JPS6112435B2 - - Google Patents

Description

[Detailed Description of the Invention] With the spread of VTRs, it has become a viable business to sell pre-recorded tapes containing movies and the like. However, for example, two
By preparing a VTR, it is possible to easily make copies of recorded tapes, that is, dubbing.

Although the act of making such duplicate tapes is prohibited by law, it cannot be regulated if it is done on a small scale, such as in ordinary households. It is also inconvenient for tape manufacturers.

In view of these points, the present invention seeks to provide a recorded tape that cannot be dubbed and a method for producing the same.

First, considering general VTRs, there are the following types of VTRs and their monitor receivers.

In FIG. 1, a signal recorded on a magnetic tape 1 is extracted by a rotary head 2, and is supplied to an FM demodulation circuit 5 and a de-emphasis circuit 6 through a playback side contact P of a changeover switch 3 and a playback amplifier 4, thereby producing a composite video signal. S _t1 . And this signal S _t1
is supplied to the VTR side contact V of the changeover switch 7 through the terminal 27, and the signal S _t1 from the switch 7 is supplied to the picture tube 9 through the video circuit 8 to reproduce the image. In addition, when receiving a broadcast signal, a high frequency signal extracted from the antenna 10 through the tuner 11 is supplied to the video detection circuit 13 through the video intermediate frequency circuit 12 to be converted into a composite video signal St ₂ , and this signal St ₂ is used for switching. A part of the output signal of the video circuit 8 is fed back to the tuner 11 and subjected to keyed AGC.

Furthermore, when recording, the composite video signal St ₃ from the input terminal 14 and the signal St ₂ supplied from the video detection circuit 13 through the terminal 28 are selected by the changeover switch 15, and the extracted signal is
Pre-emphasis circuit 1 through AGC circuit 16
7 and the pre-emphasized signal is
The signal is supplied to the rotary head 2 through the FM modulation circuit 18, the recording amplifier 19, and the recording side contact R of the changeover switch 3, and is recorded on the tape 1.

The AGC circuit 16 of the video signal recording system of such a VTR is configured as follows.

That is, the composite video signal St taken out from the changeover switch 15 has a horizontal synchronizing signal Sh and a video signal Sv, as shown in FIG. 2A. and,
This signal St is supplied to the pre-emphasis circuit 17 through the variable gain amplifier 20, and this signal St is also supplied to the synchronization separation circuit 21 to separate the horizontal synchronization signal Sh.
2. A pulse signal Sp is supplied to the delay circuit 23 and the phase inverting amplifier 24 and has a level Vp approximately equal to the white peak level of the video signal Sv at a position corresponding to the back porch of the horizontal synchronizing signal Sh as shown in FIG. 2B.
is formed.

This signal Sp and the signal St from the amplifier 20 are added in an adder circuit 25 to form an added signal Sa as shown in FIG.
6, a detection signal having a voltage value (Vp + Vh) from the tip of the signal Sh to the tip of the signal Sp (Vh is the level of the signal Sh) is extracted, and this detection signal is sent to the amplifier 20 as a control signal for its gain. Supplied.

Therefore, when the level of signal St changes, signal Sh
Since the level Vh of the pre-emphasis circuit 17 also changes, the voltage value (Vp+Vh) taken out from the detection circuit 11 changes, and the gain of the amplifier 20 is controlled so that this value becomes a constant value.
The level of the signal Sv supplied to is controlled to a constant level.

Therefore, the supplied signal St is always recorded on tape 1 at a constant level, and if the white peak of the video signal Sv becomes excessively input, especially when inputting a camera, the level of the video signal Sv will change. pulse signal
Since the voltage exceeds the level of Sp, the voltage value extracted by the detection circuit 26 changes rapidly in accordance with the level ratio of the horizontal synchronizing signal Sh and the video signal Sv, and faster gain control is performed. It is valid.

The present invention focuses on the fact that VTRs and monitor receivers are configured in this way, and although recorded tapes can be played back, when a duplicate tape is created by dubbing from this tape, this duplicate This is an attempt to prevent dubbing by preventing a normal playback screen from being obtained even when the tape is played back.

Hereinafter, to explain one example of the present invention, the third
The figure shows an apparatus for producing a recorded tape (or its master tape).

In the figure, 31 is an input terminal to which the composite video signal St (FIG. 2A) is supplied, and this signal St
is supplied to the nonlinear circuit 33 through the amplifier 33. This circuit 33 has the input/output characteristics as shown in FIG. 4, for example, and the portion of the supplied signal St below the pedestal level is expanded as shown in the figure, resulting in a synchronizing signal.
A signal Sb is generated in which the level of Sh is set to a large level Vh'.

