JPH04181897A - Microphone - Google Patents

Abstract

PURPOSE:To attain sound collection with less sound filled inside and high articulation even when a sound source is placed in the vicinity of a microphone by estimating a distance of the sound source depending on a level difference of outputs of plural microphones and controlling an equalizer to control the frequency characteristic so as to reduce the near effect. CONSTITUTION:A signal IS1 from a microphone 1a connects to one input of a level ratio calculation section 3. The signal is subjected to logarithmic compression by a logarithmic amplifier 4a able to process a bipolar signal and a signal LS1 proportional to the logarithm of the signal level by a full wave detector 5a and a smoothing circuit 6a. Similarly, a signal IS2 from a microphone 1b is a signal LS2 processed by a logarithmic amplifier 4b, a full wave detector 5b and a smoothing circuit 6b. The signals LS1, LS2 are fed to a subtractor circuit 7, in which the difference signal DS of the both is obtained. The difference signal DS is proportional to the logarithm of the ratio of the absolute value of the input signals IS1, IS2. The difference signal DS passes through an absolute value circuit 8 and fed to a clamp circuit 9. When the sound source is close to the microphone, the level ratio signal RS is increased and the emphasis of the low frequency due to the near effect is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microphone, and more particularly to a microphone whose proximity effect is reduced by an automatic variable equalizer. For example, it is applied to collecting sounds, music, etc.

Generally, a unidirectional microphone combines the outputs of a pressure type microphone unit and a sound pressure gradient type microphone unit in a synthesizer, amplifies this combined output in a preamplifier, and passes it through a low-cut filter circuit. It was configured to be taken out. In other words, the unidirectional microphone is subject to the proximity effect, in which the sound is exaggerated in a region where the sound collection distance r is smaller than the wavelength λ, and the sound is collected as a muffled sound with poor separation. In order to improve the effect, a one-stage or two-stage low-cut filter circuit was provided for the gain characteristics to correct the front frequency characteristics.

However, in the unidirectional microphone, the correction value of the front frequency characteristic is set using a low-cant filter circuit based on empirical judgment using a studio mixer, etc.
Since the directivity is not compensated for, the directivity is lost as the sound collection distance r becomes smaller in the low frequency range, and there is a problem in that a wall is required to prevent fogging at short distances.

In order to solve this problem, for example, JP-A-59-110
A "unidirectional microphone" is proposed in Japanese Patent No. 96. The device in this publication is configured to combine and extract the output of a pressure gradient type microphone unit and the output of a pressure type microphone unit through an equalizer circuit that has a distance compensation effect against the proximity effect. This has the advantage that even if the distance changes, the frequency characteristics do not change, and sound can always be picked up in a negative manner. However, the distance information that determines the equalization characteristics must be manually provided by the operator.

In addition, with directional microphones, when the distance from the sound source is small compared to the wavelength of the sound wave, a so-called proximity effect occurs in which bass is emphasized, leading to muffled sound and poor intelligibility. Conventionally, in order to deal with the occurrence of this proximity effect, an operator manually adjusted the equalizer to compensate for the frequency characteristics. Focusing on the outputs of two microphones placed close to each other, if the sound source is far away and the distance from the sound source is sufficiently large relative to the distance between the two microphones, the output levels of both microphones are almost equal, and the ratio is However, if the sound source is near both microphones, as the distance from the sound source decreases, the difference in the output levels of both microphones increases, and the output level ratio deviates from 1. Therefore, by controlling the equalizer characteristics using the output level ratio of this microphone, the equalizer characteristics automatically change according to the distance from the sound source, creating a microphone that reduces the influence of the proximity effect. can do.

The present invention was made in view of the above-mentioned circumstances.
The purpose of this invention is to provide a microphone that automatically reduces the proximity effect depending on the sound collection situation.

