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JP2000165984

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DESCRIPTION JP2000165984
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound amplification apparatus for amplifying an output sound using an electroacoustic
equipment and to a method of improving the clarity of the apparatus.
[0002]
2. Description of the Related Art Heretofore, as a method of improving the intelligibility in the
case of sound amplification in the case of sound amplification, those described in the literature
(School Technical Report EA 94-38) are known. FIG. 6 shows the configuration of a conventional
sound amplification apparatus with improved clarity. In FIG. 6, 607 is a sound field, and there are
N speakers 604 and M control points 606. An impulse response 605 between the speaker 604
and the control point 606 is obtained by measurement or prediction means. The coefficient
calculator 611 calculates the coefficient 612 by the least square method using the target
characteristic 609 in which the waveform with less reverberation is set, the transfer function
setting unit 608 in which the impulse response 605 is set, and the divergence prevention
coefficient 610. By setting this coefficient 612 in the sound field control filter 602 and
connecting it to the speaker 604 via the amplifier 603, the input audio signal 601 can be clearly
transmitted to the control point 606.
[0003]
In this way, even in the conventional sound amplification apparatus, the intelligibility of the loud
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speech can be temporarily improved.
[0004]
SUMMARY OF THE INVENTION However, in the above-described conventional method for
improving the clarity in the sound amplification apparatus, when the reverberation time is long,
the amount of calculation of the control filter required becomes enormous, and when the number
of control points increases The number of sound field control filters also increases, and the
number of impulse responses that need to be measured also increases.
[0005]
The present invention solves such conventional problems, and reduces the amount of calculation
of a sound field control filter and reduces the number of sound field control filters while
providing clear sound amplification apparatus and sound amplification apparatus It aims at
providing the clarity improvement method.
[0006]
SUMMARY OF THE INVENTION According to the present invention, there is provided an acoustic
loudspeaker and an intelligibility improvement method for calculating the coefficient of a sound
field control filter, using singular value decomposition as the method of calculating coefficients of
a sound field control filter. Among them, an element which is equal to or less than the reference
value is set to 0 and then a means for calculating a coefficient, a means for setting a part of an
impulse response between a speaker and a control point as a target characteristic, and a plurality
of control points Control means, means for reducing the coefficient length and using only a part
of the coefficients including the tap with the largest squared amplitude, and sound field control
at a plurality of locations in a sound field such as a tunnel in which the same shape continues in
one direction. The speaker and the control point are arranged at the same position at each
control location, the sound field control filter coefficient is calculated at only one of a plurality of
control locations, and the sound field control is performed at the other locations using this
coefficient means And means for calculating the sound field control filter coefficient for
controlling the plurality of control points at the same time, those having appropriately.
As a result, the amount of calculation of the sound field control filter can be reduced, and clear
sound can be performed while reducing the number of sound field control filters.
08-05-2019
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[0007]
According to the first aspect of the present invention, an input audio signal is amplified through a
sound field control filter, and then, in the sound field, the speaker outputs a loud sound toward
the control point. In a sound amplification apparatus that calculates a coefficient for a target
characteristic based on an impulse response between a signal and a control point and sets the
coefficient in a sound field control filter, singular value analysis is used as a method of
calculating the coefficient of the sound field control filter. Of the elements of the singular value
matrix for each frequency, the elements which are equal to or less than the reference value are
set to 0 and then the apparatus is provided with means for calculating coefficients, and the
calculation amount of the sound field control filter is reduced. This has the effect of being able to
perform clear speech while reducing the number of sound field control filters.
[0008]
The invention according to claim 2 of the present invention is an acoustic loudspeaker according
to claim 1, further comprising means for setting a part of an impulse response between the
speaker and the control point as a target characteristic. It has the effect of reducing the amount
of computation and performing clear sounding while reducing the number of sound field control
filters.
[0009]
The invention according to claim 3 of the present invention is the sound amplification apparatus
according to claim 1 or 2, wherein a plurality of control points are three-dimensionally arranged,
wherein the calculation amount of the sound field control filter is reduced and the sound field
control filter It has the effect of being able to carry out a clear loudspeaker while reducing the
number of
[0010]
The invention according to claim 4 of the present invention shortens the length of the coefficient,
and uses only a part of the coefficient including the tap where the square amplitude becomes
maximum as the sound field control filter coefficient according to claim 3. It is an apparatus, and
has the effect that the amount of calculation of the sound field control filter can be reduced, and
clear speech can be performed while reducing the number of sound field control filters.
