JPH0481199A - Stereophonic microphone - Google Patents

Abstract

PURPOSE:To obtain a stereo wide effect or the zoom effect by providing two nondirectional microphone units in addition to two unidirectional microphone units arranged to the left and right and adding or subtracting a difference signal output between the two nondirectional microphone units to/from the output of the unidirectional microphone units. CONSTITUTION:A differential amplifier 18 extracts the output of a left channel nondirectional microphone 15 and the output of a right channel nondirectional microphone 16. A mixer circuit 21 uses a switch 31a to select the output of an amplifier 17 of a left channel unidirectional microphone 13 and the output of the differential amplifier 18 or the output of an inverting amplifier 20 and mixes them. A mixer circuit 22 uses a switch 31b to select the output of an amplifier 19 of a right channel unidirectional microphone 14 and the output of the differential amplifier 18 or the output of the inverting amplifier 20 and mixes them. In the case of the wide position, the stereo wide effect is obtained by adding sounds in the right (H) direction and the left (J) direction only, and in the case of the tele-position, the directivity is electrically controlled by subtracting the sounds above.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a stereo microphone used as an audio input source in integrated video recorders and the like.

BACKGROUND OF THE INVENTION In recent years, integrated video recorders equipped with stereo microphones have been increasing in number. Also, a microphone has been invented that has a zooming effect in conjunction with the angle of view of the camera.

However, the current situation is that the stereo wide effect (separation) and zoom effect (directional characteristics, etc.) are not sufficient. An example of a conventional stereo microphone will be described below with reference to the drawings.

FIG. 9 is a layout diagram of a conventional stereo microphone.

1 is a unidirectional microphone unit for the left channel,
2 is a unidirectional microphone unit for the right channel. Each unit has an angle of 45° with respect 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 each microphone amplifier 3 and 4, 6a and 6b are selector switches for selecting wide position or teleposition, 7 and 8 are A left channel buffer amplifier and a right channel buffer amplifier, 9.11 a resistor, and 10.12 a capacitor, each constitute a high-pass filter. The operation of the above microphone will be explained below.

The signal obtained from the microphone unit 1 is amplified by the left channel microphone amplifier 3 and becomes a 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 a right channel audio signal B. These signals are transferred to selector switches 6a and 6.
At the wide position at b, the left channel audio signal A is given to the buffer amplifier 7 and its output is output as the left channel microphone output, and the right channel audio signal B is given to the buffer amplifier 8 and output as the right channel microphone output. be done.

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 connected to the capacitor 9. Filter circuit of resistor 10 and capacitor 11. It passes through a filter circuit of 12 resistors and enters the mixer. This mixer output C is given to buffer amplifiers 7 and 8 and output as a microphone output. In this case, the directivity characteristics of the microphone are as shown in FIG. 11 at the wide position, and as shown in FIG. 12 at the teleposition. In other words, the stereo wide effect at the wide position is obtained by changing the mounting angle of the unidirectional microphone, and the zoom effect at the teleposition is achieved by changing the frequency characteristics by the high-pass filter of resistors 10 and 12 and capacitors 9 and 11. A zoom effect is obtained by increasing the volume of the recorded sound by increasing the gain of the mixer.

Problems to be Solved by the Invention However, when the sound recorded using the microphone configured as described above is played back through a speaker, the stereo wide effect at the wide position is not sufficient (the sound is more spacious than it actually is). Also, as you can see in Figure 12, when telepositioning, the directional characteristics are broad to the left and right, so there is the problem that unintended sounds tend to enter. If you increase the mounting angle of the microphone to increase the wide effect, there is also the problem that the directional characteristics deteriorate when in teleposition.On the other hand, when in teleposition, there is also the problem that the sound of the left and right channels becomes monaural. have.

The present invention solves the above-mentioned problems by electrically changing the directional characteristics at the wide position and at the teleposition to achieve the stereo wide effect at the wide position and the zoom effect at the teleposition without creating a stereo effect. The aim is to provide a microphone that can achieve this goal.

