JPS6251031B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording and reproducing apparatus that allows variable speed images to be reproduced satisfactorily without disturbance.

In a rotating head type magnetic recording/reproducing device, such as a home VTR, it is possible to perform quick motion or slow motion image reproduction by changing the running speed of the magnetic tape while the rotating head drum is rotating. can.

However, if the tape running speed during playback is different from that during recording, the envelope of the frequency-modulated playback signal changes, and below a certain level, noise bands appear on the screen, making it difficult to see. Therefore, a tracking servo is applied to force the noise band into the vertical blanking period. Therefore, during quick motion or slow motion playback, the vertical synchronization signal is affected, causing the phenomenon of vertical shaking of the screen, and even if there is no noise, a satisfactory reproduced image cannot be obtained.

This situation will be explained with reference to the drawings in the case where 1/3 speed slow playback is performed using an azimuth recording method in which recording and playback is performed by changing the gap angles of two rotating heads.

In FIG. 1, 2A and 3A indicate recording tracks by one of the two heads, for example, the A head, and 1B and 2B indicate recording tracks by the other head, for example, the B head.
3 and 4 represent trajectories caused by the rotating head when running at 1/3 speed. In order to avoid convergence in the diagram, only the entire trajectory 1 is drawn with dotted lines, and 2, 3, and 4 only show their head start positions. Further, arrow H is the direction of head rotation, arrow T is the direction of tape running, 1 and 3 are the trajectories of the B head, and 2 and 4 are the trajectories of the A head, which are alternately traced by the A and B heads. The envelope waveform of the frequency modulated reproduction signal when tracing is performed in this way is shown in Fig. 2c, and the waveforms of the envelope 1B, 2A, 2B, and 2 correspond to the head trajectories 1, 2, 3, and 4.
The signals of recording track A are picked up in order.
Therefore, the dropout shown in v in the figure occurs once in three times. Since this dropout occurs during the vertical blanking period, it does not appear as a noise band on the screen, but the vertical synchronization signal in this portion is affected.

For this reason, it has been considered to add a pseudo vertical synchronization signal before the corrupted original vertical synchronization signal. By the way, this pseudo vertical synchronization signal is shown in Figure 2a.
If the head switching signal is only sent at the time when the head switching signal is switched, the start time of the recording track and the start time of the rotating head will shift in order, so the phase of the original vertical synchronization signal to be reproduced will change in order, causing the screen to shake vertically. will occur.

In order to avoid this, the original vertical sync signal to be reproduced and the pseudo vertical sync signal (additional v
It is necessary to change the phase of the additional v-pulse for each field so that the relative phases of the pulses (abbreviated as "pulses") coincide with each other. However, the method of change differs depending on the variable speed magnification of slow, quick, back, and still motions. Conventionally, the phase of the additional v-pulse is determined by plotting according to each individual motion and its variable speed magnification, and the additional v-pulse is was in control.

For this reason, the control method differs when the magnification changes, and the control circuit becomes complicated for models that can select from several types of variable speed magnification, and since the magnification is not fixed in continuous variable speed playback, it is not possible to prevent vertical vibration. .

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to be able to determine the phase of a pseudo vertical synchronization signal to be added by simple means, and to obtain good reproduced images without vertical fluctuation even during arbitrary variable speed reproduction. The purpose of the present invention is to provide a magnetic recording and reproducing device that can be used.

In order to achieve this object, the present invention provides that the phase of the pseudo vertical synchronization signal to be added is slow, quick,
Regardless of the back or still mode, focusing on the fact that it depends only on the envelope value and increase/decrease direction of the frequency modulated reproduced signal, we calculated the ratio of the frequency modulated reproduced signal to the maximum envelope value at the head start point as k (0 ≤ k≦1), and the H deviation between adjacent tracks is _αH , then the absolute value of the phase t of the pseudo vertical synchronization signal to be added is (1-
k) The positive and negative signs of α _H are selected so as to match the direction of increase and decrease of the envelope at the head start point.

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 3, 11 is a magnetic tape, 12 is a rotating cylinder, 13 is a head, 14 is a cylinder motor, 15 is a tack head, 16 is a capstan, 17 is a capstan motor, and 21 is a tack signal obtained from the tack head 15. 22 is a doubling circuit for obtaining the head start signal b from the head switching signal a, and 23 is a control for producing the pseudo vertical synchronizing signal (additional V pulse) e to be added. 24 is an envelope detection circuit for the frequency modulated reproduced video signal obtained from the head 13, and 25 is an AD conversion circuit for converting the absolute value of the envelope signal c into a several-bit digital signal that can be processed by the microcomputer 23. ,
26 is a differentiating circuit which detects the direction of increase/decrease in the envelope and generates an increase/decrease signal d, and 27 is a signal addition circuit which adds an additional v pulse e to the reproduced video signal from the head 13 and outputs the video output signal f.

