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JP2005136628

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DESCRIPTION JP2005136628
PROBLEM TO BE SOLVED: To provide a stereo microphone device capable of automatically
correcting sensitivity variations of nondirectional microphones in normal use of the device.
SOLUTION: An output signal of a nondirectional first ECM 1 is input to a detector 6 through an
amplifier 3 and a first LPF 5, and an output signal of a nondirectional second ECM 2 is input to a
detector 10 through a variable gain amplifier 4 and a second LPF 9. Do. The comparator 7
compares the output signals of the detectors 6 and 10. The level determination unit 8 determines
whether the output signal of the detector 6 is at a level within a predetermined range, and
outputs a signal when it is determined that the level is not within the predetermined range. The
comparator output holding unit (control unit) 12 outputs the signal of the comparison result of
the comparator 7 input through the delay unit 11 when the signal is not input from the level
determination unit 8, and the variable gain amplifier 4 outputs the comparison result. Change the
amplification factor based on the signal. The first subtractor 21 and the second subtractor 24
subtract the output signals from the amplifier 3 and the variable gain amplifier 4 from each
other. [Selected figure] Figure 1
Stereo microphone device
[0001]
The present invention relates to a stereo microphone device that subtracts output signals of two
nondirectional microphones arranged at a distance from each other to obtain directivity of the
arrangement direction of the microphones.
[0002]
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1
A conventional stereo microphone device is a uni-directional ECM in which two uni-directional
ECMs (Electret Condenser Microphones) having uniform characteristics are attached to the line
object in the left and right directions, respectively, with an angle in the left direction. In general,
the output signal of the L-channel signal is used as the output signal of the L-channel signal, and
the output signal of the unidirectional ECM with the right angle is used as the R-channel signal.
The unidirectional ECM has its directivity in the direction in which the output itself is directed, so
that a stereo microphone device can be easily realized simply by attaching a plurality of
unidirectional ECMs at different angles.
[0003]
However, in order to acoustically achieve directivity, unidirectional ECM has sound holes on both
the front and back, and the sound holes on the back have acoustic resistance from each direction.
The vibration itself of the vibrating membrane is made to have directivity by utilizing the level
difference (sound pressure difference) and the phase difference of sound waves incident on both
sound holes. Therefore, in order to give directivity to the vibration of the vibrating membrane
itself, it is necessary to secure a space around the unidirectional ECM so as not to affect the
propagation of the sound wave. As a mounting structure for holding in space by rubber is
required, a corresponding volume is also required for the entire microphone device. Therefore, it
has been difficult to mount a stereo microphone device configured using a unidirectional ECM
into a portable recording device such as a video camera, which is required to be miniaturized.
[0004]
Therefore, by arranging two nondirectional ECM with a structure having a sound hole only on
the front side at appropriate intervals in the left and right direction, the time difference of the
sound collection signal generated in each nondirectional ECM depending on the incident
direction of the sound wave is used. A stereo microphone device of a system for obtaining
directivity in the left-right direction has been adopted by electrically arithmetically processing
the output signals of the nondirectional ECM with each other (for example, see Patent Document
1). If there is no need to provide a space other than the front face of the nondirectional ECM if it
is the sound collection by the nondirectional ECM, it becomes possible to mount the
nondirectional ECM embedded in the housing, and the volume of the stereo microphone device
Can be greatly reduced, and it has become possible to cope with the miniaturization of portable
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recording devices.
[0005]
In the case of such a stereo microphone device, processing for generating a stereo sound signal
from the output signal of the nondirectional ECM is required, and this processing is called stereo
matrix processing, which will be described below.
[0006]
FIG. 4 is a block diagram showing the configuration of a conventional stereo microphone device
that performs stereo matrix processing.
In the figure, 1 is a nondirectional first ECM, 2 is a nondirectional second ECM, and the first ECM
1 and the second ECM 2 are disposed at the left and right with an interval D. The output signals
of the first ECM 1 and the second ECM 2 are respectively amplified by a predetermined ratio by
the amplifier 3 and the amplifier 41 and input to the stereo matrix processing unit 20.
[0007]
In the stereo matrix processing unit 20, the output signal of the amplifier 3 is input as it is to the
first subtractor 21 as a signal 3s, and is also input to the delay unit 22. The output signal of the
delay 22 is input to the attenuator 23, and the output signal (signal 23 s) of the attenuator 23 is
input to the second subtractor 24. Similarly, the output signal of the amplifier 41 is directly input
to the second subtractor 24 as a signal 41 s, and is also input to the delay unit 25. The output
signal of the delay 25 is input to the attenuator 26, and the output signal (signal 26 s) of the
attenuator 26 is input to the first subtractor 21.