Means for Solving the Problems In order to solve the above problems, the stereo microphone of the present invention includes two omnidirectional microphone units in addition to the two unidirectional microphone units arranged on the left and right, A difference signal circuit for extracting a difference signal component between the outputs of two omnidirectional microphone units, and an inverting circuit and a mixing circuit for adding or subtracting the difference signal output and the signal output of the unidirectional microphone unit. It is something to be prepared for.

Effect The present invention adds or subtracts the difference signal output between two omnidirectional microphone units to the conventional directional microphone unit output (or directional microphone amplifier output) with the above-described configuration, so that stereo wide effect or It is possible to obtain a zoom effect.

EXAMPLE Hereinafter, a microphone according to an example of the present invention will be described with reference to the drawings. FIG. 2 is a layout diagram of a stereo microphone in an embodiment of the present invention. In FIG. 2, 13 is a unidirectional microphone unit for the left channel, 14 is a unidirectional microphone unit for the right channel, 15 is an omnidirectional microphone unit for the left channel,
16 is a right channel omnidirectional microphone unit. The microphone units 13 and 14 are respectively installed at an angle of 30" to the left and 30 degrees to the right with respect to the front direction. Also, the distance between the microphone units 13 and 15 and the distance between the microphone units 14 and 16 is approximately 10 Iwl, respectively.
The spacing between the omnidirectional microphone units 15 and 16 is approximately 120+n+n.

FIG. 1 is a block diagram of a stereo microphone according to an embodiment of the present invention, and 13 to 16 are the aforementioned microphone units. In the figure, 17 is an amplifier connected to the output of the left channel directional microphone 13, 18 is a differential amplifier that extracts the difference between the outputs of the left channel omnidirectional microphone 15 and the right channel omnidirectional microphone 16, and 19 is a differential amplifier connected to the output of the left channel directional microphone 13. an amplifier 20 connected to the output of the directional microphone 14 for the right channel;
is an inverting amplifier with a gain of 1 that is connected to the output of the differential amplifier 18 and inverts the output. 21 is the output of the left channel amplifier 17 and the output of the differential amplifier 18 or the inverting amplifier 2
A mixing circuit 22 selects and mixes the output of the right channel amplifier 19 and the output of the differential amplifier 18 or the inverting amplifier 20 using the switch 31b. It is a mixed circuit.

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 diagram showing the direction (angle) of the sound source of the microphone units 13 to 16 of this embodiment.
If the direction G perpendicular to the axis of ~16 is 0° in front, then the H direction is 90°, the (1) direction is 180°, and the J direction is 270°. The sound source entering the omnidirectional microphone unit 15 from the J direction is R25inω2t, the sound source entering the omnidirectional microphone unit 16 is R+sinω2(t+D/v), and the sound source entering the omnidirectional microphone unit 16 from the H direction is Ll5inωIt. , omnidirectional microphone unit 151:
The input sound source is L2sincc++(t + D/v
), the output E of the differential amplifier 18 is E = L + sin ω + t + R + sin ω2 (t
+D/v)-L2sinω+(t+D/v
) −R25inω2t where L=2L+=2L2
．． If R=2RI=2R2, it is expressed as follows.

Here, ω-2πf, f-frequency, D-microphone unit amount ratio-1■=sound speed, Ll, L2. These are R1 and R2 coefficients.

FIG. 5 shows an example of the characteristics of the differential output E expressed by the above equation.

It can be seen that the gain in the frequency band (near 1 to 2 kHz) that has a large influence on the directivity characteristics is sufficient. Figure 4 shows the output E of the differential amplifier 18 in the stereo microphone of this example in an anechoic chamber. The vertical axis of the graph is the gain (dB), and the horizontal axis is the frequency (Hz).
The sensitivity in the H (90”) direction is higher than that in the (0”) direction. Also, the sensitivity in the J (270°) direction is
) direction has the same output, and the I (180°) direction has the same result as the G (0°) direction. Above 8 kHz, the 16 dB 10 ct characteristic of the low-pass filter of the amplifier is dominant. Moreover, the theoretical output is shown in FIG. The scales of the vertical and horizontal axes are the same as in FIG. Theoretically, G (0") direction, I (180"
) direction output is O.

