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JP2001231089

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DESCRIPTION JP2001231089
[0001]
FIELD OF THE INVENTION The present invention relates to microphone systems, and more
particularly to microphone systems having narrow angle directivity.
[0002]
2. Description of the Related Art A navigation system mounted on a motor vehicle often
incorporates a so-called voice response function. The core of this voice response function is to
recognize the voice emitted by the speaker who is the passenger. It is a speech recognition
device. A well-known microphone is applied to convert a speaker's voice into an electrical signal,
but in order to improve the recognition rate in the voice recognition apparatus, the speaker's
voice is made more sensitive and the speaker emits a voice. It is necessary to make the sensitivity
to sounds other than voice (for example, running noise of a car) sufficiently low.
[0003]
In order to solve the above problems, it is necessary to use a microphone having a sharp
directivity (narrow-angle directivity) while having the same gain for wideband speech with a
frequency of 300 to 5,000 hertz. . As a method of obtaining narrow angle directivity, although it
is possible to obtain directivity mechanically by combining a microphone and a sound collector,
an acoustic lens or the like, it is necessary not only to become physically large but also to change
04-05-2019
1
directivity. I can not do it either.
[0004]
In order to make it possible to change the directivity at the same time as it is compact, it is
conceivable to obtain directivity by electrical processing, but the applicant has already applied
the narrow-angle directional microphone system to which the three microphone integration
method has been applied. It has already been proposed. FIG. 1 is an explanatory view of a threemicrophone integration system, in which the order of three omnidirectional microphones MIC1,
MIC0, and MIC2 are arranged in a straight line.
[0005]
Then, a first directivity function D1 representing the directivity of the difference between the
output of the microphone MIC1 and the output of the MIC2 is expressed by [Equation 21].
[0006]
Since the value of the directivity function D1 decreases as the frequency of the sound wave
decreases, in order to maintain directivity to a low frequency range, the difference between the
output of the microphone MIC1 and the output of the MIC2 is integrated by an integrator It is
necessary to compensate for gain reduction in the low frequency range.
The second directivity function D2 representing the directivity after compensation by the
integrator is expressed by [Equation 22].
[0007]
From a practical point of view, in order to improve the directivity of the second directivity
function D 2 in the high frequency range, the frequency characteristic of the difference between
the output of the microphone MIC 1 and the output of the MIC 2 is a low frequency pass filter ( It
compensates by LPF). The third directivity function D3 representing the directivity when the
difference between the output of the microphone MIC0 and the output of the microphone MIC1
and the output of the MIC2 is added is represented by [Equation 23].
04-05-2019
2
[0008]
FIG. 2 is a graph of the third directivity function D3. The horizontal axis represents the sound
wave incident angle θ, and the vertical axis represents the value of D3, ie, the output of the 3microphone integration system.
[0009]
As can be understood from FIG. 2, the value of D3 (solid line) is maximum at zero at θ = 0 ° and
at θ = 180 °. , MIC 0 and MIC 2 need to be located on the MIC 2 side of the straight line
connecting the two speakers.
[0010]
However, FIG. 2 also shows that the three-microphone integration system also has some gain for
sound waves that are incident from the direction of θ = 90 °, that is, the perpendicular
direction of the straight line connecting the microphones MIC1, MIC0 and MIC2. In order to
improve the signal / noise ratio, that is, to reliably detect the sound wave emitted by the speaker
and to suppress the detection of noise, it is necessary to make the directivity a narrower angle.
[0011]
The present invention has been made in view of the above problems, and an object of the present
invention is to provide a narrow-angle directional microphone system having extremely sharp
directivity using a plurality of nondirectional microphones.
[0012]
A narrow angle directional microphone system according to a first aspect of the present
invention comprises an omnidirectional central microphone (MIC0) and a directional microphone
in order to realize directivity shown by a broken line in the graph shown in FIG. Combining the
outputs of the central microphone and the surrounding microphones with at least one set of
surrounding microphones disposed at symmetrical positions with respect to the central
microphone, and the incident direction of the voice to the central microphone being centered on
the first microphone with respect to the central microphone And d) directivity providing means
for providing directivity for rapidly increasing toward the maximum value in the region near 180
° when changing in the range of 0 ° to 180 °, and maintaining substantially the minimum
value in the other regions. .
04-05-2019
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[0013]
In the present invention, based on the outputs of the central microphone and at least one set of
surrounding microphones in the directivity imparting means, directivity is imparted which takes
a maximum value in a region close to 180 ° and maintains a substantially minimum value in the
other regions. Be done.
