JP2009164747

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DESCRIPTION JP2009164747
The present invention provides a microphone device, a telephone set, an audio signal processing
device, and an audio signal processing method capable of improving the quality of an audio
signal indicating the content of collected sound by reducing the influence of the proximity effect
on the sound collection of a microphone. . A microphone device according to an embodiment of
the present invention includes an audio input unit in a frequency characteristic correction unit
for an influence of a proximity effect generated according to a distance d between a microphone
of the audio input unit and a sound source. By determining the distance d from the signal level of
the audio signal Smic output from 10, it is possible to correct the frequency characteristic to
cancel the influence of the proximity effect. In addition, by using the audio signal Sf whose
frequency characteristic has been corrected, the signal compression unit 40 can perform stable
dynamic range compression, and generates an audio signal Sout with a stable signal level. It can
be output. [Selected figure] Figure 1
Microphone apparatus, telephone, voice signal processing apparatus and voice signal processing
method
[0001]
The present invention relates to a technique for reducing the influence of the proximity effect of
a microphone.
[0002]
In the telephone, various techniques are used to improve the quality of voice during a call.
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As an example, Patent Document 1 discloses a technique for blocking a signal component in a
low frequency band when ambient noise increases. JP, 2005-244541, A
[0003]
By the way, when a microphone picks up a sound from a sound source near the microphone, a
phenomenon occurs in which the level on the low frequency band side of the sound increases.
This phenomenon is called proximity effect. A user of a telephone such as a mobile phone makes
a call by bringing the microphone of the telephone close and away from the mouth of the
telephone and often the distance between the microphone and the mouth as a sound source
changes during the call. As a result, the volume level on the low frequency band side may change,
and the call quality may be degraded.
[0004]
In addition, dynamic range control, auto level control, etc. are used to automatically equalize the
volume level as much as possible in order to efficiently transmit the voice signal of the call and to
make it easy to hear the call. When the volume level in the low frequency band fluctuates, the
control of the volume level in other frequency bands may not be stabilized due to the influence of
the volume level. For example, when the volume level in the low frequency band becomes large
and becomes larger than the volume level in other frequency bands, the entire volume level is
controlled on the basis of the volume level in the low frequency band to clearly hear the voice.
There was a case where the volume level of other required frequency bands did not increase.
[0005]
The present invention has been made in view of the above-mentioned circumstances, and a
microphone device, a telephone apparatus, and the like capable of improving the quality of an
audio signal indicating the content of collected sound by reducing the influence of the proximity
effect on the sound collection of the microphone An object of the present invention is to provide
an audio signal processing device and an audio signal processing method.
[0006]
In order to solve the above-mentioned problems, the present invention provides a microphone
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for picking up sound, a generation means for generating an audio signal indicating the content of
the sound collected by the microphone, and signal levels of the audio signal generated by the
generation means. With respect to the detection means to detect and the audio signal generated
by the generation means, as the signal level detected by the detection means is larger, the output
level on the low frequency band side is relatively compared to other frequency bands. A
microphone device comprising: correction means for performing correction to lower the level;
and compression means for compressing the dynamic range of the audio signal corrected by the
correction means.
[0007]
In another preferable aspect, the correction means attenuates the output level on the low
frequency band side as the signal level detected by the detection means is larger than the sound
signal generated by the generation means. You may
[0008]
In addition, in another preferable aspect, the correction means may increase the attenuation
factor to lower frequencies when performing correction to attenuate the output level on the low
frequency band side.
[0009]
Further, in another preferable aspect, the correction unit is configured to increase the output
level on the high frequency band side as the signal level detected by the detection unit is larger
than the sound signal generated by the generation unit. You may
[0010]
In another preferred embodiment, the correction means corrects the audio signal generated by
the generation means when the signal level detected by the detection means is equal to or higher
than a predetermined level, and is less than the predetermined level. There is no need to make
corrections.
[0011]
Also, in another preferred aspect, the detection means may detect an output level in a specific
frequency band of the audio signal generated by the generation means as the signal level.
[0012]
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In another preferred embodiment, the microphone may further include a housing for integrally
housing the microphone, the generation unit, the detection unit, the correction unit, and the
compression unit.
[0013]
In another preferred embodiment, the image pickup apparatus further comprises an proximity
sensor that detects an object within a predetermined range of the sound collection direction of
the microphone, and the correction unit generates the generation unit when the object is
detected by the proximity sensor. Correction may be performed on the audio signal generated by
the above-described method, and the correction may not be performed if it is not detected.
