantitatively organizing this. In particular, the method using the sound intensity can be calculated based on the impulse response, and there is a possibility that a characteristic unique to the sound field can be extracted.

  A sound field diffusivity index (Uniformity of Arrival Directions, hereinafter also referred to as UAD value) is known as an index representing the arrival direction of reflected sound using the sound intensity (Non-Patent Document 1). The UAD value is an index representing the uniformity of the arrival direction of the reflected sound, and is defined by Expression (1).

Here, H _n is the frequency of the reflected sound represented by the sound intensity response that arrives in each of the directions divided into N. FIG. 9 shows an example of the sound intensity response. I _x (nΔt), I _y (nΔt), and I _z (nΔt) are acoustic intensity responses in the respective directions of the x, y, and z axes. Δt is discrete time, and t = nΔt. The sound intensity response is obtained by multiplying the difference in impulse response between two points separated by a minute distance by the magnitude of the sound at a specific location, and can handle the direction of sound propagation that cannot be expressed by the impulse response. The sound intensity will be described later in detail.

H _n is a vector composition of I _x (nΔt), I _y (nΔt), and I _z (nΔt) for each sample n forming the acoustic intensity envelope in FIG. 9, and the direction of the vector is the direction of arrival of sound waves. Is a value obtained by counting the frequency for each region designated in the azimuth angle φ direction and the elevation angle θ direction.

Omoto, Matsumoto, “Fundamental study on the effect of wall diffusivity on small space” Proceedings of the Acoustical Society of Japan 2009 Spring Meeting, 1-3-15, pp.1083-1086, 2009 3 Moon

  The conventional UAD value is obtained by simply counting the frequency of reflected sound coming from which direction and calculating the degree of dispersion based only on the frequency data. Although the value has the advantage that a single number can be compared, it only represents the state of sound diffusion at a certain time. In other words, the conventional UAD value is a value obtained only from the number of accumulated reflected sounds, and represents only the result of the diffusion of a sound after a certain period of time has elapsed. Therefore, further examination was necessary as an index that represents the state of sound diffusion in detail.

  The present invention has been made in view of such a problem, and a sound field diffusibility index calculating device capable of calculating a new UAD value that also includes information on the energy component of reflected sound and its temporal change, and It aims to provide a method and program.

The sound field diffusibility index calculating apparatus of the present invention includes a polar coordinate conversion unit, an acoustic intensity accumulation unit, and a sound field diffusibility index calculation unit. The polar coordinate conversion unit converts the sound intensity I _x (nΔt), I _y (nΔt) for each sample n in the x-axis, y-axis, and z-axis directions orthogonal to the origin defined at an arbitrary position in the sound field. ), I _z (nΔt) as inputs, and the direction of arrival of the acoustic intensity vector quantity I (nΔt) is converted into an azimuth angle φ and an elevation angle θ. The sound intensity accumulating unit is an imaginary virtual field obtained by dividing the elevation angle direction and the azimuth angle direction with a predetermined angular resolution, with the elevation angle direction based on the z axis and the x axis-y axis plane direction as the azimuth angle direction. Dividing into cells, the vector quantity I (nΔt) is accumulated in the time direction for each cell. The sound field diffusibility index calculating unit calculates a sound field diffusibility index that represents the degree of variation in the accumulated value of the sound intensity of each cell.

  According to the sound field diffusibility index calculating apparatus of the present invention, the sound field diffusivity index is made a function of time, so that the sound field diffusivity index can be a new index that represents the time change of the diffusion of the acoustic signal. it can. As a result, it is possible to facilitate the analysis of the acoustic environment related to the reflected sound information of the sound field such as the state of the time change of the diffusion of the acoustic signal, the convergence state thereof, and the convergence value.

The figure which shows the example of microphone arrangement | positioning at the time of measuring an impulse response in order to obtain | require an acoustic intensity response. The figure which shows the function structural example of the sound field diffusivity parameter | index calculation apparatus 100 of this invention. The figure which shows the operation | movement flow of the sound field diffusibility parameter | index calculation apparatus 100. FIG. The figure which shows an example of the polar coordinate system defined in the sound field and the sound field. The figure which shows an example of the virtual cell which divided | segmented the sound field into the azimuth angle direction and the elevation angle direction for every arbitrary angles on the basis of the origin defined in the sound field. The figure which shows a mode that the value of a sound field diffusibility parameter | index converges according to elapsed time. The figure which shows the function structural example of the sound field diffusibility parameter | index calculation apparatus 200 of this invention. The figure which shows the operation | movement flow of the sound field diffusibility parameter | index calculation apparatus 200. FIG. The figure which shows the example of an acoustic intensity response.

  Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are given to the same components in a plurality of drawings, and the description will not be repeated. The sound intensity will be described before the description of the embodiments.

[Sound intensity]
The sound intensity is an index that represents the loudness of the sound taking into account the direction of travel of the sound, and is calculated from the impulse response. FIG. 1 shows an example of arrangement of microphones when measuring an impulse response for the purpose of obtaining sound intensity at a position with a sound field.

The microphone M ₀ is located at a position (origin) where the sound field is present, and the microphones M _x , M _y are separated by a minute distance (Δx, Δy, Δz) on the x-axis, y-axis, and z-axis orthogonal to each other at that position. , M _z are arranged. The minute distance (Δx, Δy, Δz) is, for example, a distance of several centimeters.

Then, for each sample n (Δt = 1 / f) sampled at a certain sampling frequency f, an impulse response p ₀ (nΔt) at a certain position (origin) and an impulse response p _x (nΔt) in each axial direction, p _y (nΔt) and p _z (nΔt) are measured.

Acoustic intensity I _x (nΔt), I _y (nΔt), I _{y in} each axial direction obtained from these impulse responses p ₀ (nΔt), p _x (nΔt), p _y (nΔt), p _z (nΔt) _z (nΔt) can be expressed by equations (1) to (3) when expressed in continuous time t. When Expressions (1) to (3) are expressed by discrete time Δt, they can be expressed by Expressions (4) to (6).

Here, ρ ₀ is the mass density of the medium, the first term on the right side of each equation is the sound pressure near a certain position (origin), and the second term is the difference between minute distances in each axial direction, and the particle velocity in each axial direction Represents. That is, the sound intensity is the sound pressure at a certain position multiplied by the particle velocity. The magnitude I (nΔt) of the sound intensity for each sample n can be calculated by the following equation.

  In the present invention, in addition to the reflected sound arrival direction information, information on the amount of energy is also taken into account, and the acoustic information in the sound field is grasped in more detail. The only necessary measurement is the instantaneous sound intensity due to the impulse response, and by analyzing this instantaneous sound intensity sequentially, it is possible to extract features in the time evolution process of the sound direction information.

  FIG. 2 shows a functional configuration example of the sound field diffusibility index calculating apparatus 100 of the present invention. The operation flow is shown in FIG. The sound field diffusibility index calculating apparatus 100 includes a polar coordinate conversion unit 10, an acoustic intensity accumulation unit 20, and a sound field diffusibility index calculation unit 30. The sound field diffusibility index calculating apparatus 100 is realized by a predetermined program being read into a computer including, for example, a ROM, a RAM, a CPU, and the like, and the CPU executing the program.

The polar coordinate conversion unit 10 has acoustic intensities I _x (nΔt) and I _y (nΔt) for each sample n in the x-axis, y-axis, and z-axis directions orthogonal to the origin, which is an arbitrary position in the sound field. ), I _z (nΔt) as inputs, the direction of arrival of the acoustic intensity vector quantity I (nΔt) is converted into an azimuth angle φ (nΔt) and an elevation angle θ (nΔt) (step S10). The sound intensity is as described above, and every sample n means every sample digitized at the sampling frequency f, and occurs at a time interval of Δt = 125 μsec when the sampling frequency is 8 kHz, for example. is there. The acoustic intensity vector quantity I (nΔt) is calculated by the equation (7), and may be calculated by the polar coordinate conversion unit 10 or may be obtained by the acoustic intensity I _x (nΔt), I What is calculated in advance from _y (nΔt) and I _z (nΔt) may be input from the outside. Note that the direction of arrival of the sound intensity vector can be converted into the azimuth angle φ and the elevation angle θ by a general coordinate conversion process.

  Here, the origin is a coordinate defined at an arbitrary position in the sound field, and may be any place in the sound field. The sound field may be indoors or may be an outdoor space such as a schoolyard or an outdoor concert venue.

  The sound intensity accumulating unit 20 divides the sound field with the predetermined angular resolution, with the elevation angle direction based on the z axis and the x axis-y axis plane direction as the azimuth angle direction. Dividing into virtual cells, the vector amount I (nΔt) corresponding to the elevation angle and azimuth angle for each cell is accumulated in the time direction (step S20).

