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JPH05316586

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH05316586
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
directional microphone device which can be used as a sound collection system for a conference
such as a video conference or a speech input system such as speech recognition in a noisy
environment.
[0002]
2. Description of the Related Art In the sound collection system of a conference, the sound from
the height of the speaker's mouth is picked up with high sensitivity, and the noise from the
ceiling such as air conditioning sound and the noise from the floor such as footsteps Attenuation
is preferred. Also, strong directivity is required to prevent howling.
[0003]
For this reason, conventionally, a plurality of microphones of bi-directional and non-directional
are combined to obtain an output difference, or a plurality of microphones are disclosed by the
configurations disclosed in JP-A-61-72500 and JP-A-61-135296. A donut-like directivity was
obtained around a predetermined axis determined by the arrangement of the microphones. In the
directional microphone device disclosed in JP-A-61-72,500, one sound receiving element is
disposed at the center of a circle, and n (at least three) are disposed on the circumference of the
03-05-2019
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circle. Are arranged at equal intervals, and a relative gain of “1” is given to the output from
one sound receiving element at the center of the circle, and n pieces of sound receiving elements
from the circumference are The output of each of these sound receiving elements is added after
giving a relative gain of 1 / n and relative phase inversion to each output. Further, in the
directional microphone device disclosed in Japanese Patent Application Laid-Open No. 61135296, a large number of linear array microphones having different array lengths all or
partially are arranged on the same straight line, and as the frequency becomes higher The output
from the short linear array microphone is selected.
[0004]
SUMMARY OF THE INVENTION However, in a configuration in which bi-directional and nondirectional microphones are combined, it is difficult to adjust due to the combination of different
microphones, and the directivity is not so strong (for example, angle) There is a drawback of -3
dB at 45 °. Further, in the configurations disclosed in JP-A-61-72,500 and JP-A-61-135,296,
there are problems that the number of microphones, that is, the number of sound receiving
elements is large, and the shape also becomes large.
[0005]
Furthermore, in the donut shape directivity, all directions have the same sensitivity on the
horizontal plane perpendicular to the axis line giving the doughnut shape, but in the
teleconferencing system etc., it has the directivity also on this horizontal surface and It is often
desirable to be directed in the direction of interest.
[0006]
In this regard, conventionally, for example, as shown in Japanese Patent Application Laid-Open
No. 61-220590, the directivity is established by determining the angle in the vertical direction
and the horizontal direction by a configuration in which the microphones are arranged in a grid
on the plane. It was like that.
However, this configuration requires a considerable number of microphones, and since the
microphones are arranged in a grid, the shape is also large and there is a problem that it is not
necessarily suitable for installation.
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[0007]
The present invention can be made to have a sharp donut shape directivity with a relatively small
shape with a small number of sound receiving elements used and with easy adjustment, and
furthermore, perpendicular to the axis giving the donut shape An object of the present invention
is to provide a directional microphone device capable of controlling also the directivity on the
horizontal plane.
[0008]
SUMMARY OF THE INVENTION In order to achieve the above object, the invention according to
claim 1 comprises at least three sound receiving elements disposed on a straight line and sound
receiving elements disposed at both ends. Of the output signals from at least one of the sound
receiving elements disposed between the first delay means for delaying each of the output
signals of the first and second sound receiving elements disposed between the sound receiving
elements at both ends for a predetermined time A second delay means for causing the second
delay means, an output signal from the sound receiving element disposed between the sound
receiving elements at both ends, and an output signal from the second delay means while The
output signal from the first delay means is characterized by including combining means for
combining in reverse phase.
[0009]
The invention according to claim 2 is the directional microphone device according to claim 1,
wherein three sound receiving elements are arranged at equal intervals on a straight line, and the
first delay means are arranged at both ends. The output signals from the two sound receiving
elements are respectively delayed for a predetermined time, and the second delay means delays
the output signal from one sound receiving element disposed in the middle for a predetermined
time, The combining means combines the output signal from one of the sound receiving elements
disposed in the middle with the output signal from the second delaying means in the same phase,
while the two from the first delaying means are combined. It is characterized in that each output
signal is synthesized in reverse phase.
