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JP2014045253

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DESCRIPTION JP2014045253
Abstract: The present invention provides a sound field sound collecting and reproducing
technique capable of reproducing a sound field having a sense of up and down even when the
number of arrays used in the up and down directions is small. 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]
The present invention relates to a wave field synthesis technique in which a sound signal is
collected by a microphone installed in a certain sound field, and the sound field is reproduced by
a speaker using the sound signal.
[0002]
For example, Non-Patent Document 1 describes a wave field synthesis technique in which a
microphone array installed in a certain sound field picks up a signal and uses the signal to
reproduce the sound field with a speaker array. Technology is known.
09-05-2019
1
[0003]
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 problems, in the sound field collection and reproduction apparatus
according to one aspect of the present invention, at least four microphones are disposed on the
circumferential surface of a cylindrical rigid baffle having a radius Rm of a first space. Assuming
that the axial direction of the baffle is the z-axis direction, the circumferential direction of the
baffle and the φ direction, j is the imaginary unit, ω is the frequency, c is the speed of sound, k =
ω / c, n is the φ direction Let kz, l be the wave number in the z-axis direction, l be its index, Hn
<(1)> (•) be the n-th kind Hankel function, wnl be the weight determined based on n, l Space-time
frequency generated based on the signal picked up by the microphone, assuming that at least
four speakers are disposed on the peripheral surface of the virtual cylinder of radius Rs of the
second space different from the first space The post-filtering signal is applied by applying the
filter F ˜nl (ω) defined by the following equation to the domain signal P ˜nl (ω) A conversion
filter unit that generates a number D to nl (ω);
[0007]
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[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 a sound field sound
collecting and reproducing apparatus, wherein at least four microphones are disposed on a
peripheral surface of a cylindrical rigid rigid baffle with a radius Rm of a first space. The axial
direction is the z-axis direction, the circumferential direction of the cylinder of the baffle and the
φ direction, j is the imaginary unit, ω is the frequency, c is the speed of sound, k = ω / c, n is the
order in the φ direction, Let kz, l be the wave number in the z-axis direction, let l be its index, let
Hn <(1)> (•) be the first-order Hankel function of order n, wnl be the weight determined based on
n, l Assuming that four speakers are disposed on the peripheral surface of a virtual cylinder
having a radius Rs of a second space different from the first space, a frequency at which a signal
collected by the microphone array is converted into a frequency domain signal by Fourier
transform Space-time frequency domain with frequency domain signal by transform unit and
Fourier transform of space After applying the filter to the space frequency conversion unit for
converting to P ˜ nl (ω) and the filter F ˜ nl (ω) defined by the following equation for the spacetime frequency domain signal P ˜ nl (ω) And a conversion filter unit that generates signals D to
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.
[0012]
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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 ¦
regeneration method.
[0013]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0014]
In the sound field sound collecting and reproducing apparatus and method, as shown in FIG. 1, a
microphone array composed of Nz × Nφ microphones disposed on the peripheral surface of a
cylindrical rigid body baffle of a first space radius Rm. And a speaker array composed of Nz ×
Nφ speakers disposed on the peripheral surface of a virtual cylinder having a radius Rs of a
second space different from the first space, the sound source So of the first space The sound field
of the first space formed by the generated sound 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 the z-axis direction, and the circumferential direction is φ.
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The first space and the second space are mutually different spaces.
In this embodiment, the number of microphones arranged in the first space is the same as the
number of speakers arranged in the second space.
[0015]
As shown in FIG. 3, Nφ microphones are arranged at equal intervals in each of Nz circles on the
circumferential surface of the cylindrical baffle.
Nz and Nφ are predetermined integers of 2 or more. That is, by arranging two microphones in
each of two circles on the circumferential surface of the cylinder, at least four microphones are
disposed on the circumferential surface of the cylinder.
[0016]
The Nz circles on the circumferential surface of the cylinder are located at zc intervals, for
example, with zc as a predetermined distance. Further, N.phi. Microphones arranged in the same
circle are positioned at an interval of .phi.c degrees, where .phi.c is a predetermined angle.
[0017]
The microphones do not have to be strictly spaced if they are approximately equally spaced. That
is, the distances zc and φc between adjacent microphones do not have to be exactly the same
value, but may be approximately the same value.
[0018]
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 cylinder. Nz and Nφ are predetermined integers of 2 or more. At least four
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speakers are disposed on the circumferential surface of the cylinder.
