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JP2011211396

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DESCRIPTION JP2011211396
The present invention provides an acoustic system which sets a virtual sound source in a space
between a reflection surface such as a wall of a room and a listener and enables more accurate
sound image localization. An acoustic system (10) of the present invention comprises a signal
source (21) for generating a signal wave in an audible band, a plurality of carriers for an
ultrasonic band, and a plurality of modulated waves generated by modulating the carrier wave
with the signal wave. Virtual sound source SS of the signal wave at a predetermined position in
the transmission path of the modulated wave in the space between the ultrasonic speaker SP and
the reflecting surface that reflects the modulated wave emitted from the ultrasonic speaker SP
and the listener And a control unit (filter processing unit) 22 that controls the sound pressure at
the predetermined position. [Selected figure] Figure 2
Acoustic system and setting method of virtual source thereof
[0001]
The present invention relates to an acoustic system which can be suitably used mainly for a
mixed reality system and a method of setting a virtual sound source thereof.
[0002]
In recent years, mixed reality (MR) that amplifies and expands information in the real
environment by superimposing and displaying virtual information such as computer graphics
(CG) images and characters on images of the real environment (real space) captured by a camera.
Research and development related to (Mixed Reality) technology is actively conducted.
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[0003]
In addition, the auditory elements are combined with such visual mixed reality technology, and as
the sound is generated from the virtual information superimposed and displayed in the real
environment, the direction and distance of the source of the sound Attempts have also been
made to obtain higher reality by localizing (sound image localization).
For example, Patent Document 1 discloses a technique of providing a plurality of sound
generation sources inside a headphone worn by a listener and causing a listener to localize a
sound image according to the position of the sound generation source generating the sound. .
[0004]
Unexamined-Japanese-Patent No. 5-336599
[0005]
However, in the technology of Patent Document 1, the wearing of the headphones by the listener
is a precondition, and only a single person wearing the headphones can experience the virtual
environment, and an individual with head transfer function There is also a problem that the
difference in sound image localization accuracy is lowered.
Furthermore, the listener is bothered by wearing headphones.
[0006]
The present invention has been made in view of the above-described circumstances, in which a
virtual sound source is set in a space between a reflection surface such as a wall of a room and a
listener, and accurate sound image localization without wearing headphones Acoustic system and
method for constructing the same.
[0007]
The acoustic system according to the present invention comprises a signal source for generating
an audible signal wave, and a plurality of ultrasonic speakers for generating an ultrasonic wave
carrier and emitting a modulated wave modulated by the carrier wave. In order to set a virtual
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sound source of the signal wave at a predetermined position of the transmission path of the
modulated wave in the air between the listener and a reflection surface that reflects the
modulated wave emitted from the ultrasonic speaker, And a controller configured to control a
sound pressure.
[0008]
According to the setting method of the virtual sound source in the acoustic system of the present
invention, a modulated wave obtained by modulating a carrier wave of an ultrasonic band by an
audio band signal is emitted by an ultrasonic speaker, and the emitted modulated wave is
reflected by a reflection surface. A control point is set in the transmission path of the modulated
wave in the air between the reflecting surface and the listener, and a virtual sound source of the
signal wave is set by controlling the sound pressure at the control point. .
[0009]
According to the acoustic system and the virtual sound source setting method of the present
invention, the carrier wave in the ultrasonic band is modulated by the signal wave to generate
and emit a modulated wave, and the modulated wave is reflected on the reflection surface to
generate the modulated wave. Listening to the listener (signal wave) to the listener.
Also, a virtual sound source of audible sound is set between the reflecting surface and the
listener.
For this reason, it is possible to give the listener a feeling that sound is generated from the
position and direction of the air different from the position of the actual sound source, and to
perform accurate sound image localization even without wearing headphones etc. Is possible.
