JPS6322720B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom microphone that uses a secondary gradient type microphone and an M-S type stereo microphone. By increasing the spacing between the microphone units in the low range compared to the high range, it is possible to create a super-directional microphone with excellent directional characteristics without deteriorating the on-axis sensitivity. To provide a zoom microphone whose directional characteristics can be continuously varied up to narrow-angle directivity.

Generally, when constructing a zoom microphone that can vary the directivity angle from monaural to stereo, it is considered to use a quadratic tilt type microphone and an M-S type stereo microphone, and to vary the synthesis ratio of the outputs from these microphones. It will be done. The secondary gradient type microphone has unidirectional microphone units 1 and 2 arranged at a predetermined interval d as shown in FIG. The output from the unit 2 is subtracted by a subtraction circuit 4 via a phase shift circuit 3, thereby providing a narrow-angle directivity characteristic, and its frequency characteristic is shown in FIG. On the other hand, as shown in FIG. 3, the MS type stereo microphone adds and subtracts each output from the unidirectional microphone unit 5 and the bidirectional microphone unit 6 using an adder 7 and a subtracter 8, and outputs left and right outputs. The directional characteristics are shown in FIG. 4.

However, in the zoom microphone that uses the above-mentioned quadratic tilt type microphone and M-S type stereo microphone, the combination ratio of the output from each microphone is varied, so it can vary from stereo wide-angle directivity to monaural narrow-angle directivity. Although the directivity characteristics can be varied, the monaural narrow-angle directivity simply depends on the quadratic tilt type microphone, which has the disadvantage of poor low-frequency characteristics. In other words, as is clear from the frequency characteristics shown in Fig. 2, the above-mentioned quadratic gradient microphone is simply a type of microphone whose sensitivity increases as the frequency goes higher due to the relationship that causes a phase shift. , when the distance d between the unidirectional microphone units 1 and 2 is smaller than the wavelength of the sound pressure from the sound source, the unidirectional microphone units 1 and 2 are in phase, and the subtractor 4 directly subtracts them. The problem is that the output simply becomes zero, and the low-frequency characteristics deteriorate.

The present invention eliminates such conventional drawbacks, and the present invention will be described below with reference to drawings of embodiments.

FIG. 5 shows an embodiment of the zoom microphone of the present invention. In FIG. 5, 11, 12,
13 is a unidirectional microphone unit;
First and second unidirectional microphone units 1
The first and third unidirectional microphones 11 and 13 are arranged with an interval d ₁ between them, and the first and third unidirectional microphones 11 and 13 are arranged with an interval d ₂ between them. This interval d ₁ , d ₂
There is a relationship of d ₁ <d ₂ between them. 14 is a bidirectional microphone unit, 15, 16, 17,
18 is each microphone unit 1 mentioned above.
1, 12, 13, and 14; 19 is a first phase shifter for passing the signal obtained by amplifying the output from the second unidirectional microphone unit 12; 20; 21 is a second phase shifter for passing the signal amplified by the amplifier 17 from the output from the third unidirectional microphone unit 13, and 21 is a signal from the amplifier 15 and the first phase shifter 19. a first subtractor, 22
is a second subtracter that subtracts the signals from the amplifier 15 and the second phase shifter 20; 23 is a high-pass filter that passes the signal from the first subtracter 21;
24 is a low-pass filter that passes the signal from the second subtracter 22, and 25 is the high-pass filter 2.
3 and a third subtractor for subtracting the signal from the low-pass filter 24, and 26 a first attenuator for transmitting the signal from the third subtractor 25 to left and right output ends 27 and 28, respectively. Here, the first and second unidirectional microphone units 11 and 12 amplify the outputs from these microphone units 11 and 12 with amplifiers 15 and 16, and pass them through a first phase shifter 19 to the first subtractor 21
The first and third unidirectional microphone units 11 and 13 are subtracted by the high-pass filter 23 and added to the high-pass filter 23.
The output from 13 is amplified by amplifiers 15 and 17, passed through a second phase shifter 20, subtracted by a second subtracter 22, and added to a low-pass filter 24, forming a second-order gradient type microphone for low frequencies. By subtracting the output from each microphone by the third subtractor 25, a two-way quadratic tilt type microphone is constructed as a whole.

29 is an adder for adding the signal from the first phase shifter 19 and the signal from the amplifier 18; 30 is an adder for adding the signal from the first phase shifter 19 and the amplifier 1;
8, 31 is a second attenuator for transmitting the signal from the adder 29 to the right output terminal 28, and 32 transmits the signal from the subtracter 30 to the left output terminal. This is the third attenuator for. Here, the second unidirectional microphone unit 12 and the bidirectional microphone unit 14 amplify the outputs from the microphone units 12 and 14 with amplifiers 16 and 18, and amplify the outputs through the first phase shifter 19. The adder 29 and the subtracter 30 constitute an MS type stereo microphone that performs addition and subtraction.

