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JP2005072642

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DESCRIPTION JP2005072642
An object of the present invention is to make a directivity characteristic of a microphone device
high in sensitivity in a narrow angle range while maintaining a small size. In the microphone
device, the microphones 1 and 2 are disposed close to each other, and output output signals
having different phases to sound waves incident from a specific angle range. The difference
between the phase difference of the output signal of the sound wave incident on the
microphones 1 and 2 from the specific angle range from the phase difference of the output
signal of the sound waves incident on the microphones 1 and 2 from the other angle range From
the output signals of the microphones 1 and 2, the component of the sound wave from that
particular angular range is extracted. [Selected figure] Figure 1
Microphone device and sound collecting method
[0001] The present invention relates to a microphone device and a sound collection method. 2.
Description of the Related Art A microphone device senses a sound wave by a microphone,
amplifies a waveform signal output from the microphone by an amplifier, and outputs the
amplified signal. The microphones include non-directional microphones and unidirectional
microphones. The directional characteristics of a microphone device are often determined by the
directional characteristics of the microphone used in the device. FIG. 7 is a diagram showing the
directivity characteristic of the conventional microphone. The nondirectional microphone has a
substantially circular directivity as shown in FIG. 7 (A). In addition, as shown in FIG. 7B, the
unidirectional microphone has a substantially cardioid-shaped directional characteristic. In
recent years, systems used in vehicles such as automobiles, such as car navigation systems and
mobile communication systems, are becoming widespread. Such systems include, for example,
one that recognizes voice received by a microphone device and receives user's operation as voice.
There are also devices that transmit voice received by a microphone device by a mobile
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communication system. A microphone device used in such an application is desired to have a
characteristic that reliably receives the voice of the driver who is the user and does not receive
environmental noise such as traveling noise. For this reason, conventionally, in this application, a
unidirectional microphone is often arranged towards the driver near the driver in the vehicle.
When using a unidirectional microphone, although user's voice is selectively received,
environmental noise is also received more than when using a non-directional microphone. From
the word uni-directionality, a characteristic with high frontal sensitivity is imagined, but in fact,
the reception sensitivity on the side is only a few decibels lower than the reception sensitivity on
the front. Therefore, the output signal of the microphone device using such a unidirectional
microphone includes not only the driver's voice component but also components such as running
noise, which lowers the recognition rate by voice recognition, and the mobile object
Communication quality of the communication system may be degraded. Therefore, as a first
method, as a microphone used for such a microphone device, it is conceivable to use a
microphone having directivity characteristics in which the sensitivity in directions other than the
front is lower than the directivity characteristic of unidirectionality. .
Also, as a second method, when the level of the waveform signal of the microphone exceeds a
predetermined threshold based on the difference between the reception level of the driver's voice
and the traveling noise, the waveform signal is output as an output signal. It is possible to do.
[Patent Document 1] Japanese Patent Application Publication No. 2001-245396 (Page 2-Page 5,
FIG. 1). [0010] However, in the conventional microphone device, it is difficult to efficiently
extract only the voice of the user such as the driver in the vehicle. With regard to the first
method described above, there is conventionally no microphone which is more suitable than unidirectionality as practical in the above-mentioned application. There is a superdirective
microphone that has a lower directional sensitivity than the unidirectionality and a sharp
directional characteristic at the front, but the length of the superdirective microphone is, in
principle, the wavelength of the sound wave to be collected. It becomes above and will be at least
about 30 cm. For this reason, it is not realistic to install a superdirective microphone toward the
driver's mouth in the vehicle. There is also a microphone having directivity characteristics of bidirectionality, which has low sensitivity from the side. The bi-directional microphone has a
substantially 8-shaped directivity characteristic as shown in FIG. 7 (C). In the case of a bidirectional microphone, the side sensitivity is low but the back sensitivity is similar to the front.
