JPH02150834A - Sound pickup device for video camera - Google Patents

Abstract

PURPOSE:To enable acoustic zooming matching zooming operation for an image by providing a zooming-operation associated amplifier which amplifies and outputs volume associatively with the zooming operation of the camera and a nonlinear amplifier which amplifies and outputs the output of the amplifier nonlinearly. CONSTITUTION:The signal generated when a sound enters a microphone 1 is amplified by a microphone amplifier 2 and the gain of the amplitude of the amplified signal is controlled by a gain control circuit 3. The control signal 5 of the gain control circuit 3 is a voltage signal corresponding to the zooming of the optical system of the video camera and the control signal operates to increase the gain of the sound to the signal when the image is enlarged or decrease the gain when the image is reduced. The output signal of the gain control circuit 3 is inputted to a nonlinear amplifying circuit 4 to decrease the volume when the image is reduced or increase the volume when the magnification of the image is increased. Consequently, the far and near effect of the sound associated with the zooming operation is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a zoom operation in the optical system of a video camera, and transmits audio from an object to be imaged by the camera to the zoom operation that enlarges the image. This relates to a sound pickup device for a video camera that increases the volume and amplifies and captures the sound in response to a zoom operation that reduces the image.

[Conventional technology]

A video camera usually has one directional microphone attached to it, which records sound as well as video. As for the video, of course you can selectively record the scenery in the direction the lens is aiming at. However, with microphones, if the sound comes from a direction horizontally or perpendicular to the targeted direction, even a directional microphone will record the sound from these directions as well as the sound from the targeted direction. It will be done. This is because microphones have extremely poor directional selectivity.

However, by sharpening the directivity of the microphone, it is possible to suppress the volume of unnecessary sounds coming from directions other than the intended direction. In this sense, it is possible to improve the S/N ratio.

Ever since it became possible to easily enlarge or reduce the image of a video camera using the zoom operation of an optical lens, a similar function has been applied to microphone systems that collect sound. It has become generally necessary to add a function to display perspective using volume, in which the volume increases accordingly when the image is enlarged, and decreases accordingly when the image is reduced. Ta.

There are basically two types of performance required for microphone systems. One of them is to make the directivity of the microphone variable. Although omnidirectional microphones can be constructed relatively easily, it is not easy to construct compact directional microphones with good performance. Therefore, as a method to sharpen the directivity, two unidirectional microphones were placed at a distance on the axis, and the difference component between the output signals of the two was extracted.
Microphone devices such as the one described in Japanese Patent Application Laid-open No. 35596 and the one described in Japanese Patent Application Laid-Open No. 1983-66996 have been developed in which the directivity is greatly variable by combining this with - non-directional microphones. .

It is well known that sharp directivity can be obtained by arranging a plurality of microphones side by side and combining their output signals, and that the directivity changes by changing the level of each individual output signal. Including the method of arranging microphones in the axial direction, Usayo, Nishimura, Ebata, Okuda, analysis of moving sound sources Trajectory estimation using microphone array - Acoustical Society of Japan Lff (E) VC) 1.8.23 2
9 (1987).

Regarding the second performance required for the microphone system, this is required for the operation of the circuit rather than the microphone, but one idea was to automatically change the volume in conjunction with the zoom of the image. Although this is a well-known technique, simply changing the volume will cause sounds other than the targeted sound to change in parallel, so the effect of changing the S/N ratio with perspective cannot be expected. Therefore, it is conceivable to obtain an acoustic zoom effect by combining the first performance, the variable directivity effect and the volume effect, but at present, if the microphone system is miniaturized, the frequency range from the mid-range to the low-range In this case, the directivity could not be made sufficiently sharp, so the effect of the above combination was not sufficient.

