JPH0254716B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a magnetic reproduction system, and particularly to a helical scan video tape recorder (hereinafter referred to as
This tape is designed to reduce the noise that occurs in the reproduced image (so-called high-speed search image) obtained when fast-forwarding or rewinding at a speed faster than the normal tape speed in a VTR (VTR).

Generally, in a helical scan VTR,
When the tape is run faster than the normal running speed, as shown in Figure 1, the rotating video head traces 1,
2 crosses a plurality of recording tracks 3. The playback output envelope of the rotating video head becomes uneven as shown in Figure b in the section of one field, and when the output level falls below a certain level, the signal is recorded as an FM modulated wave, so the threshold Screen noise appears in areas where the level falls below the hold level. Figure c is a switching pulse for the video head. In order to eliminate such noise, a so-called auto-tracking method has been considered in which the height of the video head is moved in accordance with the movement of the tape so that the trajectory of the video head does not cross the track. In other words, if the tape moves at 10 times the speed, the head will move up and down by 10 times the track pitch. As a means of moving this head, a bimorph element using a piezoelectric element is considered. However, with this method, the piezoelectric element and control circuit are expensive, and the vertical movement range of the video head is limited to ±100 to 150 μm. The disadvantage is that it cannot perform a very high-speed picture search. Furthermore, since the bimorph element itself changes over time, the method of fixing the head height during recording is extremely troublesome and requires a complicated control system.

This invention was made in order to deal with the above-mentioned situation, and it is possible to combine each rotating video head with an auxiliary head, and when the output level of one head drops, the output of the auxiliary head next to it is automatically switched for use. Therefore, it is an object of the present invention to provide a magnetic reproduction method that relatively easily eliminates noise on the screen during picture search.

Embodiments of the present invention will be described below with reference to the drawings.

As explained in Figure 1, in a helical scan two-head VTR that uses azimuth loss, the tape is played back at a faster speed than the normal speed.
In the high-speed search mode for searching recorded content, the video head during playback will cross many recording tracks, so the playback output will have a diamond shape that changes according to the traversal, as shown in Figure 1b. Become.
Since two heads with different azimuths are used, when each head is tracing the other's track, the playback output decreases and appears as noise on the screen.

This method attempts to remove such noise, and uses a video head device having a structure as shown in FIG. Reference numeral 11 denotes a rotating disk, and video heads A and B are mounted on the outer periphery of the disk at an interval of 180° from each other, and video heads B' and A' are also mounted on the outer periphery of the disk at an interval of 180° from each other. ing. In this case, video head B' is placed next to video head A, and video head A' is placed next to video head B. Video heads A and A' have the same azimuth,
Also, video heads B and B', which have different azimuths, have the same azimuth. That is, the relationships are as shown in b and c in the same figure. The interval between adjacent video heads is set to an integral multiple of the horizontal synchronizing signal wavelength H on the tape pattern. This is to maintain continuity of the horizontal synchronizing signal when switching heads. Further, in this case, the heights of the heads (in the direction of the rotational axis) may in principle be the same height. This is because when the output of one video head during tracing is small, the output of the other video head is large.

FIG. 3 shows a reproduction signal processing system using the above video head device. The playback outputs of video heads A and B' are transmitted through preamplifiers 12 and 13, respectively.
The signal is supplied to one input terminal of each of the first and second switches 14 and 17. Furthermore, the playback outputs of video heads B and A' are supplied to the other input terminals of first and second switches 14 and 17 via preamplifiers 15 and 16, respectively. First and second switch 1
4 and 17 are controlled by head switching pulses. The output of the first switch 14 is input to a brightness reproduction processing circuit 18 and a color reproduction processing circuit 19, and is also input to a first envelope detector 22. Further, the output of the second switch 17 is input to a brightness reproduction processing circuit 20 and a color reproduction processing circuit 21, and is also input to a second envelope detector 23.
is input.

a reproduced luminance signal of the luminance reproduction processing circuit 18;
The reproduced color signal of the color reproduction processing circuit 19 is the reproduced color signal of the color reproduction processing circuit 19.
4, and this combined output is supplied to one input terminal of the third switch 26. Similarly, the reproduced luminance signal of the luminance reproduction processing circuit 20 and the reproduced color signal of the color reproduction processing circuit 21 are input to a combiner 25, and the combined output thereof is supplied to the other input terminal of the third switch 26. Ru. Color reproduction processing circuit 1
9 and 21 are supplied with an oscillation output of 3.58 MHz from a local oscillator 27.

