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JPH11205888

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DESCRIPTION JPH11205888
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to
stereo microphones that convert speech into electrical signals.
[0002]
2. Description of the Related Art Conventionally, there has been known an MS (Mid Side) stereo
microphone using a combination of a unidirectional microphone and a bidirectional microphone.
[0003]
For example, as shown in FIG. 3, this MS stereo microphone outputs a signal obtained by adding
an output signal of the mid microphone 101 and an output signal of the side microphone 102 by
an adder 103 at an appropriate ratio k as a left channel signal. A signal obtained by subtracting
the output signal of the side microphone 102 from the output signal of the mid microphone 101
by the subtractor 104 at an appropriate ratio k is output as a right channel signal.
[0004]
However, the conventional MS stereo microphone as described above uses a microphone element
having a single directivity as a mid microphone and a microphone element having a bidirectional
directivity as a side microphone. However, these two microphone elements have different
frequency characteristics from each other in structure.
04-05-2019
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[0005]
Now, assuming that the sensitivity of the mid microphone in the MS stereo microphone is Lm, the
sensitivity of the side microphones is Ls, and the angle between the sound source and each
microphone is α, the signal L for the left channel and the signal R for the right channel are It can
be expressed in
[0006]
L = Lm (1 + cos α) / 2 + Ls · sin α (1) R = Lm (1 + cos α) / 2−Ls · sin α (2) where k = Ls / Lm
(3), When normalized to Lm = 1, the above-mentioned formulas (1) and (2) respectively give L =
(1 + cos α) / 2 + k · sin α (4) R = (1 + cos α) / 2−k · sin α It is expressed as (5).
[0007]
Therefore, by changing the above-mentioned ratio k, it is possible to change the directivity axis
angle θ as a stereo microphone, and this directivity axis angle θ can be expressed as θ = 2
arctan (2k) (6) .
[0008]
By the way, as can be understood from the above formulas, if the frequency characteristics of the
mid microphone and the side microphone are not uniform, the sensitivity Lm of the mid
microphone and the sensitivity Ls of the side microphone differ depending on the frequency of
the collected sound. As the frequency changes, the pointing axis angle θ also changes, which
causes the problem that the localization of the sound image becomes unstable.
[0009]
The present invention has been made in view of the above problems, and it is an object of the
present invention to provide a stereo microphone which can pick up sound in a stable state of
sound image localization with a simple and low-cost configuration. Do.
[0010]
SUMMARY OF THE INVENTION In order to achieve the above object, a stereo microphone
according to claim 1 of the present invention comprises a first microphone having a single
directivity and a second microphone having a bidirectional directivity. Microphone, equalizer
means for changing the frequency characteristic of the signal outputted from the first
microphone, and the signal outputted from the equalizer means and the signal outputted from
the second microphone at an arbitrary ratio And adding means for outputting, subtracting means
for subtracting the signal outputted from the second microphone from the signal outputted from
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the equalizer means by the arbitrary ratio, and signal outputted from the adding means And
output means for outputting the signal output from the subtraction means as a stereo audio
signal.
[0011]
Further, according to a second aspect of the present invention, there is provided a stereo
microphone according to the first aspect of the present invention, comprising: a first microphone
having a single directivity; a second microphone having a bidirectional directivity; and a
frequency of a signal output from the second microphone. The equalizer means for changing the
characteristics, the addition means for adding and outputting the signal output from the first
microphone and the signal output from the equalizer means at an arbitrary ratio, and the output
from the first microphone A signal output from the equalizer means at a given ratio from the
signal to be output, and a signal output from the addition means and a signal output from the
subtraction means as a stereo audio signal. And output means for
[0012]
Further, according to a third aspect of the present invention, there is provided a stereo
microphone according to the first aspect of the present invention, comprising: a first microphone
having a single directivity; a second microphone having a bidirectional directivity; and a
frequency of a signal output from the first microphone. First equalizer means for changing
characteristics to a first frequency characteristic; second equalizer means for changing frequency
characteristics of a signal output from the second microphone to a second frequency
characteristic; The addition unit adds the signal output from the equalizer unit and the signal
output from the second equalizer unit at an arbitrary ratio and outputs the added signal, and the
second output signal from the first equalizer unit A subtracting means for subtracting the signal
output from the equalizer means at the arbitrary ratio and outputting the same, a signal output
from the adding means, and Characterized by comprising an output means for outputting a signal
outputted from the calculation means as a stereo audio signal.
[0013]
(Operation) With the above-described configurations, it is possible to pick up the sound in a state
where the localization of the sound image is stable with a simple and low-cost configuration.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION A stereo microphone according to an
embodiment of the present invention will be described below.
