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JPH0481199

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DESCRIPTION JPH0481199
[0001]
FIELD OF THE INVENTION The present invention relates to stereo microphones used as audio
input sources such as integrated video recorders. 2. Related Art In recent years, integrated video
recorders equipped with stereo microphones are increasing. A microphone has also been
invented which has a zooming effect linked to the angle of view of the camera. However, at
present, the stereo wide effect (separation) and the zoom effect (directional characteristic etc.)
are not sufficient. Hereinafter, an example of a conventional stereo microphone will be described
with reference to the drawings. FIG. 9 is a layout diagram of a conventional stereo microphone. 1
is a left channel single directional microphone unit, and 2 is a right channel single directional
microphone unit. Each unit has an angle of 45 ° to the front. FIG. 10 is a block diagram of a
stereo microphone. 3 is a left channel microphone amplifier, 5 is a right channel microphone
amplifier, 4 is a mixer for mixing the signals of the respective microphone amplifiers 3 and 4, 6a
and 6b are switches for selecting the wide position or teleposition, 7 and 8 are Each of the left
channel buffer amplifier and the right channel buffer amplifier, 9.11 is a resistor, and 10.12 is a
capacitor, constituting high-pass filters. The operation of the above microphone will be described
below. The signal obtained from the microphone unit 1 is amplified by the left channel
microphone amplifier 3 and becomes the left channel audio signal A. Further, the signal obtained
from the microphone unit 2 is amplified by the right channel microphone amplifier 5 and
becomes the right channel audio signal B. These signals are applied to the buffer amplifier 7 as
the left channel microphone output and the right channel audio signal B as the left channel
microphone output when the switch 6a and 6b are at the wide position. And output as the right
channel microphone output. On the other hand, when the changeover switches 6a and 6b are in
the teleposition, the left channel audio signal A and the right channel audio signal B are
respectively connected to the capacitors 9. 11. Filter circuit of resistor 10 and capacitor 11. Pass
the filter circuit of resistor 12 into the mixer. The mixer output C is applied to buffer amplifiers 7
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and 8 and output as a microphone output. The directivity characteristic of the microphone in this
case is as shown in FIG. 11 at the wide position, and as shown in FIG. 12 at the tele position.
That is, the stereo wide effect at the wide position can be obtained by the mounting angle of the
unidirectional microphone, and the zoom effect at the tele position can be obtained by changing
the frequency characteristics by the high-pass filters of the resistors 10.12 and capacitors 9 and
11. The zoom effect is obtained by increasing the size of the recorded sound by increasing the
gain of the mixer. Problems to be Solved by the Invention However, when the sound recorded by
using the microphone having the above configuration is reproduced by the speaker, the stereo
wide effect at the wide position is sufficient (a sound spread more than it actually is. Feel narrow.
Further, as shown in FIG. 12 at the time of teleposition, the directivity characteristic is broad with
respect to the left and right, so that there is a problem that sounds other than the target sound
may be easily entered. In addition, when the mounting angle of the microphone is increased to
increase the stereo wide effect, the directivity characteristic is deteriorated at the time of
teleposition. On the other hand, at the time of teleposition, there is also a problem that the
sounds of the left and right channels become monaural. The present invention solves the abovementioned problems and electrically changes the directivity characteristics at the wide position
and at the tele position to make the stereo wide effect at the wide position and the zoom effect at
the tele position a sense of stereo (without The purpose is to provide a microphone that can be
realized. Means for Solving the Problem In order to solve the above problems, the stereo
microphone of the present invention is provided with two nondirectional microphone units in
addition to the two unidirectional microphone units arranged in the left and right, The difference
signal circuit which takes out the difference signal component of the outputs of the two
nondirectional microphone units, the inverting circuit and the mixing circuit for adding or
subtracting the difference signal output and the signal output of the unidirectional microphone
unit It is what is provided. Since the present invention adds or subtracts the difference signal
output between two nondirectional microphone units to the conventional directional microphone
unit output (or directional microphone amplifier output) according to the configuration described
above, stereo wide effect or A zoom effect can be obtained. Embodiment Hereinafter, a
microphone according to an embodiment of the present invention will be described with
reference to the drawings. FIG. 2 is a layout view of stereo microphones in the embodiment of the
present invention. In FIG. 2, 13 is a left channel unidirectional microphone unit, 14 is a right
channel unidirectional microphone unit, 15 is a left channel omnidirectional microphone unit,
and 16 is a right channel omnidirectional microphone unit. is there.
The microphone units 13.14 are attached at an angle of 30 ° to the left and 30 ° to the right
with respect to the front direction. Also, the spacing between the microphone units 13 and 15
and the spacing between 14 and 16 are about 10 Iwl, and the spacing between the
nondirectional microphone units 15 and 16 is about 120 + n + n. FIG. 1 is a block diagram of a
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stereo microphone according to an embodiment of the present invention, and reference numerals
13 to 16 denote the aforementioned microphone units. In the figure, 17 is an amplifier
connected to the output of the directional microphone 13 for the left channel, 18 is a differential
amplifier for extracting the difference between the output of the nondirectional microphone 15
for the left channel and the output of the nondirectional microphone 16 for the right channel, 19
An amplifier 20 connected to the output of the right channel directional microphone 14 is a gain
1 inverting amplifier connected to the output of the differential amplifier 18 to invert the output.