[0011]
The invention according to claim 5 of the present invention performs sound field control at a
plurality of points in a sound field having the same shape continuously in one direction, such as a
tunnel, and arranges speakers and control points at the same position at each control point, The
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acoustic loudspeaker according to any one of claims 1 to 4, wherein a sound field control filter
coefficient is calculated at only one of a plurality of control points, and sound field control is
performed at the other points using this coefficient. The present invention has the effect of being
able to perform clear speech while reducing the amount of calculation of the sound field control
filter and reducing the number of sound field control filters.
[0012]
The invention according to claim 6 of the present invention is the sound amplification apparatus
according to claim 5, wherein sound field control filter coefficients for simultaneously controlling
a plurality of control points are calculated, and the amount of calculation of the sound field
control filter is reduced. And the effect of being able to perform clear speech while reducing the
number of sound field control filters.
[0013]
According to the seventh aspect of the present invention, in the sound amplification apparatus,
singular value decomposition is performed in the frequency domain as a method of calculating
coefficients of the sound field control filter, and a threshold set in advance among respective
elements of the singular value matrix The following element is an intelligibility improvement
method of performing inverse matrix calculation after setting to 0, and has an effect that clear
speech can be performed.
[0014]
The invention according to claim 8 of the present invention calculates the maximum value of
each element of the singular value matrix at each frequency, and sets the threshold value based
on the maximum value. It has the effect of being able to prevent divergence for each sound field
control filter.
[0015]
The invention according to claim 9 of the present invention is the clarity improving method
according to claim 8, wherein the threshold value is 40 dB smaller than the maximum value of
each element of the singular value matrix at each frequency. It has the effect of preventing
divergence for each filter.
[0016]
The invention according to claim 10 of the present invention is the clarity improving method
according to any one of claims 7, 8 or 9, wherein a part of the impulse response between the
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speaker and the control point is used as the target characteristic. It has the effect of expanding
the range in which clear speech can be performed to the periphery of the control point.
[0017]
The invention according to claim 11 of the present invention is the clarity improving method
according to claim 10, wherein the impulse response between the speaker and the control point
is set to 0 except for the part other than the direct sound as the target characteristic. It has the
effect of expanding the range in which clear sound can be produced not only at the control point
but also around the control point.
[0018]
The invention according to claim 12 of the present invention is the method for improving clarity
according to claim 11, in which a plurality of control points are three-dimensionally arranged,
and sterically expanding the range in which clear speech can be performed. It has an action.
[0019]
The invention according to claim 13 of the present invention is the method for improving clarity
according to claim 12, wherein the control points are arranged on a three-dimensional lattice
point whose one side is within 30 cm in length. It has the effect of three-dimensionally expanding
the range that can be done.
[0020]
The invention according to claim 14 of the present invention performs sound field control by
using only a part of coefficients including a tap at which the squared amplitude is maximum after
coefficient calculation. This is a method of improving the clarity and has the effect of reducing
the size of the required sound field control filter.
[0021]
The invention according to claim 15 of the present invention is the clarity improving method
according to claim 14, wherein the coefficient length is reduced to 1/10 or less in comparison
with the coefficient length before shortening. This has the effect of reducing the size of the filter.
[0022]
The invention according to claim 16 of the present invention performs sound field control at a
plurality of locations in a sound field such as a tunnel in which the same cross-sectional shape is
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continuous in one direction, and arranges speakers and control points at the same location at
each control location. The clarity improving method according to any one of claims 7 to 15,
wherein the loudness can be clearly performed at a plurality of locations while reducing the size
of the entire sound field control filter, and the number of required impulse responses. Have the
effect of reducing
[0023]
The invention according to claim 17 of the present invention calculates the coefficient of the
sound field control filter at only one of a plurality of control points, and executes the sound field
control at other points using this coefficient. The clarity improving method according to the
sixteenth aspect, which has an action of enabling clear sounding at a plurality of places while
reducing the scale of the entire sound field control filter, and an action of reducing the number of
necessary impulse responses.
[0024]
The invention according to claim 18 of the present invention is the clarity improving method
according to claim 17, wherein the distance between the control points is 50 m or more, and has
the effect of reducing the interference by other control points.