Therefore, even using a bi-directional microphone, it is difficult to selectively extract only the
voice from the user. It is difficult to lower the back sensitivity only by covering the back of a bidirectional microphone. The reason is that as the back of the bi-directional microphone is closed,
the characteristics of the omni-directional microphone become closer to those of the nondirectional microphone. A bi-directional microphone is a microphone that senses the direct
movement of air by sound waves. On the other hand, a nondirectional microphone is a
microphone that senses changes in barometric pressure similarly generated by sound waves
from any direction. When one side of the diaphragm of the bi-directional microphone is closed, it
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becomes structurally close to the non-directional microphone, and the diaphragm mainly
receives the change in air pressure. For this reason, as the back of the bi-directional microphone
is closed, it approaches the characteristics of non-directionality. In the second method described
above, a clear level difference is required between the output level of the audio signal and the
output level of the environmental noise in order to set the threshold described above.
However, the output level of the voice signal largely changes due to the speaker's voice volume
and individual differences of intonation, the variation of the distance between the speaker and
the microphone, and the adjustment of the voice volume by the speaker according to the ambient
noise level. Since noise also varies greatly depending on road surface conditions, vehicle types,
weather, etc., it is difficult to obtain a constant clear level difference between the two, and it is
therefore difficult to set an appropriate threshold level. The present invention has been made in
view of the above problems, and it is an object of the present invention to obtain a microphone
device and a sound collection method having high directivity in a narrow angle range while
maintaining a small size. SUMMARY OF THE INVENTION In order to solve the above problems,
the microphone devices of the present invention are disposed close to each other and have
different phases with respect to sound waves incident from a specific angular range. First and
second microphones outputting output signals, phase difference of output signals related to
sound waves incident on the first and second microphones from a specific angle range, and first
and second microphones from other angle ranges And an extraction means for extracting the
component of the sound wave from a specific angular range or a part thereof from the output
signals of the first and second microphones based on the difference between the phase difference
of the output signal related to the sound wave incident on the. Furthermore, in the microphone
device of the present invention, in addition to the microphone device of the above-mentioned
invention, the first microphone outputs signals of different phases in sound waves incident from
a specific angle range and sound waves incident from another angle range. And the second
microphone outputs an output signal of the same phase to sound waves from that particular
angular range and other angular ranges. Further, in the microphone device of the present
invention, in addition to the microphone devices of each of the above-mentioned inventions, the
correlation signal extraction means samples output signals from the first and second
microphones, and outputs two output signals between samples The component having a specific
correlation coefficient is extracted between the variation amounts of and the extracted
component is made to be the component of the sound wave from a specific angular range or a
part thereof. Furthermore, in the microphone device of the present invention, in addition to the
microphone devices of the above-mentioned inventions, the correlation signal extraction means
samples output signals from the first and second microphones, and outputs two output signals
between samples The sample is canceled according to the value of the correlation coefficient
between the variation amounts of, and the portion having the specific correlation coefficient is
extracted from the two output signals after sampling based on the remaining samples. It is a
thing.
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Furthermore, in the microphone device of the present invention, in addition to the microphone
devices of each of the above-described inventions, one of the output signals from the first and
second microphones is output to the other output signal at a stage prior to the extraction means.
And mixing means for mixing in proportions. Furthermore, the microphone device of the present
invention uses a bi-directional microphone or a hypercardioid microphone as the first
microphone in addition to the microphone devices of each of the above inventions, and a nondirectional microphone as the second microphone. Using a single microphone or a single
directional microphone. According to the sound collection method of the present invention, the
first and second microphones disposed in close proximity to each other and outputting output
signals of different phases with respect to sound waves incident from a specific angle range from
the same sound source Collecting sound waves, phase differences of output signals of sound
waves incident on the first and second microphones from a specific angle range, and outputs of
sound waves incident on the first and second microphones from other angle ranges Extracting a
component of the sound wave from a specific angular range or part thereof from the output
signals of the first and second microphones based on the difference between the phase difference
of the signals. BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an embodiment of
the present invention will be described based on the drawings. Embodiment 1 FIG. 1 is a block
diagram showing a configuration of a microphone device according to Embodiment 1 of the
present invention. In FIG. 1, the microphone 1 is a first microphone that outputs an output signal
of different phase between a sound wave incident from a specific angle range and a sound wave
incident from another angle range. In the first embodiment, the microphone 1 is a bi-directional
microphone. The directional characteristic of the bidirectional microphone is as shown in FIG. 7
(C). Further, in the bi-directional microphone, the phase of the output signal for the sound wave
incident from the 180 degree angle range on the front side bordering on the angle A in the
figure, and the output for the sound wave incident from the 180 degree angle range on the back
side The phase of the signal is 180 degrees different. Note that there is a velocity type
microphone as the bidirectional microphone, which is realized by a ribbon type microphone or
the like. The velocity microphone has a structure in which the periphery of the diaphragm is
open. If the size of the diaphragm is sufficiently smaller than the wavelength of the sound wave
when the circumference of the diaphragm is open, the air pressure on the front side of the
diaphragm and the air pressure on the back side will be the same. It does not change but moves
according to the direct movement of air.