[0010]
The invention according to claim 3 is the directional microphone device according to claim 1,
wherein four sound receiving elements are disposed on a straight line, and the first delay means
is disposed at both ends. Each output signal from one of the sound receiving elements is delayed
for a predetermined time, and the second delay means determines an output signal from one of
the two sound receiving elements disposed in the middle. The time delaying is performed, and
the combining means combines the output signal from the other sound receiving element of the
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two sound receiving elements arranged in the middle with the output signal from the second
delaying means in the same phase. On the other hand, the present invention is characterized in
that the two output signals from the first delay means are combined in reverse phase.
[0011]
In the invention according to claim 4, in the directional microphone device according to claim 1,
the first delay means delays each output signal from the sound receiving elements arranged at
both ends with the same delay time. It is characterized by being made to
[0012]
The invention according to claim 5 is characterized in that non-directional sound receiving
elements having the same characteristics as all the sound receiving elements are used.
[0013]
In the invention according to claim 6, a plurality of directional microphone units having donutlike directivity characteristics around a predetermined axis are arranged on a straight line
perpendicular to the axis, and from the plurality of directional microphone units The present
invention is characterized in that the sum of each output signal of is calculated to be output.
[0014]
In the invention according to claim 7, a plurality of directional microphone units having donutlike directivity characteristics around a predetermined axis are arranged on a straight line
perpendicular to the axis, and from the plurality of directional microphone units The respective
output signals are each delayed by a predetermined delay time, and then the sum is taken to be
output, and each of the delay times is set variably.
[0015]
According to the first to fifth aspects of the present invention, of the at least three sound
receiving elements arranged on a straight line, each output signal from the sound receiving
elements arranged at both ends is subjected to the first delay means. The output signals from at
least one of the sound receiving elements disposed between the sound receiving elements at both
ends are delayed for a predetermined time by the second delay means, respectively. While the
output signal from the sound receiving element arranged in the sound receiving element and the
output signal from the second delay means are synthesized in the same phase, the output signal
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from the first delay means is in reverse phase. Is to be synthesized.
As a result, it is possible to obtain a sharp donut shape directivity with a relatively small shape.
In particular, according to the second aspect of the invention, since only three sound receiving
elements are required, it is possible to obtain sharp donut-like directivity with only a very small
number of sound receiving elements.
Further, according to the third aspect of the present invention, since a plurality of parameters
can be used as parameters relating to the distance between the sound receiving elements, it is
possible to more easily set the incident angle without sensitivity.
In the fourth aspect of the invention, the delay time is simple, and the processing can be
performed more easily.
In the fifth aspect of the invention, since non-directional sound receiving elements having the
same characteristics are used for all the sound receiving elements, adjustment is extremely easy,
and it is possible to obtain sharp directivity.
[0016]
In the invention according to claim 6, a plurality of directional microphone units having donutlike directivity characteristics around a predetermined axis are arranged on a straight line
perpendicular to the axis, and from the plurality of directional microphone units The sum of each
output signal of is calculated and output.
This makes it possible to obtain sharp directivity in both vertical and horizontal directions in a
compact shape suitable for installation.
[0017]
In the invention according to claim 7, a plurality of directional microphone units having a donutlike directivity characteristic around a predetermined axis are arranged on a straight line
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perpendicular to the axis, and the plurality of directional microphone units are arranged. The
respective output signals are each delayed by a predetermined time and then summed up, and at
that time, since each delay time is variably set, it has a compact shape suitable for installation,
and the directivity in the horizontal direction When used in a teleconferencing system etc., only
the voice of the target speaker can be picked up.
[0018]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram of a first embodiment of a directional microphone device according to
the present invention.
The directional microphone device shown in FIG. 1 has three sound receiving elements 11, 12,
13 arranged at equal intervals on a straight line, and delay signals .tau.1, .tau.1 + .tau.2 of output
signals from the respective sound receiving elements 11, 12, 13 respectively. , And τ 2, and an
output signal from the sound receiving element 12 disposed at an intermediate position among
the three sound receiving elements 11, 12 and 13 and the output signal by (τ 1 + τ 2) The
output signals from the delay circuit 15 are combined (in other words, added) in the same phase,
and each output signal from the sound receiving elements 11 and 13 arranged at both ends is
delayed by .tau.1 and .tau.2, respectively. Each output signal from the delay circuits 14 and 16
has a combining unit 17 that combines them (that is, subtracts them) in reverse phase.
[0019]
Next, the operation of the directional microphone device having such a configuration will be
described.
