JPS6117672Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a variable directional microphone, and has a configuration in which a variable phase shift circuit is connected to the output of the microphone and mixed with the output of other microphones. In addition to being able to arbitrarily vary the directivity characteristics according to the variation of the amount, it is also possible to prevent loss of level, especially in low frequencies, by using an equalizer with a small correction amount for frequency correction.
It is an object of the present invention to provide a variable directional microphone capable of obtaining a signal without deterioration of the SN ratio.

Conventionally, as a method of varying the directivity of a microphone, as shown in FIG. Microphone 2 is installed on axis l facing forward to sound source 1.
The outputs from a and 2b are mixed in opposite phase in the mixer 3, and the mixing ratio is varied to change from primary unidirectional to secondary sound pressure gradient unidirectional (hereinafter referred to as secondary unidirectional). ) is obtained. In this case, the sensitivity of the microphone 2a is A, the sensitivity of the microphone 2b is B, the angle between the axis l of the microphones 2a and 2b and the sound source 1 is θ, the distance between the microphone 2a and the microphone 2b is D, and the wavelength constant is K. Then, the directivity pattern P which is a mixture of the output of the microphone 2a and the output of the microphone 2b is: P=A・e ^j 〓 ^t・1+cos θ/2 −B・e ^j( 〓 ^t+KDcos 〓 ⁾・1+cos θ/2... …(1
), and if the sensitivity A of the microphone 2a and the sensitivity B of the microphone 2b are the same, and A=B, then the above equation becomes P=A・1+cosθ/2・e ^j 〓 ^t・{1−e ^{j( KDcos} 〓 ⁾ } ...(2) becomes. Also, if the value of A in formula (2) is selected appropriately,
A secondary unidirectional pattern as shown in Figure 2 can be obtained, and if D = 3 cm in equation (2), the 3rd order unidirectional pattern can be obtained.
Frequency characteristics as shown in the figure can be obtained.

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
A dip occurs at a frequency of 11.3 kHz with a wavelength equal to cm), while the response tends to decrease at a rate of 6 dB/OCT at frequencies where the wavelength of the incoming sound wave is much lower than the distance D. Therefore, since it is not possible to reliably pick up sounds with low frequencies in this state, the output of the mixer 3 is frequency-corrected by an equalizer 4 having frequency characteristics opposite to those shown in FIG. The frequency characteristics near the mid-range frequency are flattened, and the frequency characteristics are output from the output terminal 5.

For this reason, in this conventional microphone, the equalizer 4 must correct approximately 29 dB at frequencies around 100 Hz, so an equalizer with a large correction amount must be used, and as a result,
It has drawbacks such as a deteriorated signal-to-noise ratio, a tendency to generate so-called wind noise, and a tendency to generate so-called touch noise when touched.

The present invention eliminates the above drawbacks, and the fourth
An example will be described below with reference to the drawings.

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, the output from the microphone 2a has a phase characteristic as shown in FIG. It is mixed in the mixer (adder) 7 in the same phase as the output from 2b. Note that this mixer 7 is not configured to vary the mixing ratio of the outputs of the microphones 2a and 2b. Phase shift circuit 6
As is clear from Fig. 5, the phase characteristics of ω are shifted in the −180° direction on the frequency axis where the ratio ω/ω _a between the angular frequency ω and the angular frequency ω _a with a 90° phase lag is greater than 1. On the frequency axis where /ω _a is smaller than 1, the phase is set to shift in the 0° direction, so
For example, the output of the phase shift circuit 6 rotates in phase by 180° with respect to the input signal in a frequency band where ω/ω _a =1, while the phase rotates by 180° with respect to the input signal in a frequency band where ω/ω _a =1. The phase does not rotate relative to the