On the other hand, the outputs of the envelope detectors 22 and 23 are input to a comparator 28 and compared in magnitude. The output of the comparator 28 is the synchronous circuit 2
9, is output in synchronization with the horizontal synchronization signal,
It is used as a switching pulse for the third switch 26.

The signal waveforms of each part of the above circuit are as shown in FIGS. 4a to 4f. FIG. 4a shows the first switch 1
For example, in an even field, it is the output of video head A, and in an odd field, it is the output of video head B. FIG. 4b shows the output of the second switch 17, which is the output of video head B' for even fields and the output of video head A' for odd fields. Figure 4c shows the synthesizer 2
4 is the reproduced video signal output from the synthesizer 25. FIG.
Since these video signals have a portion containing noise 30, the third switch 26 selects and derives a noise-free portion in the vertical period V. That is, switch 26 is controlled by a switching pulse from synchronization circuit 29 (FIG. 4f). As a result, a noise-free reproduced video signal as shown in FIG. 4e is derived.

In the brightness reproduction processing circuits 18 and 20, the FM
FM demodulation of the luminance signal is performed, and frequency conversion and the like are performed in the color reproduction processing circuits 19 and 21.

By the way, there are two systems of color reproduction processing circuits, so
In order to match the phases of the color synchronization signals obtained from the combiners 24 and 25, a reference signal of the same phase is applied from an oscillator 27. This is to prevent the color synchronization signal from becoming discontinuous at the switching point of the switch 26.

Furthermore, in order to prevent switching noise from appearing on the screen due to the switching operation of the third switch 26, a switching pulse is output using the synchronization circuit 29, and switching occurs during the horizontal blanking period or immediately before or after the horizontal blanking period. It's planned like this.

As mentioned above, the basic idea of the present invention is to extract the noise-free parts of the output from the main video head and the adjacent auxiliary video head, and to connect the parts with a good S/N ratio. be.

In order to achieve this concept, a configuration as shown in FIG. 5 may be considered, but this configuration causes a problem regarding the color signal phase, so the above embodiment is designed to solve this problem. .

That is, as shown in FIG. 5, the outputs of the first and second switches 14 and 17 are directly transmitted to the third switch 26.
The output of the third switch 26 is input to a brightness reproduction processing circuit 31 and a color reproduction processing circuit 32, and the outputs of these circuits are combined by a synthesizer 33 to produce a video signal. This is a circuit configuration used as a signal. With this kind of circuit configuration, the noise-free portions of the output signals from the main video head and the auxiliary video head are selected in advance by the third switch and sent to the normal playback processing circuit, which makes the structure seem different at first glance. It gets easier. However, the reproduction processing circuit of a VTR is usually configured as shown in FIG. 6, and phase synchronization processing is performed on color signals. That is, as explained in FIG. 6, the video head 3
The reproduced color signal (688kHz) output of No. 5 is sent to the automatic color signal control circuit (ACC circuit) via the preamplifier 36.
37. The output of the ACC circuit 37 is
This is a 688kHz signal, which is converted to the original color signal frequency (3.58kHz) in the frequency conversion circuit 38. The color signal converted to 3.58MHz is passed through a bandpass filter 39 to a comb filter 4.
0, unnecessary components are removed, and the signal is extracted. Furthermore, a burst signal is extracted from the 3.58MHz color signal, and its average amplitude level is detected. This is done by applying a gate pulse from the gate pulse generator 41 to the burst gate circuit 42 to extract a burst signal, and detecting this burst signal in the ACC detector 43. . And this
The output of the ACC detector 43 is applied to the control terminal of the ACC circuit 37, and acts to control the color signal to a constant level. The gate pulse generator 41 generates a gate pulse corresponding to the burst signal position with a certain phase delay from the horizontal synchronizing signal.
Next, the voltage controlled oscillator 46 is controlled so that the carrier signal (4.27 MHz) used in the frequency conversion circuit 38 becomes a signal synchronized with the burst signal. In other words, the burst signal is transmitted to the output of the reference oscillator 44 (3.58M
Hz), and the phase difference output is 175×
_H ( _H : horizontal synchronous frequency) voltage controlled oscillator 46
The oscillation frequency can be controlled. The output of this voltage controlled oscillator 46 is frequency-divided by a 1/4 frequency divider 74, and the frequency-divided output (688kHz) is output from the frequency conversion circuit 4.
8 is input. This frequency conversion circuit 48 includes
The output (3.58MHz) of the reference oscillator 44 is also added, thereby generating a carrier signal (4.27M
Hz) is created. This carrier signal (4.27MHz) is then input to the frequency conversion circuit 38 via the bandpass filter 49. In addition, in order to prevent the output of the voltage controlled oscillator 46 from being locked to an incorrect frequency by the APC loop including the phase comparator 45, a mislock correction circuit 5 is provided.
0, and the oscillation output is controlled to have a predetermined relationship with respect to the horizontal frequency _H. As mentioned above, the reproduced color signal (3.58MHz) is processed to have a stable phase by correcting the time axis fluctuations caused by the reproduction operation of the VTR through the carrier signal.