[0010]
In the sound system, the control unit sets the relative relationship of the sound pressure at the
plurality of control points to a predetermined value in order to set any one of the plurality of
control points set in the transmission path as a virtual sound source. It is preferable to have a
filter that
[0011]
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Further, in the virtual sound source setting method described above, one of the control points is
set as a virtual sound source by setting a plurality of control points in the transmission path and
setting a relative relationship between sound pressures at the plurality of control points. It is
preferable to set.
[0012]
Thus, by setting a plurality of control points in the transmission path of the modulation wave and
setting the relative relationship of the sound pressure at these control points to a predetermined
value, it is possible to set the virtual sound source appropriately.
For example, if the sound pressure at one control point is set to be higher than the sound
pressure at another control point, the listener can obtain a feeling that sound is generated from
the one control point, One control point can be recognized as a virtual sound source.
[0013]
It is the schematic which shows the use form of the acoustic system which concerns on
embodiment of this invention.
It is a block diagram of an acoustic system.
It is explanatory drawing which shows the acoustic transfer system model for setting the
characteristic of a filter.
It is an explanatory view showing a basic model of a sound transfer system. It is a figure which
shows the relationship between an input-output, a transfer function, and a filter. It is a graph of
the sound pressure level-frequency characteristic which shows the output result when not using
a filter. It is a graph of the sound pressure level-frequency characteristic which shows the output
result at the time of setting a filter by condition 1. FIG. It is a graph of the sound pressure levelfrequency characteristic which shows the output result at the time of setting a filter by condition
2. FIG. It is a graph of the sound pressure level-frequency characteristic which shows the output
result at the time of setting a filter by condition 3. FIG. It is a graph of a sound pressure level-
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frequency characteristic of an original signal inputted into an acoustic system. (A) is a graph
which shows the evaluation result of the sound image localization of the subjective virtual sound
source by a listener, (b) is a table ¦ surface which shows the evaluation result. (A) is a schematic
plan view which shows the usage form of an acoustic system at the time of providing the
reflective surface (reflective member) which concerns on other embodiment in the wall surface of
a room, (b) is a perspective view of a reflective member. It is a schematic plan view which shows
the usage form of the acoustic system at the time of providing the reflective surface (reflective
member) which concerns on other embodiment on the wall surface of a room. It is a perspective
view which shows the ultrasonic speaker which concerns on other embodiment. It is a schematic
plan view which shows the use form of the ultrasonic speaker shown by FIG.
[0014]
<< Configuration of Sound System >> FIG. 1 is a schematic view showing a usage of the sound
system according to the embodiment of the present invention. The sound system 10 of this
embodiment transmits the sound radiated from the speaker SP inside the room to the listener H
who is in a specific place in the room R, and the sound source is the position of the actual
speaker SP. Instead, the sound image is localized as emitted from the virtual sound source SS set
in the indoor space. Therefore, by using the acoustic system 10 in combination with mixed reality
(MR) technology for displaying a virtual space superimposed on a real space, for example, a
virtual image in which a sound emitted from the speaker SP is displayed superimposed as if in
the air It is possible to give the listener H a feeling as if it were generated from
[0015]
In the present embodiment, an ultrasonic speaker is used as the speaker SP. The ultrasonic
speaker uses an ultrasonic wave that human beings can not perceive as sound at a high
frequency of 20 kHz or more as a carrier wave, and a modulated wave that has been spread and
modulated with a signal wave in the audible band such as voice into the air with a large
amplitude causing nonlinearity. It radiates. The modulated wave is distorted due to the nonlinearity of air in the process of propagating in the air, so the signal wave which is an audible
sound is self-demodulated due to this distortion, and a highly directional sound field is formed .
Further, in the present embodiment, the virtual sound source SS is set in the transmission path of
the modulated wave reflected by the wall surface (reflection surface) W of the room R.