[0014]
Further, the present invention provides a telephone comprising the microphone device described
above, and a transmission means for transmitting an audio signal whose dynamic range has been
compressed by the compression means to the outside.
[0015]
Further, the present invention is an audio signal processing apparatus connected to a generation
means for generating an audio signal indicating collected sound content collected by a
microphone, and the audio signal is supplied from the generation means, and supplied from the
generation means Detection means for detecting the signal level of the voice signal, and the
output level on the low frequency band side with respect to the voice signal supplied by the
generation means, the larger the signal level detected by the detection means is An audio signal
processing apparatus comprising: correction means for performing correction relatively lower
than a frequency band; and compression means for compressing the dynamic range of the audio
signal corrected by the correction means. .
[0016]
The present invention is also an audio signal processing method used in a microphone device
having a microphone for picking up a voice, the method comprising: generating a voice signal
indicating the content of the sound picked up by the microphone; Detection process for detecting
the signal level of the voice signal, and for the voice signal generated in the generation process,
as the signal level detected in the detection process is larger, the output level on the low
frequency band side is set to another frequency A voice signal processing method comprising: a
correction process for performing correction to be relatively lowered compared to a band; and a
compression process for compressing the dynamic range of the audio signal corrected by the
correction process.
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[0017]
According to the present invention, a microphone device, a telephone set, an audio signal
processing device, and an audio signal processing method capable of improving the quality of an
audio signal indicating the content of collected sound by reducing the influence of the proximity
effect on the sound collection of a microphone. Can be provided.
[0018]
Hereinafter, an embodiment of the present invention will be described.
[0019]
<Embodiment> The microphone apparatus 1 which concerns on embodiment of this invention
correct ¦ amends the frequency characteristic with respect to the audio signal which shows the
sound collection content in a microphone, and outputs it.
The microphone device 1 will be described with reference to FIG.
FIG. 1 is a block diagram showing the configuration of the microphone device 1.
[0020]
The voice input unit 10 has a microphone for picking up external voice, and generates and
outputs a voice signal (hereinafter referred to as a voice signal Smic) indicating the content of the
voice collected by the microphone.
This microphone may be any microphone as long as the phenomenon of the proximity effect
occurs, such as a dynamic coil microphone or an electret condenser microphone.
In the present embodiment, in the MEMS (Micro Electro Mechanical System) technology, it is
assumed that the silicon microphone is formed on a substrate such as a silicon wafer.
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The circuit for generating the audio signal Smic of the audio input unit 10, and the configuration
of the signal level detection unit 20, the frequency characteristic correction unit 30, the signal
compression unit 40, etc. described later are integrally formed on the same silicon wafer. The
chip may be formed on another silicon wafer and may be housed in an integral non-separable
case.
Not only can cost reduction and size reduction be achieved by using an integral housing, but
processing of an audio signal can be completed inside the housing, so design can be easily
performed.
For example, the degree of influence of the proximity effect may differ depending on the
directivity characteristics of the microphone, but by integrating it is not necessary to give
versatility to various microphones, and the setting of the frequency characteristic correction unit
30 described later is optimum. It can be
[0021]
The circuit configuration of the voice input unit 10 will be described with reference to FIG.
The voice input unit 10 has a booster circuit that boosts the power supply voltage VL (3 V in this
embodiment) applied from the outside to a voltage VH (12 V in this embodiment) by a charge
pump or the like.
The power supply voltage VL is also applied to a signal level detection unit 20, a frequency
characteristic correction unit 30, and a signal compression unit 40, which are other
configurations to be described later, and used as respective power supplies.
[0022]
The microphone is a capacitor Cx, and the voltage VH boosted by the booster circuit is applied
through the high resistor RB.
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The capacitor Cx can be picked up by the capacity change due to the sound pressure of the
external sound.
Then, due to the relationship between the change in capacitance and the charge stored in the
capacitor Cx, a voltage change proportional to the sound pressure occurs in the capacitor Cx.
A high resistance body RH to which a voltage of 1.5 V is applied and an impedance conversion
FET (Field effect transistor) having a gate coupled to a coupling capacitor C1 which receives a
voltage change proportional to a sound pressure, and a constant current source CC. An audio
signal corresponding to a voltage change input to the gate is extracted from the source side.
Thus, a high impedance signal related to the capacitor Cx is generated as an audio signal
converted to a low impedance.
Then, this audio signal is output to the signal level detection unit 20 and the frequency
characteristic correction unit 30 as an audio signal Smic via the coupling capacitor C2.