Therefore, in the velocity type microphone, the vibration direction of the diaphragm is opposite
between the case where the sound wave is incident from the front side of the diaphragm and the
case where the sound wave is incident from the back side of the diaphragm. As a result, in the
velocity type microphone, the phase of the output signal is inverted when the direction of the
sound source viewed from the microphone is on the front side and on the back side. Also, the
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microphone 2 is arranged close to the microphone 1 (for example with a gap between the two
less than 1 centimeter), and the specific angular range of the microphone 1 and other angular
ranges (here all the remaining angular ranges The second microphone outputs an output signal
of the same phase to the sound wave from the angular range). That is, the microphones 1 and 2
are disposed close to each other, and output output signals having different phases to sound
waves incident from a specific angle range. In the first embodiment, the microphone 2 is a
nondirectional microphone. The directional characteristic of the nondirectional microphone is as
shown in FIG. 7 (A). From the omnidirectional microphone, an output signal of the same phase is
output over the entire angular range. As the nondirectional microphone, there is a pressure type
microphone, which is realized by a dynamic type microphone, a condenser type microphone, an
electret condenser type microphone or the like. The pressure type microphone has a structure in
which the front side of the diaphragm is open and the rear side is sealed by the housing. In the
case of a pressure type microphone, since the back side is sealed, the air pressure on the back
side of the diaphragm is constant, and the diaphragm is moved by the change in air pressure on
the front side. Thus, the pressure-type microphone outputs a waveform signal according to the
change in air pressure at the location of the microphone. Further, since the change in barometric
pressure around the microphone does not depend on the direction of the sound source viewed
from the microphone, the sensitivity is constant and the phase of the output signal is also
constant regardless of the direction of the sound source. When adjacent non-directional
microphones and bi-directional microphones receive sound waves from the same sound source at
the same timing, output signals for sound waves incident from the 180 degree angle range on
the front side of the bi-directional microphones The phase is approximately in phase with the
phase of the output signal of the nondirectional microphone. Further, the output signal for the
sound wave incident from the 180-degree angle range on the back side of the bi-directional
microphone is substantially in reverse phase to the phase of the output signal of the nondirectional microphone.
Further, the correlation signal extraction circuit 4 has a specific correlation coefficient between
the output signal S 2 of the microphone 2 obtained through the amplifier 5 and the output signal
S 1 of the microphone 1 obtained through the amplifier 5. Is a circuit that functions as a
correlation signal extraction unit that extracts a portion having a and outputs it as a component
of a sound wave from a range (a specific angle range) of the front side 180 degrees of the
microphone 1 that is a bidirectional microphone. The above-mentioned specific correlation
coefficient may be, for example, one value such as 1 and may be, for example, a range of 0.9 to
1.1. The correlation signal extraction circuit 4 is configured to detect the phase difference of the
output signal of the sound wave incident on the microphones 1 and 2 from a specific angle
range, and another angle range (angle range different from the above-mentioned specific angle
range) Function as extraction means for extracting the component of the sound wave from the
specific angle range from the output signals of the microphones 1 and 2 based on the difference
between the phase difference of the output signal of the sound wave incident on the
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microphones 1 and 2 from the The amplifier 5 is a circuit that amplifies the output signals of the
microphones 1 and 2 respectively. Next, the operation of the above apparatus will be described.
