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JPH11187478

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DESCRIPTION JPH11187478
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone apparatus incorporated in an apparatus having a noise source therein, and more
particularly to a microphone apparatus incorporated in a video integrated camera or the like.
[0002]
2. Description of the Related Art A built-in microphone device capable of collecting sound with
high S / N by reducing the effects of noise and vibration generated by mechanical systems in the
video integrated camera body and wind noise, is disclosed in Japanese Patent Laid-Open No. No.
4,225,598.
[0003]
FIG. 5 is a block diagram of a conventional microphone device proposed in the above-mentioned
publication.
The conventional microphone device removes low frequency components of the output signals of
the first and second nondirectional microphones 11 and 12 and the first nondirectional
microphone 11 which are arranged in a straight line at intervals. The output of the phase shifter
14 is mixed with the output of the high pass filter (HPF) 13, the phase shift 14 for delaying the
phase of the output signal of the second omnidirectional microphone 12, and the output of the
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high pass filter (HPF) 13 in reverse phase A subtractor 15 and an equalizer (EQU) 16 for
correcting the frequency characteristic of the output signal of the subtractor 15 are provided.
[0004]
In the conventional microphone device, low frequency components of the output signal of the
first omnidirectional microphone 11 are removed by a high pass filter (HPF) 13, and the phase of
the output signal of the second omnidirectional microphone 12 is phase-shifted 14. The output
signal of the phase shifter 14 is added to the output signal of the high pass filter (HPF) 13 in
reverse phase, and the equalizer (EQU) 16 corrects the frequency characteristic and outputs it.
[0005]
In the conventional microphone device, since the signal whose phase is delayed by the phase
shifter 14 is added to the signal whose low frequency component is removed by the high pass
filter (HPF) 13, the phase is low. The signal in the frequency range is inverted.
For this reason, when mixing the output signal of the conventional microphone device and the
output signal of another sound collecting device, the signal level in the low frequency range may
decrease, or in the worst case, the audio output may not be obtained. There is.
[0006]
Even if wind noise whose frequency component is concentrated in the low region is collected by
each of the nondirectional microphones 11, 12, the low frequency component related to the wind
noise collected by the first nondirectional microphone 11 is a high pass filter Since it is removed
by (HPF) 13, wind noise collected by the second directional microphone 12 of the two
nondirectional microphones 11 and 12 is eventually output. For this reason, although wind noise
can be made into the same level as a nondirectional microphone, wind noise is not reduced.
[0007]
The present invention has been made to solve such problems. By delaying and adding the phase
shift of the output signal of each nondirectional microphone, noise and wind noise from the
inside of the device can be reduced as low frequency components. It is an object of the present
invention to provide a microphone device capable of reducing the phase without inverting it and
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performing high S / N sound collection.
[0008]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a microphone
device according to the present invention comprises: first and second nondirectional
microphones arranged in a straight line spaced from each other; Summing the output of the first
and second phase shifters in phase with each other, the first phase shifter delaying the phase of
the output signal of the first phase, the second phase shifter delaying the phase of the output
signal of the second microphone, and And a vessel.
[0009]
In the microphone device according to the present invention, the output signal of each
microphone is phase-shifted by each phase shifter, and each signal whose phase is delayed by
each phase shifter is added by an adder.
Thus, the phase of the low frequency signal is not reversed.
Therefore, when an output signal obtained by collecting the same sound source by the
microphone device according to the present invention and an output signal obtained by
collecting sound by another sound collecting device are mixed, the signal level in the low
frequency range is There is no problem such as a drop, and the mixing can be performed
satisfactorily.
[0010]
By delaying the phase of each output signal of each nondirectional microphone arranged at a
predetermined interval on a straight line and then performing in-phase addition, the
characteristics of no directivity at low frequencies and 180 at middle and high frequencies are
obtained. It is possible to obtain unidirectional characteristics with low response in the power
direction. Therefore, when the microphone device according to the present invention is applied
to a video integrated camera, it is possible to reduce the influence of noise in the middle and high
frequency bands generated from mechanical systems in the video integrated camera.
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[0011]
By performing in-phase addition at low frequencies, wind noise distributed in a low frequency
band of 200 Hz or less where correlation is low between outputs of the omnidirectional
microphones can be averaged. Therefore, the influence of wind noise can be reduced.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the attached drawings. FIG. 1 is a block diagram of a
microphone device according to the present invention. In the microphone device according to the
present invention, the phases of the output signals of the first and second nondirectional
microphones 1 and 2 and the first nondirectional microphone 1 disposed in a straight line at
intervals from each other and the first nondirectional microphone 1 are delayed. 1, the second
phase shifter 4 that delays the phase of the output signal of the second omnidirectional
microphone 2, and the adder 5 that adds the respective output signals of the phase shifters 3 and
4 in phase And an equalizer (EQU) 6 for correcting the frequency characteristic of the output
signal of the adder 5.
