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BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall view showing an embodiment of the
present invention. FIG. 2 is a diagram showing a microphone arrangement in the present
embodiment. FIG. 3 is a circuit diagram of the microphone input circuit in the present
embodiment. 1 ······ Microphone 1.2 ······ Microphone ······································· ····· · · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · Phase inversion circuit, 14.15 · · · · · · Switch, 16.17 · · · · · · · · terminals.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microphone
input circuit for processing an output signal from a microphone, more particularly, using two
microphones, a simple circuit cut IIK), stereo recording, equivalent The invention relates to a
microphone input circuit capable of recording with a single microphone having directivity and
using 02 types of bell tone methods. -1-) Force /, y7 yk 139 Conventionally, a method of
performing stereo recording using two miters is widely used. On the other hand, a method of
using a directional microphone is known as a method of clearly recording only a target sound @
(hereinafter referred to as directional recording), but there is a device that performs stereo
recording, and it is possible to use directional recording In order to do that, it was necessary to
attach a directional microphone unit anew. On the other hand, stereo recording could not be
performed with an apparatus having a directional i-unit. So, when trying to do both stereo
roaring and directional recording, I was forced to use each device and it was very sad. The
present invention aims to switch between stereo recording and directional recording by
switching of a simple electric circuit in order to eliminate the above-mentioned drawbacks.
Hereinafter, the operation principle of the present invention will be described with reference to
the drawings. The 纂 -view is an overall view showing an example of the present invention
applied to a small-sized tape trayer. In the 纂 -figure, two microphones are arranged in parallel at
the top of the case 2-40. Figure 2 is a cabinet showing the placement of two miters. The third
diagram is a plotter diagram of the miter input circuit in the present embodiment. In FIG. 3, two
miters are spaced by 2d. tた、lはマイタ1 2はマイク2である。 7 is a sound source. Also,
8 is a point parallel to the central axis of the miter, which is the intersection of the center line
drawn at the center of the two microphones and the upper surface of the case. For example,
assuming that the distance between the sound s7 and the intersection 8 is an angle t # at which
one line connecting the R1 sound source 7 and the intersection 8t- makes an upper surface of
the case, the distance data between the sound source 7 and the microphone 1 is approximately
de ** = R + daoaa (1) The distance r3 between the sound source 7 and the microphone 2 is
approximately equal to R.sub .-- daoa LI- (2). Therefore, if the sound 117 is a point sound source,
the output V of the miter 1 is V, xV, gj & R, jkdao-θ- (6) the output V of the miter 2 is V, zV, @ jk
breath,- In the equations (3) and (4), which become jkdoooa (4) 3-41, v is a constant depending
on the strength of the sound at the sound source, 罠, the sensitivity of the microphone, and the
frequency of the sound. It is a phase constant to 壜 9.
Next, in FIG. 3, 9.10 is an amplifier which is amplified by the microphone 1 and the microphone
2Kmi and amplifies the microphone output. The gains of the two amplifiers are assumed to be
first. Reference numeral 11 denotes a phase inverting circuit which inverts the phase of the input
signal and outputs the inverted signal. The input end is connected to the changeover switch 14
and the output end is connected to the output end of the amplifier 10. Furthermore, when the
changeover switch 14.15 is interlocked and the switch 14 is set to connect the output end of the
amplifier 9 and the input end of the amplifier 13, the switch 15 is connected to the output end of
the amplifier 13 When the switch 14 is set to connect t between the output end of the amplifier
9 and the input end of the phase inverting circuit, the switch 16t is set so that the terminal 16t is
turned on (hereinafter referred to as S mode). 15 is called C mode or less p mode which is set to
connect with the output end of the amplifier 12 and the terminal 16). By the way, if the
changeover switch is in 8 mode, it is a turtle, and in the case of 4-42, the circuit is the same as an
ordinary stereo bell ring circuit] Signal appears. When the changeover switch is D% -d, in this
case, the same signal appears at the terminals 16 and 17, which is proportional to the difference
between the outputs of the microphones 1 and 2. That is, assuming that the output signals at the
terminals 16 and 17 are V, V becomes v = A, jkd... # Jhdaoaθ)-(Is) -O using the equation (4).
Here, m is a constant obtained by multiplying the gain of the input 9.10 by -j "K. (From equation
(5), V = j2m5in (kdaoa- (6) (in the case of .PHI., If kd is small, approximately V-xj3m, kdaoal- (7)).
(7) In the case of this D4-de, the two microphones equivalently function as one bi-directional
miter. As described above, according to the present invention, two miters can be used for the step
5-43 rheo brass sound, or simply one directivity miter with isometrically, simply by switching the
electric circuit. It can be used as Therefore, it is not necessary to replace the device by the sound
return method, which is effective in simplifying the recording operation and improving the
portability of the device.