JPS623638B2 - - Google Patents

Description

[Detailed Description of the Invention] In a helical scan type VTR (magnetic recording/reproducing device), a luminance signal is generally converted into an FM signal, and this FM luminance signal is magnetically transferred to a magnetic tape by two rotating magnetic heads. In this case, there is a method of recording in a track pattern as shown in FIG.

That is, 1 indicates a magnetic tape, and 2 indicates a magnetic track.The tracks 2 are formed diagonally with respect to the tape 1, and one field of FM brightness signal is recorded on one track 2, but the tracks 2 are mutually separated. It is formed so that it touches, and at this time,
A so-called H arrangement (horizontal synchronization arrangement) is performed so that the positions of the horizontal synchronization pulses Ph in track 2 are arranged on a line perpendicular to track 2. In this example, adjacent tracks 2 are arranged along the lengthwise direction.
It is sequentially shifted by 1.5H (1H is the length of track 3 corresponding to one horizontal period). Note that Pv (○ mark) indicates the vertical synchronization pulse.

Further, among the tracks 2, the heads forming every other track 2A and the heads forming every other remaining track 2B have different operating gap angles, so-called azimuth angles. Track 2A and Track 2
B and B have different azimuth angles.

Therefore, during playback, there is no crosstalk between tracks due to azimuth loss, and
Even if some crosstalk occurs between tracks, the effect can be reduced or ignored because H alignment is performed, so in such a track pattern,
Brightness signals can be recorded with high density.

However, when slow motion playback is performed from tape 1 having such a track pattern, jitter occurs on the playback screen.

That is, to perform slow motion playback at 1/3 playback speed, for example, one head needs to repeatedly scan the same track 2 three times, but
Therefore, if the tape 1 is run intermittently, the mechanism of the tape running system becomes complicated, so generally, the tape 1 is run continuously at 1/3 of the recording speed. .

Therefore, while one head is repeatedly scanning the same track 2 three times, the tape 1 is running at 1/3 the speed, so the head scanning locus corresponding to track 2A is shown by the thin line. Trajectory A ₁ ~ _{A 3} (A ₄
= A ₁ ), and the scanning trajectory of the head corresponding to track 2B is the trajectory B ₁ to B ₃ (B ₄ =B ₁ ) shown by the broken line, and the starting points of the trajectories A ₁ to A ₃ and B ₁ to _{B 3} are , are sequentially shifted by 1H with respect to the starting ends of tracks 2A and 2B. Moreover, a deviation of 0.5H occurs between the trajectories A ₁ to A ₃ and B ₁ to B ₃ .

Therefore, using the vertical synchronization pulse Pv as a reference, the positional relationship of the trajectories A ₁ to B ₃ with respect to this pulse Pv is shown by the solid line in FIG. 2, or,
Using the trajectories A ₁ to _{A 3} as a reference, it becomes as shown in FIG. 3. However, in reality, track 2 is slightly longer than one field period, and has overlapping parts before and after it, and similarly, trajectories _A1 to _B3 also have overlapping parts, as shown by broken lines.

These trajectories A ₁ to B ₃ also correspond to the playback outputs of the heads, so the outputs of one head A ₁ to _{A 3}
and the other head outputs B ₁ to B ₃ are taken out alternately every 1 field period, the time interval of the vertical synchronizing pulse Pv is divided into 1 horizontal period per 1 field period with a period of 3 field periods. It will change depending on the situation. Therefore, when such a signal is reproduced as a screen, vertical jitter occurs.

In view of these points, the present invention attempts to prevent vertical jitter from occurring during slow motion reproduction.

Let's explain one example below.

In FIG. 4, 11A and 11B indicate rotating magnetic heads, and these heads 11A and 11B are 180
It has an angular spacing of .degree. and is rotated by a motor 29 at a frame frequency. Also, the tape 1 is
The tape is run diagonally over an angular range of just over 180 degrees, and is run at, for example, 1/3 the tape speed during recording. Incidentally, on the tape 1, for example, a track pattern FM luminance signal as shown in FIG. 1 is recorded.

Further, 20 indicates a servo circuit. That is, a control pulse is reproduced from the tape 1 by the magnetic head 21 (in this case, since the tape speed is 1/3 of the recording speed, the frequency of the control pulse is 1/3 of the frame frequency), and this pulse is The signal is supplied to a multiplier circuit 23 through a reproducing amplifier 22 and converted into a frame frequency pulse, and this pulse is supplied to a phase comparator circuit 24. Furthermore, a pulse generating means 26 is provided on, for example, the rotating shaft 25 of the heads 11A, 11B.
One pulse is taken out for each revolution of 1B,
This pulse passes through the shaping amplifier 27 to the comparator circuit 2.
4.