The first attenuator 26 is curved a in FIG.
The second and third attenuators 31 and 32 have gain characteristics as shown by curve b in FIG. 7. The operations of these first to third attenuators 26, 31, and 32 are controlled in conjunction with, for example, the zoom operation of a video camera. Therefore, when using the video camera in Wide (standard) mode,
The gains of the second and third attenuators 31 and 32 are maximized, the gain of the first attenuator 26 is minimum, and the stereo output from the M-S type stereo microphone can be taken out to the left and right output terminals 27 and 28. . Meanwhile, the video camera gradually
As the state shifts to Tele (zoom up), the gain of the first attenuator 26 increases, the gains of the second and third attenuators 31 and 32 decrease, and the microphone output obtained at the output terminals 27 and 28 increases. The directional axis approaches zero degrees. When the tele state is completely established, the gains of the second and third attenuators 31 and 32 become the minimum, the gain of the first attenuator 26 becomes the maximum, and the monaural output terminals 27 and 28 from the two-way quadratic gradient microphone can be taken out. At this time, the gain of the first attenuator 26 is the same as that of the second and third attenuators 31 when wide.
The gain is set approximately 10 dB higher than the gain of 32. This is because when you zoom in and bring the image closer in distance, it also becomes closer audibly.
In the Tele state, the volume is increased compared to the Wide state.

In the zoom microphone having such a configuration, if the sound pressure signal from the sound source 33 is a low frequency signal, the first and second unidirectional microphone units 11 and 12 have a longer wavelength than the sound pressure signal.
The interval d ₁ is very short. Therefore, the 2nd
The next-gradient type microphone has a frequency characteristic shown by a broken line curve a and a 90° directivity characteristic shown by a broken line curve c in FIG. That is, as understood from the principle of the quadratic gradient microphone described above, the sound pressure from the sound source 33 is in phase between the first and second unidirectional microphone units 11 and 12, so the first subtraction is performed. It is zero because it is subtracted and canceled by the microphone unit 21, and as the frequency goes to the higher range, the difference between the first and second unidirectional microphone units 11, 12 increases.
Since there is a phase difference in the output from the oscilloscope, sound pressure is output, and the low-frequency characteristics are poor, but the directivity is sharp. On the other hand, the distance d ₂ between the first and third unidirectional microphones 11 and 13 is longer than the long wavelength of the sound pressure signal from the sound source 33, and in this case,
The quadratic slope type microphone for low frequencies has a frequency characteristic shown by the solid line curve b in FIG. 6 and a 90° directivity characteristic shown by the solid line curve d. That is, the sound pressure from the sound source 33 is transmitted to the first and third unidirectional microphones 11,
Since the signals 13 are not in phase and have a phase difference, they are subtracted by the second subtractor 22 and the sound pressure is output. Then, when the frequency becomes high and the wavelength of the sound pressure signal from the sound source 33 becomes equal to the distance d ₂ between the first and third unidirectional microphones 11 and 13, the output becomes zero and the high-frequency characteristics change. Unfortunately, the directivity will be sharp. The outputs from such high-frequency and low-frequency quadratic gradient microphones are passed through a high-pass filter 23 and a low-pass filter 24, respectively, and subtracted again by a third subtractor 25, thereby producing a two-way quadratic gradient microphone. Microphones have sharp directional characteristics within a wide frequency band. In addition, the dashed-dotted line e in Fig. 6 indicates the conventional quadratic tilt type microphone.
It shows a 90° directivity characteristic.

As described above, according to the present invention, the output from the quadratic tilt type microphone that utilizes the sound pressure difference between two unidirectional microphones, which are arranged at different intervals, is passed through a low-pass filter and a high-pass filter again. Since the 2-way quadratic gradient microphone is constructed in a subtractive manner, it is possible to obtain a narrow-angle directional characteristic over the entire frequency band, allowing the targeted sound to be heard without being affected by extraneous surrounding sounds. It has the advantage of being able to collect sound with low noise. In addition, since the synthesis ratio of the output from the two-way quadratic gradient microphone and the output from the M-S stereo microphone is variable, the combination ratio can be changed continuously from monaural narrow-angle directivity to stereo wide-angle directivity. This has the advantage that, for example, by linking a video camera with an electronic volume, it is possible to easily collect sound that corresponds to the image.

[Brief explanation of the drawing]

Figure 1 is a circuit block diagram of a quadratic gradient microphone, Figure 2 is its frequency characteristic diagram, and Figure 3 is an M-
A circuit block diagram of an S-type stereo microphone, FIG. 4 is a directional characteristic diagram thereof, and FIG. 5 is a circuit block diagram showing an embodiment of the zoom microphone of the present invention.
FIG. 6 is a frequency and directivity characteristic diagram, and FIG. 7 is a gain characteristic diagram of an attenuator used in the microphone. 11, 12, 13... Unidirectional microphone unit, 14... Bidirectional microphone unit, 15, 16, 17, 18... Amplifier, 19,
20... Phase shifter, 21, 22, 25, 30... Subtractor, 23... High pass filter, 24... Low pass filter, 26, 31, 32... Attenuator, 29... Adder.

Claims (1)

[Claims] 1. The outputs from the first and second quadratic tilt type microphones that utilize the sound pressure difference between two unidirectional microphone units arranged at different intervals are filtered through a low-pass filter and a high-pass filter, respectively. 2 configured to subtract again through the filter
A way secondary gradient type microphone, an M-S type stereo microphone configured to add and subtract outputs from a unidirectional microphone unit and a bidirectional microphone unit, respectively, the two-way secondary gradient type microphone and the M ―
A zoom microphone characterized by comprising variable means for continuously varying the synthesis ratio of outputs from an S-type stereo microphone. 2. The 2-way secondary gradient type microphone shares a unidirectional microphone unit for high and low frequencies, and is configured with a total of three unidirectional microphone units. The zoom microphone according to item 1. 3 M-S type stereo microphone is 2-way 2
The zoom microphone according to claim 1 or 2, characterized in that the zoom microphone also serves as one unidirectional microphone constituting a subtilt microphone.