[0016]
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FIG. 2 is a block diagram of an acoustic system. The sound system 10 of the present embodiment
includes a signal source 21, a filter processing unit 22, a carrier generation unit 23, a modulation
unit 24, an amplification unit 25, and an oscillator 26. Among these components, the carrier
generation unit 23, the modulation unit 24, the amplification unit 25, and the oscillator 26 are
components of the ultrasonic speaker (ultrasonic speaker system) SP of this embodiment. The
signal source 21 generates a signal wave in the audible band, such as an audio signal or an audio
signal, and outputs the signal wave to the filter processing unit 22. The filter processing unit 22
includes a filter for setting the virtual sound source SS in the space in the room, and the filter
imparts a predetermined characteristic to the signal wave and outputs the signal wave to the
modulation unit 24. Therefore, in the present embodiment, the filter processing unit 22
constitutes the control unit of the present invention.
[0017]
The carrier generation unit 23 generates a carrier consisting of ultrasonic waves of a
predetermined frequency, and outputs the carrier to the modulation unit 24. The modulation unit
24 performs spread modulation on the carrier wave input from the carrier wave generation unit
23 by the signal wave input from the filter processing unit 22 to generate a modulation wave.
Then, this modulated wave is emitted from the oscillator 26 in a state of being amplified by the
amplification unit 25.
[0018]
The signal source 21, the filter processing unit 22, the carrier wave generation unit 23, and the
modulation unit 24 according to the present embodiment are not limited to an operation unit
such as a CPU, a memory, a storage unit such as an HDD, and other personal computers
including an input / output interface It is configured. The personal computer functions as the
signal source 21, the filter processor 22, the carrier wave generator 23, and the modulator 24 by
executing software installed in the personal computer.
[0019]
<< Method of Setting Filter >> Next, although a method of setting the filter provided in the filter
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processing unit 22 will be described, the sound between the sound source and the sound
receiving point will be described using the basic model of the sound transmission system as an
example. Explain how to communicate (Basic Model of Sound Transfer System) FIG. 4 is an
explanatory view showing a basic model of the sound transfer system. In this basic model, one
sound source (speaker) SP and one sound receiving point (microphone) MIC are installed inside
the room R. The signal x (t) is input to the speaker SP, and the microphone MIC picks up the
signal radiated from the speaker SP and outputs a signal y (t).
[0020]
In FIG. 4, G (z) is a transfer function representing how sound is transmitted between the speaker
SP and the microphone MIC. The transfer function G (z) is obtained by z-transforming the
discrete sequence g (0), g (1), g (2),... Obtained by sampling the impulse response observed by the
microphone MIC. . Then, assuming that signals obtained by z-transforming the signals x (t) and y
(t) are X (z) and Y (z), respectively, there is a relationship shown in equation (1) between them.
[0021]
[0022]
On the other hand, when an input of X (z) = 1 is given to such an acoustic transmission system,
the following equation (2) can be obtained.
[0023]
[0024]
Therefore, the transfer function G (z) can be obtained by obtaining the output Y (z) obtained by
the input X (z) = 1.
Then, in the present embodiment, the characteristics of the filter are set using the relationship
between the input / outputs X (z) and Y (z) and the transfer function G (z) as described below.
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[0025]
(Sound Transfer System Model of Embodiment) FIG. 3 is an explanatory view of a sound transfer
system model for setting filter characteristics.
In order to set the virtual sound source SS on the transmission path of the modulated wave
emitted from the ultrasonic speaker SP and reflected by the reflection surface W, a plurality of
control points are set on the transmission path, and the sound pressure of this control point is
set. Control by filter.
In the present embodiment, three control points are set on the modulation wave transmission
path, and the microphones MIC1 to MIC3 are provided at each control point.
[0026]
It has been established by the "Multiple Input / Output Inverse Theorem (MINT) Theory" that the
sound pressure of N control points can be controlled by using (N + 1) or more speakers.
Therefore, also in the present embodiment, four ultrasonic speakers SP1 to SP4 are used for
three control points MIC1 to MIC3 based on the "MINT theory".