[Problem to be solved by the invention]

With conventional technology, it is not possible to make the directivity of the microphone sufficiently sharp, so signal processing by a circuit other than the microphone is required in order to emphasize the sound targeted by the video camera. If the target object emits a relatively loud sound, it is possible to distinguish between the target sound and surrounding sounds through signal processing. Conventional techniques do not take this point into consideration, and are not sufficiently effective in emphasizing only the targeted sound.

The purpose of the present invention is to improve the S/N by emphasizing the sound of the target and suppressing the surrounding noise when the target that the camera is aiming at generates a louder sound compared to the surrounding noise. It is an object of the present invention to provide a sound pickup device for a video camera that makes acoustic zoom effective.

[Means to solve the problem]

The above object is to provide a sound pickup device for a video camera that amplifies and captures the sound from the object to be imaged by the camera in conjunction with the zoom operation in the optical system of the video camera. When amplifying the output signal from at least one microphone, in conjunction with the zoom operation of the camera, the volume is increased for a zoom operation that enlarges the image, and the volume is decreased for a zoom operation that reduces the image. By including a zoom operation interlocking amplifier that amplifies and outputs a small, non-linear amplifier that amplifies and outputs the output of the amplifier in a non-linear manner such that the output of the amplifier is large when the amplitude is large and small when the amplitude is small. achieved.

FIG. 2 shows a means for solving the problem to be solved by the present invention (
FIG. 2 is a block diagram showing the above-mentioned microphone, zoom operation-linked amplifier, and nonlinear amplifier.

In the figure, ■ is at least one microphone aimed at the object to be imaged by the video camera, 2 is a microphone amplifier, and 3 is a gain control circuit, which corresponds to the zoom operation in the optical system of the video camera. This is a gain control circuit in which the gain of Teso is controlled by the voltage control signal 5. 4 is a nonlinear amplification circuit that nonlinearly amplifies an input signal and outputs the amplified signal.

[Effect] The operation will be explained below with reference to FIG.

A signal generated by sound entering the microphone 1 is amplified by the microphone amplifier 2.

Here, a unidirectional microphone 1 is used. Although the directivity of the microphone is not necessarily a necessary condition for the technical means according to the present invention, it is preferable to use a microphone that is as directional as possible, as it promotes the effects of the present invention.
It is also desirable that it be sharp.

The amplified signal is processed by the gain control circuit 3.
The gain of the signal amplitude is controlled. The control signal 5 of the gain control circuit is a voltage signal corresponding to zooming in the optical system of the video camera. That is, when enlarging the image, the control signal is operated to increase the gain for the sound signal, and when reducing the image, the control signal is operated to decrease the gain.

The output signal of the gain control circuit 3 is input to the nonlinear amplifier circuit 4. In this circuit, when the image is reduced, the sound signal as a whole is suppressed to a relatively low volume, and as the image magnification is increased, the volume gradually increases starting from a signal with a relatively large amplitude.

In this way, the operation of the nonlinear amplifier circuit 4 expands the difference between a signal with a relatively large amplitude and a signal with a relatively small amplitude, and a kind of noise reduction effect is obtained. While controlling the directivity of the microphone is the original acoustic zoom,
In the present invention, by adding a pseudo effect using the electric circuit as described above, the effect of the perspective of the sound linked to the zoom operation is enhanced.

In the present invention, since it is also possible to utilize the original zoom that controls the directivity of the microphone, a method for controlling the directivity will be explained with reference to FIG. 3 before describing an embodiment of the entire system.

FIG. 3 is a block diagram showing a microphone system and an electric circuit connected thereto. In the figure, three microphones 10, 11 and 12 are arranged on a substrate 9 along a horizontal direction 14,
It is assumed that the axes of each microphone 13°14.15 are aligned parallel to each other facing the front. The microphone spacing (between axes 13 and 14 and between axes 14 and 15) is 4.25 c each
m.

The spacing between the two outer microphones (between axes 13 and 15) is therefore 8.5 cm. Now, the speed of sound is 340m/
s, these intervals are 2KIIz and 4KH of the sound wave.
It corresponds to the length of half a wavelength at the frequency of z.