FIG. 2 shows the arrangement of the sound receiving elements 11, 12 and 13. The sound
receiving elements 11, 12 and 13 are arranged at equal intervals d on a straight line V, and all
nondirectional and identical flat. Assume that it has sensitivity. Now, the distance between
adjacent sound receiving elements is d, the speed of sound is c, the frequency is ω, and a
direction H perpendicular to the straight line V where these sound receiving elements 11, 12 and
13 are disposed is a reference angle (θ Assuming that = 0), the output signals EU, EC, and EL
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from the sound receiving elements 11, 12, and 13 for plane waves from the incident angle θ,
which is the elevation angle, each have the following order with the central sound receiving
element 12 as a phase reference. It becomes like a formula.
[0020]
EU = exp (jω (t + sin θ · d / c)) EC = exp (jωt) EL = exp (jω (t−sin θ · d / c))
[0021]
The combining unit 17 adds the output signal EC from the sound receiving element 12 and the
signal obtained by delaying this output signal EC by (τ1 + τ2), while outputting the output
signals EU and EL from the sound receiving elements 11 and 13 respectively. The signals delayed
by τ1 and τ2 are subtracted and synthesized.
As a result, the output signal EV from the combining unit 17 is expressed by the following
equation.
[0022]
EV = EC + EC · exp (−jω (τ1 + τ2)) − EU · exp (−jωτ1) −EL · exp (−jωτ2) = {1-exp (−jω
(τ1−sin θ · d /) c))} · {1-exp (-j ω (τ 2 + sin θ · d / c))} exp (j ω t)
[0023]
According to Equation 2, the output EV from the combining unit 17 becomes “0” with respect
to the incident angles θ1 (> 0) and θ2 (<0) of the following equation.
That is, the sensitivity becomes “0” at the incident angles θ1 and θ2 of the following
equation.
[0024]
[Equation 3] sin θ1 = τ1 c / d, sin θ2 = −τ2 c / d
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[0025]
Therefore, when this directional microphone device is used, for example, in a conference room,
these sound receiving elements 11, 12, 13 are arranged in the order of the sound receiving
elements 11, 12, 13 from the top on a straight line V perpendicular to the floor surface. If
arranged, the upward angle θ1 and the downward angle θ2 close to the vertical can be
arbitrarily determined by setting the delay times τ1 and τ2 and the interval d as incident
angles without sensitivity, and the delay times τ1 and τ2 By setting the distance d
appropriately, it is possible to obtain a doughnut-shaped strong directivity showing a large
sensitivity only in the vicinity of the horizontal direction H (θ = 0).
[0026]
FIG. 3 is a view showing a specific example of the directional microphone device of FIG. 1. In FIG.
3, the delay times .tau.1 and .tau.2 are set so that the incident angles .theta.1 and .theta.2 without
sensitivity have a relationship of (.theta.1 =-. Theta.2). The setting is shown.
That is, if (θ1 = −θ2) is determined, the relation of (τ1 = τ2) is derived from the equation 3
and accordingly, in FIG. 3, the delay times τ1, τ1 + τ2 and τ2 of the delay circuits 14, 15 and
16 are τ , 2τ, and τ.
In this case, Equation 2 becomes as follows.
[0027]
EV = EC + EC · exp (−j ω · 2τ) −EU · exp (−j ω τ) −EL · exp (−j ω τ) = {1-exp (−j ω
(τ−sin θ · d / c) ))} · {1-exp (-j ω (τ + sin θ · d / c))} exp (j ω t)
[0028]
From Equation 4, the output EV from the combining unit 17 when the incident angle θ is “0”
is expressed by the following equation.
[0029]
EV = {1-exp (-jωτ)} · {1-exp (−jωτ)} · exp (jωt) = − 4 · sin 2 (ωτ / 2) · exp (jω (t) −τ))
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[0030]
Here, assuming that the incident angle θ1 (= −θ2) having no sensitivity is π / 3 radians, the
unit delay time τ is 1/16000 seconds, and the sound speed c is 340 m / sec, the sound
receiving elements 11, 12 and 13 are It may be arranged at an interval d of 24.5 mm.
The unit delay time τ may correspond to the sampling cycle of an A / D converter (not shown)
that converts the output of each sound receiving element into a digital value.
[0031]
FIG. 4 is a diagram showing the directional characteristics when the directional microphone
device of FIG. 3 is set under the above conditions, and the sensitivity of the incident angle θ = 0
(horizontal direction H) at a certain angular frequency ω is 0 dB And
As can be seen from FIG. 4, in the directional microphone device of the first embodiment, a threedimensional so-called donut-shaped directivity in which the straight line V on which the sound
receiving elements 11, 12 and 13 are disposed is rotated as an axis. Has a large sensitivity only
in the vicinity of the horizontal direction H (θ = 0) perpendicular to the axis V, and has a sharp
directivity of about -12 dB or less for incident angles of π / 4 or more. have.
