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JP2014171163

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DESCRIPTION JP2014171163
Abstract: To provide a sound field sound collecting and reproducing technique capable of
reproducing a sound field with higher accuracy than conventional. SOLUTION: A filter F (ω)
defined by the following equation is applied to a space-time frequency domain signal P (ω)
generated by a conversion filter unit 3 based on a signal picked up by a microphone Then, the
post-filtering signal D ~ (ω) is generated. The spatial frequency inverse transform unit 4
transforms the filtered signal D ~ (ω) into a frequency domain signal by inverse Fourier
transform of space. The frequency inverse transform unit 5 transforms the frequency domain
signal into a time domain signal by inverse Fourier transform, and outputs the transformed time
domain signal to the speaker. [Selected figure] Figure 1
Sound field sound collecting and reproducing apparatus, method and program
[0001]
This invention is a technology of wave field synthesis (Ambisonics) that collects a sound signal
with a microphone installed in a certain sound field and reproduces the sound field with a
speaker using that sound signal. On the technology of
[0002]
As a technology of wave field synthesis (Ambisonics) that collects a signal with a microphone
array placed in a certain sound field and uses the signal to reproduce the sound field with a
speaker array, For example, the technology described in Non-Patent Document 1 is known.
[0003]
03-05-2019
1
Shoichi Koyama, 3 others, "Spatio-temporal frequency domain signal conversion method for
sound field collection and reproduction", Proceedings of the Acoustical Society of Japan,
September 2011, P. 635-636
[0004]
In the technique described in Non-Patent Document 1, it is necessary to use a planar array in
order to reproduce the image including the vertical direction.
In addition, when the number of arrays used in the vertical direction is small, the reproduction
error becomes large, and there is a possibility that the vertical feeling can not be reproduced.
[0005]
An object of the present invention is to provide a sound field sound collecting and reproducing
apparatus, method and program capable of reproducing a sound field with higher accuracy than
conventional.
[0006]
In order to solve the above-described problems, according to one aspect of the present invention,
there is provided a sound field sound collecting and reproducing apparatus, wherein the radius
of the cylindrical sound absorbing material of radius Rb is centered on the axis of the baffle and
the circumferential direction is the baffle. Assuming that at least two microphones are arranged
in each of two or more circles of Rm, Rm> Rb, the axial direction of the baffle is the z-axis
direction, the circumferential direction of the baffle and the φ direction, and j is an imaginary
unit Let ω be the frequency, c be the speed of sound, k = ω / c, n be the order in the φ
direction, kz, l be the wave number in the z-axis direction, l be its index and J n (·) be n Let H n
<(1)> (·) be an n th first kind Hankel function, A (ω) be a predetermined complex number, and
wn l be a weight determined based on n, l , At least four speakers are arranged on the
circumference of the virtual cylinder of radius Rs of the second space different from the first
space, Filter F ~nl (ω) defined by the following equation on the space-time frequency domain
signal P ~nl (ω) generated based on the signal collected by a conversion filter unit that generates
nl (ω);
[0007]
03-05-2019
2
[0008]
A space-frequency inverse transform unit that transforms the filtered signal D to nl (ω) into a
frequency domain signal by inverse Fourier transform of space, and a time domain signal that is
transformed into a time domain signal by inverse Fourier transform And a frequency inverse
converter for outputting the area signal to the speaker.