[0008]
The first subtractor 21 subtracts the output signal (signal 26 s) of the attenuator 26 from the
output signal (signal 3 s) of the amplifier 3, and outputs the signal of the subtraction result to the
equalizer 27. The second subtractor 24 subtracts the output signal (signal 23s) of the subtractor
23 from the output signal (signal 41s) of the amplifier 41, and outputs the signal of the
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subtraction result to the equalizer 28. The equalizers 27 and 28 correct and flatten changes in
frequency characteristics caused by stereo matrix processing. Then, the output signal (signal 27s)
of the equalizer 27 is obtained as an L channel signal, and the output signal (signal 28s) of the
equalizer 28 is obtained as an R channel signal.
[0009]
In the conventional stereo microphone device shown in FIG. 4, when the arrangement interval of
the first ECM 1 and the second ECM 2 is D, the delay time of the delay 22 and the delay 25 is
approximately the time required for the sound wave to travel by the distance D. Generally, they
are set equal. The principle of obtaining stereo characteristics by stereo matrix processing in this
case will be described below. Here, in order to simplify the description, it will be described using
a sine wave of a single frequency (the same shall apply hereinafter).
[0010]
FIGS. 5 to 7 respectively show stereo matrix processing in the conventional stereo microphone
device in the case where the sensitivity is equal to the first ECM 1 and the second ECM 2
arranged at the interval D and the left sound source, the front sound source and the right sound
source are used. It is an explanatory view explaining. In FIGS. 5 to 7, the upper part shows the
arrangement of the sound sources and the first ECM1 and the second ECM2, and the middle part
shows the waveforms of the input signals of the first subtractor 21 and the second subtractor 24.
The lower part shows the waveform of the output signal of the equalizer 27 and the equalizer 28.
In the waveform, the horizontal axis shows the phase, and the vertical axis shows the signal level
(the same applies hereinafter). To do).
[0011]
In the case of the left sound source, the L channel signal level close to the sound source is higher
than the R channel signal level far from the sound source (see the lower part of FIG. 5), and in the
case of the front sound source, the L channel signal level and the R channel signal level are In the
case of the right sound source, the R channel signal level close to the sound source is higher than
the L channel signal level far from the sound source (see lower part in FIG. 7). Therefore, it can
be seen that stereo characteristics are obtained by stereo matrix processing.
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[0012]
Subsequently, stereo matrix processing in the case where the arrangement interval of the first
ECM 1 and the second ECM 2 is D / 2 in the conventional stereo microphone device shown in
FIG. 4 will be described. FIGS. 8 to 10 respectively show stereo matrices in the conventional
stereo microphone device in which the sensitivity is equal to the first ECM1 and the second
ECM2 arranged at the interval D / 2, and the left sound source, the front sound source and the
right sound source are used. It is an explanatory view explaining processing. The delay time of
the delay unit 22 and the delay unit 25 is set to be substantially equal to the time required for
the sound wave to travel by a distance of D / 2, and the attenuation amount of the attenuator 23
and the attenuator 26 is It is assumed that it is equal to the case of FIG. 5 to FIG.
[0013]
By referring to the lower part of FIGS. 8 to 10, as in the case where the arrangement interval of
the first ECM 1 and the second ECM 2 is D, although the stereo characteristic by stereo matrix
processing is obtained, the arrangement interval of the first ECM 1 and the second ECM 2 is By
narrowing to D / 2 and half, it can be seen that both signal levels for the front sound source and
stereo characteristics for the left and right sound sources are reduced compared to the case
where the arrangement interval is D. Unexamined-Japanese-Patent No. 3-131199
[0014]
In order to obtain good stereo characteristics by performing stereo matrix processing in the
conventional stereo microphone device as described above, it has been required to secure an
arrangement interval of nondirectional ECM of at least 15 to 20 mm. Moreover, the sensitivity of
the omnidirectional ECM had to be managed very strictly. That is, in order to obtain stereo
characteristics by performing stereo matrix processing, it is necessary as a precondition that the
sensitivities of the nondirectional ECMs are equal (the output characteristics are equal) as
described with reference to FIGS. Met. However, since the sensitivity of an actual nondirectional
ECM is extremely large in mass-production variation, it is necessary to perform characteristic
pairing on the nondirectional ECM used for the same microphone unit for practical use. However,
the pairing accuracy is the limit in mass production in that the sensitivity difference of the
nondirectional ECM in the same microphone unit is suppressed to about 1.5 to 2.0 dB or less.
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[0015]
Therefore, stereo matrix processing in the case where the sensitivity difference between the first
ECM 1 and the second ECM 2 is 2 dB and the arrangement interval is D and D / 2 in the
conventional stereo microphone device shown in FIG. 4 will be described. 11 to 13 show the
conventional stereos when the sensitivity of the first ECM 1 is 2 dB higher than that of the
second ECM 2 by 2 dB with respect to the first ECM 1 and the second ECM 2 arranged at the
interval D, respectively. FIG. 14 is an explanatory diagram for explaining stereo matrix processing
in the microphone device, and FIGS. 14 to 16 are respectively a sensitivity of the first ECM 1
being 2 dB higher than that of the second ECM 2 with respect to the first ECM 1 and the second
ECM 2 arranged at an interval D / 2. It is explanatory drawing explaining the stereo matrix
process in the conventional stereo microphone apparatus in the case of being a left sound source,
a front sound source, and a right sound source.
