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JPH03127598

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DESCRIPTION JPH03127598
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
sound collection device that can be used for hands-free telephones and videophones and can
produce clear sound even under high noise. 2. Description of the Related Art In recent years,
hands-free communication devices such as car phones have become widespread. In these handsfree call type communication devices, a sound collection device having a noise removal function
is used so that clear calls can be made even under high noise. Hereinafter, with reference to the
drawings, an example of the above-described conventional sound collection device for hands-free
speech will be described. FIG. 8 is a block diagram of a conventional sound collection device for
hands-free communication. In FIG. 8, 81 is a directional microphone installed with the front axis
directed to the speaker direction, and 82 is a high pass filter capable of varying the cutoff
frequency between 300 and 500. FIG. 9 shows the spectrum of the output of the microphone 8I
of FIG. 8, 9 is a long time average spectrum of ambient noise collected in a normal use
environment, 92 is a long time average spectrum of voice collected in a sound insulation room It
is. In the hands-free communication, the distance between the speaker and the microphone
increases, so the sound pressure level of the speaker voice incident on the microphone decreases.
Therefore, as shown in FIG. 9, the level difference between the noise spectrum 91 and the speech
spectrum 92 becomes small. The lower the frequency, the harder the sound insulation and sound
absorption. Therefore, the noise component is concentrated in the low range. In addition, the
directivity of the microphone is often deteriorated as the frequency is lower, and noise from the
rear and the side is also collected. Due to the above reasons, the noise spectrum 91 has a higher
level of awareness as it becomes lower. As a result, the S / N becomes worse as the low frequency
O becomes lower, and the clarity of the output of the microphone 91 becomes extremely poor.
Therefore, in the conventional example of FIG. 9, low-pass frequency components with poor S / N
are removed by the high-pass filter 82 to ensure the clarity. Generally, voice communication G is
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said to be required to transmit a band of at least 300) & 3 kHz. When the cutoff frequency of the
high pass filter 82 is 300 Hz or less, noise can be removed without deteriorating the sound
quality. If the cutoff frequency is increased to 300 Hz or more, the sound quality is noticeable.
Under high noise, it is often the case that the cutoff frequency is set to about 500 Hz because
noise is better if noise removal is performed even if the sound quality is sacrificed to some
extent. SUMMARY OF THE INVENTION However, the above-described configuration has a
problem that the sound quality is deteriorated because the low frequency component of the
sound is dropped.
SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a
sound collection device capable of collecting sound with high sound quality and excellent
intelligibility even under high noise. Means for Solving the Problem In order to solve the above
problem, the sound pickup apparatus of the present invention is compared with the main
microphone installed at a position relatively far from the speaker in front of the speaker and the
side and back of the speaker. An auxiliary microphone placed near the target speaker, a high
pass filter for extracting high frequency components of the output of the main microphone, a low
pass filter for extracting low frequency components of the output of the auxiliary microphone, an
output of the high pass filter and the low pass It comprises the adder which adds with the output
of a filter and it outputs outside. In order to enable sound collection with excellent sound quality
with well-balanced low-frequency component and high-frequency component levels, the
sensitivity of the secondary microphone so that the output microphone of the primary
microphone and the secondary microphone output level are equal Should be equipped with a
sensitivity adjustment unit that automatically adjusts If a noise removal unit is provided between
the low pass filter and the adder, a better noise removal effect can be obtained. The noise
removal unit may be configured of a secondary microphone level detector, an attenuator, and an
attenuation controller. Also, noise is caused by a band division filter, a knowledge detector
provided for each divided band, an attenuator provided for each band, a low pass adder for
adding the output of this attenuator, and an attenuation amount controller You may comprise a
removal part. The secondary microphone is preferably attached to the upper part of the backrest
of the speaker's seat, the wall behind the speaker at the height of the speaker's mouth, or the
ceiling above the head of the speaker. The present invention is that the sound of normal handsfree speech picked up from the front of the speaker with a microphone 50 cm to 1 m away from
the speaker does not provide satisfactory S / for low frequencies due to noise. If the side of the
speaker or in the back, the microphone can be installed in close proximity to the speaker to
increase the sound collection level, but even if the sound is collected from the side or the speaker
of the speaker, the high frequency characteristic is deteriorated. The low range is focused on the
fact that sound can be collected sufficiently. According to the present invention, the low
frequency component is extracted from the sub microphone with high sound collection level, the
high frequency component is extracted from the main microphone with good frequency
characteristics, and the two components are output as the base. We have realized a sound
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collection device that is excellent for both frequency and frequency. Also, by adding an automatic
sensitivity adjustment unit to the secondary microphone and adding a function to automatically
adjust the sound collection level, even if the distance between the speaker and the secondary
microphone changes, The sound collection level of the main microphone can be matched.