21 is a mixing circuit in which either the output of the left channel amplifier 17 or the output of
the differential amplifier 18 or the output of the inverting amplifier 20 is selected by the switch
31 and mixed, 22 is the output of the right channel amplifier 19 and the differential amplifier 18
Or it is a mixing circuit which selects and mixes either of the outputs of the inverting amplifier
20 with switch 31b. The operation of the stereo microphone configured as described above will
be described below with reference to FIGS. 1 to 5. FIG. 3 is a view showing the directions (angles)
of the sound sources of the microphone units 13 to 16 of this embodiment, and assuming that
the direction G perpendicular to the axes of the microphone units 13 to 16 is 0 ° in the front,
the H direction is 90 °. The direction is 180 ° and the direction is 270 °. The sound source
entering the J direction nondirectional microphone unit 15 is R 25 in ω 2 t, the sound source
entering the nondirectional microphone unit 16 is R + sin ω 2 (t + D / v), and the sound source
entering the H direction nondirectional microphone unit 16 is L 15 in ω It , Non-directional
microphone unit 151: If the input sound source is L2 sincc ++ (t + D / v), the output E of the
differential amplifier 18 is E = L + sin ω + t + R + sin ω 2 (t + D / v)-L 2 sin ω + (t + D / v) −R 25
in ω 2 t where L = 2L + = 2L2. If R = 2RI = 2R2, it is represented by. Here, ω-2πf, f-frequency,
D-microphone unit amount ratio -1 ■ = sound velocity, Ll, L2. R1 and R2 coefficients. FIG. 5
shows an example of the characteristic of the differential output E represented by the above
equation. It can be seen that the gain in the frequency band (in the vicinity of 1 to 2 kHz) that is
thick for the directivity characteristics is sufficient.
FIG. 4 shows the output E of the differential amplifier 18 in the stereo microphone of this
embodiment measured in an anechoic chamber. The vertical axis of the graph is the gain (dB),
and the horizontal axis is the sensitivity in the H (90 ′ ′) direction compared to the front
sensitivity G (0 ′ ′) direction which is the frequency (Hz). The J (270 °) direction is the same
as the H (90 °) direction, and the I (180 °) direction is the same as the G (0 °) direction. The
low-pass filter of the amplifier is dominated by the 16 dB 10 ct characteristic at 8 kHz and
higher. The theoretical output is shown in FIG. The scale of the vertical and horizontal axes is the
same as in FIG. In theory, the output in the G (0 ′ ′) direction and I (180 ′ ′) direction is O.
Further, the directivity characteristic of the output E of the differential amplifier 18 is as shown
in FIG. 7, so that the sounds before and after the microphone are small and only the left and right
sounds are taken out. The figure shows polar versus angular gain. In fact, if the distance between
the nondirectional microphones is 5 cm or less, the output ratio between the front (0 °) and the
lateral direction (90 ° or 180 ′ ′) can not be obtained as shown in FIG. If the distance is 20
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cm or more, the frequency band (1 kHz to 3 kHz) that determines directivity is phase-wise
rotated and the directivity characteristic is poor (the distance between the nondirectional
microphones is suitably 5 to 20 cm or less. At the wide position, the left and right sounds can be
further increased by adding the output of the differential amplifier 18 to the right channel
amplifier 17 and the left channel amplifier 19, and at the tele position, the left and right sounds
can be further reduced by subtraction. It can be done. That is, by adding only the sound in the
right (H) direction and the left (J) direction at the wide position, the stereo wide effect can be
obtained, and at the tele position, the directivity characteristics can be electrically controlled by
decreasing in reverse. Is possible. FIG. 6 shows the directivity characteristic of the microphone of
this embodiment. It can be seen that the directional characteristics change with each position.
The frequency is 1 kHz. In addition, as shown in Fig. 2, the mounting angle of the directional
microphone unit can sufficiently obtain the stereo wide effect even at 30 ° (60 ° between the
left and right microphone units) with respect to the front, as in the conventional case. The
directivity characteristics at the tele position are further improved as compared to the
microphone directivity characteristics of 45 ° (90 ° between the left and right microphone
units) or more with respect to the front. Effects of the Invention As is apparent from the above
embodiments, the present invention provides two nondirectional microphone units in addition to
the two unidirectional microphone units arranged on the left and right, and further, the mounting
positions of these microphone units And a difference signal circuit for extracting a difference
signal output due to a difference in the position of the microphone unit, and adding the
difference signal output to the output or amplifier output of the unidirectional microphone unit
of each channel or By subtracting, it became possible to change the directivity of the microphone
and realize the stereo wide effect at the wide position and the zoom effect at the tele position.
[0002]
Brief description of the drawings
[0003]
1 is a block diagram of a stereo microphone according to an embodiment of the present
invention, FIG. 2 is a layout diagram thereof, FIG. 3 is an explanatory diagram of directivity
angles, FIG. 4 is an actual frequency characteristic diagram of the circuit E, FIG. 5 is the
theoretical frequency characteristic in the circuit E, and FIG. 6 is the directivity characteristic,
FIG. 7 is the directivity characteristic in the circuit E, and FIG. 8 is the distance between the
nondirectional microphone units 15.16. The frequency characteristic diagram in the circuit E
when making 5 cm, Fig. 9 is a layout diagram of a conventional stereo microphone, Fig. 10 is a
block diagram, Fig. 11 is a wide position directivity characteristic diagram, and Fig. 12 is It is a
teleposition directivity characteristic figure.
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13 ...... Left channel directional microphone unit, 14 ...... right channel directional microphone
unit, 15 ...... left channel omnidirectional microphone unit, 16 ...... Right channel non-directional
microphone unit, 18 ... differential amplifier, 20 ... inverting amplifier, 21 ... left channel buffer
amplifier, 22 ... right channel Buffer amplifier, 23 to 30 · · · · · · · · Resistor, 31a to 31b · · · · · · ·
Tele position, wide position switch. Name of agent Attorney Attorney Shigetaka Hino et al. 1 菓 3
0 Figure 0 (0 ') M 濱 ((Hl) IO oo lO Complete! ! [(Stz FIG. P FIG. 10 FIG. 10 FIG.
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