The color reproduction processing described above is performed, but as shown in Figure 5, if we only pay attention to noise and select and switch parts without noise in advance, the new color signal will not be affected by switching. There is a time lag between the signal and the conventional signal.
For this reason, the automatic phase adjustment (APC) shown in Figure 5
The loop is forced to respond rapidly each time it switches. However, the APC loop is not responsive enough to follow this and often results in uneven color.

In order to avoid such inconvenience, in this method, as shown in Figure 3, two systems are provided for brightness reproduction processing and color reproduction processing, and each system is
By providing an APC loop and using a common reference oscillator 27 for each APC loop, it is possible to eliminate phase disturbances in the color signal caused by switching in the third switch 26, and to obtain phase continuity. Stable output can be obtained. On the other hand, switching of the heads by the first and second switches 14 and 17 is performed during the vertical blanking period, and even if there is a disturbance in the phase, it does not appear on the screen, and the switching of the heads by the first and second switches 14 and 17 is performed during the vertical blanking period.
No problem arises due to switching between 4 and 17.

Next, the switching timing of the third switch 26 is synchronized with the horizontal synchronization signal, and
Taking into account the relationship with the APC loop, we get the following. That is, FIG. 7a and b show the synthesizers 24 and 2.
This is a video signal containing noise obtained from No. 5.
Here, when the area around the noise 51 is enlarged, it appears as shown in c of the same figure. When the reproduction output level of the video head decreases and noise appears on the screen, the control output of the APC loop in the color reproduction processing circuit is also disturbed, so the switching timing of the third switch 26 is It is better to wait until the loop is stable before doing so. Normally, the stabilization time of the APC loop is 0.2 to 0.3 m/sec, that is, 4 to 5 H periods of the horizontal scanning period. Now, if we were to send the tape at 20 times the speed, one head would cross-trace tracks with different azimuths 10 times in one field, resulting in 10 noise parts in one field. The same goes for the other auxiliary head.
Therefore, if noise-free parts are selected and connected from both, the selected section of one head will be 1/20, and since one field is 262.5H, the head switching time will be approximately every 13H. As shown in Figure 7, if the selection period is T = 13H, and the period from the noise part to the switching point is T ₁ and the period up to the next noise is T ₂ , then T = T ₁ + T ₂ , and if T ₁ = T ₂ . Then T ₁
= T ₂ = 6.5H. Considering that the width of the noise part is 2-3H, it takes 4-5H after the signal is reproduced correctly (no noise) until the third switch is switched to the output side of the video head.
If the tape speed is faster, this period becomes shorter and becomes less than the time required for the APC loop to stabilize. If the APC loop is switched before it is stabilized, it will cause color unevenness, so it is advantageous to set T ₁ > T ₂ . In other words, the switching between the main video head and the auxiliary video head is not done when the outputs of both match, but when the output of the one to be used later, or transferred, becomes to some extent larger than the output of the currently used head. It's a matter of switching. This is comparator 28
This is possible by adjusting the By setting in this way, it is possible to see a high-speed search image without color unevenness and noise even when the tape speed is increased.

Also, two color reproduction processing systems are required as reproduction processing circuits, but if the main video head and auxiliary video head can be installed within a certain accuracy, one luminance signal reproduction processing system can act as the other. , one may be omitted to simplify the circuit. In this case, a switch may be used in the luminance signal system.

FIG. 8 shows another example of the video head device according to the invention. In this head device, video head B' is provided next to video head A, and video head B'' is provided next to video head B. Video heads B, B', and B'' are set to the same azimuth. ing.

Even in such a video head device, noise can be prevented from being included in high-speed search images by using the above-mentioned reproduction processing system.
However, if the azimuths of the three heads are the same like this, this can be achieved by shifting the height between the video heads B and B'' by one pitch of the recording track. Since the azimuths are different, the heights may be the same as in the previous embodiment.