This signal Sb is supplied to a rotary head 38 through an ordinary AGC circuit 34, a pre-emphasis circuit 35, an FM modulation circuit 36, and a recording amplifier 37, and is recorded on a magnetic tape 39. The servo systems for controlling the rotational phase of the rotary head 38 and the transport speed of the tape 39 are constructed in the same manner as in the prior art.

In this way, a recorded tape (or master tape) 39 is produced, and in this case, the recorded signal Sb is the level of the horizontal synchronizing signal Sh of the composite video signal St increased.

Therefore, when this recorded tape 39 is played back by the device shown in FIG. . And in this case, this signal Sb is the synchronization signal Sh
The level of the video signal Sv is only Vh′.
is not changed in any way, so a normal playback screen can be obtained on the picture tube 9. In addition, in monitor receivers, the keyed AGC is applied to the high frequency signal system such as tuner 11, and is not applied to the video signal system from the VTR, so even if the level of the horizontal synchronizing signal Sh becomes high, the keyed AGC will not be applied to the reproduced image. There is no effect.

On the other hand, if you prepare another VTR and take out the signal Sb reproduced by one VTR from the terminal 27 and supply it to the input terminal 14 of the other VTR for recording (dubbing), the AGC circuit 16, the amplifier 20 outputs a signal as shown in FIG. 5A.
Sb is supplied to the adder circuit 25, and the amplifier 24
Since a pulse signal Sp as shown in FIG. 5B is supplied from the adder circuit 10, a signal Sc as shown in FIG. 5C is taken out from the adder circuit 10. Then, this signal Sc is supplied to the detection circuit 11, and the voltage value (Vp + Vh') from the tip of the signal Sh to the tip of the signal Sp is extracted, and the voltage value is adjusted so that it becomes the normal magnitude of (Vp + Vh). The gain of amplifier 2 is controlled.

Therefore, in the AGC circuit 16, the level of the signal Sh is reduced and at the same time the level of the signal Sv is also suppressed, and this suppressed signal is transferred to the tape 39.
recorded in

Therefore, when the duplicate tape 5 made in this way is played back, the level of the video signal Sv taken out is low and the S/N ratio is poor, so even if this signal is supplied to a monitor receiver, it is not practical. I can only play the screen.

Thus, according to the invention, recorded tape 39
If you play back a VCR and supply the playback signal to a monitor receiver, you will get a normal playback screen, but if you make a duplicate tape by feeding this signal to another VTR, this duplicate tape will not be played back. Even if the tape is played back, the playback screen will not be practical and only a useless duplicate tape will be created, so dubbing can be prevented.

In the above example, the level of the synchronization signal Sh was increased, but a non-linear circuit 33 with the opposite characteristics is used to compress the level of the synchronization signal Sh to the extent that the synchronization on the monitor receiver is not disturbed. You can do it like this. In this case, in the AGC circuit 16 of the recording VTR during dubbing, the amplifier 2
0 gain is increased more than necessary, and the video signal Sv becomes over-input in the subsequent circuit, causing the video signal Sv
Since the image is clipped in areas where the level of the image exceeds the original white peak level, when this duplicate tape is played back, the white side of the image becomes saturated, resulting in so-called white collapse, making it impractical.

In addition, the method of changing the level of the synchronization signal Sh is not limited to the case of using a non-linear circuit as described above, but it is also possible to synchronize with the synchronization signal Sh, form a pulse signal with the same phase, and adjust this to an appropriate level. It may be amplified to replace the synchronization signal Sh in the composite video signal St.

Furthermore, by attaching the above-mentioned device to a general VTR, it is possible to prevent the user from dubbing recorded broadcasts or the like.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a general VTR and monitor receiver, Fig. 2 is a waveform diagram for explanation thereof, Fig. 3 is a system diagram of an example of a device for producing a recorded tape according to the present invention, and Fig. 4 and FIG. 5 are waveform diagrams for explaining the same. 33 is a non-linear circuit, and 39 is a recorded tape.

Claims (1)

[Claims] 1. For signal recording, in which the horizontal synchronizing signal level of a composite video signal is expanded or compressed from that of a standard television signal, and this signal is recorded again.
A recorded recording medium that prevents dubbing by abnormally affecting the operation of the recording AGC of a VTR. 2. The level of the horizontal synchronization signal of the composite video signal is expanded or compressed from that of the standard television signal and recorded on the recording medium, and this signal is recorded again. A method for producing a recorded recording medium that prevents dubbing by providing