[0027]
Then, the original signal X (z) is input to the four ultrasonic speakers SP1 to SP4, the modulated
waves radiated from the ultrasonic speakers SP1 to SP4 are reflected by the reflecting surface W,
and the self-demodulated sound of the modulated waves (Audible sound) is picked up by a
plurality of microphones MIC1, MIC2 and MIC3 arranged at the control point (sound receiving
point). The outputs of the microphones MIC1, MIC2 and MIC3 are Y1 (z), Y2 (z) and Y3 (z),
respectively. The inputs X (z) are then filtered H1 (z), H2 (z), H3 (z) so that the desired outputs
Y1 (z) to Y3 (z) can be obtained at each control point MIC1 to MIC3. , H 4 (z) are processed to
predetermined characteristics.
[0028]
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FIG. 5 is a diagram showing the relationship between input / output signals and transfer
functions and filters. When the input X (z) is emitted from the ultrasonic speakers SP1 to SP4
after being processed by the four filters H1 (z) to H4 (z) and collected by one microphone MIC1,
the ultrasonic speakers SP1 to SP4 are generated. A transfer function representing how sound is
transmitted between SP4 and the microphone MIC1 can be represented by G1,1 (z), G1,2 (z),
G1,3 (z), G1,4 (z) . The transfer functions G1,1 (z) to G1,4 (z) can be obtained by the same method
as the above-described method obtained with reference to the basic model (FIG. 4). Then, the
output Y1 (z) of the microphone MIC1 can be expressed as shown in the equation (3) using the
transfer functions G1,1 (z) to G1,4 (z). Similarly, for the output Y2 (z) and the output Y3 (z), as
shown in the equations (4) and (5) using the transfer functions G2,1 to G2,4, G3,1 to G3,4 It can
be expressed in
[0029]
[0030]
Here, when the output Y (z), the transfer function G (z), and the filter H (z) are respectively
expressed as matrices as in equations (6) to (8), the above equations (3) to (5) are , Can be
expressed as equation (9).
[0031]
[0032]
[0033]
[0034]
[0035]
Then, when designing the filter, the input X (z) = 1 is input to obtain the equation (10).
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Then, by using the inverse matrix G <−1> (z) of the transfer function G (z), it becomes possible to
obtain the filter H (z) as shown in equation (11).
[0036]
[0037]
In designing the filter using equation (11), it is necessary to set the values of the outputs Y1 (z) to
Y3 (z) of the microphones MIC1 to MIC3 and their relative relationships.
Here, when it is intended to set the position of the microphone MIC1 farthest from the listener H
to the virtual sound source SS (condition 1), Y1 is generated so that the signal wave which is the
original sound is reproduced in this microphone MIC1. Determine the value of (z).
Then, the relative relationship between the sound pressures of the microphones MIC1 to MIC3 is
set as shown in the following equation (12).
[0038]
(Condition 1) Y1 (z)> Y2 (z)> Y3 (z) ... (12)
[0039]
That is, the sound pressure at the position of the microphone MIC1 farthest from the listener H is
set to be the largest, and then the sound pressure is set to decrease in the order of the
microphone MIC2 and the microphone MIC3.
By setting the relationship between the outputs Y1 (z) to Y3 (z) in this manner, the listener H can
feel the loudest audible sound produced at the position of the microphone MIC1, and an audible
sound is generated from this position. It becomes possible to localize the sound image as it does.
[0040]
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When setting the position of the microphone MIC2 to the virtual sound source SS (condition 2),
the value of the output Y2 (z) is determined so that a signal wave which is an original sound is
reproduced in the microphone MIC2.
Then, the relationship between the output Y2 (z) and the other outputs Y1 (z) and Y3 (z) is set as
shown in equation (13).