  FIG. 4 illustrates a sound field and a polar coordinate system defined in the sound field. The sound field 90 shown in FIG. 4 is a room whose planar shape is a rectangle, and the origin of the polar coordinate system is set, for example, near the center of the rectangle.

FIG. 5 shows virtual cells E _{i, j obtained} by dividing the inside of the sound field 90 shown in FIG. 4 in the elevation direction and the azimuth direction around the origin, for example, every 10 degrees. i and j represent the number of divisions related to the azimuth angle φ and the elevation angle θ, respectively.

  4, the x-axis (positive) direction is the intersection of the azimuth direction φ = 0 (degs) and the elevation direction θ = 90 (degs), and the x-axis (negative) direction is φ = 180 (degs) and θ = 90 ( degs), the y-axis (positive) direction is φ = 90 (degs) and θ = 90 (degs), and the y-axis (negative) direction is φ = −90 (degs) and θ = −90 ( degs) and the z-axis (positive) direction correspond to θ = 0 (degs), respectively. The directions of the x-axis and y-axis are indicated by lead lines in FIG.

  The vector (r, θ, φ) shown in FIG. 4 is stored in a cell indicated by r in FIG. 5, for example, a cell corresponding to θ = 45 degrees and φ = 125 degrees (cell r in FIG. 5). The magnitude r is added. r is the above-described vector quantity I (nΔt) = r. The vector quantity I (nΔt) for each sample i is accumulated in cells corresponding to the elevation angle and azimuth angle of the arrival direction for each Δt.

  That is, the sound intensity accumulating unit 20 stores on the virtual matrix how much energy has arrived from which direction by a certain time t. The origin of the polar coordinate system may be defined at any position in the sound field, for example, may be set at a corner of the sound field, or may be defined near the floor or ceiling. Further, the accuracy of the sound field diffusibility index can be improved as the number of divided cells is reduced. In addition, although the example in which the elevation angle direction and the azimuth angle direction are divided by the same angle has been described, the angles to be divided may be unequal intervals.

  The sound field diffusivity index calculation unit 30 calculates a sound field diffusibility index that represents the degree of variation in the accumulated value of the sound intensity of each cell (step S30). The sound field diffusibility index (UAD value) is calculated by Expression (8).

E _{i, j} (nΔt) is the energy accumulated in each cell until time t. That is, the sound field diffusivity index (UAD value) is obtained by subtracting the sum of the squares of the cumulative values of the acoustic intensity of each cell from the square of the sum of the cumulative values of the acoustic intensity of each cell. It is a value obtained by dividing the square of the sum of accumulated values by the value obtained by multiplying the degree of freedom. As is clear from Equation (8), the sound field diffusibility index (UAD value) is close to 0 when the variation in energy accumulated in each cell is large, and converges to a predetermined size when the variation is small. .

  Note that when the accumulated value of the sound intensity is obtained for each cell, the accumulated energy may be averaged using a two-dimensional smoothing filter. Two-dimensional smoothing means averaging a plurality of adjacent cells (for example, two, four or more). By smoothing, the value of the sound intensity can be stabilized.

  By performing this calculation sequentially for each Δt, the time evolution of the sound field diffusivity index can be calculated. The value is useful as an index representing the acoustic environment of the sound field, such as the state of the acoustic signal diffusion over time, the convergence status, and the convergence value.

  FIG. 6 schematically illustrates how the sound field diffusibility index changes according to the present invention. The horizontal axis is the elapsed time, and the vertical axis is the sound field diffusivity index (UAD value). The solid line, broken line, and alternate long and short dash line in the figure represent the difference in sound field.

  At the initial stage of the impulse response, the value of the sound intensity is small, and gradually increases with time, indicating a change that converges to a predetermined value. As described above, according to the sound field diffusibility index obtained by the sound field diffusibility index calculation apparatus 100, it is possible to quantitatively know the gradient of time evolution of the reflected sound, the time until convergence, and the convergence value. become able to.

FIG. 7 shows a functional configuration example of the sound field diffusibility index calculating apparatus 200 of the present invention. The operation flow is shown in FIG. The sound field diffusibility index calculating apparatus 200 is different from the above-described sound field diffusivity index calculating apparatus 100 in that an intensity calculating unit 40 is provided. The intensity calculation unit 40 receives the impulse responses p ₀ (nΔt), p _x (nΔt), p _y (nΔt), and p _z (nΔt) as inputs, and the sound intensity I _x (nΔt), I in each axial direction. _y (nΔt) and I _z (nΔt) are calculated by the above-described equations (4) to (6). The operation after calculating the sound intensity is the same as that of the sound field diffusivity index calculating apparatus 100.