[0016]
By referring to the lower part of FIGS. 11 to 13, although the sensitivity difference between the
first ECM1 and the second ECM2 on the left and right is 2 dB, in the output signal of the stereo
microphone device, the signal level difference between the front sound source is 6 dB. It expands
to a certain extent, and it turns out that the balance of the stereo characteristic with respect to a
left-right sound source also collapses large. Also, by referring to the lower part of FIGS. 14 to 16,
the signal level difference between the front sound source and the front sound source is further
enlarged compared to the case where the arrangement interval is D, and the balance of stereo
characteristics for left and right sound sources is further enlarged. I understand that.
[0017]
By the way, for example, as the miniaturization of portable recording devices such as video
cameras further advances, it becomes difficult to secure the arrangement interval of the
nondirectional ECM described above, and the arrangement interval of the nondirectional ECM
cuts 10 mm. It has narrowed down to As can be understood from the description given with
reference to FIGS. 11 to 16, when the nondirectional ECMs used have different sensitivities, as
the arrangement intervals of the nondirectional ECM become narrower, the output signals after
stereo matrix processing are processed. The degree of influence is increased. In fact, even if the
sensitivity difference of nondirectional ECM is small, if the nondirectional ECM is arranged at an
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interval of less than 10 mm, the signal level difference of as much as 5 to 6 dB to the output
signal after stereo matrix processing against the front sound source To expand.
[0018]
From the above, in order to obtain good stereo characteristics by performing stereo matrix
processing, it is required to suppress the sensitivity variation of nondirectional ECM used in the
same unit to zero, but in practice It is difficult to cope with mass production, and even if it can
cope with the problem, there is a problem that the cost becomes extremely high.
[0019]
Therefore, in the production process of a device to which the stereo microphone device is to be
incorporated, a method of correcting and adjusting the sensitivity variation of each
nondirectional ECM can be considered.
However, in this method, it is necessary to perform adjustment by inputting an actual sound, and
in addition, adjustment is performed so that noise is not received other than the signal sound for
adjustment and is not affected by reflections from the surroundings. Environment is required.
One example is an anechoic chamber, but installing equipment (one by one) in an anechoic
chamber to adjust the sensitivity of each omnidirectional ECM has major problems in mass
productivity and cost, and in particular, mass production Consumer devices, there is a problem
that it can not be practically coped with.
[0020]
The present invention has been made in view of such problems, and the object of the present
invention is to provide a low frequency component of an output signal of a nondirectional first
microphone and a nondirectional signal input through a variable gain amplifier. Comparing the
low frequency component of the output signal of the second microphone and controlling the
amplification factor of the variable gain amplifier based on the comparison result so that the
levels of both low frequency components to be compared become the same; It is possible to
mutually subtract the output signal of one microphone and the output signal of the second
microphone input through the variable gain amplifier, and obtain directivity of the microphone
arrangement direction based on the signal after subtraction processing By doing this, the
sensitivity variation of both microphones can be automatically corrected to match the sensitivity
of the first microphone on normal use of the device, and good stereo characteristics can be
obtained. And to provide a stereo microphone apparatus can be obtained.
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[0021]
Another object of the present invention is to determine whether the low frequency component of
the output signal of the first microphone is at a level within a predetermined range and to
determine that the signal level is within the predetermined range. A stereo microphone device
capable of automatically correcting sensitivity variations of both microphones to match the
sensitivity of the first microphone only when the sound collection level is appropriate, by
configuring the amplification factor of the amplifier to be controllable. To provide.
[0022]
Still another object of the present invention is to subtract the output signal of the second
microphone input through the variable gain amplifier from the output signal of the first
microphone, and the low frequency component of the signal resulting from the subtraction is
below a predetermined level If it is determined that the level is lower than a predetermined level,
the amplification factor of the variable gain amplifier can be controlled to limit correction of
sensitivity variations of both microphones due to wind noise. An object of the present invention
is to provide a stereo microphone device capable of preventing amplification of noise.
[0023]
A stereo microphone device according to the present invention comprises: two nondirectional
microphones spaced apart; a first subtractor for subtracting an output signal of the second
microphone from an output signal of the first microphone; and an output of the second
microphone A stereo microphone device comprising: a second subtractor for subtracting an
output signal of the first microphone from a signal; and obtaining directivity of the arrangement
direction of the microphone based on output signals of the first subtractor and the second
subtractor. A first low pass filter to which an output signal of the first microphone is input, a
variable gain amplifier to which an output signal of the second microphone is input, and a second
low pass filter to which an output signal of the variable gain amplifier is input Comparing means
for comparing the output signals of the first low pass filter and the second low pass filter, and the
comparison result of the comparing means And control means for controlling the amplification
factor of the variable gain amplifier such that the levels of the output signals of the first low pass
filter and the second low pass filter to be compared by the comparison means are the same. A
first subtractor subtracts the output signal of the variable gain amplifier from the output signal of
the first microphone, and the second subtractor derives the output signal of the first microphone
from the output signal of the variable gain amplifier. It is characterized in that the signal is to be
subtracted.