[0023]
Here, the proximity effect of the microphone will be described with reference to FIG. In various
microphones, as the sound source is closer to the microphone, a phenomenon occurs in which
the output level in the low frequency band increases as shown in FIG. The proximity effect is a
phenomenon in which the frequency characteristic on the low frequency band side changes in
this manner depending on the distance between the sound source and the microphone. Here, the
distance d in FIG. 3 indicates the distance between the sound source and the microphone (the
capacitor Cx in the present embodiment). Also, FIG. 3 shows the output level ratio normalized by
the output level in the frequency band where the horizontal axis is frequency and the vertical
axis is high frequency band, and the frequency of the output level ratio changes according to the
distance d It shows the dependency.
[0024]
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As described above, when the frequency distribution of the sound related to the sound
generation from the sound generation source is a distribution that does not depend on the
frequency (frequency distribution c in FIG. 3), the distance d becomes low when the sound
generation source approaches the microphone. The output level of the frequency part increases
and changes to the frequency distribution b and the frequency distribution a. Thus, depending on
the distance d, the frequency distribution of the audio signal Smic indicating the sound collection
content of the microphone changes.
[0025]
Returning to FIG. 1, the description will be continued. The signal level detection unit 20 detects
the signal level of the audio signal Smic output from the audio input unit 10, and outputs level
information indicating the detected signal level to the frequency characteristic correction unit 30.
The signal level detection unit 20 sequentially detects the maximum amplitude of the audio
signal Smic input from the audio input unit 10, and outputs the average value of the maximum
amplitude at a predetermined time before outputting the level information to the frequency
characteristic correction unit 30 as a signal level. As detected. The signal level may be detected
by sequentially detecting the absolute value of the audio signal Smic, determining an envelope
waveform drawn by the instantaneous peak value of the waveform of the absolute value, and
using this as the signal level. The signal level fluctuation may be stabilized by passing the signal,
and this may be used as the signal level. That is, the detection of the signal level can be
performed in various manners, and the manner of the detection of the signal level is an example
thereof.
[0026]
By the way, generally speaking, when making a call using a telephone or the like, the speaker
hardly changes the size of the voice greatly during the call. Therefore, the distance d between the
speaker's mouth, which is the sound source, and the microphone often has a specific relationship
with the size of the speaker's voice, that is, the signal level of the audio signal Smic, and the
signal level of the audio signal Smic is When the distance d is large, the distance d is small, and
when the signal level is small, it can be approximated as having an inverse correlation in which
the distance d becomes large. As described above, the magnitude of the signal level of the audio
signal Smic can estimate the degree of the effect of the proximity effect, that is, the increase in
the output level in the low frequency band.
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[0027]
The frequency characteristic correction unit 30 corrects the frequency characteristic of the audio
signal Smic input from the audio input unit 10, and outputs the result to the signal compression
unit 40 as an audio signal Sf. As shown in FIG. 4, the frequency characteristic correction unit 30
relatively increases the output level on the low frequency band side compared to other frequency
bands as the signal level indicated by the level information output from the signal level detection
unit 20 is larger. Correct the frequency characteristics to be lowered. Here, FIG. 4 shows the
frequency on the horizontal axis and the correction factor of the output level for each frequency
on the vertical axis. Then, when the signal level indicated by the input level information is small,
the frequency characteristic correction unit 30 hardly performs correction, and corrects the
audio signal Smic with the frequency distribution c1 of the correction factor, while the signal
level is larger. The audio signal Smic is corrected with the frequency distribution b1 of the
correction factor, or with the frequency distribution a1 if larger. Although the frequency
distributions a1, b1 and c1 are described in FIG. 4, this does not mean that the correction is
performed in three steps, but a part of the frequency distribution of correction factors according
to various signal levels. It is shown.
[0028]
Here, in the present embodiment, the frequency distribution a1 of the correction factor is preset
so as to become a flat frequency distribution when the audio signal Smic of the frequency
distribution a of the output level ratio in FIG. 3 is corrected with this correction factor. ing. That
is, correction is performed to reproduce the frequency distribution of the sound related to the
sound collected by the microphone by canceling out the influence of the proximity effect on the
frequency characteristics.
[0029]
Then, as described above, since the correspondence between the distance d and the signal level
of the audio signal Smic can be approximated as an inverse correlation, the audio signal Smic
corresponding to the distance d such that the frequency distribution a of the output level in FIG.
