JPS6022875B2 - variable directional microphone - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable directional microphone, which has a configuration in which a variable pass filter is connected to the output of the microphone and the output of the microphone is subtracted and mixed with the output of another microphone. It is an object of the present invention to provide a variable directional microphone that can prevent level loss particularly at reduced frequencies and that uses an equalizer with a small correction amount for frequency correction to obtain a signal without deterioration of the S/N ratio. do.

Conventionally, as a method of varying the directivity of a microphone,
As shown in FIG. 1, this microphone has a flat frequency characteristic and is unidirectional with a first-order sound pressure frequency (hereinafter referred to as "first-order unidirectional"). Hong 2
a, 2b are installed on the rattan 1 facing forward to the sound source 1, and the outputs from the microphones 2a, 2b are mixed in opposite phases in the mixer 3, and the mixing ratio is varied to create a primary unidirectional pattern. 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, the angle between the ball 1 and the blue line 1 is 0, the distance between the microphones 2a and 2b is D, and the wavelength constant is K, then the output after mixing the output of the microphone 2a and the output of the microphone 2b is P is P=A-ej's t-Koko-Ax A-B-e Punokeyu side a)-Koko-Axヱ...[・),
Sensitivity A of microphone 2a and sensitivity B of microphone 2b
are the same and A=B, then the above formula is )}pFA
-Here it becomes ヱ-ej■t-{1-epu skin side 8...■.

Also, if the value of A in the formula (■) is appropriately selected, a secondary unidirectional pattern as shown in Figure 2 can be obtained, and if D = 3 arcs in the formula (■), then the pattern shown in Figure 3 It is possible to obtain the frequency characteristics shown in FIG. In this case, since the output of the microphone 2a and the output of the microphone 2b are mixed in opposite phase, the wavelength of the incoming sound wave is the distance D (=3 11. Frequency of wavelength equal to fox). A dip occurs in the ball HZ,
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 ratio of B/ocT. Therefore, since it is not possible to reliably pick up low-frequency sounds as is, the output of the mixer 3 is frequency-corrected by an equalizer 4, which has a frequency characteristic opposite to that shown in FIG. The frequency characteristics near the Nakagusuku frequency were flattened and extracted from the output terminal 5.
For this reason, in this conventional microphone, the equalizer 4 must correct the frequency around 100Hz by about 2 motherboards, so an equalizer with a large correction amount at low frequencies must be used, and as a result, the S/N
There are also drawbacks such as a deterioration in the ratio, and a tendency to generate so-called wind noise and so-called touch noise when touched with 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 low frequency components of the output from the microphone 2b are attenuated by a variable pass filter 6 whose cutoff frequency can be varied using a circuit configuration as shown in FIG. Mix in step 7). Note that this mixer 7 is not configured to vary the mixing ratio of the outputs of the microphones 2a and 2b. At this time, at the Takagi frequency higher than the cutoff frequency of the variable high-pass filter 6, the output of the microphone 2a is not attenuated by the variable high-pass filter 6, and is mixed with the output of the microphone 2b at the same level and in the same phase. Therefore, the output of the mixer 7 is similar to the output of the conventional mixer 3 shown in FIG. 1, and it is possible to obtain substantially the same frequency characteristics as the conventional mixer 3 shown in FIG.

On the other hand, at a reduction frequency considerably lower than the cutoff frequency of the variable high-pass filter 6, the output of the microphone 2a is attenuated by the variable high-pass filter 6 and mixed with the output of the microphone 2b. Even if the output of the microphone 2b is mixed with the output of the microphone 2b, it can be considered that only the output of the microphone 2b is substantially extracted. Therefore, in this low frequency range, the frequency characteristics are flat, and substantially the same characteristics as a first-order unidirectional microphone are obtained, and there is no attenuation unlike the characteristics of the conventional microphone shown in FIG. What is the phase characteristic of variable no-pass filter 6? (w), the output of the mixture of the output of the microphone 2a including the variable pass filter 6 and the output of the microphone 2b is P=A-(Toshichigane)-ePunokegu(
Mountain)) -B-(koko ax A) -epuno-hakitsune 8)...[3}
becomes.

In addition, in the pasting formula, A is the sensitivity of the microphone 2a plus the characteristics of the variable high-pass filter 6. The cutoff frequency c in the variable high-pass filter 6 is set to 100.
For day 2, the frequency characteristics and the directivity pattern are shown in FIG. 6 and 7, respectively, when the distances D=3 and D=00,900.

As is clear from Figures 6 and 7, at the Takagi frequency, it exhibits a second-order unidirectional characteristic, which is almost the same as the conventional one shown in Figure 2, and at low frequencies, it exhibits a first-order unidirectional characteristic. In particular, in the low and mid-range 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 12 mm at most, as shown in Figure 3. It is smaller than the conventional one shown in . 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 equalizer may have the opposite characteristics, and the amount of correction required is smaller than that of the conventional equalizer shown in Figure 1. This eliminates the deterioration of the S/N ratio as in the conventional equalizer, and does not cause wind noise or touch noise. .

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 Hz, there is practically no problem.

