JPS62243102A - Erasing system in magnetic recording - Google Patents

Abstract

PURPOSE:To prevent a moire distortion, etc., from occurring on a reproduced screen of a video signal which has been rewritten, by generating white noise, annihilating it and writing it plural times in a track in which it has been written already, and erasing the signal. CONSTITUTION:As for a white noise generator, when there is no signal in an input side of an FM demodulator, the white noise is generated in an output side. As for an erasing signal, its envelope decreases gradually like an exponential function by making it pass through an attenuating circuit 2. The erasing signal being the white noise is attenuated by the attenuating circuit 2, and thereafter, written plural times in a track 5a on a floppy disk 5 in which a color video signal has been written already, by a magnetic head 4 through a recording amplifier 3. In this way, a magnetic material of the track 5a is oriented at random, its magnetization also decreased gradually and the original color video signal is erased. In this way, an erasion can be executed satisfactorily without making a moire distortion, etc., occur on a reproduced screen of a rewrite signal.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an erasing method in magnetic recording, in which white noise is used for erasing, and is particularly useful when applied to electronic still camera systems. It is.

<Prior Art> Various techniques have been proposed in the past as erasing methods for magnetic recording of video signals, particularly for magnetic recording in electronic still camera systems using floppy disks as magnetic recording media. One of these methods is called a sweep erasure method. The sweep elimination method is, first,
An erasing signal with a frequency within the video signal band (for example, 6 MHz) is written onto a track of a magnetic recording medium 1, for example, a magnetic disk, on which a video signal has already been written, and the frequency of this erasing signal is continuously increased while a similar process is performed. By repeating writing, the frequency of the erase signal is finally brought out of the band of the video signal. With this sweep erase method, the frequency of the erase signal written to the track is
In the end, since the signal is outside the band of the video signal, it can be easily cut with a filter during reproduction, and only the necessary video signal can be reproduced. That is, the original video signal is substantially erased by overwriting many erasing signals with different frequencies on the track in which the original video signal was written. As a technique very similar to the sweep cancellation method, a method similar to the sweep cancellation method has also been proposed in which the frequency of the cancellation signal is increased stepwise.

<Problems to be Solved by the Invention> In any case, the above-mentioned conventional techniques involve overwriting signals of a large number of frequencies, so there is a problem that erasing takes time. Incidentally, it takes 2 seconds (
120 rotations) or more. On the other hand, if the erasure time is shortened, the erasure signal will remain within the frequency band of the video signal, causing moiré distortion etc. on the playback screen of the new video signal. If you shorten the changing time (sweep time), even if you overwrite a relatively high frequency cancellation signal on a relatively low frequency cancellation signal, the relatively low frequency cancellation signal will be The high-frequency erase signal does not completely rewrite the data, and as a result, the relatively low-frequency erase signal remains unerased. Therefore, if we consider a certain point on the floppy disk, at this point the erase signal will remain at a relatively large level in a specific frequency spectrum within the frequency band of the video signal, and the erase signal will remain at a relatively large level on the track of the floppy disk in such a state. When a new video signal is written, when this video signal is played back, the video signal and the erased signal of a specific frequency spectrum interfere with each other, and this appears as moiré distortion on the playback screen.

As described above, in the above-mentioned prior art, there is a problem in that sufficient erasing cannot be achieved by shortening the erasing time, and if sufficient erasing is attempted, the erasing time becomes longer.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide an erasing method for magnetic recording that does not cause moiré distortion or the like on the playback screen of a rewritten video signal even in a relatively short erasing time. shall be.

9. Means to solve the above problems> A book that achieves the above objectives. The structure of IJ1 is characterized in that white noise is generated and the signal is erased by writing it multiple times to a track of a magnetic recording medium in which an old signal has already been written while gradually reducing the white noise.

Effects> According to the present invention having the above configuration, even if the cancellation signal is within the frequency band of the video signal, not only the power density spectrum becomes almost uniform over the entire frequency band, but also its level becomes uniform. The amplitude of the erase signal gradually decreases and becomes smaller during a plurality of writing operations in which the amplitude of the erase signal is attenuated.

Example of implementation Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing an apparatus for implementing an embodiment of the present invention. As shown in the figure, the white noise generator l in this embodiment is composed of an FM demodulator. That is, when there is no signal on the input side of the FM demodulator, white noise is generated on the output side, so this white noise is used. The attenuation circuit 2 gradually reduces the level of the cancellation signal which is the output signal of the FM demodulator. That is, as shown in FIG. 2, the envelope of the erase signal is gradually reduced exponentially by passing it through the attenuation circuit 2. At this time, the time it takes for the level of the erase signal to become sufficiently small, that is, the decay time T, can be determined in relation to the number of revolutions of the floppy disk 5, but the floppy disk of a still camera system, which rotates once every 1/H second, In the case of disk 7, 60 rotations is appropriate. The magnetic head 4 writes an erase signal, which is an output signal of the attenuation circuit 2 amplified via the recording amplifier 3, onto the track 5a of the floppy disk 5.

In the method of this embodiment using such a device, the erasure signal, which is white noise, sent from the white noise generator 1 that utilizes the output of the FM demodulator when there is no signal is attenuated by the attenuation circuit 2, and then sent to the recording amplifier. The color video signal is written multiple times by the magnetic head 4 via the floppy disk 3 onto the track 5a on the floppy disk 5 on which the color video signal has already been written. As a result, the orientation of the magnetic material in the track 5a becomes random and its magnetization is gradually reduced, erasing the original color video signal.

In this example, the erasure signal, which is white noise, was generated by a white noise generator I consisting of an FM demodulator. If so, there is no particular limitation, but if the circuit configuration is as shown in Figure 1, such circuit components are always included in magnetic recording/reproducing devices, so It can be easily constructed by selecting and combining the parts as appropriate and providing a selection switch for switching recording, playback, and erasing modes.
It is.

It has a practical effect of being able to do this.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, according to the present invention, the orientation of the magnetic material of the magnetic recording medium can be made random by the erase signal, and the magnetization thereof can also be gradually reduced. It is possible to perform good erasing without causing moiré distortion or the like on the reproduction screen of the rewritten signal without spending much time as in the conventional method.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a device implementing an embodiment of the present invention, and FIG. 2 is a waveform diagram showing the waveform of an erase signal passed through an attenuation circuit. In the drawing, 1 is a white noise generator, 2 is an attenuation circuit, 3 is a recording amplifier, and 4 is a magnetic head. 5 is a floppy disk,

Claims (1)

[Claims] An erasing method for magnetic recording, characterized in that white noise is generated and the signal is erased by writing multiple times on a track of a magnetic recording medium on which a signal has already been written while gradually reducing the white noise.