10-05-2019
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[0024]
The stereo microphone device according to the present invention further includes a
determination unit that determines whether the output signal of the first low pass filter is at a
level within a predetermined range, and the determination unit is at a level within the
predetermined range. When judged, the control means is characterized in that the amplification
factor of the variable gain amplifier is controlled.
[0025]
In the stereo microphone device according to the present invention, a third subtractor that
subtracts the output signal of the variable gain amplifier from the output signal of the first
microphone, and a third low pass filter that receives the output signal of the third subtractor And
the determining means is configured to determine whether the output signal of the third lowpass filter is less than or equal to a predetermined level, and the determining means determines
that the signal is less than or equal to the predetermined level. Preferably, the control means is
configured to control an amplification factor of the variable gain amplifier.
[0026]
In the stereo microphone device according to the present invention, the output signal of the first
omnidirectional microphone is input to the first low-pass filter, the output signal of the second
omnidirectional microphone is input to the variable gain amplifier, and The output signal of the
variable gain amplifier is input to the second low pass filter, and the comparison means
compares the output signals of the first low pass filter and the second low pass filter.
[0027]
The output signals of the first low-pass filter and the second low-pass filter to be compared by
the comparison means are low-frequency components of the output signals of the first and
second microphones in which the middle and high frequency components are blocked. is there.
Thus, the reason why the signal to be compared by the comparison means is a signal obtained by
extracting only the low frequency component from the output signal of the nondirectional
microphone via the low pass filter is as follows.
That is, when the sensitivities of both microphones are equal, the output signals of the two
nondirectional microphones arranged at a distance from each other have a level difference with
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respect to the incident sound from the left direction and the right direction in the middle and
high frequency components. Although the phase difference occurs, the lower the frequency
component, the less the level difference and the phase difference with respect to the incident
sound from the left and right directions, and the substantially negligible level, and hence the
incident from either direction It is because it can be considered that it is the same signal also to a
sound.
In other words, by focusing on the low frequency components of the output signals from both
microphones, when the low frequency components are equal, the sensitivities of both
microphones are equal, and a level difference occurs in both low frequency components. If so, it
can be seen that the sensitivities of both microphones are different.
That is, since the signal to be compared by the comparison means is a low frequency component
of the output signal of both microphones, the comparison means compares the sensitivity
differences unique to both microphones independently of the incident direction of the sound
wave. Become.
[0028]
Based on the comparison result of the comparison means as described above, the control means
determines the level of the output signal of the first low pass filter and the second low pass filter
(low frequency components of the output signals of both microphones) compared by the
comparison means. The amplification factor of the variable gain amplifier is controlled to be the
same.
The first subtractor subtracts the output signal of the variable gain amplifier whose amplification
factor is controlled (the output signal of the second microphone input through the variable gain
amplifier) from the output signal of the first microphone, and the second subtractor The output
signal of the first microphone is subtracted from the output signal of the variable gain amplifier
(the output signal of the second microphone input through the variable gain amplifier) whose
amplification factor is controlled.
Then, based on the output signals of the first subtractor and the second subtractor, directivity of
the microphone arrangement direction is obtained.
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[0029]
This corrects the sensitivity variation of both microphones to automatically match the sensitivity
of the first microphone in normal use of the device without the need for a special tuning
environment (e.g. an anechoic chamber) or adjustment means. Good stereo characteristics are
obtained.
In addition, since the sensitivity variation of both microphones is automatically corrected to
match the sensitivity of the first microphone during normal use of the device, there is no need to
perform prior pairing with the microphones used, and the production efficiency of the device is
improved. , The cost of pairing is reduced.
[0030]
In the stereo microphone device according to the present invention, the determination means
determines whether or not the output signal of the first low pass filter (the low frequency
component of the output signal of the first microphone) is within a predetermined range. When
the determination means determines that the level is within the predetermined range, the control
means controls the amplification factor of the variable gain amplifier.
[0031]
This eliminates the case where sound small enough to make the sensitivity difference between
both microphones indistinguishable or sound large enough to cause distortion to be excluded,
and automatically be used for both microphones only when the sound collection level is
appropriate. The sensitivity variation is corrected to match the sensitivity of the first microphone.
[0032]
In the stereo microphone device according to the present invention, the third subtractor
subtracts the output signal of the variable gain amplifier (the output signal of the second
microphone input through the variable gain amplifier) from the output signal of the first
microphone The output signal of the third subtractor is input to the third low pass filter.
