JP2669242B2 - Magnetic recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording system in a VTR, and in particular, as in the case of editing a recording tape, an F
The present invention relates to a magnetic recording method in which measures are taken at the time of recording so that demodulation noise does not occur at the beginning and the end of the (overlapping) recording at the time of recording operation in which discontinuity of the M video signal is likely to occur.

[0002]

2. Description of the Related Art In a helical scanning VTR, an FM signal (FM-modulated video signal) is continuously recorded on a recorded magnetic tape from the middle of a recording portion without using an erasing head. When partially overwriting only a few H (horizontal scanning period) sections afterward, at the joint of the recording, in most cases, the FM as shown in FIG.
A signal discontinuity occurs. The discontinuity point of the FM signal is
It is output as a phase shift amount during FM demodulation in normal reproduction, and since the shift amount is random, white inversion noise as shown in FIG. 3 (B) and black inversion property as shown in FIG. 3 (C). It is output as noise.

When it is attempted to remove the noise generated at the FM demodulation of the discontinuous point of the FM signal by the VTR reproducing circuit system, it is difficult to discriminate between the normal signal and the noise, so that the effective noise is effective. The removal circuit has not been realized yet. Further, there is no conventional technique close to the method of the present invention, in which a measure for removing noise is applied on the recording track of the tape during recording.

[0004]

When the follow-up recording as described above is performed using a general VTR, it is almost always F
When a discontinuity point of the M signal occurs and the point is demodulated,
The following disadvantages occur. White inversion noise {Fig. 3 (B)}
When noise occurs for several H's in a section where a keyed pulse of a keyed AGC (automatic gain control) is applied, a malfunction of the keyed AGC occurs at the time of dubbing. When the black inversion noise {FIG. 3 (C)} occurs and is large enough to satisfy the operation level and time width of the synchronization (signal) separation, a malfunction of the synchronization separation is caused and causes skew. When the noise portion appears on the monitor screen, the image quality deteriorates.

[0005]

SUMMARY OF THE INVENTION According to the present invention, when an arbitrary FM video signal is overwritten on a predetermined portion of a magnetic tape on which an FM video signal is recorded, the FM is recorded immediately before and immediately after the overwriting.
A magnetic recording method for recording a high frequency signal having a frequency higher than the frequency band of a video signal at a time and a level satisfying a detection condition of a dropout compensation circuit of a VTR reproduction system, thereby solving the above problems. Is.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the magnetic recording system of the present invention, a high frequency signal is selected for a predetermined time t at an appropriate level at a tape portion at the beginning or end of the recording where the discontinuity of the FM signal is likely to occur, such as during the follow-up recording. It is recorded in. This high frequency signal is FM
The frequency should be higher than the frequency band of the video signal.

To specifically implement the method of the present invention, FIG.
As shown in, when supplying an FM video signal for follow-up recording to the already recorded tape T from the input terminal In, a changeover switch (switching circuit) Sw1 is provided on the high frequency signal generator 5 side for a predetermined time t at the start of recording. And a high-frequency signal is recorded on the tape T via the recording amplifier 2, the rotary transformer RT, the video head H, and the like.

Here, the predetermined time t is a time necessary and sufficient for detecting a dropout of a dropout compensation circuit (not shown) provided in a general VTR reproduction system.
In addition, the frequency of the high frequency signal is high enough to allow recording and almost no reproduction output is obtained due to the magnetic characteristics of the video head H (normal rotary head; hereinafter also simply referred to as “head”) (for example, 11 MHz or 14.32 MHz). ), And the recording level is a level that can be erased to such an extent that the reproduction level of that portion satisfies the detection level of the dropout compensation circuit (for example, a level 20 dB lower than the reference input).

Next, after a lapse of time t, the switch Sw1 is switched to the input terminal In side to input the FM video signal, and the normal recording is performed for the required time. When the recording is completed, the changeover switch Sw1 is connected to the high frequency signal generator 5 side for a predetermined time t, and then the recording is completed. A schematic diagram of the reproduced FM signal of the tape T recorded by such an operation is shown in FIG. 5 (C), and its demodulated signal is shown in FIG. 5 (D). Comparing this figure with the conventional method {FIGS. 5 (A), (B), FIG. 3 (A), (B)}, the reproduced FM signal by the video head H in the portion where the high frequency signal is recorded is low. Since this level is reached, this part is replaced by the signal 1H before in the dropout compensation circuit. Therefore, the noise disappears, and there is no possibility that the keyed AGC malfunctions during dubbing.

