JPS59157807A - Video tape recorder - Google Patents

Abstract

PURPOSE:To eliminate the interference to the sound signal by increasing the recording level of the sound signal which works synchronously with the vertical blanking pulse of the luminance signal and receives the modulation of frequency during a working period. CONSTITUTION:A pulse generating circuit 16 is connected to a vertical synchronizing separator 17 and produces a pulse synchronous with a vertical blanking pulse. This pulse is supplied to a changeover switch 15c of a pre-emphasizing circuit 15, and buffer circuit 13 and 14 are connected via a signal line 15a during a vertical blanking period. Therefore the sound signal produces a difference of amplitude equivalent to a gain drop set at an attenuator 15d between the blanking period and other periods. Thus it is possible to avoid the S/N reduction due to the interference of the leaked signal even though the video sweep signal, etc. are partially leaked into the band of the sound signal.

Description

TECHNICAL FIELD The present invention relates to a video tape recorder that employs a frequency multiplexing method for recording a frequency-modulated audio signal superimposed on a video signal.

BACKGROUND ART Conventional video tape recorders record video signals on video tracks diagonal to the video tape, and record audio signals on audio trunks parallel to the video tape.

Therefore, the speed at which the audio head traces the audio track is, for example, /, 3'3 cm/s
It was slow like e c, so it was difficult to reproduce high quality audio. To overcome this drawback, the high tracing speed of the rotating head during playback is utilized by frequency modulating the audio signal and recording the modulated audio signal together with the video signal on diagonal video tracks on the videotape. A video tape recorder has been proposed that has enhanced audio playback capabilities.

This type of video tape recorder records the audio signal in a frequency band between the luminance signal and the chromaticity signal.
Interference between signals is avoided, and FIG. 1 shows the frequency spectrum of a video signal and an audio signal recorded by frequency multiplexing.

In the figure, the luminance signal SY is frequency modulated, and the chromaticity signal Sc is converted (low frequency conversion) into a low frequency signal that does not interfere with the -luminance signal Sy. Therefore, the frequency-modulated audio signal SA is recorded in a frequency band intermediate between the luminance signal SY and the chromaticity signal Bc.

By the way, with the recent diversification of broadcasting media, media such as text multiplex signals and test signals for the purpose of automatic line correction and checking, which are inserted into the vertical blanking period of the video signal and broadcast, are becoming more and more popular. Practical application is approaching.

In that case, when the high frequency components of the character multiplex signal, test signal, etc. inserted in the vertical blanking period are frequency modulated and recorded as a luminance signal, some of them leak into the frequency band of the frequency modulated audio signal. However, there was a problem in that it interfered with the audio signal and had an adverse effect.

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and in recording a frequency-modulated audio signal by multiplexing it with a video signal,
During the vertical blanking period, the recording level of the audio signal is increased. For example, even if a character multiplex signal, test signal, etc. are inserted during the vertical blanking period, high frequency components such as video sweep signals and multi-burst signals will not be recorded as audio. An object of the present invention is to provide a video recorder that does not cause interference to signals.

To achieve this objective, the present invention provides a configuration in which a frequency modulated audio signal, such as a frequency modulated luminance signal and a low frequency converted chromaticity signal, are multiplexed using an intermediate frequency band and recorded on the same track. In the video chi recorder of
a pulse generation circuit that generates a pulse synchronized with a vertical blanking pulse included in the luminance signal; and a pulse generation circuit that operates when supplied with the generated pulses, and records the frequency-modulated audio signal during its operation period. The gist is that a pre-emphasis circuit is provided to raise the level to a level that can eliminate interference from other signals.

According to the present invention, even when a text multiplex signal or a test signal for the purpose of automatic line correction or checking is inserted into the vertical blanking period of the video signal, the audio signal is enhanced by the Grien 7 assist circuit. It is possible to eliminate interference such as video sweep signals and multi-burst signals leaking within the frequency band, and effectively prevent a drop in the S/N ratio of audio signals, thereby diversifying frequency multiplexing type video chip recorders. It has excellent effects such as being compatible with mass media.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will now be described with reference to FIGS. 2 and 3. FIG. 2 is a circuit configuration diagram showing an embodiment of the video chip recorder of the present invention, and FIG. 3 is a recording waveform diagram of an audio signal thereof.

