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JPH05284588

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DESCRIPTION JPH05284588
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
voice input device having a function of canceling ambient noise, and more particularly to a
transmitter of a communication device such as a public telephone set, a portable telephone set or
a transceiver.
[0002]
2. Description of the Related Art As shown in FIG. 6, the transmitting part in a conventional
portable telephone has a structure in which one microphone 12 is mounted in a housing 11 and
a sound introducing hole 13 for guiding sound to a front position is provided. The microphone
12 used was a variety of microphones such as omnidirectional, unidirectional, and bidirectional.
[0003]
Among them, omnidirectional microphones are relatively sensitive and easy to mount on housing
11. However, they have no directivity and they pick up ambient noise, which is inconvenient for
use in noisy areas. May be
[0004]
In addition, in the case of a unidirectional or bidirectional microphone, since the voice is less
likely to enter the microphone due to a slight positional deviation between the microphone and
the mouth of the speaker, it is possible to mount the microphone in any position other than the
front of the microphone. In addition, it is necessary to provide a sound guide hole, which is
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troublesome in mounting, and has a problem in forming a waterproof and drip-proof structure.
[0005]
As described above, as a type of microphone used for a portable telephone, an omnidirectional
microphone picks up ambient noise, so that it can be either unidirectional or bidirectional. Things
were defective in terms of mounting and construction.
[0006]
The present invention has been made in view of the above circumstances, and an object thereof
is to provide a voice input device and a voice transmission device capable of canceling ambient
noise while using a nondirectional microphone. It is to do.
[0007]
SUMMARY OF THE INVENTION The present invention arranges the first and second two
omnidirectional microphones so as to acoustically generate a time difference, and the same audio
signal is transmitted to the first omnidirectional microphone. The voice signal is amplified when
the voice signal is input first from the microphone, and the signal processing is performed to
attenuate the voice signal when the voice signal is input first from the second nondirectional
microphone. Ambient noise can be canceled by making the voice input device directional by
utilizing the time difference due to the distance between the two nondirectional microphones.
[0008]
Further, according to the present invention, the first and second two nondirectional microphones
are disposed so as to acoustically generate a time difference, and the voice signal input from the
second nondirectional microphone is delayed and then phase inverted. And adding and
amplifying an audio signal from the phase-reversed second omnidirectional microphone and an
audio signal from the first omnidirectional microphone, wherein a distance between the two
omnidirectional microphones is obtained. It is possible to cancel the ambient noise by giving
directivity to the transmitter of the communicator using the time difference due to.
[0009]
An embodiment of the present invention will be described below with reference to the drawings.
[0010]
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FIG. 1 shows the circuit configuration, and reference numerals 21 and 22 denote first and second
nondirectional microphones arranged so as to acoustically generate a time difference.
The power supply voltage VDD is always applied to the first microphone 21 via the resistor Rs1,
and the audio signal obtained here is amplified by the amplifier 23 with an appropriate
amplification factor and then amplified by the high pass filter (HPF) 24, The low frequency
component and the high frequency component are respectively removed by the low pass filter
(LPF) 25 to extract the voice band, which is sent to the negative input terminal of the operational
amplifier 26 through the resistor Ra.
[0011]
The negative side input terminal and the output terminal of the operational amplifier 26 are
connected via a resistor Rc and a resistor rd, and an analog switch 27 composed of an FET is
connected in parallel to the resistor rd.
The positive input terminal of the operational amplifier 26 is grounded, and an amplified signal is
output from the output terminal to a processing circuit (not shown) of the next stage.
[0012]
On the other hand, the power supply voltage VDD is selectively applied to the second
microphone 22 through the analog switch 28 composed of FET and the resistor Rs2, and the
audio signal obtained here is appropriately amplified by the amplifier 29. After being amplified
with a rate, low frequency components are removed by the high pass filter 30 and delayed by the
delay circuit 31 for a fixed time.