Therefore, at high frequencies, microphone 2
The output of a is phase-rotated by 180° and sent to microphone 2.
b (by subtracting the output of microphone 2a from the output of microphone 2b), the output of mixer 7 is the same as the output of mixer 3 of the conventional example shown in FIG. It is possible to obtain almost the same frequency characteristics as the conventional one shown in FIG. on the other hand,
At low frequencies, the output of the microphone 2a is mixed with the output of the microphone 2b (adding the output of the microphone 2a and the output of the microphone 2b) without undergoing phase rotation. Microphone 2b
At low frequencies where the distance D between microphone 2a and microphone 2b can be ignored, the output of microphone 2a and microphone 2b
Even if the output of the microphone 2a is added to the output of the microphone 2a, it can be considered that an output range that is twice the output of the microphone 2a or an output that is twice the output of the microphone 2b is obtained. Therefore, at this low frequency range, the frequency characteristics are flat and substantially the same as those of a first-order unidirectional microphone, and there is no attenuation unlike the characteristics of the conventional microphone shown in FIG.

Assuming that the phase characteristic of the phase shift circuit 6 is φ(ω), the directivity pattern P that is a mixture of the output of the microphone 2a and the output of the microphone 2b is P=A・(1+cosθ/2)・e ^j( 〓 ^t- 〓 ⁽ 〓 ⁾⁾ +B・(1+cosθ/2)・e ^j( 〓 ^t-KDcos 〓 ⁾ …
...(3), and if the sensitivity A of the microphone 2a and the sensitivity B of the microphone 2b are the same, and A=B, then the above equation becomes P=A・(1+cosθ/2)e ^j 〓 ^t・{e ^-j 〓 ⁽ 〓 ⁾ +e ^-jKDcos 〓} ...(4). Here, φ(ω) is expressed as φ(ω)=2tan ⁻¹ ω/ω _a . Also, in formula (4), A・(1+cosθ/2
)・e ^j 〓 Regarding ^t as a constant and {e ^-j 〓 ⁽ 〓 ⁾ +e ^-jKDcos 〓} as a variable, the variable resistor VR ₁ of the variable primary phase shift circuit 6 is displaced to obtain a 90° phase lag angle. Change the frequency ω _a from 10Hz to 400Hz, distance D = 3cm, θ = 0
Figure 7 (θ = 90°) and Figure 8 (θ = 0°) show the frequency characteristics when ゜, 90° are substituted into the above variables.
The directivity patterns are shown in FIG. 9 (when ω _a =50Hz). As is clear from Figures 7 to 9, 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. 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 at most 13 dB at ω _a = 50 Hz. 3, which is smaller than the conventional one shown in FIG.

In this way, the frequency characteristic of the output of the mixer 7 is reduced by only about 13 dB at ω _a =50 Hz in the mid-range frequency, so the variable equalizer 8 for flattening the frequency can compensate for about 13 dB. The equalizer may have characteristics opposite to those of the equalizer, and the amount of correction required is smaller than that of the conventional equalizer shown in Fig. 1.Thereby, there is no deterioration of the S/N ratio as in the conventional equalizer, and it is less likely to cause wind noise. Less likely to cause so-called touch noise. In this case, variable equalizer 8
With the configuration shown in Fig. 10, the variable resistor VR ₂
is linked to the variable resistor VR ₁ of the variable primary phase shift circuit 6, so that the characteristics of the variable equalizer 8 can be varied at the same time as the amount of phase shift of the primary phase shift circuit 6 is varied. In addition, set the capacitance value of capacitor C ₂ to 10 times or more that of capacitor C ₁ , and use a variable resistor.
The capacitance values of the capacitors C ₁ and C ₂ and the resistance value of the resistor R are respectively selected so that the maximum amount of correction can be obtained at the maximum value of the resistance values of VR ₁ and VR ₂ . Also, resistance
The resistance value of R ₁ is selected to be larger than that of the resistor R and the variable resistors VR ₁ and VR ₂ .