  Thus, the sound intensity diffusivity index may be calculated after obtaining the sound intensity from the impulse response, or the sound field diffusivity index may be obtained using the sound intensity of the measured observation as an input. You may do it. In either case, it is possible to obtain the sound field diffusivity index (UAD value) of the present invention, which can calculate the time evolution of the reflected sound in the sound field.

  According to the sound field diffusibility index (UAD value) according to the present invention, the reflected sound environment of the sound field can be characterized by relatively easy measurement. Further, by comparing how the sound field diffusibility index changes by measuring a plurality of points in the same sound field, it is possible to define the distance at which the reflected sound arrival state changes significantly. In addition, the distance information makes it possible to give essential information such as how much the microphones should be separated when collecting information on the sound field, for example.

  The processes described in the above apparatuses and methods are not only executed in time series according to the order of description, but may also be executed in parallel or individually as required by the processing capability of the apparatus that executes the processes. .

  Further, when the processing means in the above apparatus is realized by a computer, the processing contents of functions that each apparatus should have are described by a program. Then, by executing this program on the computer, the processing means in each apparatus is realized on the computer.

  The program describing the processing contents can be recorded on a computer-readable recording medium. As the computer-readable recording medium, any recording medium such as a magnetic recording device, an optical disk, a magneto-optical recording medium, and a semiconductor memory may be used. Specifically, for example, as a magnetic recording device, a hard disk device, a flexible disk, a magnetic tape or the like, and as an optical disk, a DVD (Digital Versatile Disc), a DVD-RAM (Random Access Memory), a CD-ROM (Compact Disc Read Only). Memory), CD-R (Recordable) / RW (ReWritable), etc., magneto-optical recording medium, MO (Magneto Optical disc), etc., semiconductor memory, EEP-ROM (Electronically Erasable and Programmable-Read Only Memory), etc. Can be used.

  The program is distributed by selling, transferring, or lending a portable recording medium such as a DVD or CD-ROM in which the program is recorded. Further, the program may be distributed by storing the program in a recording device of a server computer and transferring the program from the server computer to another computer via a network.

  Each means may be configured by executing a predetermined program on a computer, or at least a part of these processing contents may be realized by hardware.

Claims (3)

Acoustic intensity I _x (nΔt), I _y (nΔt), I _z (for each sample n in the direction of each axis of the x, y, and z axes orthogonal to the origin defined at an arbitrary position in the sound field. nΔt) as an input, a polar coordinate conversion unit for converting the direction of arrival of the acoustic intensity vector quantity I (nΔt) into an azimuth angle φ and an elevation angle θ;
The inside of the sound field is divided into virtual cells obtained by dividing the elevation angle direction and the azimuth angle direction with a predetermined angular resolution, with the elevation angle direction based on the z axis and the x-axis / y-axis plane direction as the azimuth angle direction. An acoustic intensity accumulation unit that accumulates the vector amount I (nΔt) corresponding to the elevation angle and azimuth angle for each cell in the time direction;
A sound field diffusibility index calculating unit that calculates a sound field diffusibility index representing the degree of variation in the accumulated value of the vector amount I (nΔt) of each cell;
A sound field diffusibility index calculating apparatus comprising: Acoustic intensity I _x (nΔt), I _y (nΔt), I _z (for each sample n in the direction of each axis of the x, y, and z axes orthogonal to the origin defined at an arbitrary position in the sound field. n [Delta] t) as an input, a polar coordinate conversion process for converting the direction of arrival of the acoustic intensity vector quantity I (n [Delta] t) into an azimuth angle [phi] and an elevation angle [theta],
The inside of the sound field is divided into virtual cells obtained by dividing the elevation angle direction and the azimuth angle direction with a predetermined angular resolution, with the elevation angle direction based on the z axis and the x-axis / y-axis plane direction as the azimuth angle direction. Acoustic intensity accumulation process of accumulating the vector quantity I (nΔt) corresponding to the elevation angle and azimuth angle for each cell in the time direction;
A sound field diffusibility index calculating process for calculating a sound field diffusivity index representing the degree of variation in the accumulated value of the vector quantity I (nΔt) of each cell;
A sound field diffusivity index calculation method comprising:   The program for functioning a computer as a sound field diffusibility parameter | index calculation apparatus described in Claim 1.

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