[0009]
According to another aspect of the present invention, there is provided an acoustic field sound
collecting and reproducing apparatus including: two or more circles of radius Rm whose
circumferential direction is the circumferential direction of the baffle centered on the axis of the
baffle of the cylindrical sound absorbing material of radius Rb. Of at least two microphones, Rm>
Rb, the axial direction of the baffle cylinder is the z-axis direction, the circumferential direction of
the baffle cylinder and the φ direction, j is the imaginary unit, ω Let f be the speed of sound, c
be the speed of sound, k = ω / c, n be the order in the φ direction, kz, l be the wave number in
the z axis direction, l be its index and Jn (·) be the n th order A Bessel function of a kind, Hn <(1)>
(·) is an n-th kind of first Hankel function, A (ω) is a predetermined complex number, wnl is a
weight determined based on n, l, at least 4 The sound is collected by the microphone array,
assuming that the speakers are arranged on the circumference of a virtual cylinder of radius Rs
of the second space different from the first space. A frequency transform unit that transforms the
received signal into a frequency domain signal by Fourier transform; a space frequency
transform unit that transforms the frequency domain signal into a space-time frequency domain
signal P ~ nl (ω) by Fourier transform of space; And a conversion filter unit that generates a
filtered signal D ~nl (ω) by applying a filter F ~nl (ω) defined by the following equation to the
domain signal P ~nl (ω).
[0010]
[0011]
Even when the number of microphones and speakers constituting each of the microphone array
and the speaker array is small, the microphone array and the speaker array have a cylindrical
shape, and elements are densely arranged in the left-right direction, and rough elements are
arranged in the vertical direction. The sense of up and down can be reproduced.
Therefore, the sound field can be reproduced with higher accuracy than conventional.
03-05-2019
3
[0012]
FIG. 2 is a functional block diagram showing an example of a sound field sound collecting and
reproducing apparatus.
The figure for demonstrating the example of arrangement | positioning of a microphone and a
speaker.
The figure for demonstrating the example of arrangement | positioning of a microphone and a
speaker.
The flowchart which shows the example of the sound field sound collection reproduction method.
[0013]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
In the following description, the symbols "~", "<->", etc. used in the text should originally be
written directly above the previous character, but due to the limitations of the text notation
Described in.
In the formula, these symbols are described at their original positions.
Moreover, the processing performed in each element unit of a vector or a matrix is applied to all
elements of the vector or the matrix unless otherwise noted.
[0014]
03-05-2019
4
<Arrangement of Microphone Array and Speaker Array> As shown in FIG. 1, the sound field
sound collecting and reproducing apparatus and method are arranged at a position Rm away
from the axis of the baffle of the cylindrical sound absorbing material of radius Rb of the first
space. Microphone array composed of Nz × Nφ microphones, and an Nz × Nφ speaker
disposed on a peripheral surface of a virtual cylinder having a radius Rs of a second space
different from the first space Using the speaker array, the sound field of the first space formed by
the sound generated by the sound source So of the first space is reproduced in the second space.
In FIG. 1, the sound source So reproduced in the second space is expressed as a sound source So
'. The axial direction of the cylinder is taken as the z-axis direction. The first space and the second
space are mutually different spaces.
[0015]
The number of microphones disposed in the first space and the number of speakers disposed in
the second space may be different. When the number of microphones is larger than the number
of speakers disposed in the second space, the reproduction signal may be thinned. On the other
hand, when the number of microphones is smaller than the number of speakers arranged in the
second space, the reproduction signal may be interpolated by averaging the channels. As a
method of performing interpolation, for example, linear interpolation or sinc interpolation can be
applied.
[0016]
The sound absorbing material is a material having an ability to absorb sound waves, and ideally
is a material having a sound absorption coefficient of ∞. It is mainly used in buildings for the
purpose of adjusting the sound condition of the room and absorbing the noise. Specific examples
thereof include porous sound absorbing materials such as glass wool and felt, and diaphragm
sound absorbing materials that absorb vibrations using a thin plate. The type of the sound
absorbing material is not limited, and any material may be used.
[0017]
03-05-2019
5
As shown in FIG. 3, the microphones are disposed at a position Rm away from the axis of the
cylindrical baffle B of radius Rb. In other words, as Rm> Rb, the microphone is placed at a
position (Rm−Rb) away from the surface of the peripheral surface of the baffle B. For example,
the microphone is disposed by being supported by a thin rod-like member protruding
perpendicularly from the circumferential surface of the baffle B.