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The determination means determines whether or not the output signal of the third low pass filter
(the low frequency component of the signal of the subtraction result of the third subtractor) is
below a predetermined level, and the determination means is below the predetermined level
When determined, the control means controls the amplification factor of the variable gain
amplifier.
[0033]
In the above, the signal determined by the determination means is subtracted from the output
signal of the first microphone from the output signal of the second microphone input through the
variable gain amplifier, and the signal resulting from the subtraction is further processed by the
low pass through the low pass filter. The reason why only the frequency component is extracted
is as follows.
That is, the two nondirectional microphones arranged apart from each other not only output the
sound signal, but also output the wind noise generated as a result of the vibrating film being
shaken when the wind hits, as a signal. Wind noise does not depend on the spacing between
microphones and is output as an uncorrelated signal, so unlike the sound signal, a large level
difference occurs between the output signals of both microphones. This is because frequency
components are concentrated in the low frequency range.
[0034]
As described above, since the characteristic output characteristics of the omnidirectional
microphone against wind noise are set as the threshold value for determining whether to control
the amplification factor of the variable gain amplifier, the sensitivity variation of both
microphones due to wind noise Correction is limited and wind noise amplification is prevented.
[0035]
According to the present invention, the low frequency component of the output signal of the
nondirectional first microphone is compared with the low frequency component of the output
signal of the nondirectional second microphone input through the variable gain amplifier, Based
on the comparison result, the amplification factor of the variable gain amplifier is controlled so
that the levels of both low frequency components to be compared become the same, and the
output signal of the first microphone and the second input through the variable gain amplifier
The output signals of the microphones are subtracted from each other, and the directivity of the
arrangement direction of the microphones is obtained based on the signals after the subtraction
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processing.
[0036]
This corrects the sensitivity variation of both microphones to automatically match the sensitivity
of the first microphone in normal use of the device without the need for a special tuning
environment (e.g. an anechoic chamber) or adjustment means. It is possible to obtain good stereo
characteristics.
In addition, since the sensitivity variation of both microphones can be automatically corrected to
coincide with the sensitivity of the first microphone during normal use of the device, it is possible
to eliminate the need for prior pairing of the microphones used. Production efficiency can be
improved, and the cost associated with pairing can be reduced.
[0037]
Moreover, since the sensitivity variation of both microphones can be automatically corrected to
coincide with the sensitivity of the first microphone in normal use of the device, even when the
stereo microphone device of the present invention is incorporated into another device, It is not
necessary to adjust the sensitivity of both microphones in the anechoic chamber as described
above in the production process of the device, and there is no problem in mass productivity and
cost of the device.
Therefore, the stereo microphone device of the present invention can be mounted on a massproduced consumer device, a portable consumer device (for example, a video camera) which is
also required to be miniaturized, and the present invention The versatility of the stereo
microphone device can be enhanced.
[0038]
Further, according to the present invention, the amplification factor of the variable gain amplifier
is controlled when it is determined that the low frequency component of the output signal of the
first microphone is at a level within the predetermined range. This eliminates the case where
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sound small enough to make the sensitivity difference between both microphones
indistinguishable or sound large enough to cause distortion to be excluded, and automatically be
used for both microphones only when the sound collection level is appropriate. The sensitivity
variation can be corrected to match the sensitivity of the first microphone.
[0039]
Furthermore, according to the present invention, the output signal of the second microphone
input through the variable gain amplifier is subtracted from the output signal of the first
microphone, and the low frequency component of the signal resulting from the subtraction is less
than a predetermined level If determined, the amplification factor of the variable gain amplifier is
controlled. Thereby, the correction of the sensitivity variation of both microphones due to the
wind noise can be limited, and the amplification of the wind noise can be prevented.
[0040]
Hereinafter, the present invention will be described in detail based on the drawings showing the
embodiments thereof. FIG. 1 is a block diagram showing the configuration of a stereo
microphone device of the present invention which performs stereo matrix processing. In the
figure, 1 is a nondirectional first ECM, 2 is a nondirectional second ECM, and the first ECM 1 and
the second ECM 2 are disposed at the left and right with an interval D.
[0041]
An output signal of the first ECM 1 obtained by detecting the sound wave by the first ECM 1 is
input to the amplifier 3. The amplifier 3 has a constant amplification factor, and amplifies the
output signal of the first ECM 1 by a predetermined factor. The output signal of the amplifier 3 is
input to a first low pass filter 5 (hereinafter referred to as the first LPF 5).
[0042]
The first LPF 5 has a cutoff frequency of 500 Hz and extracts a low frequency component of 500
Hz or less from the output signal of the first ECM 1 amplified by the amplifier 3 by a
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predetermined ratio. The output signal of the first LPF 5, that is, the low frequency component of
the output signal of the first ECM 1 extracted by the first LPF 5 is input to the detector 6. The
detector 6 converts the low frequency component into a DC voltage component according to the
level of the low frequency component input from the first LPF 5. The DC voltage component
converted by the detector 6 is input to the comparator 7 and the level determination unit 8. In
addition, by providing a desired time constant in the detector 6, it is possible to obtain an effect
that the control of the amplification factor of the variable gain amplifier 4 to be described later
does not respond sensitively to, for example, sudden single tone generation.