The frequency characteristic correction unit 30 can be preset so that the frequency distribution
a1 of the correction factor in FIG. 4 is used when the signal level is obtained. The relationship
between the frequency distribution a of the output level and the frequency distribution a1 of the
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correction factor is the relationship between the frequency distribution b of the output level and
the frequency distribution b1 of the correction factor, the frequency distribution c of the output
level and the frequency distribution of the correction factor The same applies to the relationship
with c1. As described above, since the change in the frequency characteristic due to the effect of
the proximity effect can be reduced by performing the correction to cancel the influence of the
proximity effect, the stable frequency distribution of the sound signal Sf can be obtained, and the
sound signal Sf is related. The voice quality will be good.
[0030]
In FIG. 4, correction is made to attenuate the low frequency band side as the signal level is larger,
and correction is made to increase the attenuation factor as the frequency is lower at this
correction, but relative to other frequency bands. Any correction may be made as long as it is a
correction that lowers the output level on the low frequency band side. For example, the
correction may be to increase the output level of the high frequency band. Further, the correction
to lower the output level on the low frequency band side and the correction to increase the
output level on the high frequency band side may be used in combination. Further, although the
frequency characteristic of the audio signal Sf is set to be a frequency characteristic in which the
influence of the proximity effect is canceled out, the output level of the specific frequency band
may be set to be increased. For example, by increasing the output level of the human voice
frequency band, a clearer speech signal Sf can be obtained, and the quality can be further
improved.
[0031]
Returning to FIG. 1, the description will be continued. The signal compression unit 40 receives
the audio signal Sf output from the frequency characteristic correction unit 30, compresses the
dynamic range of the audio signal Sf, and outputs the compressed signal as an audio signal Sout.
The compression of the dynamic range is performed by amplification at an amplification factor
according to the signal level of the audio signal Sf, and the signal level of the audio signal Sf is
adjusted so as to narrow the dynamic range. For example, as shown in FIG. 5, the flat frequency
distributions a2, b2 and c2 (broken lines) having different output levels of the audio signal Sf are
all adjusted to be the frequency distribution S shown by a solid line. The signal compression unit
40 may be any circuit that performs signal level compression, such as a dynamic range control
circuit, an auto level control circuit, an auto gain control circuit, and a non-clip circuit.
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[0032]
As described above, even if the signal level of the audio signal Smic changes due to the difference
in the distance d between the sound source and the microphone, the frequency characteristic
correction unit 30 performs correction to cancel the influence on the frequency characteristic
due to the proximity effect. By compressing the dynamic range at 40, it is possible to generate
and output an audio signal Sout of a stable signal level.
[0033]
Here, for comparison with the present invention, a problem that arises when the processing in
the signal compression unit 40 is performed on the audio signal Smic without performing the
correction in the frequency characteristic correction unit 30 as in the related art will be
described.
As shown in FIG. 6, when the signal level of the audio signal Smic is small, it can be said that the
distance d between the sound source and the microphone is large, so the frequency distribution
of the output level of the audio signal Sf is affected by the proximity effect. There is no frequency
distribution c3. In this case, similar to the situation in FIG. 5, the output level of the audio signal
Sout is adjusted by the processing in the signal compression unit 40, and the frequency
distribution Sc is obtained.
[0034]
On the other hand, since it can be said that the distance d between the sound source and the
microphone is small when the signal level of the audio signal Smic is large, the frequency
distribution of the output level of the audio signal Sf is a frequency distribution a3 largely
affected by the proximity effect. Become. In this case, since the signal level of the audio signal
Smic is determined based on the high output level in the low frequency band, the output level is
adjusted by the processing in the signal compression unit 40, and the frequency distribution Sa is
obtained.
[0035]
Comparing the frequency distribution Sa and the frequency distribution Sc in which the output
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level of the audio signal Sf is adjusted in this way, the output level of the audio signal Sout
becomes equal in the low frequency band, and the compression of the good dynamic range is
performed. In the high frequency band, the output levels of the two audio signals Sout are
different, and the compression of the good dynamic range is not performed. As described above,
in the high frequency band where the output level of the audio signal Sout is not stable due to
the effect of the proximity effect, the clarity of the audio related to the audio signal is often
influenced, and the quality of the audio signal Sout is deteriorated. It will occur. The above is the
description of the configuration of the microphone device 1.