FIG. 2 shows a straight line (Y = X) of positive correlation and a straight line (negative
correlation) which are the reference of the correlation between the output signal S2 of the
microphone 2 and the output signal S1 of the microphone 1 in the microphone device according
to the first embodiment. It is a figure which shows Y = -X). When the microphones 1 and 2 sense
sound waves from the same sound source, the microphones 1 and 2 output waveform signals
corresponding thereto as output signals. At this time, the microphones 1 and 2 are disposed
close to each other at an interval shorter than the wavelength of the sound wave to be collected,
and therefore sense the sound waves from the same sound source almost simultaneously. In the
first embodiment, since microphone 1 is a bi-directional microphone and microphone 2 is a nondirectional microphone, microphone 2 receives a sound wave from a range of 180 degrees on the
front side of microphone 1. The output signal of is approximately in phase with the output signal
of the microphone 1. The output signals of the microphones 1 and 2 are amplified by the
amplifier 5 and then supplied to the correlation signal extraction circuit 4 respectively. The
phase of the output signal S 2 of the microphone 2 substantially matches the phase of the output
signal S 1 corresponding to the sound wave from the range of 180 degrees on the front side of
the microphone 1. On the other hand, the phase of the output signal of the microphone 2 and the
phase of the output signal corresponding to the sound wave from the range of 180 degrees on
the back side of the microphone 1 differ by approximately 180 degrees.
That is, the signal S1 corresponding to the sound wave from the range of 180 degrees on the
front side of the microphone 1 and the signal S2 are in phase, and the signal S1 corresponding to
the sound wave from the range of 180 degrees on the back side of the microphone 1 is opposite
to the signal S2. It becomes a phase. Therefore, the component of the output signal S1 of the
microphone 1 for the sound wave from the front side of the microphone 1 has a positive
correlation with the output signal S2 of the microphone 2, and the component for the sound
wave from the back side is It has a negative correlation with the output signal S2 of the
microphone 2 after phase shift. When the correlation signal extraction circuit 4 extracts the
component of the sound wave incident from the range of 180 degrees on the front side of the
microphone 1, the correlation signal extraction circuit 4 receives the output signal S 2 of the
microphone 2 obtained via the amplifier 5 and the amplifier 5. A portion positively correlated
with each other is extracted from the output signal S1 of the microphone 1 obtained, and the
signal Zout is output as the component of the sound wave from the range of 180 degrees on the
front side. When the sound wave component is extracted from the range of 180 degrees on the
back side of the microphone 1, the correlation signal extraction circuit 4 outputs the output
signal S 2 of the microphone 2 obtained via the amplifier 5 and the amplifier 5. The portions
negatively correlated with each other are extracted from the output signal S1 of the microphone
1 obtained through the above. Next, extraction of the correlation part of the signals S1 and S2 by
the correlation signal extraction circuit 4 will be described. The correlation signal extraction
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circuit 4 samples the output signal S1 of the microphone 1 and the output signal S2 of the
microphone 2 at a predetermined cycle, and the values of the signals S1 and S2 at each sampling
time, or between each sampling time Based on the amount of change of the signals S1 and S2, a
positive correlation portion between the signals S1 and S2 at that time is extracted. For example,
the correlation signal extraction circuit 4 extracts a positive correlation portion between the
output signals S1 and S2 as follows. FIG. 3 is a diagram for explaining extraction of a correlation
portion of an output signal of the microphone 2 and an output signal of the microphone 1 by the
correlation signal extraction circuit 4 in the microphone device according to the first
embodiment. Considering the point Z (t) by the value of the amplitude of the signals S1 and S2
obtained at time t on a plane (the plane shown in FIG. 2) in which the amplitudes of the signals
S1 and S2 are Y and X axes, For example, as shown in FIG. 3, the point Z (t) moves on the plane
along time series t =..., N−1, n, n + 1, n + 2,. The correlation signal extraction circuit 4
determines the value of the output signal Zout (t) according to the point Zo (t) obtained by
projecting the point Z (t) at that time onto the straight line (Y = X) of positive correlation.