The trace situation during high-speed search for video heads B and B'' is as shown in Figure 9.In other words, by shifting the height, one of the video heads can obtain a high output level. I can,
This is because it is sufficient to select the one with a higher level. 5
5 is a recording track, and 56 and 57 are tracking trajectories.

The above video head device also has the following advantages. The set of video heads B and B'' is a combination of heads with the same azimuth. Heads with the same azimuth can easily be integrated into a 2-gap head, and manufacturing costs can be reduced.

Furthermore, the above head device can be used not only for high-speed searches but also for still image reproduction.
In other words, video heads B' and B'' can be used for still image reproduction, and video heads A and B can be used for normal reproduction.

Next, the relationship between the above-mentioned head device and still image reproduction principle will be explained. In the case of still image playback, if you want to obtain a field-stall image (one image, one track), you need a pair of video heads that have the same azimuth and are mounted approximately 180 degrees symmetrically. Better to play. In this case, the 10th
As shown in the figure, since the tape stops during still image playback, the tracking locus 57 shifts by one pitch between the beginning and end of the track. Therefore, in order to obtain a good image without deterioration in level, it is necessary to make the track width of the head wider than the recording track width. On the other hand, during normal recording, if the head track width is made too wide, crosstalk with adjacent tracks becomes a hindrance, so the head track cannot be made very large.

Therefore, the video heads B' and B'' used for still image reproduction have a large head track, and the video heads A and B used for normal reproduction are designed to have an appropriate track width.

Furthermore, when considering still image playback, it is ideal for video heads B' and B'' to be at the same height. However, when considering image noise reduction for high-speed search, they should be at exactly the same height. Therefore, the head track width of video heads B′ and B″
Let W _B ′ and W _B ″ be larger than the track pitch P (recorded track width), i.e. 1.5P<W _B ′orW _B ″<
By setting it to 2.0P, the conditions for still image playback and high-speed search can be satisfied.

Now, if W _A = W _B = P (recording track width) W _B ′ = W _B ″ = 2P, then h = h′ = 1/2P and α as shown in Figure 11.
=β=1/2P. h and h' are the mounting steps.
However, if the head track width is more than twice the recording track pitch, crosstalk from adjacent tracks will occur, so the maximum value needs to be 2P, so W _B ′=W _B ″=1.7±0.2P. selected according to degree.

If W _B ′=W _B ″<2P, the optimal value for high-speed search playback and the optimal value for still image playback will not be compatible.
It is set at the midpoint. That is, α and β are set slightly smaller than 1/2P as shown in FIG.

Next, let's consider the head device described above and the slow motion playback of a VTR. During slow-motion playback, the tape is fed intermittently, periodically stopping and running. In this case, the rising speed and start timing of tape running are important factors in preventing noise from occurring on the screen.

In the case of this type of head device, taking slow playback at 1/2 speed as an example, as shown in Fig. 13, in the case of a still image, the video head B'', as shown in Fig. 13b,
A reproduction output of B' is obtained, and at the start of tape running, a reproduction output as shown in c of the same figure is obtained.
Figure a shows a trace locus during still image playback. That is, when recording a still image, video heads B' and B'' play back the recording track of the azimuth corresponding to these heads, and the tape is run from the trace start of video head B'', and the video is just played back. At the end of the trace in head B'', the 1/2 pitch tape is moved, and at that point the tape running speed is brought back to the normal playback tape speed.Then, the next tracing head is switched to video head A and this By setting the head trace to normal playback,
This video head A reproduces and traces the recording track of the corresponding azimuth.
Next, when moving to stop, video head A switches to B'' to slow down the tape, and when moving to video head B', the tape comes to a complete stop.The continuous playback output envelope at this time is , 1st
The result will be as shown in Figure 4. Figure 14a shows the arrangement of the trace video head. Further, b in the same figure shows the change in tape speed, c in the same figure shows the reproduction track, and d in the same figure shows the reproduction output envelope. 1/3x speed, 1/4
In the case of slow playback at double speed, you can simply lengthen the period during which the tape is stopped. For example, if you stop the tape until the time when track B is traced again by video heads B'' and B', you can play back at 1/3 slow speed. become.

In the case of the head device described in FIG. 2, slow playback is also possible in the same way as above by changing the video head B'' to B', the video head B' to B, and the video head A to A'. In the case of playback, the start-up speed of the tape can be slowed down by not only playing back track B, but also by using the playback output of video head A for one field during the playback.
Easier to control.