[0036]
As described above, in the microphone device 1 according to the embodiment of the present
invention, in the frequency characteristic correction unit 30, the voice input is performed on the
influence of the proximity effect generated according to the distance d between the microphone
of the voice input unit 10 and the sound source. By determining the distance d from the signal
level of the audio signal Smic output from the unit 10, the frequency characteristic can be
corrected to cancel the influence of the proximity effect. The audio signal Sf obtained by this
becomes stable frequency distribution, and the quality of the audio concerning the audio signal
Sf becomes good. In addition, by using the audio signal Sf whose frequency characteristic has
been corrected, the signal compression unit 40 can perform stable dynamic range compression,
and generates an audio signal Sout with a stable signal level. It can be output.
[0037]
Although the embodiments of the present invention have been described above, the present
invention can be implemented in various aspects as follows.
[0038]
<Modification 1> In the embodiment described above, the frequency characteristic correction
unit 30 corrects the frequency characteristic according to the signal level indicated by the level
information output from the signal level detection unit 20. If the level is equal to or higher than a
predetermined level, the frequency characteristic may be corrected, and if the level is lower than
the predetermined level, the frequency characteristic may not be corrected.
In this way, when the signal level is small, it can be treated as one in which the proximity effect
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has not occurred.
[0039]
<Modification 2> In the embodiment described above, the signal level detection unit 20 detects
the signal level of the audio signal Smic, but detects the output level in a specific frequency band
of the audio signal Smic as the signal level. May be If this specific frequency band is a frequency
band excluding the low frequency band where the proximity effect appears largely, the increase
in the signal level due to the proximity effect can be excluded, and the relationship between the
signal level and the distance d is directly It can be
[0040]
<Modification 3> In the embodiment described above, regarding the mode of correction of the
frequency characteristic in the frequency characteristic correction unit 30, as the signal level
indicated by the input level information is larger, the output level on the low frequency band side
is Although it was set as a mode which performs amendment of a frequency characteristic made
relatively low compared with a frequency band, it may be made to be able to change setting to
various modes. In this case, as shown in FIG. 7, a storage unit 50 may be provided which stores,
for each mode, a table in which the signal level and the frequency distribution of the correction
rate are associated with each other. . Then, a desired mode is specified by the operation of the
operation unit (not shown), and among the plurality of tables stored in the storage unit 50, a
table corresponding to the specified mode is set in the frequency characteristic correction unit
30. do it.
[0041]
The mode of correction of the frequency characteristic stored in the storage unit 50 cancels the
proximity effect as described in the embodiment, increases the output level of the human voice
frequency band in addition to the cancellation of the proximity effect, In addition, an aspect in
which the effect of canceling the proximity effect can be obtained, such as giving various acoustic
effects in addition to the cancellation of the proximity effect, that is, the larger the signal level
indicated by the input level information is, the output level on the low frequency band side Any
mode may be used as long as the mode is relatively low compared to other frequency bands. In
this case, the frequency characteristic correction unit 30 generates the sound signal Sf obtained
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by performing processing on the sound signal Smic in a mode of correcting the desired
frequency characteristic specified according to the usage condition of the speaker. it can.
[0042]
<Modification 4> In the embodiment described above, the frequency characteristic correction
unit 30 corrects the frequency characteristic as the degree of the effect of the proximity effect
increases as the signal level indicated by the input level information increases. If the speaker is
not within the predetermined range from the microphone device 1, this correction may not be
performed. In this case, as shown in FIG. 8, the proximity sensor 60 for detecting an object within
a predetermined range is provided, and the frequency characteristic correction unit 30 corrects
the frequency characteristic when the object is detected by the proximity sensor 60. If the
frequency characteristic is not detected, the frequency characteristic may not be corrected.
[0043]
The proximity sensor 60 is installed to detect the presence or absence of an object within a
predetermined range in the sound collection direction of the microphone of the voice input unit
10, and this predetermined range is set as a range around a distance at which the influence of
the proximity effect occurs. Be done. As such an approach sensor 60, a known approach sensor
such as one using light, one using a sound wave, or one using a temperature may be used. In this
way, only when there is a speaker near the microphone device 1, it is possible to perform
frequency characteristic correction that cancels out the proximity effect. The degree of influence
of the proximity effect can be determined from the signal level as described in the embodiment.