In FIG. 2, the video recorder records an audio signal superimposed on a video signal, and has two rotary heads 2a and 2b for recording and reproducing. The video signal recorded on the video chip is separated into a luminance signal and a chromaticity signal by a low-pass filter 3 and a band-pass filter, respectively. The separated luminance signal is a frequency modulator! After frequency modulation, low frequency components are removed by a high-pass filter B, and the signal is supplied to an adder 2. On the other hand, the separated chromaticity signal is converted into a low frequency signal (low frequency conversion) by a frequency converter r, and then only the low frequency signal is supplied to the adder 7 from the low pass filter 9VC.

The adder 7 adds the frequency-modulated chromaticity signal to the frequency-modulated luminance signal, as well as the frequency-modulated audio signal, which will be described later. The signal is amplified by the recording amplifier circuit IQ and then alternately supplied to the 4.2 rotating heads Ja and 2b. The video signals recorded by this video recorder also include broadcast signals such as teletext broadcasting, and therefore, during the vertical blanking period of the video signal, automatic correction of the teletext signal and line It must be noted that test signals etc. for checking purposes may be inserted.

By the way, after the audio signal is frequency modulated by a frequency modulator l/, only the band components between the luminance signal and the chromaticity signal are extracted by the bandpass filter 12, and then the audio signal is passed through a pair of buffer circuits /, ? , l*1iJ5 via a pre-emphasis circuit 15 to the adder //.

This glymphasis circuit 15 constitutes a main part of the present invention together with a pulse generating circuit /l to be described later, and functions to switch the amplitude of the audio signal between the vertical blanking period and other periods. That is, in the pre-emphasis circuit /3, a signal line /, ta that carries out signal transmission during the vertical blanking period, and a signal line 151) that carries out signal transmission during other periods are connected to each other by a changeover switch /jc. The latter signal line/, 5b is connected to the attenuator circuit/J4 for increasing the gain of about 3 or lBF. On the other hand, the pulse generation circuit/5b is connected to , connected to a vertical synchronization separation circuit 17 that separates a vertical synchronization signal from a video signal,
The vertical synchronization separation circuit/7 generates a pulse in synchronization with the vertical blanking pulse using the separated vertical synchronization signal.

This pulse is supplied as a switching pulse to the changeover switch /jc in the pre-emphasis circuit /3; Therefore, during the vertical blanking period, the changeover switch /SC switches between the buffer circuits /3. /4! They are connected to each other by signal lines /, 5'a.

Therefore, between the vertical blanking period and the non-vertical blanking period, the audio signal has an amplitude difference equal to the gain drop set in the attenuator circuit 15a. Therefore, the audio signal obtained through the glymphasis circuit 15 is as shown in FIG. As shown in FIG. 2, the signal waveform has a signal waveform in which the amplitude B of the vertical blanking period is about /,j or λ times the amplitude A of the other periods.

For this reason, as mentioned above, the video signal supplied to the video recorder has a character multiplex signal, a test signal for the purpose of automatic line correction and checking, etc. inserted in the vertical blanking period, so the audio signal is Even in the case where a part of the video sweep signal, multi-burst signal, etc. leaks within the frequency band of the signal, it is possible to satisfactorily prevent the problem that the audio signal is interfered with by these leaked signals and the S/N ratio is lowered.

In addition, when playing back the recording tape according to the present invention, the recording tape is reproduced while being glidly emphasized by the glissphasis circuit.
It may be supplied to the limiter amplifier, or it may be supplied to the limiter amplifier after reducing the level difference by providing an appropriate de-emphasis circuit or using a pre-emphasis circuit.

In this manner, the video recorder having the above structure can support diversifying broadcast media such as teletext multiplexing while employing the frequency multiplexing method.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the frequency spectrum of a video signal and an audio signal recorded by the frequency multiplexing method, Fig. 2 is a circuit diagram showing an embodiment of the video recorder of the present invention, and Fig. 3 is a diagram showing the audio 0 which is a recording waveform diagram of a signal /...Video chip recorder, //...Frequency modulator, /S...Pre-emphasis circuit, /A...No(russe generation circuit).

Claims (1)

[Claims] In a video tape recorder that multiplexes a frequency-modulated audio signal using a frequency band intermediate between a frequency-modulated luminance signal and a low-band-converted chromaticity signal and records it on the same track, the vertical a pulse generation circuit that generates a pulse synchronized with the blanking pulse; and the pulse generation circuit is supplied with the generated pulses and operates;
A video tape recorder comprising a gliemphasis circuit that increases the recording level of the frequency-modulated audio signal to a level at which interference with other signals can be eliminated during its operation.