When the output signals of the three microphones IO to 12 are simply added together by the mixing circuit 24 through the microphone amplifiers 21, 22, and 23, the sound waves arriving from the direction along the horizontal direction H are due to interference at the above two frequencies. Because of the cancellation effect, the sensitivity of the microphones 10 to 13 in the horizontal direction H is significantly lower than that in the front direction.

Since the effect of interference increases as the above-mentioned microphone spacing approaches half a wavelength, it actually covers a wide frequency range including 2KHz and 4KHz, i.e. from 1.5KHz to 6K]
(Over z, the sensitivity of the microphone system in the horizontal direction I is decreased. In other words, the directivity becomes sharper. The sensitivity decrease in the horizontal direction H with respect to the front direction is 15 to 2
reaches 0dB. Below IKHz, the directional characteristics gradually approach that of a single microphone (.

When the three microphones are arranged in the horizontal direction along the horizontal direction 11 in this way, the directivity in the front direction is improved over a range of frequencies from the mid-range to the high-range.

Next, in the microphone amplifiers 21, 22.23, if the gain of the microphone amplifier 21.23 is OdB, then the microphone 11
This means that only the microphone is operating, and the directivity is that of the microphone. In this case, the sensitivity reduction in the horizontal direction H with respect to the front direction of the unidirectional microphone is only several dB.

On the other hand, the gains of microphone amplifiers 21 and 23 are
For example, if the gain is equal to that of 2, then the gain is 20
If it is expressed as dB, the sensitivity in the front direction will be a combination of three, and will be 9.5 dB higher than in the case of − sensitivity. As for directivity, it becomes sharp as mentioned above. Therefore, when the microphone amplifiers 21 and 23 are linked to change the gain, the sensitivity directionality of the microphone system changes between a relatively wide unidirectional state in the horizontal plane and a relatively narrow state resulting from the combination of the three. It can be changed.

At this time, as the directivity changes, the sensitivity in the front direction increases to 9.5.
dll changes. In order to maintain a constant sensitivity that does not change with respect to changes in sensitivity, an amplifier 24 is provided and is linked to microphone amplifiers 21 and 23. The action of amplifier 24 decreases if the gain of microphone amplifier 21.23 increases;
When the gain decreases, the gain changes in opposite directions so that the gain increases. In this way, it is possible to configure a microphone system whose directivity changes as desired.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a block diagram showing one embodiment of the present invention. In this figure, in order to sharpen the directivity in the front direction, the three microphones 10, 11, and 12 are arranged at equal intervals along the horizontal direction H, as described above.

The output signal of each microphone is sent to the microphone amplifier 21.22.
．． 23, and the output signals of the microphone amplifiers 22 and 23 are sent to a voltage-controlled mixing circuit 30 via an adder circuit 25.
This is one of the input signals.

The output signal of the microphone amplifier 21 is sent to the voltage-controlled mixing circuit 3.
0 becomes the other input signal.

Here, the directivity of the microphone system is controlled by changing the mixing ratio of the signal paths 26 and 27. In other words, when only the signal from the microphone IO becomes the output signal of the mixing circuit 30, the directivity of the microphone system becomes the directivity of the microphones, and as the proportion of the signal in the signal path 27 increases, the directivity gradually becomes sharper. . When the ratio of the signals in the paths 26 and 27 is 1:2, the output signal amplitudes of the three microphones are equal to the sound signal coming from the front direction, and the directivity becomes the sharpest.

The voltage-controlled mixing circuit 30 is a so-called full-balanced mixing circuit, and the ratio of the signals on the paths 26 and 27 included in the signal on the output signal path 28 can be changed by the control voltage a. The control voltage signal a is a zoom signal sent from the optical system of a video camera (not shown).