The voice signal delayed by the delay circuit 31 is further subjected to high frequency
components removed by the low pass filter 32 to extract the voice band, and then the phase is
inverted by the inverting circuit 33, and then the negative side input of the operational amplifier
26 via the resistor Rb. Sent to the terminal.
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[0013]
The analog switches 27 and 28 are on / off controlled by a control signal E, and the control
signal E is input in response to the operation of a mode switch (not shown) which is turned on in
the cancellation mode for canceling ambient noise.
[0014]
The operational amplifier 26, the resistors Ra, Rb, Rc and rd and the analog switch 27 constitute
a summing amplifier 34, whose amplification factor is variably controlled by the on / off state of
the analog switch 27.
[0015]
However, as shown in FIG. 5, the microphones 21 and 22 are mounted apart by a distance l such
that an acoustically sufficient time difference occurs in the housing 41, and the conducted sound
which leads the sound to the respective front positions Holes 42, 43 are provided.
The mode switch is disposed on the housing 41. The mode switch is turned off to set the normal
mode when the ambient noise is small, and is turned on when the ambient noise is large and the
noise needs to be canceled. Operate to set the cancel mode.
Next, the operation of the above embodiment will be described.
[0016]
In the state where the ambient noise is small and the normal mode is set, the analog switches 27
and 28 are both turned off by the control signal E, so the power supply voltage VDD is not
supplied to the second microphone 22. No signal is output.
[0017]
Since the power supply voltage VDD is constantly applied to the first microphone 21 via the
resistor Rs1, the audio signal is output.
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The amplifier 23 amplifies this voice signal with an appropriate amplification factor, and the
amplified voice signal is processed by the high pass filter 24 and the low pass filter 25 so that
low frequency components and high frequency components are removed and only the voice band
is extracted. And is amplified and output to the next stage.
The amplification factor of the summing amplifier 34 at this time is "(Rc + rd) / Ra".
[0018]
In addition, when the ambient noise is large and the cancel mode is set, the analog switches 27
and 28 are both turned on by the control signal E. Therefore, not only the first microphone 21
but also the second microphone 22 is turned on. The power supply voltage VDD is supplied, and
the second microphone 22 also outputs an audio signal.
[0019]
In this case, as shown in FIG. 5, the second microphone 22 is separated from the first
microphone 21 by the distance l, so that the sound from the front of the first microphone 21 is
delayed by the distance l and The two microphones 22 will be reached.
[0020]
The delay time t1 of the voice at this time is obtained as "t1 = 1 / v (v: sound velocity)". For
example, if l = 20 [mm] and v = 340 [m / s], the delay time t1 is t1. = (20 x 10-3) / 340 = about
58.8 [μs]
[0021]
Now, the voice from the front direction of the first microphone 21 is picked up by the first
microphone 21 and amplified by the amplifier 23, and a signal a having a waveform as shown in
FIG. 2 (1) is obtained. I assume.
This voice is also picked up by the second microphone 22 with a delay of the time t1, amplified
by the amplifier 29, and sent to the high pass filter 30 as the signal b of the same waveform as
shown in FIG. 2 (2).
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[0022]
This signal is further delayed by a delay time t2 preset by the delay circuit 31 through the high
pass filter 30, and thereafter, through the low pass filter 32, the signal c output from the low
pass filter 32 is shown in FIG. Thus, the waveform is delayed by time t3 (= t1 + t2) compared to
the signal a.
This signal c is phase-inverted by the inverting circuit 33 as indicated by a broken line in FIG.
[0023]
In the summing amplifier 34, the audio signal on the first microphone 21 side is input to the
negative input terminal of the operational amplifier 26 via the resistor Ra, and the audio signal
on the second microphone 22 side is input via the resistor Rb. Become.
Here, assuming that Ra = Rb, the signal d output from the output terminal of the operational
amplifier 26 is “(Rc / Ra) + (Rc / Rb)”, and the signal a shown in FIG. The sum of the inverted
signals of the signal c indicated by the broken line in 3) is amplified by "Rc / Ra" times and
output as shown in FIG. 2 (4).