The comparison output of the comparison circuit 24 is then output to the amplifier 28.
As shown in FIG. 1, the starting point of the trajectory _A1 coincides with the starting end of the track 2A. Therefore, as shown in FIG. 2A or FIG. 3, reproduced signals A ₁ to B ₃ are obtained from the heads 11A and 11B.

The reproduction signals _A1 to _A3 of the head 11A are supplied to the switch circuit 15A through the reproduction amplifier 12A, and are also supplied to the switch circuit 15A through the reproduction amplifier 12A.
The delay time of the CCD is sequentially supplied to delay circuits 13A and 14A for one horizontal period, and their delayed outputs are supplied to a switch circuit 15A. Similarly, the reproduction signals B ₁ to _{B 3} of the head 11B are also supplied to the switch circuit 15B through the reproduction amplifier 12A, and are also sequentially supplied to the delay circuits 13B and 14B, and their delayed outputs are supplied to the switch circuit 15B. .

Furthermore, another pulse generating means 31 is provided on the rotating shaft 25.
is provided for each rotation of heads 1A and 1B.
Pulses that are shifted by one field period with respect to the pulses from the means 26 are taken out at a ratio of 1 to 3 and are supplied to the OR circuit 34 through the shaping amplifier 32, and the pulses from the multiplier circuit 23 are supplied to the OR circuit 34. 34. In this way, from the OR circuit 34, at the field frequency, and
Pulses synchronized with the rotation of heads 11A and 11B are extracted.

This pulse is then transmitted to the switching signal forming circuit 3.
As shown in FIG. 5, a staircase wave signal whose period is three field periods and whose level changes every field period is formed. Also, at this time, the control pulse from the amplifier 22 is
The signal is supplied to a forming circuit 35, and the phase of the staircase wave signal (the phase in units of field periods) is regulated. This staircase wave signal is then supplied to the switch circuits 15A, 15B as their control signals.

Thus in Figure 2 (in this figure, the signal A ₁
~ B ₃ moving to the right corresponds to the signal being delayed), the signals A ₁ and B ₂ are delayed by one horizontal period and taken out, and the signals B ₁ and A ₃ are taken out as they are, and the signals A ₂ and B ₃ are extracted with a delay of two horizontal periods, and therefore, the time axes of the signals A ₁ to B ₃ are corrected so that the time intervals of the vertical synchronizing pulses Pv are equal.

And signals A ₁ to _{A 3} from the switch circuit 15A
are supplied to the switch circuit 16, and signals B ₁ to _{B 3} from the switch circuit 15 are supplied to the switch circuit 16. Further, pulses from the amplifiers 27 and 32 are supplied to a flip-flop circuit 36 to form a rectangular wave signal that is inverted every field period, and this signal is supplied to the switch circuit 16 as its control signal.

In this way, the switch circuit 16 outputs the signals A ₁ to
A ₃ is taken out alternately, ie, serially, every one field period. This extracted signal is then supplied to the FM demodulation circuit 18 through the limiter 11 to demodulate the original luminance signal, which is then extracted to the terminal 19.

Thus, according to the present invention, since fluctuations in the time axis during slow motion playback are corrected, there is no vertical jitter on the playback screen. Moreover, there is no need for the tape 1 running system to be an intermittent running mechanism, and it does not become complicated.

It is also possible to reproduce slow motion at any speed using a variable delay circuit.

[Brief explanation of the drawing]

1 to 3 and 5 are diagrams for explaining the present invention, and FIG. 4 is a system diagram of an example of the present invention. 13A to 14B are delay circuits, 18 is an FM demodulation circuit, and 20 is a servo circuit.

Claims (1)

[Claims] 1. A screen based on the video signal is recorded in slow motion from a magnetic tape on which the video signal is recorded as one magnetic track for each unit section, and a plurality of magnetic tracks are sequentially adjacent to each other and are recorded diagonally to the running direction. During reproduction, the magnetic tape is continuously run at a speed slower than that during recording in accordance with the slow motion ratio, and the reproduced video signal is moved to a position in the length direction of the adjacent magnetic track. A magnetic reproducing device that corrects the time axis of the reproduced video signal by periodically delaying the time corresponding to the amount of shift by the ratio of the slow motion.