[0018]
In other words, Nφ microphones are equally spaced at each of Nz circles whose circumferential
direction is the circumferential direction of the cylindrical sound absorbing material baffle B with
the axis of the cylindrical sound absorbing material baffle B as the center. Be placed. Nz and Nφ
are predetermined integers of 2 or more. That is, by arranging two microphones in each of two
circles whose circumferential direction is the circumferential direction of the baffle B, at least
four microphones are disposed at positions Rm away from the axis of the baffle B.
[0019]
The microphones may be spaced at any distance. That is, each of the distances zc and φc
between adjacent microphones can take arbitrary values. However, the sound field can be
reproduced with high accuracy by arranging the microphones at equal intervals, that is, setting
the same value to each of zc and φc which are the intervals between adjacent microphones.
[0020]
The microphone is disposed outward of the circumferential surface of the baffle of the cylindrical
sound absorbing material.
[0021]
The speakers are also arranged in the same manner as the microphones.
That is, as shown in FIG. 3, Nφ speakers are arranged at equal intervals in each of Nz circles on
the circumferential surface of the virtual cylinder. Nz and Nφ are predetermined integers of 2 or
03-05-2019
6
more. At least four speakers are arranged on the circumferential surface of the virtual cylinder.
[0022]
Nz circles on the circumferential surface of the virtual cylinder are located at zc intervals, for
example, with zc as a predetermined distance. Further, Nφ speakers arranged in the same circle
are located at intervals of φc degrees, with φc as a predetermined angle.
[0023]
The speakers do not have to be strictly spaced if they are approximately equally spaced. That is,
the distances zc and φc, which are the intervals between adjacent speakers, do not have to be
exactly the same value, and may be approximately the same value. Also, the speakers may be
arranged at any intervals. That is, an interval φc between adjacent speakers can take an
arbitrary value. However, the sound field can be reproduced with high accuracy by arranging the
speakers at substantially equal intervals, that is, by setting φc, which is an interval between
adjacent speakers, to substantially the same value.
[0024]
The distance Rm from the axis of the baffle in which the microphone is disposed is, for example,
about 2 cm. The distance Rm from the baffle axis can form sharp directivity as the value is larger,
but more microphones are required. Also, Rm and Rs can reproduce a wider area as their values
are larger, but more microphones and speakers are required. It is desirable to set Rm and Rs
experimentally in consideration of the frequency of the signal to be collected.
[0025]
The radius Rs of the cylinder in which the speaker is disposed is, for example, about 1.5 m.
Although Rm ≦ Rs or Rs ≦ Rm may be satisfied, when Rm ≦ Rs, the accuracy of sound field
reproduction is improved.
03-05-2019
7
[0026]
The speaker may be disposed in the air of the second space in an acoustically transparent state,
or may be disposed in the second space in an acoustically non-transparent state. The acoustically
transparent state is a state in which the same transfer characteristic as the transfer characteristic
of the second space in which the speaker is not disposed is maintained. For example, the speaker
is placed in the air of the second space by being suspended by a thread or fixed by a thin rod.
Also, the speaker may be disposed at a predetermined distance from the circumferential surface
of the baffle of the cylindrical sound absorbing material, as in the microphone. In this case, the
speaker is disposed inward of the circumferential surface of the baffle of the sound absorbing
material.
[0027]
The position of the microphone Mi-j in the first space is expressed as (Rm, φm, i, zm, j) [i = 1,
2,..., Nφ, j = 1, 2,. The position of the speaker Si-j in the second space is expressed as (Rs, φs, i,
zs, j) [i = 1, 2,..., Nφ, j = 1, 2,.
[0028]
<Sound Field Sound Collection and Reproduction Device> As shown in FIG. 1, the sound field
sound collection and reproduction device includes a frequency conversion unit 1, a space
frequency conversion unit 2, a conversion filter unit 3, a space frequency inverse conversion unit
4, and a frequency inverse conversion unit 5. For example, the window processing unit 6 is
included to perform the processing of each step illustrated in FIG.
[0029]
The microphones M1-1, M2-1,..., MNφ-Nz arranged in the first space collect the sound emitted
by the sound source S in the first space to generate a time domain signal.
The generated signal is sent to the frequency converter 1. A signal of time t collected in the
microphone Mi-j of (Rm, φm, i, zm, j) is denoted as pij (t).
03-05-2019
8
[0030]
<Frequency Converter 1> The frequency converter 1 converts the signal pij (t) collected by the
microphones M1-1, M2-1,..., MNφ-Nz into a frequency domain signal Pij (ω) by Fourier
transformation. (Step S1). The generated frequency domain signal P ij (ω) is sent to the spatial
frequency converter 2. ω is a frequency. For example, frequency domain signal P ij (ω) is
generated by short time discrete Fourier transform. Of course, the frequency domain signal P ij
(ω) may be generated by another existing method. Alternatively, the frequency domain signal Pij
(ω) may be generated using a method such as overlap ad. When the input signal is long or when
the signal is continuously input as in real time processing, processing is performed every frame,
for example, every 10 ms. The frequency domain signal P ij (ω) is defined, for example, as
follows. J in the argument of the function exp is an imaginary unit.
[0031]
[0032]
<Spatial Frequency Transform Unit 2> The spatial frequency transform unit 2 transforms the
frequency domain signal Pij (ω) into the space-time frequency domain signal P ~n1 (ω) by
Fourier transform of space (step S2).
The space-time frequency domain signals P ~nl (ω) are calculated for each ω. The converted
space-time frequency domain signal P ~nl (ω) is sent to the conversion filter unit 3. Specifically,
the spatial frequency transform unit 2 calculates P ~nl (ω) defined by equation (1).
[0033]
[0034]
kz, l is the wave number in the z-axis direction, and l is its index.
The wave number is the so-called spatial frequency or angular spectrum. Equation (1) is an
03-05-2019
9
example of conversion to the space-time frequency domain, and Fourier transform of space may
be performed by another method. Also, a method may be used in which equations (0) and (1) are
combined to perform two-dimensional DFT.
[0035]
<Transformation Filter Unit 3> The conversion filter unit 3 applies the filters F to nl (ω) defined
by the equation (2) to the space-time frequency domain signal P to nl (ω), and outputs the signal
D after filtering generate ~ nl (ω) (step S3). The post-filtering signal D ~nl (ω) is sent to the
spatial frequency inverse transform unit 4.
[0036]
[0037]
In equation (2), c = ω / c is the wave number, where c is the speed of sound.
A (ω) is a predetermined complex number. For example, A (ω) = 1 + 0 × i = 1. Also, wnl is a
weight determined as follows based on n and l, for example. In the following equation, nc is a
predetermined value and a cutoff value of n. kc is a predetermined value and a cutoff value of kz.
α n and α z are predetermined values, for example, 0.05. Of course, other weighting functions
may be used as wnl.
[0038]
[0039]
Hn <(1)> (·) is an n-th kind Hankel function.
The n-th first kind Hankel function Hn <(1)> (x) is defined as follows using the n-th first kind
Bessel function Jn (x) and the second kind Bessel function Yn (x) Ru.
03-05-2019
10
[0040]
[0041]
<Spatial Frequency Inverse Transform Unit 4> The spatial frequency inverse transform unit 4
transforms the filtered signal D ~nl (ω) into a frequency domain signal Dij (ω) by inverse Fourier
transform of space (step S4).
The converted frequency domain signal Dij (ω) is sent to the frequency inverse transform unit 5.
Specifically, the spatial frequency inverse transform unit 4 calculates the frequency domain
signal Dij (ω) defined by the equation (3).
[0042]
[0043]
<Frequency Inverse Transform Unit 5> The frequency inverse transform unit 5 converts the
frequency domain signal Dij (ω) into a time domain signal P <d> ij (t) by inverse Fourier
transform (step S5).