[0032]
Thus, in the directional microphone device of the first embodiment shown in FIGS. 1 and 3, only
three sound receiving elements 11, 12, 13 arranged at equal intervals on a straight line as sound
receiving elements are used. The sensitivity to any two angles θ1 and θ2 can be eliminated, and
in spite of the small and simple configuration, it is possible to obtain a donut-like sharp
directivity.
In addition, non-directional sound receiving elements having the same characteristics can be
used for all the sound receiving elements, and when using non-directional sound receiving
elements having the same characteristics for all the sound receiving elements, only the sensitivity
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is adjusted. The adjustment is extremely easy because it does not require adjustment of other
characteristics or selection of elements.
[0033]
When these sound receiving elements 11, 12 and 13 are installed perpendicular to the floor and
near the height of the speaker's mouth, the horizontal direction is θ = 0, θ1 is obliquely
upward, θ2 is obliquely inclined In the downward direction, it is possible to provide a directional
microphone system for a conference, which can pick up only the voices of a plurality of speakers.
[0034]
FIG. 5 is a block diagram of a second embodiment of the directional microphone device according
to the present invention.
The same reference numerals as in FIG. 1 denote the same parts in FIG. The directional
microphone device of FIG. 5 has delay times .tau.1, .tau.1 + .tau.2, and .tau.2 of the output signals
from the four sound receiving elements 11, 12a, 12b and 13 arranged on a straight line and the
sound receiving elements 11, 12b and 13, respectively. The output signal from the sound
receiving element 12a and the output signal from the sound receiving element 12b which are
arranged in the middle of the delay circuits 14, 15 and 16 to be delayed by and the four sound
receiving elements 11, 12a, 12b and 13 The output signals from the delay circuit 15 delayed by
(τ1 + τ2) are combined (in other words, added) in phase, and the output signals from the sound
receiving elements 11 and 13 disposed at both ends are respectively τ1 and τ2 The output
signals from the delay circuits 14 and 16 delayed by only the combining unit 17 are combined
(i.e., subtracted) in reverse phase.
[0035]
Next, the operation of the directional microphone device having such a configuration will be
described. FIG. 6 shows the arrangement of the sound receiving elements 11, 12a, 12b and 13. In
the example of FIG. 6, the distance between the sound receiving elements 11, 12a and between
the sound receiving elements 12b, 13 is set to d1, and the distance between the sound receiving
elements 11, 12b is set to d2. Further, it is assumed that each of the sound receiving elements
11, 12a, 12b, and 13 are all nondirectional and have the same flat sensitivity.
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[0036]
In this case, the output EV from the combining unit 17 is expressed by the following equation,
assuming that the sound receiving element 12a is a phase reference.
[0037]
EV = {1-exp (-jω (τ1-sin θ · d1 / c))} · {1-exp (−jω (τ2 + sin θ · d2 / c))} · exp (jωt)
[0038]
According to Equation 6, in the second embodiment, the output EV from the combining unit 17 is
“0” with respect to the incident angles θ1 (> 0) and θ2 (<0) of the following equation.
That is, the sensitivity becomes “0” at the incident angles θ1 and θ2 of the following
equation.
[0039]
sin θ1 = τ1c / d1, sin θ2 = −τ2c / d2
[0040]
As can be seen by comparing Eq. 7 with Eq. 3, in the second embodiment, two parameters d1 and
d2 can be used as parameters relating to the interval, so the incident angles .theta.1 and .theta.2
for setting the sensitivity to "0" are determined. In addition, the freedom of selection of the delay
times .tau.1 and .tau.2 can be enhanced, and the setting of the incident angles .theta.1 and
.theta.2 for making the sensitivity "0" becomes easier than in the first embodiment.
[0041]
FIG. 7 is a view showing a specific example of the directional microphone device of FIG. 5. In FIG.
7, the delay times .tau.1, .tau.1 + .tau.2, and .tau.2 of the delay circuits 14, 15, 16 are respectively
set to .tau., 2.tau. It is shown.
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In this case, Equation 6 becomes as follows.