Next, the output signal of the mixing circuit 30 is transmitted to the voltage controlled amplifier circuit 3.
1, and the gain for that amplitude is controlled. The purpose of this circuit is to maintain the recording level of the microphone system 10, 11, and 12 approximately constant within an amplitude range of ±10 dB, thereby making the most effective use of the operating range of the subsequent circuit system. The voltage control signal is an envelope signal obtained with a predetermined time constant with respect to the output signal of the microphone system.

The output signal of the voltage control amplifier circuit 31 also becomes the input signal of the voltage control amplifier circuit 32. The voltage control amplifier circuit 32
The operation is such that the gain of the voltage control amplifier circuit 32 changes over a range from 0 to 6 dB depending on the voltage a of the signal corresponding to the zoom of the image in a video camera (not shown). That is, when the image is enlarged, the gain of the voltage control amplifier circuit 32 becomes 6 dB at maximum. For normal enlarged images, it is OdB.

The output signal of the voltage control amplifier circuit 32 is transmitted to the nonlinear amplifier circuit 4.
becomes the input signal. The nonlinear amplification circuit 4 nonlinearly amplifies the input signal by increasing the amplification factor when the amplitude is large and decreasing the amplification factor when the amplitude is small, thereby adjusting the volume in relation to the zoom operation of the video camera. Emphasize the feeling.

FIG. 4 shows a specific example of a fully balanced mixing circuit as the mixing circuit 30 in FIG.

In the figure, vl and V2 indicate two input signal voltages, and Vo indicates an output voltage. Vc represents a control voltage, and when this value changes, the mixing ratio of input signal voltages (1) and (2) changes. If Vc=O, then V o = V 1 +
V2, and as Vc increases, the mixing ratio changes.

Vc is the control signal a in FIG. 1, and as mentioned above, this is the zoom signal sent from the optical system of the video camera.

FIG. 5 is a circuit diagram showing a specific example of the nonlinear amplifier circuit 4 in FIG. 1.

What is shown in FIG. 5 is a precision function generator constructed from monolithic operational amplifiers. In order to make the input/output characteristics for the input voltage Vs at the input terminal 41 and the output voltage Vo at the output terminal 45 not a straight line but an arbitrary slope having several bending points, Use the same number of operational amplifiers.

Now, if the number of bending points is n, then (n-1-1) operational amplifiers are required. In this example, the human output characteristic has four bending points as shown in FIG. 6, so the required number of operational amplifiers is five in total.

In FIG. 6, between bending points b2 and b3, the ratio of human power to output is 1:0.5, while between bending points b1 and b
2 and between b3 and b4, the ratio is 1:1. Furthermore, for b1 and above and b4 and below, it is January 2.

The operational amplifier 42 in FIG. 5 constitutes the positive side characteristics of the input signal Vs, and the operational amplifier 43 constitutes the negative side characteristics, and there are other operational amplifiers each, but these are omitted in FIG. 5. The operational amplifier 44 serves as an adder.

Although the nonlinear amplifier circuit shown in FIG. 5 is generally well known, it will be explained in more detail with reference to FIG. 6 as well.

Suppose now that the input signal Vs increases from 0 in a positive direction and reaches point b2 in FIG. Then, the 51st Δ operational amplifier 42 adjusts its variable resistor Rh42 in advance (thereby causing it to operate).The amplification factor of the operational amplifier 42 is appropriately selected (thereby, the subsequent output signal Vo becomes The magnitude can be changed along the gradient between b2° and b1.

Assume that the input signal Vs further increases and reaches point b1. Then, the operational amplifier on the positive side (not shown) in FIG. 5 operates further by adjusting its variable resistance in advance. By appropriately selecting the amplification factor of the operational amplifier (not shown), the magnitude of the subsequent output signal Vo can be changed along a high slope after bt.

Next, consider the case where the input signal Vs increases from O in the negative direction. Assume that the input signal Vs increases from 0 in a negative direction and reaches point b3 in FIG.

Then, the operational amplifier 43 in FIG.
By adjusting 43 in advance, it is possible to operate.

By appropriately selecting the amplification factor of the operational amplifier 43, the magnitude of the subsequent output signal Vo can be adjusted to b3. It can be made to change along the gradient between b4.

Assume that the input signal Vs further increases and reaches point b4. Then, the operational amplifier on the negative side (not shown in Figure 5) becomes
Further operation is achieved by adjusting the variable resistance in advance. By appropriately selecting the amplification factor of the operational amplifier (not shown), the magnitude of the subsequent output signal Vo can be changed along a high negative slope after b4.

In this way, the circuit of FIG. 5 can perform the nonlinear amplification operation as shown in FIG. 6.

In the above embodiment shown in FIG. 1, three microphones were used, but the method of changing the directivity is not necessarily limited to this. It is possible to use two microphones, or it is possible to use a larger number of microphones. Further, in some cases, the intended effect of the present invention can be expected by simply using the final stage nonlinear amplifier circuit in the above embodiment while keeping the directivity of the microphone constant.

Next, in the above embodiment, the fully balanced mixing circuit 30 is used to keep the change in sensitivity almost constant due to the change in the directivity of the microphone. However, this mixing circuit is not absolutely necessary, and the increase in sensitivity caused by sharpening the directivity of the microphone is left as is, and the characteristics of the nonlinear amplifier circuit 4 in the final stage allow the increase in sensitivity to continue. By compensating to some extent, the ultimate goal can be achieved.

[Effects of the Invention] According to the present invention, it is possible to effectively bring about acoustic zoom in accordance with the zoom operation (enlargement, reduction) of an image in a video camera. The original acoustic zoom effect is brought about by changing the directivity of the microphone system from a wide state to a narrow state, or vice versa. However, since the wavelength of the sound waves is large, it is experienced that this change in directivity alone is not sufficient to achieve a sufficient effect.

The method of processing sound using a nonlinear functional circuit as the volume increases according to the present invention provides a particularly remarkable effect when the object to be imaged (subject) is emitting a relatively loud sound.

As the image of the subject expands, the volume increases and surrounding noise decreases, creating a psychological effect as if the source of the sound were moving closer to the camera. Similarly, when the image is reduced in size, a psychological effect is produced in which the sound source seems to move away.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram explaining the invention in detail, and Fig. 3 is a block diagram of a microphone system and an electric circuit connected thereto, explaining control of microphone directivity. Figure 4 is a circuit diagram showing a concrete example of the balanced mixing circuit using voltage control in Figure 1, Figure 5 is a circuit diagram showing a concrete example of the nonlinear amplifier circuit in Figure 1, and Figure 6 is a circuit diagram showing a concrete example of the nonlinear amplifier circuit in Figure 1. FIG. 3 is a characteristic diagram showing an example of characteristics of an amplifier circuit. Explanation of symbols 10.11.12...Microbon, 21.2223
...Microphone amplifier, 25...Addition circuit, 30...
Voltage controlled balanced mixed circuit, 31... Voltage controlled amplifier circuit, 32... Voltage controlled amplifier circuit, 4... Nonlinear amplifier circuit. Agent: Patent Attorney Akio Namiki I! 2 figures! 3 Figure 4 Illustration 5 Illustration 6 Illustration

Claims (1)

[Scope of Claims] 1. A sound collection device for a video camera that amplifies and captures sound from a target to be imaged by the camera in conjunction with a zoom operation in an optical system of the video camera, comprising: When amplifying the output signal from at least one microphone directed toward the target, in conjunction with the zoom operation of the camera, the volume is increased for a zoom operation that enlarges the image, and the volume is increased for a zoom operation that reduces the image. a zoom operation-linked amplifier that amplifies and outputs the volume at a low volume, and a nonlinear amplifier that nonlinearly amplifies and outputs the output of the amplifier, which is large when the amplitude is large and small when the amplitude is small. A sound collection device for a video camera, comprising: