JPH05266404A - Audio amplifier circuit for camera-incorporated type vtr - Google Patents

Abstract

PURPOSE:To improve frequency characteristic and to eliminate unnatural feeling in tone quality by detecting an audio signal level amplified in a microphone amplifier circuit, and controlling a filter circuit by an output signal from a control circuit corresponding to the signal level, that is, when the level is low, the filter circuit is operated, and when the level is high, the filter circuit is stopped. CONSTITUTION:An audio signal picked up by a microphone 1 is amplified by a amplifier circuit 2, one part of the output signal is passed through a filter circuit 3, and is inputted to an audio signal processing circuit 4 which performs recording and reproducing. Also, the other part of the output signal amplified in the circuit 2 is inputted to a detecting circuit 5, and a signal level is detected. In this case, the circuit is set so that when an input signal level reaches the prescribed value or more an output signal varies, and a control circuit 6 is operated by the output signal and the filter circuit 3 is controlled. Therefore, sound of an object aimed is increased by attenuating frequency elements of sound produced by rotation of a drum of a VTR section in accordance with characteristics of the circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice amplification circuit for controlling the frequency characteristic of a voice signal, and is applied to a camera-integrated VTR.

[0002]

2. Description of the Related Art Generally, at the time of shooting with a camera-integrated VTR, a voice signal from a microphone is amplified by a microphone amplifying circuit and input to a voice signal processing circuit for recording / reproducing, and the sound of a desired subject is reproduced. At the same time, the sound generated from the VTR itself with a built-in camera is also recorded, and the VTR itself with a built-in camera is one of the sources of the noise sound. Usually, the largest sound generated from the camera-integrated VTR itself is the sound generated when the drum of the VTR section rotates, and has a certain frequency component as shown in FIG.

Therefore, at the time of shooting, the frequency characteristic of the sound amplification circuit is set to a high level as shown in FIG. 5, for example, so as not to pick up the frequency component of the sound emitted from the camera-integrated VTR itself when the drum is rotated. It is considered that the area side is cut. However, with such a frequency characteristic, the frequency range for picking up the sound is narrowed, and the sound quality is largely sacrificed.

Therefore, as shown in FIG. 6, it is not necessary to narrow the frequency region by reducing the frequency characteristic of the sound amplification circuit so that only the frequency component of the sound produced when the drum rotates is reduced. The voice amplification circuit is constructed. That is, as shown in the block diagram of FIG.
The audio signal from is amplified by the microphone amplification circuit 11, passes through the filter circuit 12 having the frequency characteristic shown in FIG. 4, and is then input to the audio signal processing circuit 13 for recording / reproduction. As described above, in the conventional sound amplification circuit, the filter circuit 12 removes only the frequency component of the sound generated when the drum rotates, so that the sound generated from the camera-integrated VTR itself is not significantly sacrificed. Has been reduced.

[0005]

As described above, the VTR
In a conventional sound amplification circuit using a filter circuit that removes only the frequency component of the sound generated in the section, especially the sound generated when the drum rotates, a certain frequency component is not recorded. This leaves an unnatural sound quality in that the sound from the subject corresponding to the frequency component cannot be heard.

In view of the above-mentioned problems, the present invention aims to provide a sound amplification circuit for a camera-integrated VTR that reduces the sound generated from the camera-integrated VTR itself and eliminates the unnatural sound quality. And

[0007]

A camera-integrated V according to the present invention
In order to achieve the above-mentioned purpose, the voice amplification circuit of TR is
A microphone widening circuit to which a signal from a microphone is input, a detection circuit to which a voice signal from the microphone widening circuit is input and which detects the signal level, a filter circuit which changes the frequency characteristic of the voice signal, and And a control circuit for controlling the filter circuit according to an output signal from the detection circuit.

[0008]

[Function] The detection circuit detects the audio signal level amplified by the microphone amplification circuit, controls the filter circuit by the output signal from the control circuit according to the signal level, and when the audio signal level is low, the filter circuit When the audio signal level becomes high, the operation of the filter circuit is stopped and the frequency characteristic of the audio amplification circuit changes.

[0009]

Embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the audio signal picked up by the microphone 1 is amplified by the microphone amplification circuit 2, and a part of its output signal passes through the filter circuit 3 and then the audio signal processing circuit 4 for recording / reproduction. Is input to. The other part of the amplified voice signal is input to the detection circuit 5 which detects the signal level. In the detection circuit 5, the output signal is set to change when the input signal level exceeds a certain value, and the control circuit 6 is operated by the output signal to control the filter circuit 3.
The filter circuit 3 has the characteristics shown in FIG.
It is designed to attenuate the frequency component of the sound produced when the drum rotates.

FIG. 2 shows a specific example of the detection circuit 5, the control circuit 6 and the filter circuit 3. The detection circuit 5 is composed of a diode D, a capacitor C1, and an operational amplifier OA. The audio signal amplified by the microphone amplification circuit 2 is detected by the diode D and the capacitor C1, and the level of the detection signal and the comparison voltage V _ref are obtained. Is compared with the operational amplifier OA,
When the detection signal level is higher than the comparison voltage V _{ref, the} "L" signal is output from the operational amplifier OA, and when it is low, the "H" signal is output. The control circuit 6 includes resistors R1 and R2 and a transistor Q1. When the output signal from the detection circuit 5 is "H", the transistor Q1 is turned on and the capacitor C
2. The filter circuit 3 including the coil L is operated (the frequency characteristic is changed so as to attenuate the frequency component of the sound at the time of drum rotation), and when it is "L", the transistor Q1 is OF
It becomes F, and the operation of the filter circuit 3 stops (improvement of frequency characteristics).

[0011]

According to the present invention, the frequency characteristic of the audio amplification circuit is changed by detecting the signal level from the microphone and controlling the operation of the filter circuit according to the signal level. When the sound is low and the sound produced by the camera-integrated VTR itself is dominant, the VT
When the frequency component of the sound emitted by R itself is suppressed and the sound of the target subject becomes louder and becomes more dominant than the sound emitted by the VTR itself with a built-in camera, the frequency characteristics are improved and the sound quality is unnatural. Can be eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

2 is a circuit diagram showing a specific example of a detection circuit, a control circuit, and a filter circuit in the embodiment of FIG.

FIG. 3 is a diagram showing frequency components of a sound emitted when the drum of the VTR unit rotates.

FIG. 4 is a diagram showing characteristics of a filter circuit.

FIG. 5 is a diagram showing the frequency characteristics of the sound amplification circuit when the high frequency side is cut so as to drop the frequency component of the sound generated when the drum of the VTR unit rotates.

FIG. 6 is a diagram showing a frequency characteristic of the sound amplification circuit when only a frequency component of a sound generated when the drum of the VTR unit is rotated is dropped.

FIG. 7 is a block diagram of a conventional voice amplification circuit.

[Explanation of symbols]

 1 Microphone 2 Microphone amplification circuit 3 Filter circuit 4 Audio signal processing circuit 5 Detection circuit 6 Control circuit

Claims (1)

[Claims] 1. A microphone widening circuit to which a signal from a microphone is input, a detection circuit to which a voice signal from the microphone widening circuit is input and which detects the signal level, and a frequency characteristic of the voice signal is changed. An audio amplification circuit of a camera-integrated VTR comprising a filter circuit and a control circuit for controlling the filter circuit according to an output signal from the detection circuit.