[0042]
EV = {1-exp (-jω (τ-sin θ · d1 / c))} · {1-exp (−jω (τ + sin θ · d2 / c))} · exp (jωt)
[0043]
According to Equation 8, the output EV from the combining unit 17 becomes “0” with respect
to the incident angles θ1 (> 0) and θ2 (<0) of the following equation.
That is, the sensitivity becomes “0” at the incident angles θ1 and θ2 of the following
equation.
[0044]
sin θ1 = τ c / d1, sin θ2 = −τ c / d2
[0045]
As can be seen from Equation 9, in the configuration of FIG. 7, incident angles θ1 and θ2
having no sensitivity can be determined arbitrarily and extremely easily by setting the intervals
d1 and d2 appropriately.
[0046]
In the configurations of FIG. 1, FIG. 3, FIG. 5, and FIG. 7, there is attenuation in the low band, but
this can be corrected by adding an equalizer or the like.
[0047]
FIG. 8 is a block diagram of a third embodiment of the directional microphone device according
to the present invention.
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In this directional microphone device, a plurality of sets 10, 20, ..., 80 of directional microphone
units having a donut-like directional characteristic are arranged around a predetermined axis,
and a plurality of sets of directional microphone units 10 to 80 are provided. Each output signal
is summed up by the summing unit 200 and output.
Here, each of the directional microphone units 10 to 80 has, for example, the configuration
shown in FIG.
FIG. 9 shows the arrangement of the directional microphone units 10 to 80. Referring to FIG. 9,
the directivity as shown in FIG. 3 having a donut-like directivity characteristic around a
predetermined axis V A plurality of sets 10 to 80 of microphone units are arranged on a straight
line H1 perpendicular to the axis V.
[0048]
In such a configuration, the directional microphone units 10 to 80 are arranged at equal intervals
dH on the straight line H1 as shown in FIG. 9, and the sound receiving elements of the directional
microphone units 10 to 80 are arranged in a grid Assuming that a direction H2 perpendicular to
the lattice plane L is a reference angle, the outputs of the directional microphone units 10 to 80
with respect to a plane wave (θ = 0) from the incident angle φ on the horizontal plane spanned
by H1 and H2. E0 to E7 can be obtained by Equation 5.
That is, each output En (n = 0, 1, ..., 7) is expressed by the following equation, where E0 is a
phase reference.
[0049]
En = −4 · sin 2 (ω τ / 2) · exp (j ω (t−n · sin φ · dH / c))
[0050]
The summing unit 200 obtains the sum of the outputs E0 to E7 from the directional microphone
units 10 to 80, and sets the sum as the overall output EH.
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That is, the total output EH is expressed by the following equation with N = 8.
[0052]
In the above equation, in the case of φ = 0, the following equation is obtained.
[0053]
EH = −4N · sin 2 (ω τ / 2) · exp (j ω t)
[0054]
10 and 11 show phase characteristics with respect to the incident angle φ when the interval dH
is 148.75 mm and τ is 1/16000 seconds (= A / D sampling period) in the configurations of FIGS.
8 and 9. 10 shows phase characteristics at 2 kHZ (ωτ = π / 4) and FIG. 11 at 0.5 kHZ (ωτ =
π / 16).
In each figure, the sensitivity of φ = 0 was 0 dB.
From FIGS. 10 and 11, in the third embodiment, sharp directivity is obtained in the vertical
direction (θ direction) as in the first and second embodiments, and in addition to this, the
horizontal direction ( It can be seen that sharp directivity can be obtained in the φ direction as
well.
In addition, the directional microphone device shown in FIGS. 8 and 9 has a short vertical shape,
and has a rectangular shape as a whole, so that it can be easily handled as a practical device and
can be easily installed. can do.
[0055]
FIG. 12 is a block diagram of the fourth embodiment of the directional microphone device
according to the present invention. In FIG. 12, the same parts as in FIG. 8 are denoted by the
same reference numerals. The directional microphone device of FIG. 12 is intended to make the
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direction of directivity in the horizontal direction (φ direction) variable in the third embodiment,
and therefore, plural sets of directional microphone units 10 to 80 are used. The respective
output signals E0 to E7 are delayed by predetermined delay times .tau.H0 to .tau.H7 by the delay
units 110 to 180, respectively, and then input to the summing unit 200. At this time, information
on delay times τH 0 to τH 7 is variably set from the outside in each of the delay units 110 to
180.
[0056]
In such a configuration, it is now assumed that delay times τH0 to τH7 are set in the delay
units 110 to 180 as follows with respect to the target incident angle φ0 in the horizontal
direction (φ direction). However, it is assumed that N = 8.
