JPH01137900A - Microphone system - Google Patents

Abstract

PURPOSE:To sensitively absorb an aimed sound with a small-sized microphone system by constituting each microphone so as to move at a constant speed toward the aimed sound. CONSTITUTION:Plural microphones 2 and 3 are respectively moved to an aimed sound 1 at the constant speed. Thus, by moving the microphones to the aimed sound 1 at the constant speed, the aimed sound 1 frequency-shifts to a high frequency range by a Doppler effect. Since the phase difference becomes larger as the frequencies becomes higher in a set delaying time, the suppressing effect other than the aimed sound increases in a set size, on the contrary, the set suppressing effect can be realized for the sound other than the aimed sound with the smaller sized microphone system than the ones obtained by a usual technique.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to miniaturization of a microphone system that picks up only target sounds in a specific location with high sensitivity.

[Conventional technology]

The microphone system of a camera-integrated VTR generally collects sound regardless of the content being filmed. That is, when recording a distant video using zoom, nearby noise unrelated to the content is picked up. Therefore, there is a need for a microphone system that can pick up only the target sound in a specific location with high sensitivity. As a publicly known technique for realizing this, Japanese Patent Application Laid-open No. 103900/1984 can be cited.

[Problem that the invention seeks to solve]

The above conventional technology picks up the target sound with high sensitivity by arranging a plurality of directional microphones facing the target sound, and adding and synthesizing the respective output signals by matching the phases of only the target sound with a time axis delay line. Sounds other than the target sound are attenuated in accordance with the phase difference.

Therefore, in order to ensure sufficient attenuation for sounds other than the target sound, it is necessary to increase the interval between the microphones and to increase the phase difference between the sound sources.

That is, the above-mentioned conventional technology does not give consideration to miniaturization. For example, in order to expect an effect in the audible band, the microphones must be installed at intervals of about 1 m or more, which is impractical for application to a camera-integrated VTR.

An object of the present invention is to provide a smaller microphone system with effects equivalent to or better than those of the prior art.

Means for Solving Problem C] The above object is achieved by moving each of the plurality of microphones toward the target sound at a constant speed. Alternatively, this can be achieved by moving the microphone in an arc relative to the target sound.

[For production]

By moving the microphone toward the target sound at a constant speed, the frequency of the target sound is shifted to a higher frequency range due to the Doppler effect. For the same delay time, the higher the frequency, the larger the phase difference becomes. Therefore, with the same magnitude, the suppression effect for sounds other than the target sound increases. Conversely, the same suppression effect for sounds other than the target sound can be achieved in a smaller size than with conventional technology. This can be achieved with a microphone system.

〔Example〕

Examples of the present invention will be described below. FIG. 1 is a block diagram illustrating an embodiment of the present invention. In the figure, 1 is the sound source and 2 to 4 are microphones.

It is moving at high speed in the direction of sound source 1. 5 to 7 are amplifiers that amplify the output of microphones 2 to 4, and 8 is amplifier 5 to
This is an adder that adds and synthesizes the output signals of 7 at a ratio of 1:2:1.

In this embodiment, the target sound from the sound source 1 is selectively outputted to the output terminal 9, and sounds at other locations are suppressed. The principle of operation will be explained using FIG.

Microphones 2 and 3 are placed equidistantly Ω from the sound source 1 at an angle of 0. For example, when the sound source 1 has a frequency ωs (rad/5ee) and the sound source has a frequency ωS' at infinity, the outputs P2 of the microphones 2 and 3 are as follows. When P3 is calculated respectively, it becomes as follows due to the Doppler effect.