The time domain signal P <d> ij (t) obtained for each frame by the inverse Fourier transform is
appropriately shifted and linearly summed to be a continuous time domain signal. As the inverse
Fourier transform, an existing method such as a short time discrete inverse Fourier transform
may be used. The time domain signal P <d> ij (t) is sent to the window function unit 6.
[0044]
<Window Function Unit 6> The window function unit 6 multiplies the time domain signal P <d> ij
(t) by the window function to generate a post-window function time domain signal dij (t) (step
S6). The window function post-time domain signal dij (t) is sent to the speakers Si-j, S2-1, ..., SN
03-05-2019
11
[phi] -Nz.
[0045]
For example, a so-called Tukey window function γj defined by the following equation is used as
the window function. Ntpr is a score to which a taper is applied, and is an integer of 1 or more
and Nφ or less and Nz or less. Of course, other window functions may be used.
[0046]
[0047]
The speaker arrays S1-1, S2-1,..., SNφ-Nz reproduce the sound based on the window function
after time domain signal dij (t).
Specifically, the speaker Si-j reproduces sound based on the window function after time domain
signal dij (t) as i = 1,..., Nφ, j = 1,. Thereby, the sound field of the first space can be reproduced in
the second space.
[0048]
As described above, by making the microphone array and the speaker array cylindrical, even if
the number of microphones and speakers constituting the microphone array and the speaker
array is small, the elements are densely arranged in the left and right direction, and the up and
down direction The upper and lower senses can be reproduced as a rough element arrangement.
Therefore, the sound field can be reproduced with higher accuracy than in the prior art.
[0049]
<Theoretical Background> Hereinafter, the reason why the filters F to nl (ω) are represented as
Expression (2) will be described.
03-05-2019
12
[0050]
Let the position vector of the reproduction region be r '= (r, φ, z), let the cylindrical surface on
which the secondary sound source be arranged be S, and let the position vector on S be rs' = (Rs,
φs, zs) .
Let the sound pressure at position r 'in the reproduction region be P (r', ω) at frequency ω, and
the signal of the secondary sound source at position rs 'be the transfer function from D (rs', ω),
rs 'to r' Let G (r'-rs', ω) be. At this time, the sound field synthesized in the reproduction area by
the secondary sound source can be written as follows.
[0051]
[0052]
This expression is nothing but a convolution operation of the functions D (·) and G (·) with respect
to the variables φ and z.
Therefore, according to the convolution theorem, equation (4) can be expressed as follows in the
helical wave spectral region.
[0053]
[0054]
Here, the equation (5) is expanded for the case where the secondary sound source can be
approximated as a monopole characteristic.
このとき、
03-05-2019
13
[0055]
[0056]
であるから、
[0057]
[0058]
となる。
ここで、
[0059]
[0060]
である。
From the Hankel function addition theorem,
[0061]
[0062]
であるから、
[0063]
03-05-2019
14
[0064]
となる。
Substituting equation (6) into equation (5),
[0065]
[0066]
となる。
[0067]
The ideal sound field can be provided from the sound pressure on the cylindrically shaped sound
absorbing baffle using an omnidirectional microphone array or the like.
Let P (rm ', ω) be the sound pressure distribution on the sound collecting side cylindrical surface,
P (r', ω) is the incident sound field Pi (r ', ω) and the scattered sound field Ps (r', ω) It can write
in the sum with).
[0068]
[0069]
From the boundary condition that the sound pressure gradient is zero on the sound absorbing
baffle,
[0070]
[0071]
03-05-2019
15
となる。
Writing Pi (r ', ω) and Ps (r', ω) in the helical wave spectral domain,
[0072]
[0073]
From the boundary condition of equation (8), the following relationship is established.
[0074]
[0075]
したがって、
[0076]
[0077]
となる。
Since the sound field to be reproduced is the incident sound field Pi (·), the ideal sound field can
be written in the helical wave spectral region as follows.
[0078]
[0079]
What is desired to be obtained here is a conversion equation from the cylindrical sound pressure
03-05-2019
16
distribution P (rm ', ω) to the drive signal D (rs', ω) of the secondary sound source.