Here, the cutoff frequency of the variable pass filter 6 can be adjusted from 50Hz to 10k by means of a variable resistor VR.
As the microphone 2a is displaced over a range of HZ
Gradually, only frequency components in the Takagi direction are extracted.

As a result, the frequency characteristics are as shown in Figure 8A (cutoff frequency 50Hz to 150Hz) and Figure 8B (cutoff frequency 400Hz to 10kHz), when the cutoff frequency is low, the outputs of microphones 2a and 2b are substantially relative to each other. Because it can be regarded as subtractively mixed over a wide frequency range, secondary unidirectionality can be obtained, and when the cutoff frequency is high, the output of microphone 2b is substantially the same as the output of microphone 2a. Since it is largely extracted over a relatively wide frequency range, it is possible to obtain first-order unidirectionality, and the range from first-order unidirectionality to second-order unidirectionality can be varied continuously. . In this case, the variable equalizer 8 is configured as shown in FIG. 9, and its variable resistor V
By interlocking R2 with the variable resistor VR of the variable pass filter 6 shown in FIG. 5, the characteristics of the variable equalizer 8 can be varied at the same time as the variable resistor VR is varied. By obtaining a characteristic opposite to the characteristic, the frequency can be corrected as the directional characteristic changes. In addition, in Fig. 9, capacitor C2 and resistors R3 and R4 are approximately 2 to 1 in Fig. 8 A and B.
Determine the correction characteristics corresponding to the Takagi frequency of 0kHz oo, and set capacitors C3 and C4 and resistors R5 and R? ,VR2
Then, the correction characteristics for the Nakagusuku frequency of oo in FIGS. 8A and B are determined. Note that the characteristic of the variable pass filter 6 may be 12 lu/MT or other values, and the correction characteristic of the variable equalizer 8 may be set in accordance with these cases.

As mentioned above, the variable directional microphone according to the present invention has the following features:
A variable/pass filter whose cutoff frequency can be varied is connected to the output of at least one microphone, and its output is connected to a mixer that adds inverse phase to the output of other microphones, and the output of the mixer is set to the variable frequency as described above. / Since the structure is such that the correction amount is supplied to an equalizer that can vary the amount of correction in conjunction with varying the cutoff frequency of the pass filter,
At high frequencies, a second-order unidirectional pattern is obtained, similar to the conventional one, and at low frequencies, the first-order unidirectional pattern is obtained because it can be regarded as equivalent to the output from a single first-order unidirectional microphone. You can obtain a directional pattern, and the response will not deteriorate like conventional ones, so
Compared to the frequency characteristics of conventional ones in which the outputs of the primary unidirectional microphones are simply subtracted and mixed, it is possible to prevent level loss in reduction, and thus flatten the frequency characteristics of the mixed signal. This makes it possible to reduce the correction amount of the equalizer for frequency correction, thereby improving the S/N ratio, and without causing so-called wind noise or touch noise. Since a high-pass filter is used, the directivity can be arbitrarily varied from the above-mentioned first-order unidirectionality to second-order unidirectionality.This allows the directivity to be adjusted in conjunction with the zoom mechanism of a video camera, etc. By making it variable, the sense of unity between the screen and the sound can be emphasized.In this case, the secondary sound pressure unidirectionality is particularly noticeable in the middle and high frequencies, so it is possible to emphasize the sense of unity between the screen and the sound. It is possible to clearly collect the above-mentioned medium and high frequency sounds within a narrow and limited range, for example, normally,
It has features such as being effective for zooming, which clearly picks up only bird voices in the mid-high frequency range, which are difficult to hear because they are buried in surrounding noise.

[Brief explanation of the drawing]

Figure 1 is a block system diagram of an example of a conventional variable directivity microphone, and Figures 2 and 3 are a secondary sound pressure frequency unidirectional characteristic diagram and its frequency characteristic diagram obtained by the circuit shown in Figure 1, respectively. , FIG. 4 is a block system diagram of an embodiment of the variable directional microphone according to the present invention, FIG. 5 is a specific circuit diagram of the variable pass filter shown in FIG. 4, and FIGS. 6 and 7. are frequency characteristic diagrams in the 900 direction and oo direction and their directivity characteristic diagrams obtained by the circuit shown in FIG.
FIGS. A and B are frequency characteristic diagrams in the 900 direction and 00 direction obtained by varying the cutoff frequency using the circuit shown in FIG. 4, and 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...Variable/
・Pass filter, 7...Mixer (subtractor),
8...Variable equalizer, VR.・・・・・・Variable resistor. Figure 1 Figure 2 Figure 4 Figure 5 Rudder diagram 〇 Ship Figure 7 Figure 9 Figure 〇 Ship ○ Figure Rudder

Claims (1)

[Claims] 1. In a variable directional microphone that mixes outputs from a plurality of primary sound pressure gradient unidirectional microphones to vary its directivity, the output of at least one microphone among the plurality of unidirectional microphones. A variable high-pass filter whose cutoff frequency can be varied is connected to a mixer that adds the output of the variable high-pass filter to the output from the other primary sound pressure gradient unidirectional microphone in reverse phase, and the mixing 1. A variable directional microphone characterized in that the output of the variable high-pass filter is supplied to an equalizer whose correction amount can be varied in conjunction with varying the cut-off frequency of the variable high-pass filter.