[0025]
The invention according to claim 19 of the present invention is the clarity improving method
according to claim 16, wherein a sound field control filter coefficient for simultaneously
controlling a plurality of control points is calculated, and the scale of the entire sound field
control filter is reduced. However, it has the effect of being able to perform clear speech at
multiple locations.
[0026]
The invention according to claim 20 of the present invention is the clarity improving method
according to claim 19, wherein the filter coefficient is calculated using only an impulse response
between a speaker and a control point in each control location, It has the effect of being able to
perform clear sounding at multiple locations while reducing the overall scale of the sound field
control filter.
[0027]
The invention according to claim 21 of the present invention is the method for improving clarity
as claimed in claim 20, wherein the distance between the control points is 50 m or more, and has
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the effect of reducing interference by other control points.
[0028]
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to
5.
(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
In FIG. 1, an input sound signal 101 is connected to N sound field control filters 102.
The output of the sound field control filter 102 is connected to N speakers 104 in the sound field
107 via N amplifiers 103 respectively.
In the sound field 107, the impulse response 105 between the N speakers 104 and the M control
points 106 is measured, and based on this, the acoustic transfer function matrix 108 is
calculated for each frequency.
The acoustic transfer function matrix 108 is singular value decomposed by the singular value
decomposition calculator 109.
One of the outputs of the singular value decomposition calculator 109 is input to the inverse
matrix calculator 111 via the singular value evaluator 110.
Another output of the singular value decomposition calculator 109 is input to the inverse matrix
calculator 111 as an input speech signal.
The coefficient calculator 113 calculates the coefficient 114 based on the target characteristic
112 and the output of the inverse matrix calculator 111.
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The coefficient 114 is set to the sound field control filter 102.
[0029]
Next, the operation of the first embodiment will be described.
In the sound field 107, N × M impulse responses 105 between N speakers 104 and M control
points are obtained by measurement or simulation.
The impulse response 105 is converted to the frequency domain by a method such as FFT, and
the acoustic transfer function matrix 108 is calculated at each frequency.
Here, the acoustic transfer function matrix 108 is represented by C (M, N).
Each element of the matrix C is a complex number.
The subscripts M and N mean that the matrix is an M-by-N matrix.
The singular value decomposition calculator 109 performs singular value decomposition of the
matrix C as shown in equation (1).
C = UWVT (1) U (M, N): M × N column orthogonal matrix ((i = 1 to M) U U ik U jn = δkn, 1 <k
<N, 1 <n <N) W (N, N): N × N diagonal matrix (diagonal components wj [j = 1 to N] nonnegative)
VT (N, N): N × N orthogonal matrix V transpose
[0030]
When W obtained by the equation (1) is used as it is, if there is an element having a value close
to 0 or almost 0 among the elements of W, the coefficient 114 of the sound field control filter
corresponding to that element is There is a problem of diverging.
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Therefore, divergence is prevented for each sound field control filter in the singular value
evaluator 110 by the following method.
[0031]
The singular value evaluator 110 finds the maximum value Wmax of each element of the
singular value matrix W.
Next, the ratio of each element to the maximum value Wmax is determined.
If the ratio is less than or equal to the reference value, the value of the element wj is set to 0.
The reference value may be in the range of −60 dB to −20 dB, and it is appropriate to set −40
dB.
[0032]
The inverse matrix calculator 111 calculates the inverse matrix of C according to equation (2).
C-1 = V [diag (1 / wj)] UT .. Formula (2) diag (1 / wj): N × N diagonal matrix with an element of 1
/ wj [j = 1 to N]
[0033]
Impulse responses with few reverberation components are set as targets at M control points,
converted into frequency domains, and a matrix B (M) is set as a target characteristic 112 at each
frequency.
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The coefficient calculator 113 calculates the solution X (N) according to equation (3).
X = C-1B ・ ・ ・ Formula (3)
[0034]
X is obtained for each frequency, the frequency characteristics of the N sound field control filters
are obtained, and each is converted to the time domain by a method such as inverse FFT to
obtain coefficients 114. By setting this coefficient in the sound field control filter 102, the control
point 106 can be clearly loudened. Thus, clear sound can be performed while preventing
divergence for each sound field control filter.