(Condition 2) Y1 (z) = Y2 (z)> Y3 (z) ... (13)
[0041]
Here, the reason that Y1 (z) = Y2 (z) is that even if the output Y1 (z) at the position of the
microphone MIC1 is the same as the output Y2 (z) at the position of the microphone MIC2, the
microphone MIC1 This is because the audible sound at the position is attenuated before being
transmitted to the listener H and the sound pressure is reduced because the user H is separated
from the listener H.
Therefore, by setting the outputs Y1 (z) to Y3 (z) of the microphones MIC1 to MIC3 as described
above, the listener H can feel the loudest audible sound generated at the position of the
microphone MIC2, and The sound image can be localized so that an audible sound is generated
from the position.
[0042]
Similarly, when setting the position of the microphone MIC3 to the virtual sound source SS
(condition 3), the value of the output Y3 (z) is determined so that the signal wave which is the
original sound is reproduced in the microphone MIC3. The relationship between the output Y3
(z) and the other outputs Y1 (z) and Y2 (z) is set as shown in equation (14).
(Condition 3) Y1 (z) = Y2 (z) = Y3 (z) ... (14)
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[0043]
Also in this case, as in the above, even if the outputs Y1 (z) and Y2 (z) in the microphones MIC1
and MIC2 are the same as the output Y3 (z) in the microphone MIC3, the microphones MIC1 and
MIC2 Because of the separation, the audible sound at the position is attenuated before being
transmitted to the listener H, and the sound pressure is reduced. Therefore, by setting the
outputs Y1 (z) to Y3 (z) of the microphones MIC1 to MIC3 as described above, the listener H can
sense the loudest audible sound generated at the position of the microphone MIC3. The sound
image can be localized so that an audible sound is generated from the position.
[0044]
(Measurement Result of Output) The output result of the microphones MIC1 to MIC3 acquired by
setting the filter by the method as described above is shown in FIGS. 7 to 9 are graphs of sound
pressure level-frequency characteristics showing the output when a filter is used. Moreover, FIG.
6 is a comparative example, and is a graph of the sound pressure level-frequency characteristic
which shows the output when not using a filter. The input was white noise having a sound
pressure level-frequency characteristic shown in FIG.
[0045]
FIG. 7 shows an output result when the filter is set according to the above (condition 1). In this
case, the position of MIC1 is taken as the virtual sound source SS. In this case, the output of
MIC1 is high, the output of MIC2 is suppressed by about 1.8 dB on average compared to MIC1,
and the output of MIC3 is suppressed by about 4.6 dB on average.
[0046]
FIG. 8 shows an output result in the case where the filter is set according to the above (condition
2). In this case, the position of MIC2 is taken as the virtual sound source SS. In this case, the
outputs of MIC1 and MIC2 are high, and the output of MIC3 is suppressed by about 4.0 dB on
average compared to MIC1 and MIC2.
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[0047]
FIG. 9 shows an output result in the case where the filter is set according to the above (condition
3). In this case, the position of MIC3 is taken as the virtual sound source SS. In this case, it can be
seen that there is almost no difference in the sound pressure levels of MIC1 to MIC3.
[0048]
Therefore, it is understood that the sound pressure at the position of each of the microphones
MIC1 to MIC3 can be appropriately controlled by using the filters H1 (z) to H4 (z).
[0049]
(Sound Image Localization Result) FIG. 11A is a graph showing an evaluation result of sound
image localization of a subjective virtual sound source by a listener, and FIG. 11B is a table
showing the evaluation result.
In this evaluation, using the filters H1 (z) to H4 (z) set as described above, as shown in FIG. 3, the
virtual sound source SS is set in the indoor space, and several listeners It is evaluated whether
the virtual sound source SS can be localized accurately. The virtual sound source SS was set at a
position separated from the wall W by distances (presentation distances) L1 to L3, and the
listener performed evaluation at a position separated from the wall W by a distance L4. The
position of the virtual sound source SS was 60 cm (= L1), 100 cm (= L2), and 140 cm (= L3) from
the wall W, and the position of the listener H was 150 cm (= L4) from the wall W. And the
distance from the position of the virtual sound source SS which each listener H localized to the
wall surface W was measured, and the average response distance was obtained.