In the narrow-angle directional microphone system according to the second invention, the
surrounding microphones are arranged symmetrically with respect to the center microphone at a
first predetermined distance from the center microphone on a first straight line passing through
the center microphone. Two non-directional microphones, a front microphone (MIC1) and a rear
microphone (MIC2), and a second predetermined from the center microphone on a second
straight line intersecting perpendicularly with the first straight line at the center microphone An
upper microphone (MICA) and a lower microphone (MICB), which are two omnidirectional
microphones arranged symmetrically with respect to MIC 0 with a spacing of.
[0014]
According to the present invention, the directivity of the combined output of the five
nondirectional microphones arranged in a cross shape takes a maximum value for voice incident
from a direction of 180 ° with respect to the first straight line. .
In a narrow-angle directional microphone system according to a third aspect of the present
invention, the directivity imparting means imparts a first directivity characteristic based on the
outputs of the front microphone and the rear microphone, and a central microphone A second
directivity imparting means for imparting a second directivity characteristic based on the outputs
of the upper microphone and the lower microphone, and a first directivity characteristic and a
second one imparted by the first directivity imparting means. And D. combining means for
combining with the second directivity characteristic given by the directivity giving means.
[0015]
In the present invention, the first eight-shaped directivity characteristic is based on the outputs
of the front microphone and the rear microphone, and the second eight-shaped directivity based
on the outputs of the central microphone, the upper microphone and the lower microphone.
Characteristics are obtained, and by combining the first and second eight-character directivity
04-05-2019
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characteristics, the directivity is maximized with respect to voice incident from a direction of 180
° with respect to the first straight line. can get.
[0016]
In a narrow-angle directional microphone system according to a fourth aspect of the present
invention, two non-directional microphones in which the peripheral microphones are arranged
symmetrically with respect to the central microphone at a predetermined distance from the
central microphone on a straight line passing through the central microphone Consisting of a
front microphone (MIC1) and a rear microphone (MIC2) that are
[0017]
According to the present invention, the directivity of the combined output of the three
nondirectional microphones arranged in a straight line takes a maximum value for voice incident
from a direction of 180 ° with respect to the straight line.
In a narrow-angle directional microphone system according to a fifth aspect of the present
invention, the directivity imparting means applies a third directivity imparting means to impart a
third directivity characteristic based on an output difference between the front microphone and
the rear microphone; A fourth directivity imparting means for imparting a fourth directivity
characteristic based on the outputs of the front microphone and the rear microphone, and a
signal and a fourth directivity characteristic imparted by the third directivity imparting means
And second combining means for combining with the signal to which the fourth directivity
characteristic has been imparted by the directivity imparting means.
[0018]
In the present invention, in the third directivity imparting means, the first eight-shaped
directivity characteristic is based on the outputs of the front microphone and the rear
microphone, and in the fourth directivity imparting means, the central microphone, the front
microphone The second eight-shaped directivity characteristic is obtained based on the output of
the rear microphone and the rear microphone, and the light is incident from the direction of 180
° with respect to the straight line by combining the first and second eight-shaped directivity
characteristics. Directivity which maximizes the sensitivity to the voice.
[0019]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a layout view of
microphones of a narrow angle directional microphone system according to the first invention,
wherein a central microphone MIC0, a front microphone MIC1, and a rear used in the above
three microphone integration system. The upper microphone MICA and the lower microphone
MICB are added to the microphone MIC2 so as to form a cruciform.
[0020]
The sound pressure P0 detected by the central microphone MIC0 placed at the center can be
expressed by [Equation 24].
[0021]
Then, the sound pressures P1 and P2 detected by the front microphone MIC1 and the rear
microphone MIC2 can be expressed by [Equation 25].
[0022]
Similarly, the sound pressures PA and PB detected by the upper microphone MICA and the lower
microphone MICB can be expressed by [Equation 26].
[0023]
Therefore, the difference .DELTA.P21 between the sound pressure P2 and P1 detected by the
rear microphone MIC2 and the front microphone MIC1, and the sum .SIGMA.PAB of the sound
pressure PA and PB detected by the upper microphone MICA and the lower microphone MICB
Can be represented by
[0024]
Therefore, the directivity functions D21 and DAB of the difference sound pressure ΔP21 and the
harmonic pressure Σ PAB are respectively expressed by [Equation 28].
