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JPH04181898

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DESCRIPTION JPH04181898
[0001]
Field of the Invention The present invention relates to a microphone, and more particularly to a
microphone in which the collection of unwanted sound is reduced by variable attenuation means.
For example, it is applied to sound collection such as voice and music. In order to pick up sound
at a borderline with many noises, directional microphones are widely used which exhibit high
sensitivity in a specific direction of arrival of sound waves. The directional microphones include a
wave type and a pressure gradient type. That is, the first is a waveform microphone whose
directivity is a wave coherence, and the second is a pressure gradient microphone whose
directivity is a pressure difference between two points or the power of the pressure difference.
The first type of microphone, i.e. the directivity is somehow due to wave interference, the size of
the microphone must be comparable to the wavelength of the sound wave in order to obtain
some directivity. Representative microphones of this type are reflector, lens and linear
microphones. The size of the pressure gradient microphone, which is the second type of
microphone, is smaller than the wavelength compared to the waveform micropong. In addition,
[acoustic engineering J '(HAPPY F. Translated by 0 LS NO, Masashi Nishimaki et al., Modern
Science Company S, 34. 6.1, pp. 344-379) describes the microphone in detail. The directivity is
obtained using the sound pressure difference of 2 points in the pressure gradient type and the
interference of sound waves in the wave type, but it is difficult to obtain good directivity
characteristics over a wide frequency band in either case, and sufficient noise rejection I was not
able to get the effect. The present invention has been made in view of the above-described
circumstances, and estimates the direction of arrival of sound by focusing on the magnitude
relationship between the output levels of a plurality of microphone elements, and changes the
output level of the microphone device It is an object of the present invention to provide a
microphone that prevents the collection of unnecessary sound by causing the In order to achieve
the above object, the present invention comprises: (1) a plurality of microphone elements, and
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comparison means for comparing magnitudes of levels of signals from at least two of the
microphone elements; A variable attenuation means for attenuating a signal from the microphone
element with an attenuation factor which changes according to a control signal from the
comparison means and outputting the same; or (2) a plurality of microphone elements and the
microphone elements Comparing means for comparing levels of signals from at least two
microphone elements; delay means for delaying and outputting a signal from the microphone
element for a predetermined time; and comparing means for outputting an output signal of the
delay means And a variable attenuation means for attenuating and outputting at an attenuation
rate which changes according to a control signal from
Hereinafter, the present invention will be described based on an embodiment of the present
invention. FIG. 1 is a block diagram for explaining an embodiment (claim 1) of the microphone
according to the present invention, in which la and lb are nondirectional microphone elements, 2
is a variable attenuation means, 3 is a comparison means , 4a and 4b are residual wave detectors,
5a and 5b are smoothing circuits, 6 is a comparator, and 7 is a smoothing circuit. In the
embodiment of the present invention, the nondirectional microphone element 1a is disposed in
the positive direction on the X axis, and the nondirectional microphone element 1b is disposed in
the negative direction on the X axis. The signal from the microphone element 1a is attenuated by
the variable attenuation means 2 and becomes an output signal O8. In the embodiment of the
present invention, the output signal of the microphone element 1b is used only to control the
attenuation factor of the variable attenuation means. When the X coordinate of the sound source
is positive, the distance from the microphone element 1a to the sound source is shorter than the
distance from the microphone element 1b to the sound source. Therefore, the output level of the
microphone element 1a becomes larger than the output level of the microphone element 1b.
When the sound source has a negative X coordinate, the distance from the microphone element
1a to the sound source is longer than the distance from the microphone element 1b to the sound
source. Therefore, the output level of the microphone element 1a is smaller than the output level
of the microphone element 1b. Therefore, the positive and negative of the X coordinate of the
sound source can be estimated by comparing the magnitudes of the output levels of the two
microphone elements 1a and 1b. The output of the microphone element 1 a is connected to the
input ICI of the comparison means 3, and the output of the microphone element 1 b is connected
to the other input IC 2 of the comparison means 3. The output of the comparison means 3 is
connected to the control input AC of the variable attenuation means 2. The variable attenuation
means 2 multiplies the signal input AS by the control input AC and outputs a signal output OS.
That is, if it is configured to generate an output signal that becomes 1 when the input ICI of the
comparison means 3 is larger than the input IC2 at 0S = ASXA, and generate an output signal
that becomes 0 otherwise. If the X coordinate of the sound source is positive, the output level of
the microphone element 1a becomes larger than the output level of the microphone element 1b,
and the comparison means 3 generates a signal of 1. Since the variable attenuation means 2
multiplies the control input AC having a value of 1 by the output AS of the microphone element
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1a, the output signal of the microphone element 1a appears as it is at the output of the variable
attenuation means 2. However, when the X coordinate of the sound source is negative, the output
level of the microphone element 1a becomes smaller than the output level of the microphone
element 1b, and the comparison means 2 generates a signal of O.