Next, another circuit configuration example capable of realizing the method of the present invention will be described with reference to FIG. As shown in the figure, two recording amplifiers are used, a high-frequency signal and FM for follow-up recording.
Signal processing such as individually amplifying video signals is performed. Moreover, changeover switch Sw2 and the switch Sw3 are configured to operate contradictory manner in conjunction, when the recording of the high-frequency signal, an input side of the recording amplifier 4 for FM video signal, mute via a capacitor C ₃ ing. In addition,
The trap circuit 6 is a circuit having a characteristic of transmitting only a specific high-frequency signal, and the trap circuit 7 is a circuit of a characteristic of transmitting an FM video signal without passing a specific high-frequency signal. Various filters such as a satisfactory BPF (bandpass filter) may be used.

Another example of a circuit configuration that can realize the method of the present invention will be described with reference to FIG. As shown in the figure, two recording amplifiers are used, and changeover switches Sw4 and Sw5 are connected to the output sides of the recording amplifiers 3 and 4, respectively.
The changeover switch Sw4 and the switch Sw5 are also configured to operate in a contradictory manner so that the output side of the recording amplifier 4 for FM video signals is opened (Of
f) Then, only the high frequency signal is input to the resistor R, the capacitor C1,
Recording is performed on the tape T via the rotary transformer RT and the video head H.

In the above description, the high frequency signal generator 5 is newly provided in order to realize the method of the present invention, but instead of providing this high frequency signal generator 5, it is used in a normal VTR. An erasing signal of 11 MHz or a high frequency signal of 14.32 MHz of color burst 4 fsc may be used. Further, the predetermined time t and the recording level are set to the time (the time necessary and sufficient for detecting the dropout) to satisfy the operation of the dropout compensating circuits of all general VTR reproducing systems. If it has a specific standard, a value that applies to the standard (for example, time t = 1 ns
ec, the recording level may be 11 MHz, and the recording head current may be 20 mAp-p｝.

[0013]

As described above, the magnetic recording system of the present invention has the following excellent features. When a tape recorded by the method of the present invention is reproduced by a VTR, the FM missing portion shown in FIG. 5 (C) satisfies the detection condition of the dropout compensation circuit of the VTR reproduction system. Not only is avoided, but the signal is replaced by the signal 1H earlier to compensate for the noise portion. By compensating the noise part, it is possible to prevent malfunctions of keyed AGC and sync separation. Since it is a measure against recording tape, it is not limited to a specific playback device, and compatibility with respect to a noise removing action is achieved.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of a first embodiment device capable of realizing a magnetic recording system of the present invention.

FIG. 2 is a signal waveform diagram showing discontinuity of an FM signal which is likely to occur at a seam of recording.

FIG. 3 is a signal waveform diagram for explaining demodulation noise generated at the time of reproduction at a discontinuous portion of an FM signal.

FIG. 4 is a circuit block diagram of an apparatus according to a second embodiment capable of realizing the magnetic recording system of the present invention.

FIG. 5 is a diagram illustrating a difference between a demodulated signal when the system of the present invention is not used and a case where the system is used.

FIG. 6 is a circuit block diagram of a device according to a third embodiment which can realize the magnetic recording system of the present invention.

[Explanation of symbols]

 2-4 Recording amplifier 5 High-frequency signal generator 6, 7 Trap circuit H Magnetic (video) head RT Rotary transformer Sw1 ~ Sw5 Changeover switch T Magnetic tape

Claims (1)

(57) [Claims] 1. A high-frequency signal having a frequency equal to or higher than a frequency band of the FM video signal immediately before and immediately after overwriting an arbitrary FM video signal on a predetermined portion of a magnetic tape on which the FM video signal is recorded. Is recorded at a time and level satisfying the detection conditions of the dropout compensation circuit of the VTR reproducing system.