[0043]
An output signal of the second ECM 2 obtained by detecting the sound wave by the second ECM
2 is input to the variable gain amplifier 4. The variable gain amplifier 4 is, for example, a voltage
control type variable gain amplifier, has a variable amplification factor, and amplifies the output
signal of the second ECM 2 by an arbitrary factor based on the control of the comparator output
holding unit 12 described later. An output signal of the variable gain amplifier 4 is input to a
second low pass filter 9 (hereinafter referred to as a second LPF 9).
[0044]
Similar to the first LPF 5, the second LPF 9 extracts a low frequency component of 500 Hz or less
from the output signal of the second ECM 2 which has a cutoff frequency of 500 Hz and is
amplified by the variable gain amplifier 4 at an arbitrary magnification. The output signal of the
second LPF 9, that is, the low frequency component of the output signal of the second ECM 2
extracted by the second LPF 9 is input to the detector 10. The detector 10 converts the low
frequency component into a DC voltage component in accordance with the level of the low
frequency component input from the second LPF 9. The DC voltage component converted by the
detector 10 is input to the comparator 7. By providing the detector 10 with a desired time
constant, it is possible to obtain an effect that the control of the amplification factor of the
variable gain amplifier 4 to be described later does not respond sensitively to, for example,
sudden single tone generation.
[0045]
The comparator 7 is a comparator using an operational amplifier, compares whether the output
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signal of the detector 10 is equal to or more than the output signal of the detector 6 as a
reference signal, and as a result of comparison, When it is above the output signal, it outputs a
signal of positive voltage value, and when it is less than the output signal of the detector 6, it
outputs a signal of negative voltage value. The signal of positive or negative voltage value output
from the comparator 7 is input to the delay unit 11. The delay unit 11 delays the signal input
from the comparator 7 by a preset time and outputs the delayed signal to the comparator output
holding unit 12.
[0046]
The output signals of the amplifier 3 and the variable gain amplifier 4 are also input to the third
subtractor 13. The third subtractor 13 subtracts the output signal of the variable gain amplifier 4
from the output signal of the amplifier 3 and outputs a signal of the subtraction result. The
output signal of the third subtractor 13 is input to a third low pass filter 14 (hereinafter referred
to as the third LPF 14). The third LPF 14 has a cutoff frequency of 100 Hz and extracts low
frequency components of 100 Hz or less from the output signal of the third subtractor 13. The
output signal of the third LPF 14, that is, the low frequency component of the output signal of
the third subtractor 13 extracted by the third LPF 14 is input to the detector 15. The detector 15
converts the low frequency component into a DC voltage component according to the level of the
low frequency component input from the third LPF 14. The DC voltage component converted by
the detector 15 is input to the level determination unit 8.
[0047]
The level determination unit 8 determines whether the output signal of the detector 6 is at a level
within a predetermined range set in advance, and determines that the output signal of the
detector 6 is not at a level within the predetermined range. A signal for notifying that the level is
out of the predetermined range is output to the comparator output holding unit 12
(interruption). The level determination unit 8 also determines whether the output signal of the
detector 15 is less than or equal to a predetermined level set in advance, and determines that the
output signal of the detector 15 is not greater than the predetermined level. The comparator
output holding unit 12 outputs a signal for notifying that it exceeds the level (interrupt).
[0048]
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The comparator output holding unit 12 outputs the signal of the positive or negative voltage
value of the comparator 7 input through the delay unit 11 to the variable gain amplifier 4 as it is.
However, when a signal is input from the level determination unit 8 (when there is an interrupt),
the comparator output holding unit 12 outputs a signal of positive or negative voltage value of
the comparator 7 to the variable gain amplifier 4 When the signal of positive or negative voltage
value of the comparator 7 at the time when the signal is inputted from the level judgment unit 8
is held and the signal from the level judgment unit 8 is not inputted, the held comparison The
positive or negative voltage value of the amplifier 7 is output to the variable gain amplifier 4.
[0049]
The variable gain amplifier 4 decreases the amplification factor so as to reduce the output signal
of the second ECM 2 when the signal of the positive voltage value of the comparator 7 is input
from the comparator output holding unit 12. If a negative voltage signal is input, the
amplification factor is increased to increase the output signal of the second ECM 2. Thus, the
comparator output holding unit 12 operates as control means for controlling the amplification
factor of the variable gain amplifier 4. Thus, the output signal of the second ECM 2 is controlled
to be at the same level as the output signal of the first ECM 1.