Thereby, the negative correlation portion between the signals S1 and S2 is removed, and only the
positive correlation portion is extracted. As described above, according to the first embodiment,
the microphones 1 and 2 are disposed close to each other, and output output signals having
different phases with respect to sound waves incident from a specific angle range. The phase
difference between the output signal of the sound wave incident on the microphones 1 and 2
from the specific angle range and the phase difference of the output signal on the sound waves
incident on the microphones 1 and 2 from the other angle range From the output signals of the
microphones 1, 2 the component of the sound wave from that particular angular range is
extracted based on the difference. [0047] Thereby, without using superdirective microphones,
for example by using microphones such as non-directional microphones or bi-directional
microphones, the directional characteristics of the microphone device can be kept small and
specific narrow angular range Can be highly sensitive. Consequently, for example, by mounting
this microphone device in front of the driver (for example, near the sun visor) in the car, the
driver's voice can be reliably extracted. Second Embodiment The microphone device according to
the second embodiment of the present invention is obtained by changing the method of
extracting the positive or negative correlation portion between the signals S1 and S2 by the
correlation signal extraction circuit 4. FIG. 4 is a diagram for explaining extraction of a
correlation portion of the output signal S 2 of the microphone 2 and the output signal S 1 of the
microphone 1 by the correlation signal extraction circuit 4 in the microphone device according to
the second embodiment. The correlation signal extraction circuit 4 according to the second
embodiment samples the output signal S2 of the microphone 2 and the output signal S1 of the
microphone 1, and changes the amount of change of the signal S1 between samples and the
amount of change of the signal S2. Cancel the sample depending on the value of the correlation
coefficient between When the correlation signal extraction circuit 4 extracts a positive
correlation part, the correlation coefficient between the variation amounts is not positive
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between the point Z (m-1) and the point Z (m). In that case, cancel that point Z (m). For example,
in FIG. 4, since the correlation coefficient between the variation is not positive between the point
Z (n) and the point Z (n + 1), the point Z (n + 1) is canceled and the point Z (n) is The point Z '(n +
2) to be considered next is located away from the point Z (n) by the amount of change of the
signals S1 and S2 from the time n + 1 to the time n + 2. Then, the correlation signal extraction
circuit 4 outputs the signal Zout obtained by the uncancelled sample as a component of the
extracted sound wave.
As described above, according to the second embodiment, the correlation signal extraction circuit
4 samples the output signal S 2 of the microphone 2 and the output signal S 1 of the microphone
1 and outputs two output signals S 1 and S 2. The samples are canceled according to the value of
the correlation coefficient between the amounts of change between the samples, and a portion
having a specific correlation coefficient between the two output signals S1 and S2 is extracted.
Thus, it is possible to reliably reduce the component of the sound wave incident from outside the
specific angle range that is the target of sound collection. Third Embodiment The microphone
device according to the third embodiment of the present invention uses a microphone with
hypercardioid characteristics as the microphone 1. FIG. 5 is a diagram showing an example of the
directivity of the microphone of the hypercardioid characteristic in the microphone device
according to the third embodiment. Although hypercardioid characteristics may also refer to
directivity characteristics in the case where vibrations due to air velocity changes and vibrations
due to air pressure changes are mixed at a specific ratio, as shown in FIG. As shown in, all the
directivity characteristics 21 in which there are two angles (angles from the front) α at which
the phase of the output signal is inverted (front angle) and the sensitivity on the front side and
the sensitivity on the back side are called hypercardioid characteristics. Such hyper-cardioid
characteristics, for example, incompletely close the back side of the diaphragm of the bidirectional microphone, and the movement of the diaphragm is due to the direct movement of air
and to the change in air pressure. It is realized by making things mixed. In a microphone with
high parkard geoid characteristics, an output signal of a sound wave incident from an angle
range from the front in FIG. 5 in both directions from the angle α is incident from an angle
range of 180 degrees on the front side of the bi-directional microphone In the same manner, the
phase is different from that in the case of incidence from the remaining angle range. Further, the
angle α at which the phase changes can be made smaller than 90 degrees by pointing the side
with the lower sensitivity of the microphone of this hypercardioid characteristic to the front.
Thus, by using the microphone of this hypercardioid characteristic as the microphone 1 instead
of the bi-directional microphone, the angle range in which the sound wave to be extracted is
incident is set to an angle range 2α narrower than 180 degrees. It can be narrowed. As
described above, according to the third embodiment, by using a microphone with hypercardioid
characteristics as the microphone 1, it is possible to narrow the angular range in which the
extracted sound wave is incident.
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The same effect can be obtained by using a microphone of this hypercardioid characteristic as
the microphone 1 in the microphone device according to the second embodiment described
above and the fourth embodiment described later. Fourth Embodiment The microphone device
according to the fourth embodiment of the present invention is the microphone device according
to the first embodiment in which a circuit for inverting and mixing the output signal of the
microphone 2 to the output signal of the microphone 1 at a predetermined ratio is added It is.
FIG. 6 is a block diagram showing the configuration of a microphone device according to
Embodiment 4 of the present invention. In FIG. 6, a coefficient circuit 11 is a circuit that outputs
a signal obtained by multiplying an input signal by a predetermined coefficient. When the
coefficient is larger than 1, an amplifier is used as the coefficient circuit 11, and when the
coefficient is 1 or less, a voltage dividing circuit or the like is used as the coefficient circuit 11.
The phase inverter 3 is a circuit that inverts the phase of an input signal and outputs the inverted
signal, and the adder 12 is a circuit that outputs the sum of two input signals. The coefficient
circuit 11, the phase inverter 3 and the adder 12 function as mixing means for mixing the output
signal of the microphone 2 with the output signal of the microphone 1 at a predetermined ratio.
The other components in FIG. 6 are the same as those of the first embodiment, and thus the
description thereof is omitted. The operation of the above apparatus will now be described. In the
microphone device according to the fourth embodiment, the coefficient circuit 11 and the phase
inverter 3 add the signal S2a obtained by inverting the phase after multiplying the output signal
S2 of the microphone 2 by a predetermined coefficient. Output to 12. The adder 12 supplies a
signal S1a obtained by adding the signal S2a to the output signal S1 of the microphone 1 to the
correlation signal extraction circuit 4 instead of the signal S1. Thus, according to the coefficient
of the coefficient circuit 11, it is possible to electrically set the incident angle α at which the
phase of the signal S1a is reversed smaller than 90 degrees inherent to the bidirectional
microphone. Therefore, in the microphone device according to the fourth embodiment, the sound
from the angle range (= 2α) from the front to both sides from the angle α is extracted. For
example, when the microphone 1 is a bi-directional microphone, the microphone 2 is a nondirectional microphone, and the sound source is in front of the microphone 1, the output signal
S1 of the microphone 1 and the output signal S2 of the microphone 2 are The signal S2a that has
passed the phase inverter 3 and the output signal S1 of the microphone 1 have the opposite
phase.
Therefore, in this case, assuming that the amplitudes of the output signals of microphones 1 and
2 are the same and the coefficient of coefficient circuit 11 is 0.5, the amplitude of signal S1a
after calculation by adder 12 is the output signal of microphone 1 It is half the amplitude of S1.
In this case, the signal S1a is in phase with the signal S1. In the same case, when the sound
source is on the back of the microphone 1, the signal S1 and the signal S2 are in phase, so the
amplitude of the signal S1a is 1.5 times the amplitude of the signal S1. Become. In this case, the
signal S1a is in phase with the signal S1. However, the phase of the signal S1a is reversed
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between when the sound source is in front of the microphone 1 and when it is in the back.
Furthermore, in the same case, when the sound source is on the side of the microphone 1, the
signal S1a is substantially the same as the signal S2a because the amplitude of the signal S1 is
smaller than the amplitude of the signal S2a. Therefore, an angle α at which the phase of the
signal S1a reverses exists at an angle other than 90 degrees from the front. When the coefficient
of the coefficient circuit 11 is 0.5, the angle at which the phase of the signal S1a is inverted to an
angle at which the amplitude of the output signal of the microphone 1 becomes a value obtained
by multiplying the amplitude of the output signal of the microphone 2 by 0.5. α is present. Since
the sensitivity of the microphone 1 which is a bi-directional microphone is approximately
proportional to the cosine of the angle from the front, the angle α at which the phase of the
signal S1a is reversed is approximately 60 degrees. Thus, by inverting and mixing the output
signal of the microphone 2 with the output signal of the microphone 1 at a predetermined ratio,
one signal S 1 a supplied to the correlation signal extraction circuit 4 according to the ratio The
incident angle α of the sound wave whose phase is inverted is electrically set. Further, by
changing the coefficient of the coefficient circuit 11, it is possible to change the angle α at which
the phase of the signal S1a is inverted. Thus, the directivity characteristic of the microphone 1
having bi-directionality can be electrically converted to the hypercardioid characteristic as shown
in FIG. 5 by the microphone 2, the coefficient circuit 11, the phase inverter 3 and the adder 12.
can do. The other operations of the microphone device according to the fourth embodiment are
the same as those of the first embodiment, and thus the description thereof will be omitted. As
described above, according to the fourth embodiment, the coefficient circuit 11, the phase
inverter 3 and the adder 12 are arranged in front of the correlation signal extraction circuit 4
and the output signal S 2 of the microphone 2 is Are inverted and mixed at a predetermined rate
to the output signal S1.
