JPS5846769B2 - Recorded recording medium and its production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION With the spread of VTRs (magnetic recording and reproducing devices), pre-recorded video tapes containing movies and the like are being sold.

However, if two VTRs are prepared, copies can be easily dubbed from recorded tapes.

Dubbing of recorded tapes like this is prohibited by law, but if it is done on a small scale in households,
This cannot be regulated and is inconvenient for tape manufacturers and copyright holders.

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

Let's explain one example below.

In the figure, 10 is a mask VTR (reproduction VTR), 2
0 indicates a slave VTR (recording VTR) for producing a recorded tape.

In the master VTR 10, a luminance signal (color or black and white video signal) is reproduced from the master tape 11 by the rotating magnetic head 12, and this signal is transmitted to the reproduction circuit 13.
→Line 33-→The luminance signal is supplied to the rotating magnetic head 22 through the recording circuit 23, and this luminance signal is, for example, one field of which becomes one diagonal magnetic trunk, and a vertical blanking period at the end of the magnetic track. It is recorded on the magnetic tape 21 in such a manner that

At the same time, the magnetic head 1 is transferred from the master tape 11.
5 reproduces the audio signal, and this signal is supplied to the magnetic head 25 through the reproduction amplifier 16 → line 36 → recording amplifier 26, and the AC bias signal from the bias oscillation circuit 27 causes the tape 21 to be magnetized in its length direction. recorded as a track.

In this case, in the present invention, for example, the line 36
A mixing circuit 41 is provided, to which an alternating signal Sa of a specific frequency, for example 2]-kHz, is supplied from an oscillation circuit 42, and the alternating signal Sa is mixed with the audio signal supplied to the recording amplifier 26.

Note that the frequency of the AC bias signal from the bias oscillation circuit 27 is set to be sufficiently high, for example, 80 kHz, in order to eliminate beat interference with the alternating signal Sa.

Therefore, the magnetic tape 21 records the luminance signal and audio signal of the master tape 11, and the audio signal is mixed with the alternating signal Sa.

This tape 21 is a recorded tape.

Therefore, when this recorded tape 21 is played back using a general VTR and monitor receiver, the brightness signal and audio signal of the tape 21 are played back normally.

However, in this case, the audio signal is mixed with the alternating signal Sa, but its frequency is 21 kHz, which is outside the audible frequency range or close to it, so the monitor receiver's speakers hardly reproduce it as sound. Even if it is played, the volume is so low that it is almost impossible to listen to it.

Therefore, when simply reproducing the recorded tape 21, it can be reproduced without any problem.

On the other hand, when two VTRs are prepared and the recorded tape 21 is dubbed, when the audio signal is recorded on the magnetic tape for duplication in the recording VTR, the alternating signal mixed with the audio signal is A beat signal is generated between Sa and an AC bias signal for recording this audio signal.

Therefore, the frequency of the AC bias signal is, for example, 20 k.
Hz, the frequency of the beat signal is 1 kHz
z. Therefore, when an audio signal is recorded on a magnetic tape for duplication, this beat signal is recorded on the tape together with the audio signal.

Therefore, when playing a dubbed duplicate tape,
At the same time as the audio 1. kHz beat sounds will also be played, which is not practical.

Therefore, dubbing can be prevented.

In this way, according to the present invention, there is no problem when simply reproducing the recorded tape 21, but dubbing can be prevented.

Furthermore, there is no need to change the configurations of the mask VTR 10 and slave VTR 20.

Note that instead of the tape 210, a recording medium such as a magnetic card or a so-called video disk may be used.

[Brief explanation of the drawing]

The figure is a system diagram of an example of the present invention. 10 is a master VTR, and TR 120 is a slave VTR.

Claims (1)

[Scope of Claims] 1. A beat frequency at which an audio signal is recorded and which is at a frequency outside the audible frequency or a frequency close thereto, and which is the same as the frequency of an AC bias signal for recording the audio signal in a magnetic recording/reproducing device. A recorded recording medium in which the audio signal is mixed with an alternating signal of a frequency that can be recorded and reproduced by the audio signal recording and reproducing system of the magnetic recording and reproducing apparatus and is audible. 2 At a frequency outside the audible frequency or a frequency close to this,
And, the beat frequency with the frequency of the AC bias signal for recording the audio signal in the magnetic recording and reproducing device is a frequency that can be recorded and reproduced by the audio signal recording and reproducing system of the magnetic recording and reproducing device and can be heard. A method for producing a recorded recording medium in which an alternating signal of a certain frequency is mixed with an audio signal and recorded on the recording medium.