[0050]
The output signals of the amplifier 3 and the variable gain amplifier 4 are also input to the stereo
matrix processing unit 20. In the stereo matrix processing unit 20, the output signal of the
amplifier 3 is input as it is to the first subtractor 21 as a signal 3s, and is also input to the delay
unit 22. The delay unit 22 delays the output signal of the amplifier 3 by time t and outputs the
delayed signal to the attenuator 23. The time t is set substantially equal to the time required for
the sound wave to travel by the distance of D (D is the arrangement interval of the first ECM 1
and the second ECM 2). The output signal (signal 23s) of the attenuator 23 is input to the second
subtractor 24.
[0051]
Similarly, in the stereo matrix processing unit 20, the output signal of the variable gain amplifier
4 is input as it is to the second subtractor 24 as the signal 4s, and is also input to the delay unit
25. The delay unit 25 delays the output signal of the variable gain amplifier 4 by time t and
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outputs it to the attenuator 26. The output signal (signal 26s) of the attenuator 26 is input to the
first subtractor 21.
[0052]
The first subtractor 21 subtracts the output signal (signal 26 s) of the attenuator 26 from the
output signal (signal 3 s) of the amplifier 3, and outputs the signal of the subtraction result to the
equalizer 27. The second subtractor 24 subtracts the output signal (signal 23 s) of the subtracter
23 from the output signal (signal 4 s) of the variable gain amplifier 4, and outputs the signal of
the subtraction result to the equalizer 28. The equalizers 27 and 28 correct and flatten changes
in frequency characteristics caused by stereo matrix processing. Then, the output signal (signal
27s) of the equalizer 27 is obtained as an L channel signal, and the output signal (signal 28s) of
the equalizer 28 is obtained as an R channel signal.
[0053]
The operation relating to the control of the amplification factor of the variable gain amplifier 4 in
the stereo microphone device configured as described above will be described below with
reference to the flowcharts of FIG. 2 and FIG.
[0054]
First, the comparator 7 compares the output signals of the detectors 6 and 10 (S1), and outputs
the signal of the comparison result to the comparator output holding unit 12 through the delay
unit 11.
Specifically, the signal of the comparison result is a signal of a positive voltage value when the
output signal of the detector 10 is greater than or equal to the output signal of the detector 6
and less than the output signal of the detector 6 Is a signal of negative voltage value. Next, the
comparator output holding unit 12 outputs the signal of the comparison result of the comparator
7 to the variable gain amplifier 4 (S2).
[0055]
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The variable gain amplifier 4 changes the amplification factor based on the signal of the
comparison result of the comparator 7 input from the comparator output holding unit 12 (S3),
and returns. Specifically, when a signal of a signal of a positive voltage value is input, the variable
gain amplifier 4 decreases the amplification factor to reduce the output signal of the second ECM
2 that is input, and a signal of a negative voltage value Is input, the amplification factor is
increased to increase the output signal of the input second ECM 2.
[0056]
Parallel to the operation of amplification factor control of variable gain amplifier 4 above, level
determination unit 8 determines whether the output signal of detector 6 is at a level within a
predetermined range, and the output signal of detector 15 is predetermined. If it is determined
that the output signal of the detector 6 is not within the predetermined range and / or the output
signal of the detector 15 is not below the predetermined level, Output and interrupt the
comparator output holding unit 12.
[0057]
When the level judging section 8 receives an interrupt, the comparator output holding section 12
holds the signal of the comparison result of the comparator 7 inputted at the time of the
interrupt without outputting the signal to the variable gain amplifier 4 ( S4).
Then, the variable gain amplifier 4 does not receive the signal of the comparison result of the
comparator 7 from the comparator output holding unit 12 and therefore fixes the amplification
factor when the signal is not input (S5) and returns.
[0058]
By the operation of the amplification factor control of the variable gain amplifier 4 as described
above, the stereo microphone device of the present invention automatically detects the sensitivity
of the second ECM 2 on the normal use of the device even if there is a difference in sensitivity
between the first ECM 1 and the second ECM 2 Correction to match the sensitivity of the first
ECM 1 and replacing the signal 41 s with the signal 4 s, it is possible to obtain good stereo
characteristics as described using FIG. 5 to FIG. Even when the arrangement interval of the
second ECM 2 is changed from D to D / 2, the signal 41 s is similarly replaced with the signal 4 s
to obtain good stereo characteristics as described with reference to FIGS. 8 to 10. Can.
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[0059]
Further, in the stereo microphone device of the present invention, when the level determination
unit 8 determines whether the output signal of the detector 6 is within the predetermined range,
it is determined that the level is not within the predetermined range. Since the signal is output to
interrupt the comparator output holding unit 12 and the amplification factor of the variable gain
amplifier 4 is fixed, the sound or distortion is so small that the sensitivity difference between the
microphones of the first ECM 1 and the second ECM 2 is unclear. If the sound that is loud
enough to occur is being collected, that is, the output signal of the first LPF 5 is out of the
coverage of the detector 6, the sensitivity of the second ECM 2 is adjusted only when the sound
collection level is appropriate. In normal use, the correction can be automatically made to
coincide with the sensitivity of the first ECM 1.