[0013]
The second nondirectional microphone 2 is disposed behind the first nondirectional microphone
1. The first and second nondirectional microphones 1 and 2 are arranged at a predetermined
distance d (e.g. 12 mm). In each of the microphones 1 and 2, the microphone 1 is disposed
forward and the microphone 2 is disposed rearward, with the direction between the microphones
directed to the imaging direction of the video integrated camera (front direction of the video
integrated camera). Also, in the video recording type camera with stereo recording type in a
mounting form different from the above, the left and right two microphone devices according to
the present invention are provided and arranged so that the inter-microphone direction is the
front direction of the video integrated camera. Do. The microphones of the left channel are
arranged with their microphones directed to the left relative to the front of the video integrated
camera, and the microphones of the right channel are directed from the front of the video
integrated camera. Also, the right direction may be oriented.
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[0014]
In the microphone device according to the present invention, the phase of the output signal of
the first nondirectional microphone 1 is delayed by the first phase shifter 3, and the phase of the
output signal of the second nondirectional microphone 2 is shifted to the second phase. The
phase signal is delayed by the phase shifter 4 and the output signals of the phase shifters 3 and 4
are in-phase added in the adder 5 and the signal obtained by in-phase addition is corrected in the
frequency characteristic by the equalizer (EQU) 6 and output.
[0015]
The sensitivity of the first nondirectional microphone 1 is A, the sensitivity of the second
nondirectional microphone 2 is B, the phase characteristic of the first phase shifter 3 is ψa (ω),
and the second phase shifter 4 Assuming that the phase characteristic is ψb (ω), the angle
between the directions between the microphones and the sound source (not shown) is θ, the
distance between the microphones is d, and the sound speed is C, the combined output P output
from the adder 5 is It is represented by.
Here, ω is each frequency (ω = 2πf).
[0016]
When the sensitivity A of the first nondirectional microphone 1 and the sensitivity B of the
second nondirectional microphone 2 are equal, the combined output P is simplified to several 2.
[0017]
Further, the directivity pattern D (θ) is expressed by equation 3.
[0018]
FIG. 2 is a graph showing the phase characteristic of the phase shifter.
The ordinate represents the phase angle in radians, and the abscissa represents the normalized
angular frequency (ω / ω0).
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[0019]
Here, as the first and second phase shifters 3 and 4, phase shifters having a characteristic that
the phase delay angle is π / 2 radians (90 degrees) at the reference angular frequency ω0
shown in FIG. Reference angular frequency ωa0 at which the characteristic of the phase shifter 3
of 1 is −π / 2 radians (−90 degrees) is 338 Hz (hertz), and the characteristic of the second
phase shifter 4 is −π / 2 (−90 degrees) When the reference angular frequency ωb0 is 10.6
KHz (kilohertz), the distance d between the nondirectional microphones 1 and 2 is 12 mm
(millimeters), and the speed of sound C is 344 m / s (meters / sec) FIG. 3 shows the frequencyresponse characteristics of the adder output with the parameter θ being the angle θ between
the sound source and the sound source, and FIG. 4 shows the directivity characteristics at 4 KHz
(kilohertz).
[0020]
As shown in FIGS. 3 and 4, the microphone device according to the present invention can obtain
non-directional characteristics at low frequencies (300 Hz or less), and respond in the direction
of 180 degrees at middle and high frequencies. Low unidirectionality characteristics can be
obtained.
[0021]
As described above, in the microphone apparatus according to the present invention, the output
signal of each nondirectional microphone is phase shifted by each phase shifter, and each signal
delayed in phase by each phase shifter is an adder. Since the addition is performed in the above,
the phase of the signal in the low frequency range is not inverted.
Therefore, when an output signal obtained by collecting the same sound source by the
microphone device according to the present invention and an output signal obtained by
collecting sound by another sound collecting device are mixed, the signal level in the low
frequency range is There is no problem such as a drop, and the mixing can be performed
satisfactorily.
[0022]
According to the present invention, the microphone device is configured to delay the phases of
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the output signals of the nondirectional microphones arranged at predetermined intervals on a
straight line and then add the in-phase, so that nondirectional characteristics at low frequencies
are obtained. In the middle and high frequencies, it is possible to obtain uni-directional
characteristics with low response in the direction of 180 degrees.
Therefore, when the microphone device according to the present invention is applied to a video
integrated camera, it is possible to reduce the influence of noise in the middle and high
frequency bands generated from mechanical systems in the video integrated camera.
[0023]
By performing in-phase addition at low frequencies, wind noise distributed in a low frequency
band of 200 Hz or less where correlation is low between outputs of the omnidirectional
microphones can be averaged.
Therefore, the influence of wind noise can be reduced.
[0024]
Brief description of the drawings
[0025]
1 is a block diagram of a microphone device according to the present invention
[0026]
Fig. 2 Graph showing phase characteristic of phase shifter
[0027]
3 is a graph showing the frequency response characteristic of the microphone device according
to the present invention
[0028]
Fig. 4 Graph showing directivity characteristics at 4 KHz (kilohertz) of the microphone device
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according to the present invention
[0029]
Fig. 5 Block diagram of the conventional microphone device
[0030]
Explanation of sign
[0031]
1 ... 1st nondirectional microphone, 2 ... 1st nondirectional microphone, 3 ... 1st phase shifter, 4 ...
2nd phase shifter, 5 ... adder, 6 ... equalizer.
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