Cram school COS θ P2 = Asin((1+-ωst+φ)+Bs1n((
1+-(11s't+φ'))0
Straw Oto◎
汲◎(φ″=φ′+2πd・ωs′/
death. ) As shown in the above equation, the signal from sound source 1 is picked up by microphone 2 as (1+-)ωs, (tb.: sound velocity) and by microphone 3 as (1+-)(,)S. The signals of microphone 2 and microphone 3
The signal from the sound source at infinity is picked up in the same phase as = (l-c
O3θ)□+□ 1+, o shi0 = ((1-cos θ)rt+2πd) -O Sound is collected at white. The sound at infinity is suppressed by one phase difference A.
Since φ=π, if the moving speed of the microphone is increased, the size O of the microphone system can be reduced, and miniaturization can be realized.

t-=O, that is, when a fixed microphone is used, one phase difference is Δφ, = 2 πQ (1-cos θ)□, and the minimum θ such that Aφ=π is determined, and the size of the microphone system is determined. For example, the frequency 1kl (
Focusing on the vicinity of z (12=1m) microphones 2 and 3
The interval ω is close to 1 m.

However, if the microphone is moved at a speed V, the phase difference /φ can be increased even if θ is small, and it is possible to at least reduce the distance ω between the microphones 2 and 3 by half or less.

Next, an example of how to specifically move the microphone will be described with reference to FIG. Third
The figure is a block diagram illustrating a similar effect to moving the microphones by arranging a large number of microphones in a straight line with respect to the sound source and sequentially switching and scanning the microphones instead of moving the microphones. In the figure, 11 to 16 are microphones.

17 to 22 are amplifiers that amplify the output of the microphone, 2
3 sequentially switches the outputs of amplifiers 17 to 22 to output terminal 2.
This is a switch that outputs to 4.

It is desirable that the distance between the microphones 11 to 16 is sufficiently small relative to the wavelength of the audio signal, for example, about 1 cm. Also, the number of microphones.

Three or more are required.

In this embodiment, the microphone amplifiers 17 to 22 are arranged before the switch 23, but the microphone amplifiers may be arranged after the switch. In this case, only one microphone amplifier is required and other amplifiers can be omitted.

In order to expect the effect of miniaturization by moving the microphone, the microphone must be moved at a high speed of at least several tens of B/sed, which is difficult to realize. However, as shown in this example, by arranging a large number of microphones,
The method of sequentially switching and scanning can easily achieve the same effect as moving a microphone at high speed.

In the embodiments described so far, since the Doppler effect is used, the target sound can be picked up with high sensitivity, but on the other hand, it is converted to a higher frequency than the actual sound. An embodiment of converting the sound picked up by the microphone system of the present invention into an actual frequency will be described with reference to FIGS. 4 and 5.

In the figure, 31 is an A/D converter that converts the collected audio signal into a digital signal, 32 is a memory such as a RAM, and 33 is a D converter that converts the digital signal into an analog signal.
34 is a memory control circuit, 35 is a microphone system using the Doppler effect, and 36 is an input signal frequency converter.

The operation of this frequency converter 36 will be explained using the timing chart of FIG.

Assuming that 5a is a signal generated from a sound source, the sound picked up by a microphone moving at high speed (or when multiple microphones are sequentially switched) is converted to a high frequency as shown in 5b.

For example, if a microphone is moved toward a sound source at the speed of sound, the frequency of the picked up sound will be twice that of the sound source. Since the distance the microphone can move is limited, it actually reciprocates on a straight line connecting the microphone and the target sound. In the figure, it moves toward the sound source at a speed of 2 during the period B, and moves away from the sound source at the speed of sound during the period C. In other words, the microphone system 35 travels back and forth over a distance of B x tP (= c x + y0) in a period of A.
The signal output from is as shown in 5b. The signal of 5b is A
The signal is input to the /D converter 31 and converted into a digital signal. At this time, a clock signal fw having a sufficiently high frequency relative to the audio signal is input from the controller 34. The audio signal converted into a digital signal is stored in the memory 32 at the frequency fw.
is written for period B.

The digital signal written in the memory 32 is during the period fw of A.
It is read out at the frequency of X-, converted into an analog signal 5d by the D/A converter 33, and outputted to the output terminal 9. Therefore, the nine-frequency converter 36 restores the signal to the same frequency as the sound source and outputs it. As shown in this embodiment, by restoring the sound picked up by a microphone using the Doppler effect to its original frequency using the frequency converter 36, only the target sound can be picked up with high sensitivity, faithful to the frequency of the sound source. It is what makes the effect possible. Further, in this embodiment, the frequency converter 36 is configured using the digital memory 32, but the present invention is not limited to this, and an analog memory such as a CCD may be used.