[0025]
Here, since the directivity function D21 of the difference sound pressure ΔP 21 becomes smaller
as the sound becomes lower frequency, it is necessary to compensate the gain in the low
frequency range by the integral operation {1 / (jωτ)}. Become.
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Here, τ is an integration constant.
Then, the directivity function D21 'of the difference sound pressure ΔP21 after integral
compensation is expressed by [Equation 29].
[0026]
The integration constant τ is determined so that D21 '=-1 at θ = 0 °.
That is, when kd << 1 holds, D21 'can be approximated as [Equation 30].
[0027]
Therefore, if θ = 0 ° and D21 '=-1 are substituted, the integration constant τ is determined by
the following equation (31).
[0028]
Here, assuming that d = 0.02 m and C = 340 m, the integration constant τ is 120 μsec.
FIG. 4 is a graph of directivity functions DAB and D21 ', where (a) shows the directivity function
DAB and (b) shows the directivity function D21'.
As can be seen from this graph, as the directivity function DAB of the harmonic pressure Σ PAB
becomes smaller as the value of (kh) becomes smaller, the directivity function changes from a
figure of eight to an ellipse and further to a true circle.
Conversely, when the value of (kl) increases, the figure of 8 becomes flat and directivity
deteriorates.
04-05-2019
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[0029]
We now find a function f that can obtain a figure of eight characteristic over a wide frequency
band of 300 to 5,000 Hertz.
FIG. 5 is a graph when cos (khsinθ) is viewed as a function of θ, and its change range is
expressed by [Equation 32].
[0030]
Therefore, in order to make the minimum value of the function f zero, it is necessary to subtract
the minimum value cos (kh) from cos (khsinθ), so the function f is expressed by [Equation 33].
[0031]
When the first term and the second term on the right side are respectively Taylor expanded, the
function f can be approximated by [Equation 34].
[0032]
Here, with regard to the optimum value of the distance l between the central microphone MIC0
and the front microphone MICA or the rear microphone MICB, that is, how the cos (kh) can be
approximated in a wide frequency band by Fourier expansion. .
An approximate expression by Taylor expansion of cos (kl) is expressed by [Equation 35].
[0033]
FIG. 6 is a graph of cos (kh) and an approximation equation, and it can be seen that l = 2 cm can
be approximated to a higher frequency (about 5,000 hertz).
Therefore, l = 2 cm in the following discussion.
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Since the approximate function of the function f is a function of ω 2, the value increases in
proportion to the square of the frequency of the sound wave.
Then, when it is divided by ω 2 and corrected so as to be a constant value regardless of the
frequency, the function f is expressed by [Equation 36].
[0034]
The integration constant τ 'is determined using [Equation 37] so that f = 1 at θ = 0 °.
[0035]
Therefore, if the integration constant τ is 120 μs, then τ 'is 14 μs.
From the above, in the narrow-angle directional microphone system according to the present
invention, the directivity function Dd represented by [Equation 38] may be realized in the form of
an electric circuit.
[0036]
Alternatively, as described above, an LPF may be inserted in the second term in order to improve
the characteristics in the high frequency range.
The directivity function Dd in this case is expressed by [Equation 39].
[0037]
In order to consider the configuration with specific hardware elements, Eq. 40 can be obtained
by decomposing Eq. 39 using Euler's formula.
[0038]
FIG. 7 is a functional diagram of the narrow angle directional microphone system according to
04-05-2019
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the present invention, wherein five microphones, ie, the central microphone MIC0, the front
microphone MIC1, the rear microphone MIC2, the upper microphone MICA and the lower
microphone MICB are directed It is connected to the input terminals 70, 71, 72, 7A and 7B of the
property imparting unit 7.
[0039]
The output of the central microphone MIC0 is led to the first summing element 702 via the
computing element 701 which performs the operation represented by [Equation 41] on the
output.
This part corresponds to the first term in [·] of [Equation 40].
[0040]
The outputs of the upper microphone MICA and the lower microphone MICB are summed in the
second summing element 703 and subjected to the operation represented by [Equation 42] in the
first integrating element 704 to obtain the first summing element 702. Led to
This part corresponds to the second term in [·] of [Equation 40].
[0041]
The outputs of the front microphone MIC 1 and the rear microphone MIC 2 are led to the first
summing element 702 through the LPF 706 after the output of the front microphone MIC 1 is
subtracted from the output of the rear microphone MIC 2 in the subtraction element 705.
This part corresponds to the third term in [·] of [Equation 40].
Then, the output of the first addition element 702 is output to the output terminal 708 through
the second integration element 707. The second integral element 707 corresponds to the first
04-05-2019
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integral element of [Equation 38].