In order to achieve the above-mentioned object, the present invention provides (1) a plurality of microphone elements and a level for calculating and outputting a level ratio of signals from at least two of the microphone elements; further comprising: a ratio calculation section; and a variable equalizer that equalizes and outputs a signal from the microphone element with an equalization characteristic that changes depending on the level ratio signal from the level ratio calculation section; ) The variable equalizer is characterized in that its transfer function changes depending on the level ratio signal from the level ratio calculating section. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a configuration diagram for explaining an embodiment of a microphone according to the present invention, and in the figure, 1 (la.

lb) is a unidirectional microphone, 2 is a variable equalizer, 3
is a level ratio calculation unit, 4a and 4b are logarithmic amplifiers, and 5a and 5
b is an aftereffect detector, 6a and 6b are smoothing circuits, 7 is a subtraction circuit, 8 is an absolute value circuit, 9 is a clamp circuit, 10 is a voltage source,
11 is an antilogarithmic amplifier.

In the embodiment of the present invention, two
Using two unidirectional microphones la and lb, the signal from microphone 1a is compensated by variable equalizer 2 and becomes an output signal O8. The output signal of the microphone 1b is used only to control the characteristics of the variable equalizer 2.

The microphones la and lb are arranged at intervals of several centimeters to several tens of centimeters. When the sound source is far away from both microphones la and lb, the distances from the sound source to the two microphones are approximately equal, and the output levels of both microphones la and lb are also approximately equal. However, if the sound source is relatively close to both microphones la and lb, the output levels of both microphones will differ. For example, in FIG. 2, the distance d between the microphones la and lb is
is 5■, and the distance r1 from microphone 1a to the sound source is 5
country, the distance r from microphone 1a to the sound source
2 is 10], and the ratio of rl and r2 is 2.

Therefore, the output level ratio of the microphones la and lb also has a value greater than 1. From the output level ratio of these two microphones, it is possible to estimate the sound source distance.
By controlling the variable equalizer using this distance information, the proximity effect can be automatically reduced.

Note that in the embodiment of the present invention, the microphone la is used.

1b is a unidirectional microphone arranged with its directivity axes aligned, but it is of course possible to use other directional microphones, such as a bidirectional microphone, and the number of microphones is not limited to two. , the output of two microphones among the plurality of microphones may be used. Various configuration methods are possible for the level ratio calculation section 3, but
In the embodiment of the present invention, logarithmic amplifiers 4a, 4b, subtraction circuit 7
, a configuration using an antilogarithmic amplifier 11 will be explained. The signal ISI from the microphone 1a is connected to one input of the level ratio calculator 3. This signal is logarithmically compressed by a logarithmic amplifier 4a capable of handling both positive and negative polarity signals, and converted into a signal LSI proportional to the logarithm of the signal level by a full wave detector 5a and a smoothing circuit 6a. Similarly, the signal IS2 from the microphone 1b is processed by the logarithmic amplifier 4b, the full wave detector 5b, and the smoothing circuit 6b to become the signal LS2. These signals L
SI and LS2 are added to the subtraction circuit N7, and the difference signal D between them is
Find S. Logarithmic function formula 1 %() That is, the difference signal DS is proportional to the logarithm of the ratio of the absolute values of the input signals ISI and IS2. Note that FIG. 3 shows a circuit diagram of the level ratio calculation section, and the reference numbers are the same as those in FIG. 1. The difference signal DS further passes through an absolute value circuit 8 and is applied to a clamp circuit 9. The clamp circuit 9 shown in FIG. 4 includes a resistor 9a, two rectifiers 9b and 9c, and a voltage source 10.
It consists of When the voltage value of the signal from the absolute value circuit is smaller than the voltage value of the voltage source 10, the rectifier 9c becomes conductive, the rectifier 9b becomes the cutoff state, and the output of the voltage source 10 appears at the output of the clamp circuit. Further, when the voltage value of the signal from the absolute value circuit 8 is larger than the voltage value of the voltage source 10,
The rectifier 9b is in a conductive state, the rectifier 9C is in a cutoff state,
The output of the absolute value circuit 8 appears at the output of the clamp circuit 9. In this way, the clamp circuit 9 consists of an absolute value circuit 8, a voltage source 1
It is configured to output the larger of the two outputs of 0. The output of the clamp circuit 9 is antilogarithmically converted by an antilogarithmic amplifier 11, and becomes a value obtained by dividing the larger one of ISI and IS2 by the smaller one. The signal R8 is used to control the characteristics of the other ship 2, such as variables.