Thereby, the directivity characteristic of the microphone 1 can be made hypercardioid
characteristic by the electronic circuit, and a part of the specific angle range (here, the range of
the front side 180 degrees) of the microphone 1 Component of the sound wave from both sides
of the range of α degrees). Further, the coefficient of the coefficient circuit 11 may be variable.
In that case, it is possible to easily change and set the angular range (= 2α) to be the target of
sound collection. Therefore, for example, even if this microphone device is applied to a
microphone device of a video camera with a zoom function and the angle range (= 2α) to be a
target of sound collection is changed in conjunction with the magnification of the zoom lens.
Good. By doing so, it is possible to mainly collect sound from a place within the range of the
image being recorded. In the fourth embodiment, the above-mentioned mixing means is added to
the microphone device according to the first embodiment, but the above-mentioned mixing
means is added to the microphone devices according to the other second and third embodiments.
The same effect can be obtained. Although the above-described embodiments are preferable
examples of the present invention, the present invention is not limited to these, and various
modifications may be made without departing from the scope of the present invention. Changes
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are possible. For example, the correlation signal extraction circuit 4 in each of the above
embodiments can be realized by a digital signal processor or the like. In that case, A / D
converters for converting the output signals of the microphones 1 and 2 into digital signals are
appropriately provided in the front stage of those circuits. The elements, circuits and the like
subsequent to the microphones 1 and 2 in the above embodiments may operate satisfactorily
only in the frequency band of human voice. Although the microphone 2 in each of the above
embodiments is a nondirectional microphone, it may be a unidirectional microphone.
Furthermore, in the narrow angle range different from the specific angle range of the
microphone 1, the microphone 2 in each of the above embodiments has different phases in the
sound wave from the narrow angle range and the sound wave from the remaining angle range. It
may be a hypercardioid microphone which outputs an output signal. However, in that case, since
the sound waves from the narrow angle range may be extracted as well as the sound waves from
the specific angle range of the microphone 1, the direction and the angular width of the narrow
angle range may It is assumed that the conditions of the ambient noise due to the place etc., the
conditions such as voice recognition, etc. are acceptable according to the type of application
using this device.
According to the present invention, it is possible to obtain a microphone device and a sound
collection method having high sensitivity in a narrow angle range while keeping the size small.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a
microphone device according to Embodiment 1 of the present invention. FIG. 2 is a diagram
showing a straight line of positive correlation and a straight line of negative correlation, which is
a reference of correlation between an output signal of the microphone 2 and an output signal of
the microphone 1 in the microphone device according to the first embodiment. FIG. 3 is a
diagram for explaining extraction of a correlation portion of an output signal of the microphone
2 and an output signal of the microphone 1 by a correlation signal extraction circuit in the
microphone device according to the first embodiment. FIG. 4 is a diagram for explaining
extraction of a correlation portion of an output signal of the microphone 2 and an output signal
of the microphone 1 by a correlation signal extraction circuit in the microphone device according
to the second embodiment. FIG. 5 is a diagram showing an example of directivity characteristics
of a microphone of hypercardioid characteristics in a microphone device according to a third
embodiment. FIG. 6 is a block diagram showing a configuration of a microphone device
according to Embodiment 4 of the present invention. FIG. 7 is a view showing directivity
characteristics of a conventional microphone. Explanation of the code 1 microphone (first
microphone) 2 microphone (second microphone) 3 phase inverter (phase inversion means,
mixing means) 4 correlation signal extraction circuit (correlation signal extraction means,
extraction means) 11 coefficient circuit (Mixing means) 12 Adder (Mixing means)
04-05-2019
11
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