Various other embodiments are possible as the video head device used in the present invention. An example is shown in FIG. Figure a shows an example in which the arrangement of the main video head and auxiliary video head explained in Fig. 8 is swapped, and figure b shows an example in which the arrangement of the main video head and auxiliary video head explained in Fig. 2 is changed. An example of switching video heads B and A' back and forth,
Figure c is an example in which the video heads A, A', and A'' have the same azimuth.

As mentioned above, this invention is a helical scan type VTR that utilizes the azimuth of the video head.
By using four video heads and adding the same-phase color synchronization reference signal to two color demodulation circuits, we can obtain reproduced images free of noise and color unevenness, as well as slow playback, still image playback, It is possible to provide a magnetic reproduction method that can suppress noise even during double-speed or triple-speed reproduction.

[Brief explanation of the drawing]

FIGS. 1a, b, and c are explanatory diagrams showing trace trajectories, playback outputs, and head switching pulses during high-speed search in a VTR, and FIGS. 2a, b, and c show an example of a video head device according to the present invention. FIG. 3 is a circuit configuration diagram showing an embodiment of the present invention, FIGS. 4 a to f are operation signal diagrams shown to explain the operation of the circuit in FIG. 3, and FIG. A circuit diagram shown for comparison to explain the advantages of this invention, FIG. 6 is a circuit configuration diagram of a color reproduction processing system, and FIGS. 7 a, b, and c are head switching timings of a switch according to this invention. FIGS. 8a, b, and c are configuration explanatory diagrams showing other examples of the video head device according to the present invention, and FIG. Fig. 10 is an explanatory diagram showing the trace locus during high-speed search of the VTR used. Fig. 10 is an explanatory diagram showing the trace locus during still image playback of the VTR. Figs. 11 and 12 are the video of the head device of Fig. 8. Figures 13a, b, and c are explanatory diagrams explaining how to set the head step and track width.
Figures 14a to 14d are explanatory diagrams showing trace trajectories and partial playback outputs during still image playback when the video head device shown in Figure 8 is used. Figures 15a, 15b and 15c, shown to explain the operation mode during playback, are diagrams showing other examples of the video head device according to the present invention, respectively. A, B...Main video head, A', B'...Auxiliary video head, 14, 17, 26...Switch,
18, 20... Brightness reproduction processing circuit, 20, 21...
...Color reproduction processing circuit, 22, 23...Envelope detector, 24, 25...Synthesizer, 27...Local oscillator, 28...Comparator, 29...Synchronization circuit.

Claims (1)

[Claims] 1. In a magnetic reproducing method in which recording azimuth waves reproduce mutually different signals on adjacent recording tracks using a helical scan method, first and second recording azimuth waves with different azimuths are arranged on the outer periphery of a rotating disk at positions approximately 180° different from each other. A second main video head is disposed, third and fourth auxiliary video heads are disposed adjacent to each of the first and second main video heads, and the first and third video heads are connected to the first video head. group, 2nd
and a fourth video head as a second set, the video heads of at least one set have different azimuths from each other, and the gap interval of the two video heads of each set that are close to each other is equal to the horizontal synchronization on the recording track. Processing the output from the main video head among the signals obtained from rotary head devices arranged apart from each other by a positive number of signal intervals and a field changeover switch that selects the first and second sets for each field. First thing to do
a color reproduction processing circuit and a second color reproduction processing circuit that processes the output of the auxiliary video head side, and a reference signal serving as a reference for color signal processing is supplied from the same oscillator with the same phase or a constant phase relationship. selecting and deriving one of the outputs of the two systems of circuits and the first or second color reproduction processing circuit according to a comparison result of reproduction output levels of the main video head and the auxiliary video head; A magnetic reproducing method characterized by comprising a horizontal synchronization changeover switch means. 2. When the two adjacent video heads have the same azimuth, the heights of the two adjacent video heads are shifted by an odd multiple of the track pitch, and when the azimuths are different, the heights of the two video heads are made to be substantially the same or the heights are approximately the same as the track pitch. 2. The magnetic reproducing system according to claim 1, wherein the magnetic reproducing method is shifted by an even number of times. 3. To compare the output levels of the main video head and the auxiliary video head and select the output of either side, the maximum output of the side to which the output will be transferred after switching should be 2. The magnetic reproducing system according to claim 1, wherein the switching timing is obtained closer to the point.