The magnetic tape 11 is caused to travel in the direction of arrow T by a capstan 16 driven by a capstan motor 17 at a speed corresponding to each variable speed magnification. A recording pattern is traced by a head 13 attached to a rotating cylinder 12 driven by a cylinder motor 14, and a reproduced video signal is obtained.

The head start signal b, envelope absolute value signal (converted to a digital value), and increase/decrease signal d obtained from each circuit are input to the microcomputer 23, which operates based on the clock and performs input signal judgment and delay operations. , an additional v pulse e is output.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 4 in the case of slow motion where the variable speed magnification is 1/3. In FIG. 1, it is assumed that the position of the vertical synchronizing signal recorded on the recording track is the lower end of the track. Then, in the first playback trajectory 1, from the head start to α _H (in the VHS system, α _H
= 1.5H≈95.25 μs), the vertical synchronization signal for track 1B is obtained, so if the additional v pulse e is output after α _H using the head start as a reference, there should be no vertical shaking of the screen.

Similarly, in the next field, second trajectory 2, the head start and track 2A vertical synchronization signals have a difference of 1/3α _H , so an additional v pulse must be output after 1/3α _H. It's a good thing. Conversely, in the third reproduction trajectory 3, a 2B vertical synchronization signal exists 1/3α _H before the head start, and this can be expressed as a -1/3α _H delay. Also, in the fourth playback trajectory 4, α
_H , below 3v (v is 1 field period)
16.7ms).

In reality, the vertical sync signal is approximately
Since it was recorded after 6.5H, the additional v pulse e
It is desirable to attach it about 3 hours before that. Assuming that the phase difference at that position with respect to the head start is t ₀ , the time t ₀ (approximately 3.5H) has elapsed since the head start is the reference phase, and α _H , 1/3 α _H , −1/3 are respectively expressed as the reference phase.
It is sufficient to add an additional pulse e after _αH . These values are the additional v-pulse phase t and are shown in FIG. 4 as the additional v-pulse e. Note that this reference phase pulse w can be generated internally by delaying the head start signal b by _t0 using the microcomputer 23.

By the way, the absolute value of the additional v pulse phase t with respect to the reference phase pulse w is expressed as the ratio k to the maximum value of the envelope signal c (this is taken as 1) at the beginning of each field, that is, at the head start point.
When (0≦k≦1), it is always expressed as (1-k)α _H. It can also be seen that the sign is positive in the increasing section of the envelope, negative in the decreasing section, and 0 in the section from increasing to decreasing or from decreasing to increasing.

The above explanation has been about 1/3x slow motion, but other variable speed magnifications can also be considered, such as the slope difference of the trace during playback with respect to the recorded pattern, and the amount of movement (1/3 At 3x speed, there is a proportional relationship between 1/3α _H ), and there is also a proportional relationship between the slope difference and the slope of the envelope, so it is easy to understand that the phase t of the additional v pulse can be uniquely determined. Will.

Returning to FIG. 3, the operation of the microcomputer 23 until the additional v pulse is added to the video signal is as follows. Every time the head start signal b is input from the doubler circuit 22 to the microcomputer 23, the absolute value k of the envelope signal c is
Then, an increase/decrease signal d representing the direction of increase/decrease at that point obtained by differentiating the envelope signal c is read and stored in the memory. By the obtained absolute value, (1-
k) Calculate α _H , and on the other hand, if the signal d is positive, select a positive sign, and conversely, if d is negative, select a negative sign.
After _t0 ±(1-k) _αH has elapsed, an additional v-pulse e of a predetermined width (approximately 3H) is output. By adding the additional v pulse e to the reproduced signal in the signal addition circuit 27, a video output signal f is obtained.

It is clear that the apparatus of Figure 3 is generally applicable to all variable speed playbacks other than 1/3x slow motion.

Another embodiment of the present invention that develops the above-described technique will be described with reference to FIGS. 5 and 6. As is clear from the above description, in general, for all variable speed reproduction of slow and quick motions, the phase t of the additional v-pulse e is has periodicity.

An example of a constant variable speed magnification will be described below, but for general cases where the magnetic tape running speed is not constant over time, the optimal It will be easily understood that the same implementation can be achieved by adding a pseudo vertical synchronization signal to each field.