As a result, even if the posture of the speaker changes, it is possible to realize a sound collection
device that can output natural and clear speech with good low- and high-range rehearsal.
Furthermore, noise removal is performed only on the low frequency components, and high
frequency components are output as they are without performing noise removal processing, so
that noise is effectively removed without degrading the clarity and naturalness. ing. By attaching
the secondary microphone to the upper part of the backrest of the speaker's seat, the wall behind
the speaker at the height of the speaker's mouth, or the ceiling above the speaker's head, the
secondary microphone can be unaware of the speaker It is possible to bring the speaker close to
the speaker. EXAMPLE A sound pickup apparatus according to an embodiment of the present
invention will be described with reference to the drawings. FIG. 1 is a block diagram of a sound
pickup apparatus according to an embodiment of the present invention. In FIG. 1, 1) is a main
microphone, 12 is a secondary microphone, 13 is a high pass filter, 14 is a sensitivity adjuster,
15 is a low pass filter, and 16 is an adder. The operation of the sound collection device
configured as described above will be described below. The voice of the speaker is picked up by
both the main microphone 1) and the sub microphone 12. The output of the main microphone 1)
is extracted by the high pass filter 13 and only the high frequency component is input to the
adder 16. The output of the secondary microphone 12 is adjusted in level by the sensitivity
adjuster 14, and the low pass component is extracted by the low pass filter 15 and is led to the
adder 16. The high frequency component and the low frequency component are added by the
addition 2S16 and become an external output. The voice collected by the main microphone 1)
placed in front of the speaker separately from the speaker is not good for low-frequency S / use
as described in the conventional example. The voice collected by the secondary microphone 12
placed close to the speaker behind the speaker has high frequency characteristics disturbed by
the speaker's diffraction, which is not preferable in terms of sound quality, but the incident
speaker voice level becomes high. Excellent for S /. First, the output of the secondary microphone
12 is level-adjusted by the sensitivity adjuster 14 in order to correct the level difference with the
main microphone 1) due to the distance difference. In the secondary microphone output after
level adjustment, high pass components with poor frequency characteristics are removed by the
low pass filter 15, and only low pass components that are excellent in both frequency
characteristics and S / H are extracted. On the other hand, the output of the main microphone 1)
is a high pass filter 13 to remove bad low frequency components for S /, and only high frequency
components excellent in both frequency characteristics and S / are extracted. The high frequency
component from the high pass filter 13 and the low frequency component from the low pass
filter 15 are added by the adder 16, and an output having excellent frequency characteristics and
S / for all frequency bands is output to the outside from the adder 16. Ru.
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As the main microphone, it is general to use a single directional microphone with less mixing of
noise and reflected sound, but if using a super directional microphone such as a linear array
microphone or a line microphone, S / Can be further improved. As described above, according to
this embodiment, the main microphone 1 is provided with the sub microphone 12, the sensitivity
adjuster 14, the low pass filter 15, the high pass filter 13, and the adder 16, and the high
frequency component is By collecting the sound with the main microphone 1) and collecting the
low frequency component with the sub microphone 12, it is possible to make a good hands-free
call for S /. The main microphone 1) is placed away from the speaker, and the secondary
microphone 12 is placed on the side or back of the speaker, so that both microphones do not
interfere with the movement of the speaker and impair the hands-free communication. There is
no. Hereinafter, a second embodiment of the present invention will be described with reference
to the drawings. FIG. 2 is a block diagram of a sound collection device showing a second
embodiment of the present invention. In FIG. 2, reference numeral 20 denotes an automatic
sensitivity adjustment unit, and the other parts are the same as those of the embodiment of FIG.
21 is a main microphone level detector tl, 22 is a secondary microphone level detector, 23 is an
attenuation controller, and 24 is an attenuator. The operation of the sound collection device of
FIG. 2 configured as described above will be described below. The main microphone level
detector 21 detects the sound level collected by the main microphone ll. The sub microphone
level detector 22 detects the sound level collected by the sub microphone 12. The attenuation
control unit 23 compares the output of the main microphone level detector 21 with the output of
the sub microphone level detector 22, and controls the attenuation of the attenuator 24 so that
the human power levels of the high pass filter 13 and the low pass filter 15 become equal. : Fll.