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[0015]
FIG. 1 is a block diagram showing the configuration of a stereo microphone according to an
embodiment of the present invention. In FIG. 1, 1 is a mid microphone, 2 is a side microphone, 3
is an adder, 4 is a subtractor, and 5 is a fifth Equalizer 1 and 6 are second equalizers.
[0016]
In the stereo microphone shown in FIG. 1, the signal output from the mid microphone 1 is
supplied to the adder 3 and the subtractor 4 via the first equalizer 5, and the signal output from
the side microphone 2 is the second. Are supplied to the adder 3 and the subtractor 4 via the
equalizer 6.
[0017]
Incidentally, the directional axis angle θ of the MS type stereo microphone is expressed as θ = 2
arctan (2 k) as shown in the equation (6), and is outputted from the first equalizer 5 in the adder
3 As the value of the addition ratio k of the signal and the signal output from the second
equalizer 6 changes, the pointing axis angle θ also changes.
[0018]
The value of the addition ratio k is determined by the ratio of the sensitivity of the mid
microphone 1 to the sensitivity of the side microphone 2, but the sensitivity of the microphone is
the level of the signal output from the microphone for voice having a predetermined frequency.
In the case where the frequency characteristic of the microphone is not flat, when the frequency
of the collected sound changes, the level of the signal output from the microphone also changes,
ie, the collected sound The change in the frequency of changes the sensitivity of the microphone.
[0019]
However, although a uni-directional microphone element is used for the mid microphone and a
bi-directional microphone element is used for the side microphone, it is very difficult in terms of
structure to flatten these frequency characteristics. The frequency characteristics of each of the
mid microphone and the side microphone are set to frequency characteristics different from each
other as shown in (a) and (b) of FIG.
[0020]
Further, in FIG. 2C, the frequency characteristic of the mid microphone shown in FIG. 2A and the
frequency characteristic of the side microphone shown in FIG. , And is a superimposed view so
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that the levels at 1 kHz, which is used when expressing sensitivity, coincide, and the mid
microphone is a side microphone in a frequency band lower than the frequency indicated by
vertical line A in the drawing as shown. The sensitivity is higher than that of the mid microphone
in the frequency band higher than the frequency indicated by the vertical line A in the figure, and
the sensitivity is lower than that of the side microphone.
[0021]
That is, when the addition ratio k in the adder 3 is set based on the sensitivity of each of the mid
microphone and the side microphone at a frequency of 1 kHz, the directivity axis angle θ of the
stereo microphone is set according to the equations (3) and (6). At a frequency band lower than
1 kHz with a frequency of 1 kHz, the directivity axis angle θ becomes smaller and the sense of
voice spread is reduced, and at a frequency band higher than the frequency 1 kHz, the directivity
axis angle θ becomes larger When the sound having a wide range of frequencies from low to
high frequencies is picked up by this stereo microphone, the localization of the sound image
becomes unstable due to the fluctuation of the frequency.
[0022]
Therefore, in the present embodiment, the frequency characteristic of the signal output from the
mid microphone 1 is adjusted by the first equalizer 5, and the frequency characteristic of the
signal output from the side microphone 2 is adjusted by the second equalizer 6 And equalize the
frequency characteristics of both microphones (for example, the first equalizer 5 has equalizing
characteristics to flatten the frequency characteristics of the mid microphone 1 so as to flatten
the frequency characteristics of the respective microphones, By giving equalizing characteristics
that flatten the frequency characteristics of the side microphone 2 with the equalizer 6 of 2), the
value of the amplification ratio k of the amplifier 3 does not change no matter what frequency of
sound is picked up, and the directivity axis angle Since θ does not change, it is possible to obtain
a stereo audio signal in which the localization of the sound image is stable, and a microphone
whose frequency characteristics are not uniform Since the way can be used in phones element,
the yield is improved, it becomes as the cost can be reduced.
[0023]
In the present embodiment, in order to match the frequency characteristics of the mid
microphone and the frequency characteristics of the side microphones at all frequencies, an
equalizer is provided in each of the output stages of the mid microphone and the side
microphones. In order to match the frequency characteristics of the other microphones with the
frequency characteristics of the other microphones, even if the equalizer is provided only at the
output stage of one of the microphones, it is stable even if the frequency of the collected sound
changes The localization of the sound image can be obtained.
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[0024]
As described above, according to the present invention, it is possible to provide a stereo
microphone which can pick up sound with a stable and low-cost configuration with stable
localization of a sound image.
[0025]
Brief description of the drawings
[0026]
1 is a block diagram showing the configuration of a stereo microphone according to an
embodiment of the present invention.
[0027]
2 is a diagram for explaining the operation of the stereo microphone shown in FIG.
[0028]
3 is a block diagram showing the configuration of a conventional MS-type stereo microphone.
[0029]
Explanation of sign
[0030]
1 Mid Microphone 2 Side Microphone 3 Adder 4 Subtractor 5 First Equalizer 6 Second Equalizer
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