In FIG. 6, if the variable speed magnification is generally n, the trace locus at this time will be the shaded portion in 31. Therefore, the amplitude of the envelope 32 after one field is (1-n), where the maximum value is 1. In other words, the period of the envelope is 2/1-nv. Although this figure shows the case of slow motion (n<1), the same applies to quick motion (n>1), so it can generally be written as |2/1-n|v.

Therefore, at n times the speed, it is sufficient to cyclically switch the phase t of |2/1-n|, which is determined by (1-k) _αH , and the AD conversion circuit 2 in FIG.
5. The configuration shown in FIG. 5 without the differentiating circuit 26 is possible.

In order to switch the |2/1-n| type cyclically, the head start signal b may be switched by a signal obtained by frequency-dividing the |2/1-n| frequency dividing means. In this case, the order of the phases t to be switched is fixed, but the initial value is not fixed. This initial value is determined by the shape of an envelope, and the shape of the envelope is determined by the phase relationship with the control signal g obtained from the control head 18.

However, if the control signal g is used directly as a reference, the first additional v-pulses e may be too close together, causing an error. Therefore, if the initial value is determined by the signal h obtained by delaying the control signal g by a certain predetermined amount, the desired additional v pulse can be generated. In the example of 1/3 speed slow motion, the control signal g is delayed by the microcomputer 23 and the delayed signal h is generated as shown in FIG.
is created and reset to the initial value t=1/3α _H at the output point of h (in this example, at the center of 1B) to set the initial state. Although the microcomputer 23 is used here, the same operation is |
Of course, it can also be realized by configuring it with a 2/1-n| frequency divider circuit and individual logic circuits such as a control signal delay circuit.

As described above, according to the present invention, the phase of the pseudo vertical synchronization signal to be added can be determined by simple means, and a good reproduced image can always be obtained without vertical shaking of the screen during arbitrary variable speed reproduction. can.

[Brief explanation of the drawing]

Figure 1 is a plan view showing the trajectory of the recording track on the magnetic tape and the rotating head during slow playback at 1/3 speed, and Figure 2 is a waveform showing the envelope waveform, dropout, and head switching signal of the playback signal at that time. 3 is a block diagram of a magnetic recording/reproducing apparatus according to one embodiment of the present invention, FIG. 4 is a waveform diagram for explaining its operation, and FIG. 5 is a block diagram of a magnetic recording/reproducing apparatus according to another embodiment of the present invention. The block diagram in FIG. 6 is a diagram illustrating the cycle of the envelope during variable speed playback. 11... Magnetic tape, 12... Rotating cylinder, 13
... head, 15... tack head, 16... capstan, 18... control head, 21... tack signal processing circuit, 22... doubling circuit, 23... microcomputer, 24... envelope detection circuit,
25...AD conversion circuit, 26...differentiation circuit, 27...signal addition circuit.

Claims (1)

[Scope of Claims] 1. In a rotating head type magnetic recording/reproducing device that performs variable speed playback at a tape running speed different from that during recording, when a phase t has elapsed with reference to the head start time or a time a certain predetermined phase later than the head start time. pulse generating means for outputting a pulse of a predetermined width at a time;
means for adding the pulse to the reproduced video signal as a pseudo vertical synchronization signal, and the phase t is a ratio of the maximum value of the envelope of the frequency modulated reproduced signal at the head start point to k(0
≦k≦1), and the number of H deviations between adjacent tracks is α _H , its absolute value is selected as (1-k) α _H , and its positive and negative signs are the increasing and decreasing directions of the envelope at the relevant head start point. A magnetic recording/reproducing device characterized in that the magnetic recording/reproducing device is selected so as to match the above. 2. A head start signal is obtained using means for doubling the head switching signal, and an envelope increase/decrease detecting means is provided, and the pulse generating means is generated according to the envelope value at the time of the head start and the output of the envelope increase/decrease detecting means. 2. The magnetic recording and reproducing apparatus according to claim 1, wherein a predetermined pseudo vertical synchronization signal is output. 3. Obtain the head start signal by doubling the head switching signal, and when the variable speed multiplier is n (slow motion playback where n<1), the doubled signal is divided into |2/1-n| minutes. The phase t of the |2/1-n| types selected according to the first term is periodically switched by the means for rotating, and the control signal is delayed by a predetermined amount, and the control signal is delayed by the |2/1-n| minutes. 2. The magnetic recording and reproducing apparatus according to claim 1, wherein the circumferential means is returned to an initial state.