After that, as in the first embodiment, the high frequency component of the main microphone is
taken out by the high pass filter 13, the low frequency component of the sub microphone is
taken out by the low pass filter 15, both are added in the addition 2S16, and the result is output
to the outside. Although the sound collection level hardly changes even if the speaker changes
the posture slightly because the main microphone (1 is placed away from the speaker, the sound
collection response of the sub microphone 12 is largely due to the change in the speaker's
posture Change. Therefore, in the first embodiment shown in FIG. 1, although the sound quality
is changed when the speaker position changes, the sound quality does not change in the
embodiment of FIG. As described above, in the present embodiment, by providing the function of
automatically adjusting the sensitivity of the secondary microphone 12 by providing the
automatic sensitivity adjustment unit 20, it is possible to prevent the change in the sound quality
due to the change in the posture of the speaker.
Even if the posture of the speaker changes, it is always possible to pick up the sound with the
highest sound quality. A third embodiment of the present invention will be described below with
reference to the drawings. FIG. 3 is a block diagram of a sound collection device showing a third
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embodiment of the present invention. In FIG. 3, reference numeral 30 is a noise removing unit,
31 is a level detector, 32 is an attenuation controller, and 33 is an attenuator. The other
components are the same as those of the embodiment of FIG. The operation of the sound
collection device of FIG. 3 configured as described above will be described below. The level
detector 31 detects the output level of the low pass filter 15. The attenuation controller 32
controls the amount of attenuation of the attenuator 32 to be large when the output of the level
detector 31 is small, and controls the amount of attenuation of the attenuator 32 to be small
when the output of the level detector 31 is large. The low frequency component thus controlled
is added to the high frequency component by the adder 16 and output to the outside. Even in the
embodiment of FIG. 1, good S / N sound collection is possible, but the S / N is insufficient for use
under high noise. As mentioned above, the noise is mainly in the low range. Therefore, if only the
low frequency components are subjected to the electrical noise removal processing, sufficient
communication performance can be ensured even under high noise. Since noise is mainly low
frequency, the need for noise removal in high frequency components is low. Furthermore, since
the intelligibility of the call is greatly affected by the transmission characteristics of the high
frequency component, the malfunction of the noise removal in the high frequency component
significantly reduces the intelligibility of the call. For this reason, it is better to apply noise
removal only to the low frequency components as in this embodiment. As described above, in the
present embodiment, if the noise removing unit 30 is provided and noise removal is performed
on the low frequency component, the sound collection with high S / N more than the
embodiment of FIG. Is possible. The fourth embodiment of the present invention will be
described below with reference to the drawings. FIG. 4 is a block diagram of a sound collection
device showing a fourth embodiment of the present invention. In FIG. 4, 40 is a noise removing
unit, 41 is a band division filter, 42 is a level detector, 43 is an attenuation controller, 44 is an
attenuator, 45 is a low-pass adder, and the others are FIG. The configuration is similar to that of
the embodiment of the present invention. The operation of the sound collection device of FIG. 4
configured as described above will be described below. The low band component of the sub
microphone 2 is divided into a plurality of band components by the band division filter 41. The
level detector 42 provided for each band detects the output level for each band. The attenuation
controller 43 determines the attenuation of the attenuator 44 provided for each band from the
output of the level detector 42 provided for each band.
When the output of the level detector 42 is small, the attenuation amount of the attenuator 44 is
large, and when the output of the level detector 42 is large, the attenuation amount of the
attenuator 44 is small. The plurality of band components controlled in this manner are added by
the low band adder 45 and output to the adder 16 as the low band component. The low
frequency component is added to the high frequency component by the adder 16 and output to
the outside. By adopting such a configuration, noise removal can be performed only in a
frequency band in which the S / N is poor, and noise removal in a frequency band in which the S
/ N is good can be prohibited. As a result, it is possible to reduce the loss of the voice component
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and to remove the noise component efficiently, thereby improving the intelligibility of the
speaker. As described above, in the present embodiment, the low-frequency component is divided
into a plurality of bands by providing the noise removing unit 40, and noise removal is
performed in each of the bands, whereby the intelligibility of the embodiment shown in FIG.
