JPH05970Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a noise removal circuit for high-fidelity VTRs.

(b) Prior art Since high-speed VTRs can record audio signals in two places, the audio track and the video track, a special high-speed VTR is used to record new audio on the audio track while reproducing the high-speed signal on the video track. Dubbing becomes possible. This dubbing can also be used for karaoke, and is also disclosed on page 35 of the July 1983 issue of the magazine "Television Technology" published by Denshi Gijutsu Publishing Co., Ltd. FIG. 2 is a circuit block diagram schematically showing this dubbing (karaoke) circuit. As is clear from this figure, the high-frequency audio circuit (HF) consists of a high-frequency recording circuit 1 that modulates the microphone input into FM, and a high-frequency reproduction circuit 2 that demodulates the reproduced FM signal.
The FM signal is multiplexed onto the low-frequency side of the video signal and recorded on the video track, and during playback, the frequency is separated by a bandpass filter. In addition, in the normal normal audio circuit A, the microphone input is amplified by the recording amplifier 3, and then AC bias recording is performed by the audio head H via the recording/playback switch S. At the time of playback, the playback signal is amplified and derived by the playback amplifier 4. There is.
The outputs of both amplifiers are selectively derived according to the mode by a monitor switch SW.

In the dubbing mode, the high-speed recording circuit 1 and the reproduction amplifier 4 are inactivated, and the output of the high-speed reproduction circuit 2 and the output of the recording amplifier 3 via the monitor switch SW are respectively derived. Each of these outputs is input to the mixing circuit 5 via the first and second switches S1 and S2, which are closed during dubbing, and the mixing output is supplied to the monitor speaker.

Recording and reproducing devices usually perform muting to remove noise when setting and canceling modes. Therefore, muting is also performed when setting and canceling this dubbing mode. However, if the output of the high-fidelity reproduction circuit 2 and the output of the recording amplifier 3 are muted when setting and canceling the dubbing mode, the microphone input will be interrupted from the mixing output. Particularly when this dubbing mode is used for karaoke, the microphone sound from the monitor speaker is inconveniently interrupted due to muting. Therefore, when using it for karaoke, it is necessary to limit muting of the microphone input.

(c) Purpose of the invention Therefore, the present invention is characterized by canceling muting of audio input in dubbing mode.

(d) Structure of the invention The present invention is characterized in that an audio signal is temporarily selected in place of the mixing output when setting and canceling the dubbing mode.

(E) Embodiment The present invention will be described below with reference to an illustrative embodiment.

FIG. 1 shows the audio switching circuit of a Hi-Fi VTR. In this embodiment, in the playback mode, one of the playback outputs can be selected by selectively switching between the high playback output and the normal playback output that is played back from the audio head using the monitor switch SW. There is. Further, the high-fidelity reproduction output and the normal reproduction output are input to a mixing circuit 5, and a mixing output is derived by adding both outputs. Therefore, the second selection switch 7 inputs the first selection output and the mixing output.
By selectively switching both outputs, either one of the two reproduction outputs or the mixing output can be amplified and output to the monitor speaker.

The switching of the first and second selection switches 6 and 7 is as follows.
The selection states of both are controlled by first and second switching control circuits 8 and 9. The first and second switching control circuits 8 and 9 control the switching of both selection switches 6 and 7 in accordance with the first and second operation outputs issued by operating the manual switch in the playback mode. When the first and second operation outputs are at a high level, the switching state shown in FIG. 1 is realized. Therefore, in order to perform mixing playback, the second operating output must be set to low level, and to reproduce the high-speed playback output alone, the first operating output must be set to low level and the second operating output must be set to high level. must be set.

In this embodiment, when the dubbing mode is set, a high-level dubbing control signal a is generated during the dubbing mode setting period, and the high-level recording/reproducing circuit
HF is set to playback mode, normal recording/playback circuit A is set to recording mode, and monitor switch SW is set to EE.
output (i.e. amplified output of the audio input signal to be recorded)
Select.

The dubbing control signal a, which is at a high level during the dubbing mode setting period, is input to the delay circuit 10 and is input to the exclusive OR circuit 11 together with the delayed output.
This exclusive OR output is at a high level for a certain period of time (several hundred milliseconds) at the start and end of dubbing mode setting. This high level period includes the noise generation timing of the high-speed playback output, and the exclusive OR output is the first and second switching control circuit 8,
9, the first and second selection switches 6,
7 derives the EE output by being switched to the side shown. However, during the dubbing mode setting period excluding this high level period, both selection switches 6 and 7 are
The output can be arbitrarily selected according to the first and second operation outputs.

Therefore, the high-eye noise that occurs at the start and end of the dubbing mode setting is prevented from occurring by switching the first and second selection switches 6 and 7, and the EE output is independently controlled by both operation outputs. Or, if it is derived by mixing, the EE output of the monitor speaker will not be interrupted temporarily.

In this embodiment, a muting circuit is placed after the second selection switch 7 in consideration of noise occurring at the start and end of the playback mode setting. Only works. Regarding the placement location of the muting circuit, it goes without saying that it may be placed after the first selection switch 6 if the switching in the dubbing mode described above is also done in the playback mode. .

(f) Effects of the invention Therefore, according to the invention, the generation of high-speed noise is prevented at the start and end of the dubbing mode setting, and the EE output is not interrupted, so the effect is great.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.
FIG. 3 is an explanatory diagram of waveforms of the same essential parts, and FIG. 2 is a conventional circuit block diagram. Explanation of main drawing numbers, 5...Mixing circuit, 6...
...First selection switch, 7...Second selection switch.

Claims (1)

[Claims for Utility Model Registration] By setting the high-speed recording/reproducing circuit to the playback mode and setting the normal recording/playback circuit to the recording mode, the EE output of the normal recording/playback circuit and the high-speed playback circuit of the high-speed recording/playback circuit In a hi-fi VTR that outputs the output to a monitor speaker via a mixing circuit to set a dubbing mode, the EE is given priority over the hi-fi playback output during a certain period of time at the start and end of the dubbing mode setting.
a first selection switch that selects an output; and a second selection switch that selects the output of the first selection switch and supplies it to the monitor speaker with priority over the output of the mixing circuit during each fixed period at the start and end of the setting of the dubbing mode. A noise removal circuit consisting of a selection switch and a selection switch.