[0035]
Second Embodiment FIG. 2 shows a second embodiment of the present invention. In FIG. 2, the
input sound signal 201 is connected to N sound field control filters 202. The output of the sound
field control filter 202 is connected to N speakers 204 in the sound field 207 via N amplifiers
203 respectively. In the sound field 207, impulse responses 205 between the N speakers 204
and the M control points 206 are measured. Based on the impulse response 205, the acoustic
transfer function matrix 208 is calculated for each frequency. The impulse response 205 is also
input to the target characteristic setting unit 215. The acoustic transfer function matrix 208 is
input to the singular value decomposition calculator 209. The singular value decomposition
calculator 209 performs singular value decomposition of the acoustic transfer function matrix
208. One of the outputs of the singular value decomposition calculator 209 is input to the
inverse matrix calculator 211 via the singular value evaluator 210. Another output of the
singular value decomposition calculator 209 is input to the inverse matrix calculator 211. The
coefficient calculator 213 calculates the coefficient 214 based on the target characteristic 212
which is the output of the target characteristic setting unit 215 and the output of the inverse
matrix calculator 211. The coefficient 214 is set to the sound field control filter 202.
[0036]
Next, the operation of the second embodiment will be described. In the sound field 207, N × M
impulse responses 205 between N speakers 204 and M control points are obtained by
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measurement or simulation. M control points are arranged on a straight line. The distance d
between the control points is preferably 30 cm or less, and in practice it is appropriate to be 10
cm. The impulse response 205 is converted to the frequency domain by a method such as FFT,
and the acoustic transfer function matrix 208 is calculated at each frequency. The acoustic
transfer function matrix 208 is an input of the singular value decomposition calculator 209.
Here, the acoustic transfer function matrix 208 is represented by C (M, N). Each element of the
matrix C is a complex number. The subscripts M and N mean that the matrix is an M-by-N matrix.
The singular value decomposition calculator 209 performs singular value decomposition of the
matrix C as shown in equation (1).
[0037]
When W obtained by the equation (1) is used as it is, if there is an element having a value close
to 0 or almost 0 among the elements of W, the coefficient 214 of the sound field control filter
corresponding to that element is There is a problem of diverging. Therefore, the singular value
evaluator 210 prevents divergence for each sound field control filter by the following method.
[0038]
The singular value evaluator 210 finds the maximum value Wmax of each element of the
singular value matrix W. Next, the ratio of each element to the maximum value Wmax is
determined. If the ratio is less than or equal to the reference value, the value of the element wj is
set to 0. The reference value may be in the range of −60 dB to −20 dB, and it is appropriate to
set −40 dB.
[0039]
The target characteristic setting unit 215 receives the impulse response 205 and calculates the
direct sound part of the impulse response 205. The calculation method of the direct sound part
of the impulse response is performed as follows. One of the N speakers 204 is selected, and taps
that maximize the squared amplitude of the impulse response between that speaker and the M
listening points are respectively determined. The window function is multiplied around the tap,
and the range of tap ± T where the squared amplitude becomes maximum is set as the direct
sound part of the impulse response. The shape of the window function may be a rectangular
window or a Hanning window. The optimum magnitude of T is within the range in which the
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direct sound response of the speaker used is contained. Generally, it is in the range of 10 to 50
taps. The direct sound parts of the M impulse responses thus obtained are converted to the
frequency domain by a method such as FFT, and the matrix B (M) is set as the target
characteristic 212 at each frequency. The inverse matrix calculator 211 calculates the inverse
matrix of C according to equation (2).
[0040]
The coefficient calculator 213 calculates the solution as a solution X (N) according to equation
(3). By obtaining X for each frequency, the frequency characteristics of the N sound field control
filters are calculated. The frequency characteristics of the respective sound field control filters
are converted to the time domain by a method such as inverse FFT to obtain coefficients 214. By
setting this coefficient in the sound field control filter 202, it is possible to clearly louden at the
control point 206 and its surroundings. Thus, clear sound can be performed while preventing
divergence for each sound field control filter.
[0041]
Third Embodiment FIG. 3 shows a third embodiment of the present invention. In FIG. 3, the input
sound signal 301 is connected to N sound field control filters 302. The output of the sound field
control filter 302 is connected to the N speakers 304 in the sound field 307 via N amplifiers 303
respectively. In the sound field 307, impulse responses 305 between the N speakers 304 and the
M control points 306 are measured. Based on the impulse response 305, an acoustic transfer
function matrix 308 is calculated for each frequency. The impulse response 305 is also input to
the target characteristic setting unit 315. The acoustic transfer function matrix 308 is input to
the singular value decomposition calculator 309. The singular value decomposition calculator
309 performs singular value decomposition of the acoustic transfer function matrix 308. One of
the outputs of the singular value decomposition calculator 309 is input to the inverse matrix
calculator 311 via the singular value evaluator 310. Another output of the singular value
decomposition calculator 309 is input to the inverse matrix calculator 311. The coefficient
calculator 313 calculates the coefficient 314 based on the target characteristic 312 which is the
output of the target characteristic setting unit 315 and the output of the inverse matrix
calculator 311. The calculated coefficient 314 finds a tap with the maximum squared amplitude
at the maximum value detector 316, and a window function is multiplied by the coefficient
length changer 317 around that tap to obtain the range of taps ± T where the squared
amplitude becomes maximum. Is calculated as a new coefficient, and is set in the sound field
control filter 302.
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[0042]
Next, the operation of the third embodiment will be described. In the sound field 307, N × M
impulse responses 305 between N speakers 304 and M control points 306 are obtained by
measurement or simulation. The M control points 306 are three-dimensionally arranged. The
distance d between the control points 306 is preferably 30 cm or less, and in practice, 10 cm to
20 cm is appropriate. In the practical arrangement of control points 306, 27 control points are
arranged at a distance d of 10 cm in a cube having a side length of 20 cm, which is 1.5 m in
height from the floor surface.
[0043]
The impulse response 305 is converted to the frequency domain by a method such as FFT, and
the acoustic transfer function matrix 308 is calculated at each frequency. The acoustic transfer
function matrix 308 is an input of the singular value decomposition calculator 309. Here, the
acoustic transfer function matrix 308 is represented by C (M, N). Each element of the matrix C is
a complex number. The subscripts M and N mean that the matrix is an M-by-N matrix. The
singular value decomposition calculator 309 performs singular value decomposition of the
matrix C as shown in equation (1).
[0044]
When W obtained by the equation (1) is used as it is, if there is an element having a value close
to 0 or almost 0 among the elements of W, the coefficient 314 of the sound field control filter
corresponding to that element is There is a problem of diverging. Therefore, divergence is
prevented for each sound field control filter in the singular value evaluator 310 by the following
method.
[0045]
The singular value evaluator 310 finds the maximum value Wmax of each element of the
singular value matrix W. Next, the ratio of each element to the maximum value Wmax is
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determined. If the ratio is less than or equal to the reference value, the value of the element wj is
set to 0. The reference value may be in the range of −60 dB to −20 dB, and it is appropriate to
set −40 dB.
[0046]
The target characteristic setting unit 315 receives the impulse response 305 and calculates the
direct sound part of the impulse response 305. The calculation method of the direct sound part
of the impulse response 305 is performed as follows. One of the N speakers 304 is selected, and
taps that maximize the squared amplitude of the impulse response between that speaker and the
M listening points are respectively determined. The window function is multiplied around the tap,
and the range of tap ± T where the squared amplitude becomes maximum is set as the direct
sound part of the impulse response. The shape of the window function may be a rectangular
window or a Hanning window. The optimum magnitude of T is within the range in which the
direct sound response of the speaker used is contained. Generally, it is in the range of 10 to 50
taps. The direct sound parts of the M impulse responses thus obtained are converted to the
frequency domain by a method such as FFT, and the matrix B (M) is set as the target
characteristic 312 at each frequency. The inverse matrix calculator 311 calculates the inverse
matrix of C according to equation (2).
[0047]
The coefficient calculator 313 calculates as a solution X (N) according to equation (3). X for each
frequency is determined, the frequency characteristics of the N sound field control filters are
determined, and each is converted to the time domain by a method such as inverse FFT to obtain
N reduced pre-coefficients. The maximum value detector 316 finds taps that maximize the
squared amplitude of the pre-shortening coefficient. The coefficient length changer 317
multiplies the window function around the tap where the squared amplitude of the preshortening coefficient is maximized, and sets the range of taps ± T where the squared amplitude
is maximized as a new coefficient. The shape of the window function may be a rectangular
window or a Hanning window. Although it is appropriate to set the size of T to 1/10 of the length
of the pre-reduction coefficient, it may be further shortened.
[0048]
By setting the coefficients 314 thus calculated in the sound field control filter 302, it is possible
to clearly louden at the control point 306 and its surroundings, and to perform clear loudness
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while reducing the scale of the sound field control filter. Can.
[0049]
(Fourth Embodiment) FIG. 4 shows a fourth embodiment of the present invention.
In FIG. 4, an input sound signal 401 is connected to N sound field control filters 402. The output
of the sound field control filter 402 is distributed to the N speakers 404 at the control point A
416 and the N speakers 418 at the control point B 417 in the sound field 407 through N
amplifiers 402 respectively. The sound field 407 is a sound field such as a tunnel in which the
same cross-sectional shape is continuous in one direction. In the sound field 407, an impulse
response 405 between the speaker 404 and the control point 406 is defined at the control point
A416, and an impulse response 419 between the speaker 418 and the control point 420 is
defined at the control point B417. Based on the impulse response 405, an acoustic transfer
function matrix 408 is calculated for each frequency. The impulse response 405 is also input to
the target characteristic setting unit 415. The acoustic transfer function matrix 408 is input to
the singular value decomposition calculator 409. The singular value decomposition calculator
409 performs singular value decomposition of the acoustic transfer function matrix 408. One of
the outputs of the singular value decomposition calculator 409 is input to the inverse matrix
calculator 411 via the singular value evaluator 410. Another output of the singular value
decomposition calculator 409 is input to the inverse matrix calculator 411. The coefficient
calculator 413 calculates the coefficient 414 based on the target characteristic 412 which is the
output of the target characteristic setting unit 415 and the output of the inverse matrix
calculator 411. The coefficient 414 is set to the sound field control filter 402.
[0050]
Next, the operation of the fourth embodiment will be described. In the sound field 407, N × M
impulse responses 405 between the N speakers 404 at the control point A 416 and the M
control points 406 are obtained by measurement or simulation. Here, N × M impulse responses
419 between the N speakers 418 of the control point B 417 and the M control points 420 are
not used.
[0051]
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The sound field 407 is a shape such as a tunnel in which the same cross-sectional shape is
continuous in one direction. Therefore, the cross-sectional shape in control location A416 and
control location B417 is the same. The larger the distance L between the control point A 416 and
the control point B 417, the better, and it is necessary that the distance L be 50 m or more.
[0052]
At the control point A 416, the M control points 406 are three-dimensionally arranged. The
distance d between the control points 406 is preferably 30 cm or less, and in practice, 10 cm to
20 cm is appropriate. In the practical arrangement of control points 406, 27 control points are
arranged at a distance d of 10 cm in a cube having a side length of 20 cm, which is 1.5 m in
height from the floor surface. In addition, the speaker 404 is disposed at the control point A 416.
The speakers 404 are disposed so as to cover the control points 406, respectively, and are
disposed close to each other so that the distance between the speakers is as narrow as possible.
[0053]
At the control point B 417, the control point 420 is arranged the same as the control point 406
at the control point A 416. Further, the speaker 418 is also arranged the same as the speaker
404 at the control point A 416. As described above, arranging the loudspeaker and the control
point in the same manner at each of the control point A 416 and the control point B 417 has an
effect of enhancing the correlation between the impulse response 405 at the control point A 416
and the impulse response 419 at the control point B 417.
[0054]
The N × M impulse responses 405 between the N speakers 404 at the control point A 416 and
the M control points 406 are respectively converted to the frequency domain by a method such
as FFT, and the acoustic transfer function matrix 408 is calculated at each frequency. Do. The
acoustic transfer function 408 is an input of the singular value decomposition calculator 409.
Here, the acoustic transfer function matrix 408 is represented by C (M, N). Each element of the
matrix C is a complex number. The subscripts M and N mean that the matrix is an M-by-N matrix.
The singular value decomposition calculator 409 performs singular value decomposition of the
matrix C as shown in equation (1).
08-05-2019
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[0055]
When W obtained by the equation (1) is used as it is, if there is an element having a value close
to 0 or almost 0 among the elements of W, the coefficient 414 of the sound field control filter
corresponding to that element is There is a problem of diverging. Therefore, divergence is
prevented for each sound field control filter in the singular value evaluator 410 by the following
method.
[0056]
The singular value evaluator 410 finds the maximum value Wmax of each element of the
singular value matrix W. Next, the ratio of each element to the maximum value Wmax is
determined. If the ratio is less than or equal to the reference value, the value of the element wj is
set to 0. The reference value may be in the range of −60 dB to −20 dB, and it is appropriate to
set −40 dB.
[0057]
The target characteristic setting unit 415 receives the impulse response 405 and calculates the
direct sound part of the impulse response 405. The method of calculating the direct sound
portion of the impulse response 405 is as follows. One of the N speakers 404 is selected, and
taps that maximize the squared amplitude of the impulse response between that speaker and the
M listening points are respectively determined. The window function is multiplied around the tap,
and the range of tap ± T where the squared amplitude becomes maximum is set as the direct
sound part of the impulse response. The shape of the window function may be a rectangular
window or a Hanning window. The optimum magnitude of T is within the range in which the
direct sound response of the speaker used is contained. Generally, it is in the range of 10 to 50
taps. The direct sound parts of the M impulse responses thus obtained are converted to the
frequency domain by a method such as FFT, and the matrix B (M) is set as the target
characteristic 412 at each frequency. The inverse matrix calculator 411 calculates the inverse
matrix of C according to equation (2).
[0058]
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The coefficient calculator 413 calculates the solution as a solution X (N) according to equation
(3). X is obtained for each frequency, the frequency characteristics of the N sound field control
filters are obtained, and N coefficients 414 are obtained by converting each to the time domain
by a method such as inverse FFT. By setting the coefficients 414 thus calculated in the sound
field control filter 402, the control point 406 of the control point A 416 and its periphery, and
the control point 420 of the control point B 417 and its two peripheral points can be clearly
amplified. It is possible to perform clear sounding at a plurality of locations while reducing the
size of the entire sound field control filter. Although the number of control points is two here, it is
apparent that the same result can be obtained even if the number of control points is two or
more.
[0059]
(Fifth Embodiment) FIG. 5 shows a fifth embodiment of the present invention. In FIG. 5, an input
sound signal 501 is connected to N sound field control filters 502. The output of the sound field
control filter 502 is distributed to the N speakers 504 at the control point A 516 and the N
speakers 518 at the control point B 517 in the sound field 507 through N amplifiers 503
respectively. The sound field 507 is a sound field such as a tunnel in which the same crosssectional shape is continuous in one direction. In the sound field 507, an impulse response 505
between the speaker 504 and the control point 506 is defined at the control point A516, and an
impulse response 519 between the speaker 518 and the control point 520 is defined at the
control point B517. Further, an impulse response 521 and an impulse response 522 are defined
between the control point A 516 and the control point B 517. Based on the impulse response
505 and the impulse response 519, an acoustic transfer function matrix 508 is calculated for
each frequency. The impulse response 505 and the impulse response 522 are also input to the
target characteristic setting unit 515. The acoustic transfer function matrix 508 is input to the
singular value decomposition calculator 509. The singular value decomposition calculator 509
performs singular value decomposition of the acoustic transfer function matrix 508. One of the
outputs of the singular value decomposition calculator 509 is input to the inverse matrix
calculator 511 through the singular value evaluator 510. Another output of the singular value
decomposition calculator 509 is input to the inverse matrix calculator 511. The coefficient
calculator 513 calculates the coefficient 514 based on the target characteristic 512 which is the
output of the target characteristic setting unit 515 and the output of the inverse matrix
calculator 511. The coefficient 514 is set in the sound field control filter 502.
[0060]
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Next, the operation of the fifth embodiment will be described. In the sound field 507, N × M
impulse responses 505 between the N speakers 504 of the control point A 516 and the M
control points 506 are obtained by measurement or simulation. Furthermore, N × M impulse
responses 519 between the N speakers 518 of the control point B 517 and the M control points
520 are determined by measurement or simulation. Here, also, the impulse response 521 and the
impulse response 522 between the control point A 516 and the control point B 517 are not used.
[0061]
The sound field 507 is a shape such as a tunnel in which the same cross-sectional shape is
continuous in one direction. Therefore, the cross-sectional shape in control location A516 and
control location B517 is the same. It is preferable that the distance L between the control point A
516 and the control point B 517 is as wide as possible, and 50 m or more is necessary, and in
practice, it is preferably 100 m or more.
[0062]
At control point A 516, M control points 506 are arranged three-dimensionally. The distance d
between the control points 506 is preferably 30 cm or less, and in practice, 10 cm to 20 cm is
appropriate. In the practical arrangement of control points 506, 27 control points are arranged
at a distance d of 10 cm in a cube having a side length of 20 cm, which is 1.5 m above the floor
surface. Further, the speaker 504 is disposed at the control point A 516. The speakers 504 are
disposed so as to cover the control points 506, respectively, and are disposed close to each other
such that the distance between the speakers is as narrow as possible.
[0063]
At the control point B 517, the control point 520 is arranged the same as the control point 506
at the control point A 516. Further, the speaker 518 is also arranged the same as the speaker
504 at the control point A 516. As described above, arranging the loudspeaker and the control
point in the same manner in each of the control point A 516 and the control point B 517 has an
effect of enhancing the correlation between the impulse response 505 in the control point A 516
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and the impulse response 519 in the control point B 517.
[0064]
The acoustic transfer function matrix A is calculated by converting the N × M impulse responses
505 between the N speakers 504 of the control location A 516 and the M control points 506 into
the frequency domain by a method such as FFT. Further, the acoustic transfer function matrix B
is calculated by converting the N × M impulse responses 519 between the N speakers 518 at
the control location B 517 and the M control points 520 into the frequency domain by a method
such as FFT. . The acoustic transfer function matrices A (N, M) and B (N, M) are complex matrices
of N rows and M columns, respectively. Here, the acoustic transfer function matrix C (N, 2M) is
calculated by combining A and B as shown in equation (4).
[0065]
The matrix C obtained in this manner is referred to as an acoustic transfer function matrix 508.
The acoustic transfer function matrix 508 is input to the singular value decomposition calculator
509. The singular value decomposition calculator 509 performs singular value decomposition of
the matrix C as expressed by equation (1).
[0066]
When W obtained by the equation (1) is used as it is, if there is an element having a value close
to 0 or almost 0 among the elements of W, the coefficient 514 of the sound field control filter
corresponding to that element is There is a problem of diverging. Therefore, divergence is
prevented for each sound field control filter in the singular value evaluator 510 by the following
method.
[0067]
The singular value evaluator 510 obtains the maximum value Wmax of each element of the
singular value matrix W. Next, the ratio of each element to the maximum value Wmax is
determined. If the ratio is less than or equal to the reference value, the value of the element wj is
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set to 0. The reference value may be in the range of −60 dB to −20 dB, and it is appropriate to
set −40 dB.
[0068]
The target characteristic setting unit 515 receives the impulse response 505 and the impulse
response 522, and calculates the direct sound part of the impulse response 505 and the impulse
response 522. The calculation method of the direct sound part of the impulse response is
performed as follows. One of the N speakers 504 is selected, and taps that maximize the squared
amplitude of the impulse response between that speaker and the M listening points are
respectively determined. The window function is multiplied around the tap, and the range of tap
± T where the squared amplitude becomes maximum is set as the direct sound part of the
impulse response. The shape of the window function may be a rectangular window or a Hanning
window. The optimum magnitude of T is within the range in which the direct sound response of
the speaker used is contained. Generally, it is in the range of 10 to 50 inches. The direct sound
parts of the M impulse responses thus obtained are converted to the frequency domain by a
method such as FFT, and the matrix B (2M) is set as the target characteristic 512 at each
frequency. The inverse matrix calculator 511 calculates the inverse matrix of C according to
equation (2).
[0069]
The coefficient calculator 513 calculates the solution as a solution X (N) according to equation
(3). For each frequency, X is obtained, the frequency characteristics of the N sound field control
filters are obtained, and each is converted to the time domain by a method such as inverse FFT to
obtain N coefficients 514. By setting the coefficient 514 thus calculated in the sound field control
filter 502, the control point 506 of the control point A 516 and its surroundings, and the control
point 520 of the control point B 517 and its two surrounding points can be clearly amplified. It is
possible to perform clear sounding at a plurality of locations while reducing the size of the entire
sound field control filter. Although the number of control points is two here, it is apparent that
the same result can be obtained even if the number of control points is two or more.
[0070]
As described above, the present invention performs singular value decomposition in the
frequency domain as a method of calculating coefficients of the sound field control filter, and
among the elements of the singular value matrix, elements smaller than a preset threshold value.
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Is a sound amplification apparatus that performs inverse matrix calculation after setting 0, and a
method of improving the clarity thereof, and can perform clear sound while reducing the number
and calculation amount of sound field control filters.
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