Further, the directivity characteristics of the output E of the differential amplifier 18 are as shown in FIG. 7, and the sounds before and after the microphone are small and only the sounds on the left and right sides are extracted.

The diagram is in polar coordinates and represents gain versus angle. In practice, if the distance between omnidirectional microphones is 5 cm or less,
and the lateral direction (90° or 180”)
As shown in the figure, if the distance between omnidirectional microphones is 20 cm or more, the frequency band that determines the directivity (1kHz)
z ~ 3kHz) rotates in phase, resulting in poor directivity characteristics. Therefore, it is appropriate to set the distance between omnidirectional microphones within 5 to 20 cm. When using a wide position, this differential amplifier 18
The left and right sounds can be further increased by adding the output to the right channel amplifier 17 and the left channel amplifier 19, and the left and right sounds can be further decreased by subtracting at the time of teleposition.

In other words, in the wide position, a stereo wide effect is obtained by adding only the sound in the right (H) direction and the left (J) direction, and in the tele position, the directional characteristics are electrically controlled by decreasing it. is possible.

FIG. 6 shows the directional characteristics of the microphone of this embodiment. It can be seen that the directional characteristics change depending on each position. Note that the frequency is 1 kHz. In addition, as shown in Figure 2, the mounting angle of the directional microphone units can be 30° each to the front (60° between the left and right microphone units) to obtain the stereo wide effect. 45 each for the front
Compared to the directional characteristics of microphones with a distance of 90 degrees or more between the left and right microphone units, the directional characteristics at teleposition have been further improved.

Effects of the Invention As is clear from the above embodiments, the present invention provides two omnidirectional microphone units in addition to the two unidirectional microphone units arranged on the left and right, and furthermore, the mounting positions of these microphone units are fixed. A difference signal circuit is provided to take out the difference signal output due to the difference in the position of the microphone units, and the difference signal output is added to the output of the unidirectional microphone unit or the amplifier output of each channel. By subtracting, it is possible to change the directional characteristics of the microphone and achieve a stereo wide effect when in a wide position and a zoom effect when in a teleposition.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a stereo microphone according to an embodiment of the present invention, FIG. 2 is a layout diagram of the same, FIG. 3 is an explanatory diagram of the directivity angle, and FIG. 5
Figure 1 shows the theoretical frequency characteristics of the circuit E, Figure 6 shows the directional characteristics, Figure 7 shows the directional characteristics of the circuit E, and Figure 8 shows the spacing between the omnidirectional microphone units 15 and 16. A frequency characteristic diagram of the same circuit E when the distance is 5 cm, and Figure 9 is a layout diagram of a conventional stereo microphone.
FIG. 10 is a block diagram of the same, FIG. 11 is a wide position directional characteristic diagram, and FIG. 12 is a teleposition directional characteristic diagram. 13... Left channel directional microphone unit, 14... Right channel directional microphone unit, 15... Left channel omnidirectional microphone unit, 16... Right channel omnidirectional microphone unit, 18...Differential amplifier, 2
0...Inverting amplifier, 21...Left channel buffer amplifier, 22...Right channel buffer amplifier, 23-30...Resistor, 31a-3
1b...Tele position, wide position selector switch. Name of agent Patent attorney Shigetaka Awano and 1 other famous figure 3θ Figure 0 (0') M Hamagaimata (Hl) IOoo IO ni charge!
! [(stznFigure P Figure Figure 10 Figure 12

Claims (1)

[Claims] Two unidirectional microphone units arranged on the left and right, two omnidirectional microphone units installed close to the unidirectional microphones, and the output of the two omnidirectional microphone units. A stereo microphone comprising: a circuit for taking a difference signal; and an inverting circuit and a mixing circuit for adding or subtracting the difference signal to respective outputs of the two unidirectional microphone units.