[0042]
The directivity imparting unit 7 can be realized digitally using a DSP (Digital Signal Processor),
but can also be realized using an analog circuit. FIG. 8 is an example of the analog circuit
according to the first embodiment, and the circuits given the same reference numerals as those
in FIG. 7 correspond to the operation elements in FIG. That is, in addition to the fact that the
output of the central microphone MIC0 is directly supplied to the inverting input terminal of the
first operational amplifier OP1 functioning as an adder, the central operation is performed by a
square circuit composed of two NPN transistors 81 and 82. The squared value of the output of
the microphone MIC0 is provided.
[0043]
In the second operational amplifier OP2 functioning as a summing integrator, the output of the
first operational amplifier OP1 and the outputs of the upper microphone MICA and the lower
microphone MICB are summed and integrated. In the third operational amplifier OP3 functioning
as an adder, the outputs of the front microphone MIC1 and the rear microphone MIC2 are added,
and the output of the third operational amplifier OP3 is supplied to the input terminal of the
fourth operational amplifier OP4 functioning as an LPF. Be done.
[0044]
In the fifth operational amplifier OP5 functioning as a summing integrator, the output of the
second operational amplifier OP2 and the output of the fourth operational amplifier OP4 are
integrated and integrated. FIG. 9 is a characteristic graph of the first embodiment, which shows
the case where the frequency of the sound wave is 300 Hz, 1000 Hz and 3000 Hz from above.
As can be seen from this figure, substantially constant directivity characteristics can be obtained
regardless of the frequency in the entire voice frequency band.
[0045]
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In the first embodiment described above, the distance l between the central microphone MIC0
and the front microphone MICA or the rear microphone MICB is 2 cm, but in order to obtain the
desired directivity, the variation of the sensitivity of each microphone is strict Need to manage. In
order to reduce the influence of this variation, the distance l between the central microphone
MIC0 and the front microphone MICA or the rear microphone MICB may be increased, but the
approximation of the approximate expression of cos (kh) is degraded.
[0046]
The second embodiment solves this problem, and uses up to the third term of Taylor expansion
to maintain the approximation of the approximate expression of cos (kh). FIG. 10 is a graph of
cos (kh) when l is a parameter, and when l is increased, the change of cos (kh) becomes steep,
and the upper limit frequency which can be approximated by [Equation 35] is 4,000 hertz or less
Because of the decrease, directivity may be deteriorated in a high frequency range.
[0047]
Therefore, cos (kh) is approximated by [Equation 43] to improve the degree of approximation.
[0048]
FIG. 11 is a graph of the best approximation curve, a = 4.8 × 10 −9, b = 2.8 × 10 −18, and a
sufficient degree of approximation is maintained up to 5,000 hertz. be able to.
Therefore, the directivity function Dd 'of the second embodiment is expressed by [Equation 44].
[0049]
By further transforming [Equation 44] and inserting two LPFs in order to compensate for the
deterioration of the characteristics in the high frequency range, [Equation 45] is obtained.
[0050]
FIG. 12 is a functional diagram of the second embodiment based on [Equation 45], and five
microphones, ie, the central microphone MIC0, the front microphone MIC1, the rear microphone
MIC2, the upper microphone MICA and the lower microphone MICB It is connected to the input
04-05-2019
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terminals 120, 121, 122, 12A and 12B of the directivity imparting unit 12.
[0051]
The outputs of the central microphone MIC0, the upper microphone MICA and the lower
microphone MICB are summed in a first summing element 1201, integrated in a first integrating
element 1202 and directed to a second summing element 1203.
This part corresponds to the first term in [·] of [Equation 45].
The output of the central microphone MIC 0 is subjected to an operation corresponding to the
second term in [·] of [Equation 45] in the operation element 1204 and is led to the second
addition element 1203.
[0052]
In the second addition element 1203, the output of the first integration element 1202 and the
output of the calculation element 1204 are added, and are led to the third addition element 1206
through the first LPF 1205. The outputs of the front microphone MIC1 and the rear microphone
MIC2 are led to the third summing element 1206 through the second LPF 1208 after the output
of the front microphone MIC1 is subtracted from the output of the rear microphone MIC2 in the
subtraction element 1207. This part corresponds to the third term in [·] of [Equation 45].
[0053]
Then, the output of the third adding element 1206 is output to the output terminal 1210 via the
second integrating element 1209. The second integration element 1209 corresponds to an
integration element other than [·] of [Equation 45]. Although the first LPF 1205 is essential, the
second LPF 1208 can be omitted.