When the conversion equation is determined assuming that the secondary sound source has a
monopole characteristic, equations (7) and (9) may be solved simultaneously.
[0080]
[0081]
It is as follows when written in filter form.
[0082]
[0083]
ただし、
[0084]
[0085]
である。
[0086]
It should be noted that since the characteristics of the filter are essentially the same, this
equation is multiplied by 4 and A (ω), which is a predetermined constant for adjusting the
frequency characteristic, and a weight wnl for attenuating the evanescent wave It may be
multiplied.
Then, this equation agrees with equation (2).
[0087]
03-05-2019
17
[Modifications, Etc.] Each part constituting the sound field sound collecting and reproducing
apparatus may be provided in either the sound collecting apparatus arranged in the first space or
the reproduction apparatus arranged in the second space.
In other words, the processing of each of the frequency conversion unit 1, the space frequency
conversion unit 2, the conversion filter unit 3, the space frequency inverse conversion unit 4, the
frequency inverse conversion unit 5, and the window function unit 6 is arranged in the first
space It may be performed by the sound collection apparatus, and may be performed by the
reproduction apparatus arrange | positioned to 2nd space.
The signal generated by the sound collection device is transmitted to the reproduction device.
[0088]
The positions of the first space and the second space are not limited to those shown in FIG.
The first space and the second space may be adjacent to or separated from each other.
Also, the orientation of the first space and the second space may be any.
[0089]
The processing of the window function by the window function unit 6 may be performed at any
stage, or may be performed in multiple stages.
That is, the window function unit 6 is between the microphone array and the frequency
conversion unit 1, between the frequency conversion unit 1 and the spatial frequency conversion
unit 2, between the spatial frequency conversion unit 2 and the conversion filter unit 3, and a
conversion filter unit It may be provided between at least one of the space frequency inverse
transform unit 4 and the space frequency inverse transform unit 5.
03-05-2019
18
When processing of the window function is performed on the signal input to each part of each
part of the sound field collection and reproduction device, processing of the window function is
performed in the same manner as described above instead of the input signal. Process the signal
after the
[0090]
In addition, the window function unit 6 may be omitted.
In this case, the speaker Si-j reproduces sound based on the time domain signal P <d> ij (t) as i =
1,..., Nφ, j = 1,.
[0091]
As long as the sound field sound collecting and reproducing apparatus includes the conversion
filter unit 3, it does not have to include other units.
For example, the sound field sound collection and reproduction apparatus may be configured of
the conversion filter unit 3, the spatial frequency inverse conversion unit 4, and the frequency
inverse conversion unit 5.
Further, the sound field sound collecting and reproducing apparatus may be configured of the
frequency conversion unit 1, the spatial frequency conversion unit 2, and the conversion filter
unit 3.
[0092]
The processing of the frequency conversion unit 1 and the processing of the spatial frequency
conversion unit 2 may be performed simultaneously.
03-05-2019
19
Similarly, the process of the spatial frequency inverse transform unit 4 and the process of the
frequency inverse transform unit 5 may be performed simultaneously.
Also, the space frequency conversion unit 2 and the space frequency inverse conversion unit 4
may be interchanged.
[0093]
The sound field sound collecting and reproducing apparatus can be realized by a computer.
In this case, the processing content of each part of this apparatus is described by a program.
And each part in this apparatus is implement | achieved on a computer by running this program
by computer.
[0094]
The program describing the processing content can be recorded in a computer readable
recording medium.
Further, in this embodiment, these devices are configured by executing a predetermined program
on a computer, but at least a part of the processing contents may be realized as hardware.
[0095]
The present invention is not limited to the above-described embodiment, and various
modifications can be made without departing from the spirit of the present invention.
[0096]
Reference Signs List 1 frequency conversion unit 2 space frequency conversion unit 3 conversion
filter unit 4 space frequency inverse conversion unit 5 frequency inverse conversion unit 6
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window function unit
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