Up to now, we have described an example in which the microphone is moved toward the target sound, but next we will explain an example in which the microphone is moved in a direction that forms 90 degrees with respect to the line connecting the microphone and the sound source, using Fig. 6. explain.

Microphone 2 and microphone 4 as shown in FIG.
is moved toward the microphone 3 at a speed that makes a 90-degree angle with the sound source 1. When calculations similar to those in FIG. 2 are performed, the output P2 of microphone 2 and the output P of microphone 3 are respectively bsin θ P2=Asin ((11st+φ)+Bs1n((1
+-) (11s" is 10φ') ty.

P, = Asin ((11st+φ)+Bs1n(ω
s”t+φ〃)φ〃=φ/+2πdωS′/?.

Therefore, the signals from the sound source 1 are in the same phase, and the signals from the infinitely distant sound source are collected with a phase difference=sin θ (uJt, +2iQtan θ) □.

As in the case of FIG. 2, by increasing the speed, it is possible to reduce the size θ of the microphone system.

In addition, the feature of this embodiment is that the Doppler effect does not act on the target sound, so the target sound is not frequency-converted and the fourth
This can be realized with a simple configuration without requiring the frequency converter 36 as shown in the figure.

The same effect can also be obtained by arranging a large number of microphones 43, 44 in an arc centered on the target sound instead of moving the microphones as shown in the embodiment in FIG. can be achieved.

In the embodiments described so far, the microphones are arranged concentrically with respect to the source of the target sound, but other embodiments will now be described.

In FIG. 9, 51 is a delay line. There is a difference in the distance between the target sound source and the target sound source between the microphone 2 and the microphone 3. Therefore, the delay line 51 is used to give a delay time τ (τ=-L) corresponding to the path insertion c", and then the adder 8 performs addition synthesis. As a result, the target sound is added to the adder 8.
are added in the same phase, and it is possible to expect exactly the same effect as when the microphones shown in FIGS. 1 and 2 are placed at the same distance Ω from the target sound. Here, the delay line 51 is, for example, CC
In the case of a type using a lock like D, the delay time can be changed by making the clock frequency variable.

That is, by changing the delay time τ, the distance Q to the target sound changes, making it possible to focus on the sound source at an arbitrary position.

A case where a similar effect is achieved by arranging a large number of microphones will be explained using FIG. 10. In the figure, 52 is a plurality of microphones, 53 is an amplifier, 54 is a delay line that delays the output signals of the microphones 52, and 55 is a switch that sequentially switches between the plurality of microphones. Even when a plurality of microphones 52 are arranged, if the delay time is given to each one by the delay lines 51 and 54 according to the path difference to the target sound,
You can focus on the target sound at any location.

〔Effect of the invention〕

According to the present invention, by moving the microphone or sequentially switching multiple microphones, it is possible to expand the phase between the microphones that is generated for a sound source other than the target sound, thereby reducing the interval between microphones. I can do things. As a result, with a small microphone system, it is possible to achieve the purpose of picking up only the target sound with high sensitivity and suppressing sounds in places other than the target sound.

[Brief explanation of the drawing]

FIG. 1 is a block diagram explaining one embodiment of the present invention, and FIG.
3 is an explanatory diagram of the operation principle, FIG. 3 is an explanatory diagram of the microphone arrangement, FIGS. 4 and 5 are explanatory diagrams of the operation, and FIGS. 6 to 10 are explanatory diagrams of other embodiments of the present invention. 2.3.4...Microphone, 8...Adder, 23
Fig. l Fig. 3; Fee 70τ + '7 6: Zeng + Crystal Ne 1 9: Sat Q1 Shinji Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. g

Claims (1)

[Claims] 1. In a microphone system configured to add and synthesize the outputs of multiple microphones and pick up only the target sound in a specific location with high sensitivity, each microphone is configured to move at a constant speed toward the target sound. A microphone system featuring: