KR940007694Y1 - Circuit for preventing interference at audio process for video recording and reproducing device - Google Patents

Abstract

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Description

Interference prevention circuit of audio processing part of video recorder

1 is a graph showing a standard television broadcasting system.

2 is a circuit diagram of a conventional audio processing unit.

3 is a circuit diagram of an audio processing unit configured with an interference prevention circuit of the present invention.

4 is a graph showing the characteristics of the automatic level regulator used in the interference prevention circuit of the present invention.

* Explanation of symbols for main parts of the drawings

9: output selector 10: high frequency modulator

20; Automatic level control

The present invention relates to an interference prevention circuit of an audio processing unit of an image recording and reproducing apparatus which prevents the audio processing unit from over-modulating an audio signal to interfere with the video signal.

As shown in FIG. 1, the standard television broadcasting system currently has a standard deviation of 87.5% in the video signal 1V _PP and ± 50MHz 100% in the audio signal 1.24V _PP . Therefore, in a television audio system and a linear audio system with a narrow dynamic range of about 35 dB, over-modulation of the audio signal does not cause any interference to the video signal.

However, the high-fidelity video recorder with a wide dynamic range of about 80-90dB is over-modulated by ± 360MHz 700% when outputting 10bBm to the audio signal 8.9V _PP , resulting in the interference component of the audio signal. .

However, the conventional speech processing unit is not provided with means for adjusting the level of the speech signal. That is, the conventional audio processing unit selects the television broadcast signal, the AV input signal AVI, and the external input signal EXTI tuned by the tuner 1, as shown in FIG. Output, attenuates the peak noise in the peak noise attenuator (3), amplifies the modulation and recording amplifier (5) in the modulator (4), and then supplies the sound head (AH) through a switch (SW) and a rotation transformer (T). The audio signal is recorded and recorded on the video tape, and the audio signal reproduced on the video tape is amplified by the preamplifier 6 through the rotation transformer T and the switch SW, demodulated by the demodulator 7, and the peak noise attenuator 8 Attenuates the peak noise at 0 and inputs it with the output select key 9, and the output selector 9 selects the output signal and the reproduced audio signal of the input selector 2 to the AV signal AVO and the external signal EXTO. In addition to the output box, the high frequency modulator 10 was configured to output high frequency modulation.

However, the conventional voice processing unit as described above has no means for adjusting the voice signal input to the high frequency modulator 10 and the level, so that the level of the voice signal output by the output selector 9 and input to the high frequency modulator 10 is increased. When large, the high frequency modulator 10 causes the audio signal to be over-modulated to interfere with the video signal, and an interference pattern is generated on the playback screen, thereby causing discomfort to the user.

In order to solve the above problems, the present invention devises a speech processing unit interference prevention circuit which prevents the audio signal from being overmodulated to interfere with the video signal by automatically adjusting the level of the audio signal input to the high frequency modulator. If it described in detail with reference to the accompanying drawings of Figures 3 and 4 as follows, where the same parts as in the prior art have the same reference numerals.

3 is a circuit diagram of an audio processing unit in which an interference prevention circuit of the present invention is constructed, as shown in FIG. 3, the tuning signal of the tuner 1 selectively outputted by the output selector 9, the AV input signal AVI, and an external input signal ( EXTI) and a video recording / reproducing apparatus for inputting a reproducing audio signal to the high frequency modulator 10 to perform high frequency modulation, in the audio processing section, by adjusting the output level of the audio signal of the output selector 9 and inputting it to the high frequency modulator 10. It was provided with an automatic level controller 20.

When the level of the input audio signal is 0-1.24V _PP as shown in FIG. 4, the automatic level controller 20 causes the level of the output audio signal to be linear to 0-1.24V _{PP and} is equal to or greater than 1.24V _PP. In this case, the level of the output audio signal is set to 1.24V _PP .

According to the present invention configured as described above, when the level of the voice signal selected by the output selector 9 is small, that is, when the level is 1.24V _PP or less and 5dBm or less, the automatic level controller 20 outputs the level of the voice signal as it is and then the high frequency modulator. It is inputted to (10) and high frequency modulated.

When the level of the audio signal selected and output by the output selector 9 is large, that is, when the level of the audio signal is greater than or equal to 1.24 V _PP and 5 dBm or more, the level of the audio signal is kept constant at 1.24 V _PP and input to the high frequency modulator 10. Therefore, the audio signal is not overmodulated in the high frequency modulator 10 so as not to interfere with the video signal.

As described above, in the present invention, when the level of the audio signal inputted to the high frequency modulator is large, the audio signal is adjusted in the hi-fi type video recorder so that the audio signal is not overmodulated by the high frequency modulator. Interference is prevented so that the screen of the playback video signal is clear.

Claims (2)

In the audio processing unit of the video recording and reproducing the high frequency modulator outputs the audio signal selected by the output selector, the automatic level for adjusting the level of the audio signal output by the output selector so as not to be overmodulated by the high frequency modulator An interference preventing circuit of an audio processing unit of an image recording and reproducing apparatus provided with a controller. The method of claim 1, wherein the automatic level adjuster is linearly adjusted to 0-1.24V _PP when the level of the input audio signal is 0-1.24V _PP , and is constantly adjusted when it is 1.24V _{PP or} more. Interference prevention circuit of audio processing part of video recorder.