[0050]
From the results shown in FIG. 11, although the position of the virtual sound source SS set using
the filter does not exactly coincide with the position of the virtual sound source localized by the
listener H, the wall W to the virtual sound source SS As the distance increases, the distance from
the wall W localized by the listener to the virtual sound source also increases. Therefore, it has
been confirmed that the virtual sound source SS can be set to such an extent that the distance
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from the wall surface W can be distinguished by using the filter. In addition, it has been found
that when the filter is not used, the virtual sound source SS is localized as being located closest to
the wall surface W.
[0051]
<< Other Embodiments of Reflecting Surface >> FIG. 12 (a) is a schematic plan view showing a
state in which a reflecting surface (reflection member) according to another embodiment is
provided on the wall of a room, and FIG. 12 (b) is a reflection. It is a perspective view of a
member. In the acoustic system 10 mentioned above, although the example which makes the
wall surface W of a room a reflective surface and reflects a modulated wave was shown, as
shown in FIG.12 (b), the reflective member 31 provided with several reflective surfaces is room R
It may be provided for the wall surface of The reflecting member 31 is formed in a square
pyramid having a square base and side surfaces of an equilateral triangle. And by using such a
reflecting member 31, it becomes possible to set the reflection direction of the modulated wave
as desired. For example, as shown in FIG. 12A, a plurality of ultrasonic speakers SP directed in
different directions are collectively provided at one place, and the self-demodulated wave (signal
wave) emitted from each speaker SP is a listener H Can be focused on.
[0052]
FIG. 13 is a schematic plan view showing the usage of the acoustic system in the case where a
reflective surface (reflective member) according to still another embodiment is provided on the
wall of a room. The reflecting member 31 is formed in a hemispherical shape. By using such a
reflecting member 31, it becomes possible to diffuse the modulated wave after reflection to some
extent (expand the directivity range). Therefore, it is possible to expand the audible area of the
self-demodulation wave and to cope with the movement of the listener H.
[0053]
<< Another Embodiment of Ultrasonic Speaker >> FIG. 14 is a perspective view showing an
ultrasonic speaker according to another embodiment. This ultrasonic speaker SP is provided with
a plurality of oscillators 26 in a polyhedron housing 41. In the illustrated example, oscillators 26
are provided for a plurality of faces included in a regular icosahedron. Each oscillator 26 is
attached to the housing 41 so as to be adjustable in angle so that the radiation direction of the
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modulation wave can be adjusted.
[0054]
By using such an ultrasonic speaker SP, it is possible to radiate a modulated wave from any one
place in the room R in any direction, and it is possible to set a virtual sound source at any place
in the room R. Further, as shown in FIG. 15, by using the ultrasonic speaker SP and the reflecting
member 31 in combination, it is possible to concentrate on a specific part of the room R and
transmit the modulated wave. Further, in the acoustic system 10 shown in FIG. 3, the plurality of
ultrasonic speakers SP <b> 1 to SP <b> 4 can also be configured by the ultrasonic speakers SP
shown in FIG. 14.
[0055]
The casing 41 constituting the ultrasonic speaker SP is not limited to a regular icosahedron, and
may be a polyhedron different from this, and the oscillator 26 is not each face of the casing 41
but each vertex May be provided.
[0056]
The present invention is not limited to the above embodiment, and can be suitably modified
within the scope described in the claims.
For example, the acoustic system of the present invention is not limited to use with a mixed
reality system, but can also be used as an acoustic system installed in exhibition halls, concert
halls and the like.
[0057]
DESCRIPTION OF SYMBOLS 10 Sound system 21 Signal source 22 Filter processing part H
Listening person MIC1-MIC3 microphone (control point) SP1-SP4 ultrasonic speaker SS virtual
sound source
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