[0044]
<Modification 5> In the embodiment described above, the frequency characteristic correction
unit 30 corrects the frequency characteristic according to the absolute signal level of the audio
signal Smic indicated by the input level information. The frequency characteristic may be
corrected according to the signal level. In this case, the frequency characteristic correction unit
30 uses the signal level indicated by the level information input at a specific timing, such as the
timing when level information is first input after the power is turned on, and the operation timing
of the operation unit (not shown). Are stored as signal levels (hereinafter referred to as reference
signal levels). The frequency characteristic may be corrected according to the signal level ratio to
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the reference signal level of the signal level indicated by the level information inputted
thereafter. At this time, the frequency characteristic correction unit 30 assumes that the degree
of influence of the proximity effect is larger as the signal level ratio is larger, and the frequency
characteristic correction unit 30 relatively lowers the output level on the low frequency band
compared to other frequency bands. It may be set to perform correction.
[0045]
In this way, when the speaker of the microphone device 1 is changed, the reference voice level is
determined as the reference signal level according to the speaker even if the voice size of the
speaker is different. Because the frequency characteristic correction unit 30 can correct the
frequency characteristic more precisely. When storing the reference signal level, the frequency
characteristic correction unit 30 may store the reference signal level in association with the
speaker. Then, if the speaker is identified by the operation of the operation unit (not shown) and
the frequency characteristic correction unit 30 uses the reference signal level corresponding to
the speaker, the speaker who has stored the reference signal level once When the microphone
device 1 is used again, the reference signal level may not be stored again.
[0046]
<Modification 6> Microphone device 1 in an embodiment mentioned above may be used for
telephones, such as a mobile phone. In this case, as shown in FIG. 9, the telephone set may
include the microphone device 1 and the transmission unit 70 that transmits the audio signal
Sout or the audio signal Sf to another telephone set. Since the distance between the mouth
serving as a sound source and the microphone tends to be short during a call, and the distance
tends to fluctuate during use, the user of the telephone improves the call quality by using this
microphone device 1 Can.
[0047]
<Modification 7> Although the microphone device 1 in the embodiment described above has the
voice input unit 10, it is also possible to use the voice signal processing device having the signal
level detection unit 20, the frequency characteristic correction unit 30, and the signal
compression unit 40. Good. This audio signal processing apparatus can obtain the effects of the
present invention as long as an external audio input unit 10 for supplying an audio signal Smic
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indicating the content of collected sound by the microphone is connected.
[0048]
Here, the relationship between the sound volume of the sound collected by the microphone of
the externally connected voice input unit 10 and the signal level of the supplied voice signal Smic
(hereinafter referred to as input / output characteristics) is the type of microphone, voice signal
It may change depending on the generation method of Smic. In this case, the frequency
characteristic correction unit 30 can correct the signal level indicated by the input level
information according to the input / output characteristic of the externally connected audio input
unit 10, and the frequency characteristic correction unit 30 can respond according to the
corrected signal level. The correction of the frequency characteristic may be performed.
[0049]
At this time, as shown in FIG. 7, the input / output characteristics of the plurality of voice input
units 10 are stored in the storage unit 50, and the frequency characteristic correction unit 30
operates the operation unit (not shown) from the plurality of input / output characteristics. The
input / output characteristics of the specified voice input unit 10 may be read out and used to
correct the signal level. In this way, the audio signal processing device receives the supply of the
audio signal Smic from the audio input unit 10 having various microphones, and according to the
signal level corrected by the input / output characteristic corresponding to the audio input unit
10, It is possible to output an audio signal Sout that has been corrected for frequency
characteristics that cancels out the proximity effect.
[0050]
It is a block diagram showing composition of a microphone device concerning an embodiment. It
is a circuit diagram showing composition of an audio input part concerning an embodiment. It is
explanatory drawing about the proximity ¦ contact effect. It is explanatory drawing which shows
frequency distribution of the correction factor in the frequency characteristic correction ¦
amendment part which concerns on embodiment. It is explanatory drawing about dynamic range
compression of the audio ¦ voice signal of this invention in the signal compression part which
concerns on embodiment. It is explanatory drawing about the dynamic range compression of the
conventional audio signal in the signal compression part which concerns on embodiment. It is a
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block diagram which shows the structure of the microphone apparatus which concerns on the
modifications 3 and 7. FIG. FIG. 13 is a block diagram showing the configuration of a microphone
device according to a modification 4; FIG. 16 is a block diagram showing the configuration of a
telephone set according to a modification 6;
Explanation of sign
[0051]
DESCRIPTION OF SYMBOLS 1 ... Microphone apparatus, 10 ... Voice input part, 20 ... Signal level
detection part, 30 ... Frequency characteristic correction part, 40 ... Signal compression part, 50 ...
Storage part, 60 ... Approach sensor, 70 ... Transmission part
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