[0054]
04-05-2019
13
FIG. 13 shows an example of the analog circuit according to the second embodiment, in which
the outputs of the upper microphone MICA and the lower microphone MICB are added and the
output of the central microphone MIC0 is subtracted in the first operational amplifier OP1
functioning as an adder / subtractor. It is then integrated in a second operational amplifier OP2
which functions as an integrator. In addition to the output of the central microphone MIC0 being
directly supplied to the inverting input terminal of the third operational amplifier OP3
functioning as an adder, the central microphone calculated by the second-order differential
circuit composed of two NPN transistors 131 and 132 The second derivative of the output of
MIC0 is provided. The output of the third operational amplifier OP3 is differentiated at the fourth
amplifier OP4, which functions as a differentiator.
[0055]
A fifth operational amplifier OP5 functioning as a subtractor subtracts the output of the second
operational amplifier OP2 from the output of the fourth amplifier OP4, and the output of the
fourth amplifier OP4 functions as the first LPF 1205. The operational amplifier OP6 of In a
seventh operational amplifier OP7 functioning as a subtractor, the outputs of the front
microphone MIC1 and the rear microphone MIC2 are subtracted. In the circuit diagram, the
second LPF 1208 is omitted.
[0056]
In the eighth operational amplifier OP8 functioning as a summing integrator, the output of the
sixth operational amplifier OP6 and the output of the seventh operational amplifier OP7 are
integrated and integrated. FIG. 14 is a characteristic graph of the second embodiment, showing
the characteristics of the speech frequencies from 300 Hz, 1000 Hz and 3000 Hz from above. As
can be seen from this figure, the directivity is almost the same over a wide frequency range.
[0057]
In the first invention, two more microphones are added to the three microphones used in the
conventional three-microphone integration system, and it is necessary to use a total of five
microphones in total. Therefore, the microphone system according to the second invention aims
to obtain sharp directivity with the number of microphones remaining three.
04-05-2019
14
[0058]
FIG. 15 is a layout view of microphones of a narrow angle directional microphone system
according to the second invention, wherein a central microphone MIC0, a front microphone
MIC1, and a rear microphone MIC2 are used as in the three microphone integration system. The
difference between the outputs of the front microphone MIC1 and the rear microphone MIC2
calculated in the subtraction element 150 is the same as in the 3-microphone integration system,
and the low frequency pass filter (LPF) 151, the integrator 152, and the first adder It is led to the
second adder 154 via 153. Then, it is added to the output of the central microphone MIC0 in the
second adder 154 and becomes an output.
[0059]
In the narrow-angle directional microphone system according to the second aspect of the
invention, the outputs of the central microphone MIC0, the front microphone MIC1 and the rear
microphone MIC2 are shown by dashed lines, and the directivity of the three microphone
integration system represented by solid lines in FIG. A correction is made to the above addition
result via the correction function C defined in [Equation 46] for correcting to the directivity
shown.
[0060]
That is, in the microphone system according to the second invention, the correction function φ
(θ) with respect to the output of the central microphone MIC0 is represented by [Equation 47].
[0061]
FIG. 16 is a graph showing the ideal characteristic of the correction function φ (θ), and the ideal
characteristic is "1" up to a predetermined range (eg -120 ° ≦ θ ≦ 120 °), otherwise It is a
square wave that is "-1".
The Fourier expansion of the correction function φ (θ) of the rectangular wave results in
[Equation 48].
04-05-2019
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[0062]
Sin (kd · cos θ) can be approximated by [Equation 49] if kd << 1.
[0063]
Therefore, the directivity function of the output difference between the front microphone MIC1
and the rear microphone MIC2 after integration correction is expressed by [Equation 50].
[0064]
Next, the sum cos (kd · cos θ) of the outputs of the front microphone MIC1 and the rear
microphone MIC2 is Taylor-expanded, and further, using the double angle formula, the following
equation is obtained.
[0065]
Solving [Equation 51] for cos 2θ yields [Equation 52].
[0066]
Substituting the equations 50 and 52 into the equation 48, the correction function φ (θ) is
expressed by the equation 53.
[0067]
Here, when the last term cos (kd) is subjected to Taylor expansion approximation, the correction
function φ (θ) is expressed by [Eq. 54].
[0068]
However, since θ changes from “1” to “−1” at θ = 120 °, τ, τ ′ and a are as in
[Equation 55].
[0069]
If d = 2 cm and c = 340 m / s, then τ = 107 (μ sec), τ '= 29 (μ sec), a = 2.02 × 10 -9.
Therefore, the directivity function Dd ′ ′ of the narrow-angle directional microphone system
04-05-2019
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according to the second invention is expressed by [Equation 56].
[0070]
FIG. 17 is a functional diagram of the narrow angle directional microphone system according to
the second invention, wherein the central microphone MIC0, the front microphone MIC1 and the
rear microphone MIC2 are input terminals 170, 171 of the directivity imparting unit 17. And
172 are connected.
The outputs of the front microphone MIC1 and the rear microphone MIC2 are connected to a
first summing element 1701 which calculates their sum and a subtraction element 1702 which
calculates their difference.
[0071]
The output of the central microphone MIC 0 is added to the output of the first summing element
1701 in the second summing element 1704 via the computing element 1703 which performs the
operation {-2 (1-aω 2)}.
The output of the second summing element 1704 passes through the first integrating element
1705 to one terminal of the third summing element 1706, and the output of the subtracting
element 1702 passes through the low pass filter 1707 for the third summing. It is connected to
the other terminal of the element 1706.
[0072]
The output of the third summing element 1706 is summed with the output of the central
microphone MIC0 in the fourth summing element 1709 via the second integrating element 1708
to produce the output of the narrow-angle directional microphone system according to the
second invention It becomes.
FIG. 18 shows an example of the analog circuit of the narrow-angle directional microphone
04-05-2019
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system according to the second invention, wherein the first operational amplifier OP1 calculates
the sum of the output of the front microphone MIC1 and the output of the rear microphone
MIC2, The operational amplifier OP2 calculates the difference between the output of the front
microphone MIC1 and the output of the rear microphone MIC2.
The third operational amplifier OP3 functions as an LPF, and the fourth operational amplifier
OP4 functions as a third summing element.
Furthermore, the fifth operational amplifier OP5 functions as a fourth summing element.
[0073]
FIG. 19 is a characteristic graph of the narrow angle directional microphone system according to
the second invention, and although the gain slightly decreases as the frequency increases, it
becomes possible to obtain the same directivity regardless of the frequency.
[0074]
According to the narrow angle directional microphone system according to the present invention,
at least one set of surrounding microphones is arranged around the central microphone, and the
narrow angle is achieved by performing electrical arithmetic processing by the analog circuit or
the digital element. It becomes possible to realize directivity.
[0075]
Furthermore, when digital elements are used, it is possible to easily change the directivity by
exchanging programs.
[0076]
Brief description of the drawings
[0077]
13 is an explanatory view of a microphone integration system.
[0078]
2 is a graph of the third directivity function D3.
04-05-2019
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[0079]
3 is a layout diagram of the microphone of the narrow angle directional microphone system
according to the first invention.
[0080]
4 is a graph of directivity functions DAB and D21 '.
[0081]
FIG. 5 is a graph of cos (khsinθ).
[0082]
6 is a graph of the approximate expression of cos (kh).
[0083]
7 is a functional diagram of the narrow angle directional microphone system according to the
first embodiment of the present invention.
[0084]
8 is an example of an analog circuit of the first embodiment.
[0085]
9 is a characteristic graph of the first embodiment.
[0086]
It is a graph of cos (kh) when FIG. 10 h is made a parameter.
[0087]
FIG. 11 is a graph of the best approximation curve.
[0088]
04-05-2019
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12 is a functional diagram of a narrow angle directional microphone system according to a
second embodiment of the present invention.
[0089]
13 is an example of an analog circuit according to the second embodiment.
[0090]
14 is a characteristic graph of the second embodiment.
[0091]
15 is a microphone layout diagram of a narrow angle directional microphone system according
to the second invention.
[0092]
16 is a graph showing an ideal characteristic of the correction function φ (θ).
[0093]
17 is a functional diagram of a narrow angle directional microphone system according to the
second invention.
[0094]
18 is an example of an analog circuit of the narrow angle directional microphone system
according to the second invention.
[0095]
19 is a characteristic graph of the narrow angle directional microphone system according to the
second invention.
[0096]
Explanation of sign
[0097]
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MIC0, MIC1, MIC2, MICA, MICB: non-directional microphone 7: directivity imparting unit 701:
arithmetic element 702: first sum arithmetic element 703: second sum arithmetic element 704:
first integral element 705: difference Arithmetic element 706 ... LPF 707 ... second integral
element
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