[0019]
The Nz circles on the circumferential surface of the 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.
[0020]
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.
[0021]
The radius Rm of the cylinder in which the microphone is disposed is, for example, 25 to 50 cm.
Further, 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.
[0022]
The microphone is disposed outward of the circumferential surface of the cylinder. Moreover, the
speaker is disposed toward the inside of the circumferential surface of the cylinder.
[0023]
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
09-05-2019
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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 speakers may be disposed on cylindrical rigid baffles, similar to the microphones.
[0024]
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,.
[0025]
The sound field sound collecting and reproducing apparatus includes, for example, a frequency
converter 1, a space frequency converter 2, a conversion filter 3, a space frequency inverse
converter 4, a frequency inverse converter 5, and a window function unit 6, as shown in FIG. ,
And perform the processing of each step illustrated in FIG.
[0026]
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).
[0027]
The frequency converter 1 converts the signal pij (t) picked up by the microphones M1-1, M21,..., 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
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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.
[0028]
[0029]
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).
[0030]
[0031]
kz, l is the wave number in the z-axis direction, l is its index, and n is the order in the φ direction.
The wave number is the so-called spatial frequency or angular spectrum. Equation (1) is an
example of conversion to the space-time frequency domain, and Fourier transform of space may
be performed by another method.
[0032]
The conversion filter unit 3 applies the filter F to nl (ω) defined by the equation (2) to the spacetime frequency domain signal P to nl (ω) to apply the filter-processed signal D to nl (ω) Generate
(step S3). The post-filtering signal D ˜nl (ω) is sent to the spatial frequency inverse transform
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unit 4.
[0033]
[0034]
In equation (2), c = ω / c is the wave number, where c is the speed of sound.
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.
[0035]
[0036]
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 first Bessel
function Jn (x) and the second Bessel function Yn (x).
[0037]
[0038]
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 S 4).
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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).
[0039]
[0040]
The frequency inverse transform unit 5 transforms 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.
[0041]
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 [phi] -Nz.
[0042]
For example, a so-called Tukey window function wij defined by the following equation is used as
a 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.
[0043]
[0044]
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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.
[0045]
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 horizontal direction, and the vertical 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.
[0046]
Hereinafter, the reason why the filters F to nl (ω) are expressed as shown in equation (2) will be
described.
[0047]
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)
Let G (rs'-r ', ω) be. At this time, the sound field synthesized in the reproduction area by the
secondary sound source can be written as follows.
[0048]
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[0049]
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.
[0050]
[0051]
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、
[0052]
であるから、
[0053]
となる。
ここで、
[0054]
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である。 From the Hankel function addition theorem,
[0055]
であるから、
[0056]
となる。
Substituting equation (6) into equation (5),
[0057]
となる。
[0058]
The ideal sound field can be provided from the sound pressure on the cylindrical rigid 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).
[0059]
[0060]
From the boundary condition that the sound pressure gradient is zero on the rigid baffle,
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Writing Pi (r ', ω) and Ps (r', ω) in the helical wave spectral domain,
[0061]
From the boundary condition of equation (8), the following relationship is established.
[0062]
[0063]
したがって、
[0064]
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.
[0065]
[0066]
What is desired to be obtained here is a conversion equation from the cylindrical sound pressure
distribution P (rm ', ω) to the drive signal D (rs', ω) of the secondary sound source.
If the conversion equation is to be determined assuming that the secondary sound source has
monopole characteristics, equations (7) and (8) may be solved simultaneously.
[0067]
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[0068]
It is as follows when written in filter form.
[0069]
ただし、 である。
[0070]
[Modifications, Etc.] The number of microphones disposed in the first space may be different
from the number of speakers disposed in the second space.
When the number of microphones constituting the microphone array is larger than the number
of speakers constituting the speaker array, the time-domain signal dij (t) may be thinned after the
window function.
On the other hand, when the number of microphones constituting the microphone array is
smaller than the number of speakers constituting the speaker array, the interpolation may be
performed by averaging the time domain signal dij (t) after the window function. .
[0071]
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 reproducing
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.
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The signal generated by the sound collection device is transmitted to the reproduction device.
[0072]
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.
[0073]
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. 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
[0074]
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,.
[0075]
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
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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.
[0076]
The processing of the frequency conversion unit 1 and the processing of the spatial frequency
conversion unit 2 may be performed simultaneously. 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.
[0077]
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.
[0078]
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.
[0079]
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.
[0080]
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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