[0057]
τHn = (N-1-n · sin φ0) dH / c; n = 0, 1,.7
[0058]
At this time, the output EH from the summing unit 200 is expressed by the following equation.
[0060]
In FIGS. 13 and 14, in the configuration of FIG. 12, the interval dH is 148.75 mm, τ is 1/16000
seconds (= A / D sampling period), and the target incident angle φ0 is π / 6 radian. FIG. 13
shows the phase characteristic at 2 kHZ (ωτ = π / 4) and FIG. 14 shows the phase
characteristic at 0.5 kHZ (ωτ = π / 16).
In each figure, the sensitivity of φ = 0 was 0 dB.
As can be seen from FIGS. 13 and 14, in the third embodiment, the directivity from the horizontal
direction is controlled by giving a variable delay to the output from each of the directional
microphone units 10 to 80. The target incident angle in the φ direction can be made variable. As
a result, for example, in a video conference system or the like, only the voice of the target
speaker can be picked up by matching the target angle of incidence to the target speaker. Here,
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the target incident angle φ0 can be obtained by detecting the phase difference between the
outputs of the directional microphone unit.
[0061]
In the third and fourth embodiments described above, there is a problem that the directivity is
too strong and side lobes appear in the high region, but the output of each of the directional
microphone units 10 to 80 has characteristics respectively. The above problem can be solved by
providing different low pass filters. Furthermore, it is also possible to change the strength of
directivity by making the characteristics of each low pass filter variable. In the third and fourth
embodiments, it has been described that the directional microphone units 10 to 80 are
configured as shown in FIG. 3, but in the case where they are configured as shown in FIG. 1, FIG.
5, and FIG. Also, similar directional characteristics can be obtained.
[0062]
Further, in the configuration of each embodiment described above, for example, the output signal
from each sound receiving element is input through the A / D converter, and the subsequent
processing is processed by a DSP (digital signal processor) or the like, A memory can be used for
the part, and counter technology can be used to count each delay time, which can be easily
realized with actual hardware. In addition, a table reference technique can be used for the
calculation of obtaining the delay time of each delay unit from the incident angle.
[0063]
As described above, according to the first to fifth aspects of the present invention, of the at least
three sound receiving elements arranged on a straight line, the sound receiving elements
arranged at both ends are used. The respective output signals of are each delayed for a
predetermined time by the first delay means, and the output signal from at least one of the sound
receiving elements arranged between the sound receiving elements at both ends is The delaying
means delays for a predetermined time, and the output signal from the sound receiving element
arranged at the sound receiving element at both ends and the output signal from the second
delay means are synthesized while being in phase, while the first Since output signals from the
delay means are synthesized in reverse phase, sharp donut shape directivity can be obtained with
a relatively small shape. In particular, according to the second aspect of the invention, since only
03-05-2019
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three sound receiving elements are required, it is possible to obtain sharp donut-like directivity
with only a very small number of sound receiving elements. Further, according to the third aspect
of the present invention, since a plurality of parameters can be used as parameters relating to the
distance between the sound receiving elements, it is possible to more easily set the incident angle
without sensitivity. In the fourth aspect of the invention, the delay time is simple, and the
processing can be performed more easily. Further, in the invention according to claim 5, since
non-directional sound receiving elements having the same characteristics are used for all the
sound receiving elements, the adjustment can be performed extremely easily, and all nondirectivities having the same characteristics are obtained. Also in the case of using the sound
receiving element, it is possible to obtain a sharp donut-like directivity characteristic.
[0064]
Further, according to the invention of claim 6, a plurality of directional microphone units having
donut-like directivity characteristics are disposed on a straight line perpendicular to the axis, and
the plurality of directional microphones are arranged around a predetermined axis. Since the
output signals from the units are summed up and output, it is possible to obtain sharp directivity
in both vertical and horizontal directions in a compact shape suitable for installation.
[0065]
Further, according to the invention of claim 7, a plurality of directional microphone units having
donut-like directivity characteristics are disposed on a straight line perpendicular to the axis line
around the predetermined axis line, and the plurality of directional microphones are arranged.
Each output signal from the unit is delayed by a predetermined time and summed up, and at that
time, each delay time is variably set, so a compact shape suitable for installation Thus, the
direction of the directivity in the horizontal direction can be controlled, and when it is used for a
video conference system etc., only the voice of the intended speaker can be picked up.
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