Sound collection becomes possible. Next, an embodiment regarding the mounting position of the
microphone will be shown. The fifth embodiment of the present invention will be described
below with reference to the drawings. FIG. 5 is an external view of a hands-free communication
device showing a fifth embodiment of the present invention. FIG. 5 shows an example of a
handsfree video telephone terminal. In FIG. 5, 51 is a main microphone and 52 is a sub
microphone. The main microphone 5 is installed at a position of about 50cn + -1 m in front of the
speaker, and the submicrophone 52 is attached to the top of the backrest of the speaker's seat,
and both the main microphone 51 and the submicrophone 52 It is a microphone arrangement
that is excellent in hands-free communication and does not interfere with posture or hand
movement. Since there is no obstruction between the main microphone 51 and the speaker, the
main microphone 51 can pick up the voice of the speaker with high sound quality. In addition,
since the secondary microphone 52 is close to the speaker's mouth, the voice of the speaker can
be incident at a high level, and the low frequency component can be collected at a high S / N. The
sixth embodiment of the present invention will be described below with reference to the
drawings. FIG. 6 is an external view of a hands-free communication device showing a sixth
embodiment of the present invention. In FIG. 6, 61 is a main microphone and 62 is a sub
microphone. As in the embodiment of FIG. 5, the main microphone 61 is installed at a position of
about 50 cm-1 m in front of the speaker, but the sub-microphone 62 is on the wall behind the
speaker, the height of the speaker's mouth Is attached to In the embodiment of FIG. 5, it is
difficult to use in the home or office because seat processing and wiring work are required, but if
it is a method of mounting on a wall as in this embodiment, the setting becomes extremely easy.
But it will be easy to install.
The seventh embodiment of the present invention will be described below with reference to the
drawings. FIG. 7 is an external view of a hands-free communication device showing a seventh
embodiment of the present invention. In FIG. 7, 71 is a main microphone and 72 is a sub
microphone. The main microphone 71 is shown in FIG. As in the embodiment of FIG. 6, it is
installed at a position of about 50 cm to 1 m in front of the speaker, but the sub microphone is
attached to the ceiling above the speaker's head. If the layout of the microphone shown in FIG. 6
is not possible due to layout restrictions in the room, it is desirable to adopt this embodiment. If
the ceiling is high, it is necessary to use a suspension. It can be used more conveniently by using
a lifting type suspension. Effects of the Invention As described above, according to the present
invention, the main microphone for high-frequency sound component collection located
relatively far from the speaker in front of the speaker, and relatively close to the speaker on the
side or back of the speaker A low frequency audio component secondary microphone installed at
a position, a high pass filter for extracting high frequency components of the output of the main
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microphone, a low pass filter for low frequency components of the output of the secondary
microphone, and an output of the high pass filter By providing an adder for adding the output of
the low-pass filter and outputting the result to the outside, it is possible to collect sound with a
good S / N even in a hands-free call. Further, by providing the automatic sensitivity adjuster, it is
possible to prevent the change in sound quality when the posture of the speaker changes, and by
providing the noise removing unit, it is possible to remove noise without losing intelligibility. S /
N is further improved. Furthermore, by attaching the secondary microphone to the upper part of
the seat back, the secondary microphone can be brought closer to the speaker without
interfering with the movement of the speaker. Also, by mounting the secondary microphone on
the wall behind the speaker and at the height of the speaker's mouth, the secondary microphone
can be easily installed. In addition, attaching the secondary microphone to the ceiling above the
head of the speaker further increases the freedom of attachment.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a block diagram of a sound collection device according to a first embodiment of the
present invention, FIG. 2 is a block diagram of a sound collection device according to a second
embodiment of the present invention, and FIG. 3 is a third embodiment of the present invention.
FIG. 4 is a block diagram of the sound collection device in the embodiment, FIG. 4 is a block
diagram of the sound collection device in the fourth embodiment of the present invention, and
FIG. 5 is a microphone attachment of the sound collection device in the fifth embodiment of the
present invention. Is an external view of the state, FIG. 6 is an external view of the microphone
attachment of the sound collecting apparatus according to the sixth embodiment of the present
invention, and FIG. 7 is a microphone of the sound collecting apparatus according to the seventh
embodiment of the present invention Mounting is an external view of the state, FIG. 8 is a block
diagram of a conventional sound collecting device, and FIG. 9 is a frequency characteristic
diagram of an output signal of the microphone of FIG.
1) · · · · · · · · Main microphone, 12 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · 7 · · · · · · · · · · · · Filter, 16 ..... Adder, 20 ..... Automatic sensitivity
adjustment unit, 30.40 ..... Noise removal unit, 51. , 52.62.72 · · · · · · · · · · secondary microphone.
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