[0060]
Further, in the stereo microphone device according to the present invention, the level
determination unit 8 determines whether the output signal of the detector 15 is less than or
equal to a predetermined level, and determines that the signal is not less than the predetermined
level. Since output is performed and interrupts the comparator output holding unit 12 and the
amplification factor of the variable gain amplifier 4 is fixed, correction of sensitivity variations of
the first ECM 1 and the second ECM 2 by wind noise is limited, and wind noise amplification is
performed. It can be prevented.
[0061]
In the embodiment described above, the stereo microphone device of the present invention is
configured to perform stereo matrix processing using two nondirectional microphones, but
stereo using the three or more nondirectional microphones The present invention can also be
applied to matrix processing.
[0062]
It is a block diagram which shows the structure of the stereo microphone apparatus of this
invention which performs a stereo matrix process.
It is a flowchart which shows operation | movement which concerns on control of the
amplification factor of the variable gain amplifier in the stereo microphone apparatus of this
invention.
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It is a flowchart which shows operation | movement which concerns on control of the
amplification factor of the variable gain amplifier in the stereo microphone apparatus of this
invention.
It is a block diagram which shows the structure of the conventional stereo microphone apparatus
which performs a stereo matrix process.
It is explanatory drawing explaining the stereo matrix process in the conventional stereo
microphone apparatus in case sensitivity is equal to both the 1st ECM and 2nd ECM arrange |
positioned by the space | interval D, and it is a left sound source. It is explanatory drawing
explaining the stereo matrix process in the conventional stereo microphone apparatus in case
sensitivity is both equal with respect to the 1st ECM and 2nd ECM arrange | positioned by the
space | interval D, and it is a front sound source. It is explanatory drawing explaining the stereo
matrix process in the conventional stereo microphone apparatus in case sensitivity is equal to
both the 1st ECM and 2nd ECM arrange | positioned by the space | interval D, and it is a right
sound source. It is explanatory drawing explaining the stereo matrix process in the conventional
stereo microphone apparatus in case sensitivity is equal to both the 1st ECM and 2nd ECM
arrange | positioned by space | interval D / 2, and it is a left sound source. It is explanatory
drawing explaining the stereo matrix process in the conventional stereo microphone apparatus in
case sensitivity is equal to both the 1st ECM and 2nd ECM arrange | positioned by space |
interval D / 2, and it is a front sound source. It is explanatory drawing explaining the stereo
matrix process in the conventional stereo microphone apparatus in case sensitivity is both equal
and is a right sound source with respect to 1st ECM and 2nd ECM arrange | positioned by space |
interval D / 2. It is explanatory drawing explaining the stereo matrix process in the conventional
stereo microphone apparatus in case the sensitivity of 1st ECM is 2 dB higher than 2nd ECM, and
it is a left sound source with respect to 1st ECM and 2nd ECM arrange | positioned by the space |
interval D. It is explanatory drawing explaining the stereo matrix process in the conventional
stereo microphone apparatus in case the sensitivity of 1st ECM is 2 dB higher than 2nd ECM, and
it is a front sound source with respect to 1st ECM and 2nd ECM arrange | positioned by the
space | interval D. It is explanatory drawing explaining the stereo matrix process in the
conventional stereo microphone apparatus in case the sensitivity of 1st ECM is 2 dB higher than
2nd ECM, and it is a right sound source with respect to 1st ECM and 2nd ECM arrange |
positioned by the space | interval D. An explanatory view for explaining stereo matrix processing
in a conventional stereo microphone device in the case where the sensitivity of the first ECM is 2
dB higher than that of the second ECM and is the left sound source with respect to the first ECM
and the second ECM arranged at the interval D / 2. is there. An explanatory view for explaining
stereo matrix processing in a conventional stereo microphone device in the case where the
sensitivity of the first ECM is 2 dB higher than that of the second ECM and is a front sound
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source with respect to the first ECM and the second ECM arranged at an interval D / 2. is there.
An explanatory view for explaining stereo matrix processing in a conventional stereo microphone
device in the case where the sensitivity of the first ECM is 2 dB higher than that of the second
ECM and is the right sound source with respect to the first ECM and the second ECM arranged at
an interval D / 2. is there.
Explanation of sign
[0063]
1 first ECM (nondirectional) 2 second ECM (nondirectional) 3 amplifier 4 variable gain amplifier
5 first LPF (first low pass filter) 6, 10, 15 detector 7 comparator 8 level determination unit 9
second LPF (second 2 Low-pass filter) 11, 22 and 25 Delay unit 12 Comparator output holding
unit (control means) 13 Third subtractor 14 Third LPF (Third low pass filter) 20 Stereo matrix
processing unit 21 First subtractor 23, 26 Attenuator 24 second subtractor 27, 28 equalizer
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