JPS6022876B2 - variable directional microphone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable directional microphone, and in particular, by connecting a pass filter to the output of the microphone and subtracting and mixing the output of the microphone and the output of another microphone. It is an object of the present invention to provide a variable directional microphone that can prevent level loss at a reduced frequency and that uses an equalizer with a small correction amount for frequency correction to obtain a signal without deterioration of the S/N ratio. .

Conventionally, as a method of varying the directivity of a microphone,
As shown in Fig. 1, a microphone 2 with flat frequency characteristics and primary sound pressure unidirectionality (hereinafter referred to as primary unidirectionality)
a and 2b are installed on axis 1 facing forward to sound source 1, and the outputs from microphones 2a and 2b are mixed in opposite phases in mixer 3, and the mixing ratio is varied to create primary unidirectionality. There is an example of obtaining secondary sound pressure annoyance unidirectionality (hereinafter referred to as secondary unidirectionality) from . In this case, the sensitivity of microphone 2a is A, the sensitivity of microphone 2b is B, and the sensitivity of microphone 2a is
, 2b's axis 1 and the sound source 1 is 8, the distance between the microphones 2a and 2b is D, and the wavelength constant is K, then the output P which is a mixture of the output of the microphone 2a and the output of the microphone 2b is: P=A-ei's t-; Kogi A-B- ej ('s t+K hit S8) - here Eヱ ---'・', and the sensitivity A of the microphone 2a and the sensitivity B of the microphone 2b are the same, If A=B, the above formula becomes P=
A-koko ax 2 ej no t- {11ei (KDCoS8)} ...■
becomes.

Moreover, if the value of A in formula (2) is appropriately selected, a second-order unidirectional pattern as shown in FIG. 2 can be obtained.
2}, if D=3 arcs, a frequency characteristic as shown in FIG. 3 can be obtained. This one is microphone 2
Since the output of microphone a and the output of microphone 2b are mixed in opposite phase, the wavelength of the incoming sound wave is equal to the distance D (=3 arcs) between microphone 2a and microphone 2b, as shown in Fig. 3. Frequency 11. A dip occurs in the water HZ, and on the other hand, at frequencies where the wavelength of the incoming sound wave is much longer than the distance D, the response tends to decrease at a rate of B/oct. Therefore, since it is not possible to reliably collect low frequency sounds as it is, the output of mixer 3 is
The output shown in the figure was frequency corrected by an equalizer 4 having a frequency characteristic opposite to the frequency characteristic shown in Fig. 3 to reduce the frequency and flatten the frequency characteristic near the Nakagusuku frequency, and then output it from the output terminal 5. . For this reason, in this conventional microphone, the equalizer 4 must correct by about 2 MB at frequencies around 100Hz, so an equalizer with a large correction amount at low frequencies must be used, and as a result, the S/N ratio is low. It also has drawbacks such as being susceptible to so-called wind noise and so-called touch noise when touched by the hand.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIG. 4 and the following figures.

FIG. 4 shows a block system diagram of an embodiment of the variable directional microphone according to the present invention, in which the same parts as in FIG. 1 are given the same numbers. In the figure, microphone 2a
The output of the circuit has a circuit configuration as shown in Fig. 5, and has an attenuation characteristic of /Mt at a cutoff frequency of 10 points, for example.
The low frequency components are attenuated by the pass filter 6, the level is appropriately adjusted by the variable resistor VR, and mixed by the mixer (subtractor) 7 in the opposite phase to the output from the microphone 2b. Note that this mixer 7 is connected to the microphones 2a and 2b.
It is not configured to vary the mixing ratio of the output. At this time, if the resistance value of variable resistor VR is adjusted to the maximum, /
・At the Takagi frequency that is higher than the cutoff frequency of the pass filter 6, the output of the microphone 2a is not attenuated by the pass filter 6 and is mixed at the same level and phase as the output of the microphone 2b. The output of mixer 7 is similar to the output of mixer 3 in the secondary example shown in FIG. 1, and it is possible to obtain substantially the same frequency characteristics as the conventional mixer shown in FIG.

On the other hand, at low frequencies considerably lower than the cutoff frequency of the high-pass filter 6, the output of the microphone 2a is attenuated by the high-pass filter 6 and mixed with the output of the microphone 2b. Even if you mix microphone 2
It can be considered that only the output of b is taken out. Therefore, at this low frequency, the frequency characteristics are flat and approximately the same characteristics as a first-order unidirectional microphone are obtained, and the third-order unidirectional microphone has flat frequency characteristics.
There is no attenuation unlike the characteristics of the conventional one shown in the figure. Letting the phase characteristic of the high-pass filter 6 be J(■),
The output P which is a mixture of the output of the microphone 2a including the high-pass filter 6 and the output of the microphone 2b is P=A
-(Earth rowing A) -ePunoke◇(no)) -B-(Kokoroko) -ePunoto dish skin a). ...[3' (of) becomes.

However, A=No.
FIG. 6 shows the frequency characteristics and FIG. 7 shows the directivity patterns when the distance D is 00Hz and the distances D=3, 8, and 9, respectively.

As is clear from Figures 6 and 7, at high frequencies it exhibits a second-order unidirectional pattern, which is almost the same as the conventional one shown in Figure 2, and at low frequencies, it exhibits a first-order unidirectional pattern. Especially in the low and middle frequencies, the response does not deteriorate like the conventional one shown in Figure 3, and the difference between the highest and lowest values is about 1 phantom B at most. Third
4.0 mm thicker than the conventional one shown in the figure. In this way, the frequency characteristic of the output of the mixer 7 only decreases by about 1 B at the Nakagusuku frequency, so the equalizer 8 for flattening the frequency has the characteristics shown in FIG. 6 that can correct about 1 B. The correction amount can be smaller than that of the secondary equalizer shown in Figure 1, and as a result, there is no deterioration of the S/N ratio as in the conventional case, and there is no wind noise or touch noise. Hateful.