In the embodiment of the present invention, the variable equalizer 2 is composed of buffer amplifiers 2a, 2b, a capacitor 2c, a photocoupler 2d, and a resistor 2e, as shown in FIG. 5(a). The photocoupler 2d is composed of a light emitting diode and a photoconductive element, and is configured such that the larger the current flowing through the light emitting diode, the smaller the resistance value of the photoconductive element. Photo coupler 2
The photoconductive element d and the capacitor 2c constitute a high-pass filter. When the level ratio signal RS from the level ratio calculation unit 3 increases, the current flowing through the light emitting diode of the photocoupler 2d increases as shown in FIG. 5(b).
The resistance value of the photoconductive element decreases, the cutoff frequency of the high-pass filter increases, and the low-frequency attenuation of the variable equalizer increases.

Therefore, if the sound source is far away, the level ratio signal R3
is small, and the amount of low-frequency attenuation of the variable equalizer is small, but when the sound sources are close, the level ratio signal R8 becomes large,
The amount of low frequency attenuation of the variable equalizer increases, and as a result, it is possible to reduce the enhancement of the low frequency range due to the proximity effect. In the embodiments of the present invention, the variable equalizer is configured with a high-pass filter, but it may also be configured to function as another type of filter, such as for compensating for characteristics specific to the microphone element.

FIGS. 6(a) and 6(b) show an example in which another ship is provided with variable characteristics such as low-frequency enhancement to compensate for the low-frequency attenuation characteristics of the microphone element.

As is clear from the above explanation, according to the present invention, the distance to the sound source is estimated based on the level difference between the outputs of multiple microphones, and other ships are controlled by controlling the frequency characteristics, so the proximity effect is avoided. Even when the sound source is near the microphone, it is possible to collect sound with high clarity and less muffled sound.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining an embodiment of the microphone according to the present invention, FIG. 2 is a diagram for explaining the output level ratio between a sound source and a plurality of microphones, and FIG.
The circuit diagram of the level ratio calculation section, Figure 4 is the connection diagram of the clamp circuit, Figure 5 is the circuit diagram of the variable equalization amount and a diagram showing the frequency characteristics, and Figure 6 is the diagram of the other variable equalizers. FIG. 3 is a diagram showing a circuit diagram and frequency characteristics. 1 (la, lb)...unidirectional microphone, 2
. . . variable equalizer, 3 . . . level ratio calculation unit, 4a. 4b...logarithmic amplifier, 5a, 5b...full wave detector,
6a, 6b...Smoothing circuit, 7...Subtraction circuit, 8...
- Absolute value circuit, 9... Clamp circuit, 10... Voltage source, 11... Anti-logarithmic amplifier. r----"--ko1 Fig. 2 Fig. 4 (O) (b) Fig. 6 j-center inverse →

Claims (2)

[Claims] 1. a plurality of microphone elements; a level ratio calculation unit that calculates and outputs a level ratio of signals from at least two of the microphone elements; and a level ratio calculation unit that calculates and outputs a level ratio of signals from at least two of the microphone elements; A microphone characterized in that it is equipped with a variable equalizer that equalizes and outputs an equalization characteristic that changes depending on a level ratio signal. 2. 2. The microphone according to claim 1, wherein the variable equalizer has a transfer function that changes according to a level ratio signal from a level ratio calculating section.