[0024]
Next, the case where there is noise from the front direction of the second microphone 22 will be
considered.
An audio signal of this noise is first picked up by the second microphone 22 and amplified by the
amplifier 29 to obtain a signal b having a waveform as shown in FIG. 3 (2).
This voice is also picked up by the first microphone 21 delayed by the time t1, amplified by the
amplifier 23, and sent to the high pass filter 24 as the signal a of the same waveform as shown in
FIG. 3 (1).
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[0025]
Now, assuming that the delay time t2 of the delay circuit 31 is set to a value equal to the time t1,
the signal c output from the low pass filter 32 has the same timing as the signal a as shown in
FIG. 3 (3). It becomes a waveform.
Since this signal c is phase-inverted by the inverting circuit 33 as shown by the broken line in
FIG. 3 (3) and then sent to the summing amplifier 34, both of the input signals are substantially
canceled in the operational amplifier 26 of the summing amplifier 34 As shown in FIG. 3D, only a
very small level of signal can be obtained as the output signal d of the operational amplifier 26.
[0026]
As described above, by setting the mode switch to the cancel mode side, the audio signal input on
the first microphone 21 side is greatly amplified, and the audio signal input on the second
microphone 22 side is It is attenuated and canceled.
Therefore, assuming that the first microphone 21 is mounted on the mouth of the talker and the
second microphone 22 is mounted on the ambient noise side by applying this technology to, for
example, a portable telephone, the noise is canceled and the talker is It will be possible to
transmit the voice of
[0027]
The analog switch 27 is on / off controlled by the mode switch when the amplification factor of
the summing amplifier 34 is constant: in the case of only the audio signal inputted by the first
microphone 21 in the normal mode and in the cancel mode In the case of the voice signal
obtained by adding the voice signal input by the first microphone 21 and the voice signal input
by the second microphone 22, the sound pressure level of the voice signal is largely different. To
achieve the same sound pressure level in both modes.
[0028]
The delay circuit 31 is for correcting the delay of the sound of the distance 1 between the first
microphone 21 and the second microphone 22, and the delay time may change depending on the
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frequency of the input signal. Therefore, it is desirable that the digital delay circuit or the circuit
as shown in FIG. 4 can set the delay time by the clock width.
[0029]
That is, in FIG. 4A, 51 and 52 are analog switches turned on by the signals g and h shown in FIG.
4B, respectively. The input signal from the high pass filter 30 is grounded at one end via the
analog switch 51. The other end of the capacitor C1 is connected to the positive input terminal of
the operational amplifier 53.
The operational amplifier 53 is connected in negative feedback, and the output terminal thereof
is connected to the positive input terminal of the operational amplifier 54 through the analog
switch 52 and the other end of the capacitor C2 whose one end is grounded.
The operational amplifier 54 is also negative feedback connected, and the signal obtained from
the output terminal is output to the low pass filter 32 of the next stage as a delayed signal.
[0030]
As described above, according to the present invention, the first and second two nondirectional
microphones are arranged so as to acoustically generate a time difference, and the same audio
signal is transmitted to the first nondirectional. The voice signal is amplified when the voice
signal is input first from the voice microphone, and the signal processing is performed to
attenuate the voice signal when the voice signal is input first from the second nondirectional
microphone. Ambient noise can be canceled by making the voice input device directional by
utilizing the time difference due to the distance between the two nondirectional microphones.
[0031]
Further, according to the present invention, the first and second two nondirectional microphones
are disposed so as to acoustically generate a time difference, and the voice signal input from the
second nondirectional microphone is delayed and then phase inverted. Since the voice signal
from the phase-reversed second omnidirectional microphone and the voice signal from the first
omnidirectional microphone are added and amplified, the distance between the two
omnidirectional microphones is dependent on the distance between the two omnidirectional
microphones. Ambient noise can be canceled by giving directivity to the transmitter of the
communicator using the time difference.
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