In addition, in the case of general recording, the effect of low frequency signals below 200Hz is almost the same whether recorded with secondary unidirectionality or primary unidirectionality. Even if only the first-order unidirectivity can be obtained at low frequencies below around 200 days, there is practically no problem.

Here, as the resistance value of the variable resistor VR is shifted from the maximum to the minimum direction, the output level from the microphone 2a decreases, and at the minimum resistance value, only the output from the microphone 2b is produced.

This allows the resistance value of the variable resistor VR to be varied and
Microphone 2 including pass filter 6 of formula 3
By changing the ratio of the sensitivity A of the microphone 2b to the sensitivity B of the microphone 2b, the frequency characteristics of the variable resistor V
Secondary unidirectionality can be obtained when the resistance value of R, is maximum, and primary unidirectionality can be obtained when the resistance value of variable ladder VR, is minimum. The range up to the next unidirectionality can be varied continuously. In this case, the variable equalizer 8 is configured as shown in FIG. 9, and its variable resistor VR2 is moved to the variable resistor VR, shown in FIG. Furthermore, if a characteristic opposite to that shown in FIG. 8 is obtained, the frequency can be corrected as the directional characteristic changes. Furthermore, when the resistance value of the variable resistor VR is the minimum, the resistance value of the variable resistor VR2 is the minimum. A correction characteristic corresponding to the medium-high frequency of the frequency characteristic 00 in FIG. 8 is determined by using the capacitors C2 and C3, and a correction characteristic corresponding to the low frequency by using the resistors R3, R4 and VR2. Note that the characteristics of the high-pass filter 6 may be 1 phantom B/Mt or other characteristics, and the correction characteristics of the variable equalizer 8 may be set in accordance with these cases. As described above, the variable directional microphone according to the present invention connects a high-pass filter with a fixed cutoff frequency to the output of at least one microphone, and changes the output of the high-pass filter to the output of the high-pass filter. Connect the variable resistor to the output of the variable resistor and the other above-mentioned primary sound pressure frequency unidirectional microphone to the output of the variable resistor to the output from the above primary sound pressure frequency unidirectional microphone. A mixer that performs negative phase addition is connected, an equalizer is connected to the output of the mixer, and the correction amount of the equalizer is varied by changing the resistance value of the variable resistor. In terms of frequency, a second-order unidirectional pattern is obtained like the conventional one, and at low frequencies, a first-order unidirectional pattern is obtained because it can be regarded as equivalent to the output from a single first-order unidirectional microphone. pattern, and its response does not deteriorate like in conventional ones, so the frequency response is particularly low compared to the conventional one, which is simply subtractive mixing of the output of a primary unidirectional microphone. It is possible to prevent level loss, and therefore it is possible to reduce the correction amount of the equalizer for frequency correction so that the frequency characteristics of the mixed signal are flat, thereby improving the S/N ratio. It does not generate so-called wind noise or touch noise, and since the mixing ratio is configured to be variable, the directivity can be arbitrarily varied from the above-mentioned first-order unidirectionality to second-order unidirectionality. For example, if the directivity is varied in conjunction with the zoom mechanism of a video camera, the sense of unity between the screen and the sound can be emphasized. , it can pick up sounds in a wide range in front of the microphone, and is effective, for example, when picking up surrounding sounds, including sounds in the low frequency range, and birdsong, especially in the middle and high frequency ranges. be.

It has the following features.

[Brief explanation of drawings]

Figure 1 is a block system diagram of an example of a variable directivity microphone, and Figures 2 and 3 are diagrams of secondary sound pressure and unidirectional characteristics obtained by the circuit shown in Figure 1, and their frequencies. 4 is a block system diagram of an embodiment of the variable directional microphone according to the present invention, and FIG. 5 is a specific circuit diagram of the path filter shown in FIG. 4, and FIGS. 6 and 7
The figure shows a frequency characteristic diagram in the 90 o direction and oo direction obtained by the circuit shown in Fig. 4, and its directional characteristic diagram, and Fig. 8 shows a 90° frequency characteristic diagram obtained by varying the mixing ratio by the circuit shown in Fig. 4.
A frequency characteristic diagram in the 0o direction and the oo direction, FIG. 9 is a specific circuit diagram of the variable equalizer shown in FIG. 4. 1...Sound source, 2a, 2b...Microphone, 5...Output terminal, 6...High-pass filter, 7...Mixer (subtraction) container), 8...
...Variable equalizer, VR, ...Variable resistor. Figure 1 Figure 2 Figure 4 Figure 5 Ship diagram ○ Ball Figure 7 Figure 9 Unillustrated ship

Claims (1)

[Claims] 1. In a variable directional microphone that mixes the outputs from a plurality of primary sound pressure gradient unidirectional microphones and varies the mixing ratio by a predetermined amount to vary the directivity, one of the plurality of unidirectional microphones mentioned above A high-pass filter with a fixed cutoff frequency is connected to the output of at least one microphone, a variable resistor for varying the output of the high-pass filter is connected to the output of the high-pass filter, and the variable resistor and other A mixer is connected to the output of the first-order sound pressure gradient unidirectional microphone to add the output of the variable resistor in reverse phase to the output from the first-order sound pressure gradient unidirectional microphone, and the mixing 1. A variable directional microphone, characterized in that an equalizer is connected to the output of the variable resistor, and the correction amount of the equalizer is varied in conjunction with varying the resistance value of the variable resistor.