Since the variable attenuation means 2 multiplies the control input AC having a value of O by the
output of the microphone element 1a with the value of O, the output of the variable attenuation
means 2 becomes 0, and the signal picked up by the microphone element 1a is the output of the
microphone device It does not appear on O8. Therefore, if the microphone device according to
the present invention is arranged such that the sound source for which sound collection is
desired is located in the positive direction on the X axis, noise collection from the unwanted
sound source from the unnecessary sound source located at a location corresponding to negative
Can be effectively suppressed. In the present invention, the comparison means 3 comprises full
wave detectors 4a, 4b, smoothing circuits 5a, 5b, 7 and a comparator 6. The input ICI of the
comparison means 3 is detected and smoothed by the residual wave detector 4a and the
smoothing circuit 5a to form a signal LSI indicating the level of the input signal. Similarly, the
input IC 2 is processed by the full wave detector 4 b and the smoothing circuit 5 b to become LS
2. The comparator 6 outputs a value of 1 when the LSI is larger than LS2, and outputs a value of
0 otherwise. The output of the comparator 6 is smoothed by the smooth port N7. The smoothing
circuit 7 serves to prevent noise from being mixed into the output O 8 due to the rapid change of
the attenuation factor of the variable attenuation means 2. FIG. 2 is a diagram showing another
embodiment (claim 2) of the microphone according to the present invention, in which 8 is a delay
means, and the other parts having the same functions as those in FIG. It is attached. The
difference from the embodiment shown in FIG. 1 is that the a force signal of the microphone
element 1a is directly supplied to the signal power As of the variable attenuation means 2, but in
the embodiment shown in FIG. Are supplied via. According to the first aspect of the invention,
when the sound source for which the sound collection is desired starts to sound, the control
input AC of the variable attenuation means 2 is changed slightly behind by the smoothing
circuits 5a, 5b, 7 in the comparison means 3. For this reason, there is a drawback that the start
part of the pronunciation is not picked up. In the invention of claim 2, in order to correct the
delay of the control input, the delay means 8 delays the signal of the signal input AS. By the
operation of the delay means 8, since the signal input AS arrives after the change of the control
input AC, it is possible to prevent the dropout of the start part of the sound generation. The delay
time of the delay means 8 is set to be longer than the delay time by the smoothing circuits 5a, 5b
and 7. FIG. 3 is a view showing still another embodiment (claim 3) of the microphone according
to the present invention, wherein 9a. 9b is a logarithmic amplifier, 10a and 10b are full wave
detectors, 11a and 11b are smoothing circuits, 12 is a subtraction circuit, 13 is a comparator, 14
is a smoothing circuit, and the other parts having the same functions as in FIG. It is attached with
the reference number of.
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One input ICI of the comparison means 3 is connected to the output of the microphone element
1a. This signal is logarithmically compressed by the logarithmic amplifier 9a capable of handling
both positive and negative polarity signals, and the residual wave detector 10a and the
smoothing circuit 11a become a signal LSI proportional to the logarithm of the signal level.
Similarly, the signal IC2 from the microphone element 1b is processed by the logarithmic
amplifier 9b, the full wave detector 10b, and the smoothing circuit 11b to become a signal LS2.
These signals LSI and LS2 are applied to the subtraction circuit 12 to obtain a difference signal
DS between them. Formula of the logarithmic function% formula% () That is, the difference signal
DS is proportional to the logarithm of the ratio of the absolute value of the input signals ICI, IC2
of the comparison means. The difference signal DS is compared by the comparison circuit 13
with the reference value CC8. The comparator 13 outputs a value of 1 when the difference signal
DS is larger than the reference value CC8, and outputs a value of 0 otherwise. The output of the
comparator 13 is smoothed by the smoothing circuit 14. The smoothing circuit serves to prevent
noise from being mixed into the output O 8 due to the rapid change of the attenuation factor of
the variable attenuation means 2. In the embodiment of the present invention, after the
logarithms of the absolute values of the input signals ICI and IC2 are determined, comparison
with the reference value ccS is performed, so that accurate comparison is performed for a wide
range of sound magnitudes. Is possible. In addition, the sound collection range can be changed
by changing the setting of the reference value CC8 according to the purpose. For example, if the
reference @CCS is set to a large positive value, the comparator 13 sets the value 1 only when the
sound source is near the microphone element 1a and the output of the microphone element 1a is
sufficiently larger than the output of the microphone element 1b. It outputs, and the output O8
comes to appear. In the above embodiment, an element showing non-directivity is used as the
microphone element, but it is also possible to use an element showing other directivity, for
example, a-directional element. In the above embodiment, only the output signal of one
microphone element 1a is directly or indirectly applied to the signal input of the variable
attenuation means 2, but using the sum or difference of the outputs of a plurality of microphone
elements It is also possible to configure. Summer-As apparent from the explanation of one rice or
more, according to the present invention, the following effects can be obtained. (1) An effect
corresponding to claim 1: Since the variable attenuation means for changing the output level is
controlled by estimating the sound source direction based on the magnitude relationship of the
outputs of the plurality of microphone elements, the collection of unnecessary sound is
prevented It is possible. 2) Effects corresponding to claim 2: In addition to the effects of the
microphone device of claim 1, since the delay of the control is corrected by the delay means, it is
possible to prevent the dropout of the start part of the sound generation.
[0002]
Brief description of the drawings
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[0003]
1 is a block diagram for explaining one embodiment of the microphone according to the present
invention, FIG. 2 is a diagram showing another embodiment of the microphone according to the
present invention, and FIG. 3 is a further embodiment of the microphone according to the
present invention It is a figure which shows another Example.
la, lb · · · non-directional microphone element, 2 · · · variable attenuation means, 3 · · · comparison
means, 4a, 4b · · · full wave detector, 5a, 5b · · · smoothing circuit, · · · · comparison , 7 ...
smoothing circuit. Patent applicant Ricoh Co., Ltd.
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