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

On the other hand, as is clear from Fig. 8, the larger ω _a is, the closer the frequency characteristics are to flatness (that is, the closer the frequency characteristics are to the characteristics of a first-order unidirectional microphone, which is flat), and ω _a The smaller the frequency characteristic is, the less flat the frequency characteristic is (that is, the frequency characteristic approaches approximately the same characteristic as the characteristic of the secondary unidirectional microphone shown in FIG. 3 within the microphone's generally used band). Therefore, by varying the amount of phase shift in the variable primary phase shift circuit 6, desired directivity characteristics can be obtained, and this amount of phase shift can be continuously varied from ω _a =10Hz to ω _a =400Hz. If possible, the range from the first-order unidirectionality to the second-order unidirectionality can be continuously varied.

Furthermore, in addition to using a variable first-order phase shift circuit as shown in FIG. 6, the same effect can be obtained by using a variable second-order phase shift circuit as the phase shift circuit.

Furthermore, the number of microphones to be used is not limited to two; in FIG.
It is also possible to provide omnidirectionality, first-order unidirectionality, and second-order unidirectionality by providing three microphones and varying the mixing ratio of the outputs from the three microphones in total.

Furthermore, the frequency characteristics shown in FIGS. 7 and 8 may be obtained by connecting an appropriate combination of variable primary or variable secondary phase shift circuits to the output sides of the microphones 2a and 2b in FIG. 4. good.

As mentioned above, the variable directional microphone according to the present invention has a variable phase shift circuit connected to at least one microphone, and a mixing circuit that mixes the output from this circuit with the output from other microphones. Since the directional characteristics are connected, the directional characteristics can be arbitrarily varied according to the variable phase shift amount of the variable phase shift circuit.Thereby, for example, if the directional characteristics are varied in conjunction with the zoom mechanism of a video camera, the screen In addition, since the amount of phase shift is varied in order to vary the directional characteristics, it is possible to emphasize the sense of unity between the sound and the sound, so it is possible to use a buffer circuit like a conventional microphone configured to vary the mixing ratio of the output of each microphone. There is no need to provide a microphone, and the circuit can be easily configured. Also, since the output of the microphone is phase-shifted and mixed with the output of other microphones, at high frequencies, the output from the microphone is essentially subtracted and mixed. This results in a secondary unidirectional pattern similar to the conventional one, while at low frequencies it is essentially the same as adding and mixing the outputs from the microphones. As a result, the output after mixing has a substantially flat frequency characteristic and can be considered equivalent to the output from a single first-order unidirectional microphone, so its directivity becomes a first-order unidirectional pattern. Since the response does not drop like in conventional microphones, the frequency response is significantly lower than that of conventional microphones, which simply subtract and mix the output of a primary unidirectional microphone. Therefore, the equalizer correction amount for frequency correction to flatten the frequency characteristics of the mixed signal can be set to a small value, thereby improving the S/N ratio. It has features such as not producing wind noise or so-called touch 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 diagrams of secondary sound pressure gradient unidirectional characteristics and their frequencies obtained by the circuit shown in Figure 1, respectively. Figure 4 is a block system diagram of an embodiment of the variable directional microphone of the present invention, Figures 5 and 6 are phase characteristic diagrams of the phase shift circuit shown in Figure 4 and their specific circuit diagrams. , 7th
8 and 8 are frequency characteristic diagrams in the 90° direction and 0° direction, respectively, obtained by the circuit shown in FIG. 4, and FIG. 9 is a directional characteristic diagram obtained by the circuit shown in FIG. FIG. 10 is a specific circuit diagram of the variable equalizer shown in FIG. 4. 1...Sound source, 2a, 2b...Microphone, 5
...Output terminal, 6...Variable primary phase shift circuit, 7...
Mixer (adder), 8...variable equalizer.

Claims (1)

[Scope of utility model registration request] In a variable directional microphone that mixes the outputs from a plurality of primary sound pressure gradient unidirectional microphones to vary the directivity thereof, a variable transfer to at least one microphone among the plurality of unidirectional microphones is provided. A variable directional microphone comprising a phase circuit connected to the variable phase shift circuit, and a mixing circuit for mixing an output from the variable phase shift circuit with an output from another unidirectional microphone.