JPS6232867B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotary head type magnetic recording and reproducing apparatus that allows variable speed reproduction of an odd number or a fraction of an odd number to be performed satisfactorily.

Rotating head type magnetic recording and reproducing devices, such as home VCRs, can perform quick playback, slow playback, or reverse playback by changing the running speed of the magnetic tape while rotating the rotary head cylinder. Still playback is also possible by stopping the running of the tape and performing a playback operation, which allows the magnetic recording and playback device to be used in a wider range of applications and become more versatile.

However, when variable speed playback is actually performed by changing the tape running speed, regular tracing is not performed, resulting in portions (dropouts) where the head does not pick up the signal, resulting in noise bands on the playback screen.

This situation will be explained with reference to the drawings in the case where double-speed reproduction is performed using an azimuth recording method in which recording and reproduction are performed by changing the gap angles of two rotary heads.

In FIG. 1, A1 and A2 indicate recording tracks by one of the two heads, for example the A head, B1 and B2 indicate recording tracks by the other head, for example the B head, and arrow H indicates the direction of head rotation; Arrow T is the tape running direction.
1 and 2 represent trajectories created by the rotary head in an optimal tracking state (a state in which the noise band is pushed into the vertical retrace period) when running at double speed. In FIG. 1, it is assumed that the playback head width is the same as the track pitch (recording track width), and 1 is B.
Head 2 is the locus of the A head.

Therefore, the output picked up by each head is as shown in Figure 2a.
It becomes a triangle corresponding to the head locus as shown in FIG. Here, 3 is the B head output and 4 is the A head output. Figure b shows the dropout output corresponding to the noise panning that occurs. If the head width is the same as the track pitch, the output at the edge will be zero, so if the head does not pick up a predetermined amount (approximately 10%) or more of the signal, dropout will occur as shown in Figure 2b. As shown in FIG. 3, noise bands 5 and 6 of that width will appear on the playback screen 7.

In order to reduce this noise band, conventionally, an unbalanced head with two heads having different widths has been used. For example, FIG. 4 shows a trace locus at double speed when the width of the A head is the same as the track pitch and the width of the B head is wider than the track pitch.

When tracking is done with an unbalanced head so that the head trajectory shifts slightly to the left in the diagram, the trajectory 12 of the A head becomes thicker than that in Figure 1, while the wider trajectory 11 of the B head also shifts by more than the same amount. You can get a wider effect and it will become thicker.
Therefore, the head output and dropout output become as shown in a and b of FIG. 5, and the head output at the end of the head trajectory is increased. Thereby, as shown in FIG. 6, it is possible to prevent noise bands from appearing on the reproduction screen 7.

However, although this kind of effect can certainly be obtained in the case of slow playback of an even number or a fraction of an even number,
This has the disadvantage of having the opposite effect for odd multiples or fractions of odd numbers.

In general, noiseless playback can be performed without changing the slope of the playback trajectory (with no more than one noise band on the screen, it can be pushed into the vertical retrace period).The variable speed magnification is 3x speed or less or 1/3x speed or more. . Considering the quick and slow functions, the larger the quick playback magnification is, the better, and the smaller the slow playback magnification, the better, so in practice, these magnifications are 3 each.
It is preferable to select 2x or 1/3x speed.

However, when triple speed playback is performed with the unbalanced head, the head trajectories become as shown in 21 and 22 in Fig. 7, and even in the optimal state with a slight shift in tracking, a portion of zero output occurs at the start of head A (trajectory 22). Therefore, the head output and dropout output become as shown in a and b in FIG. 8, and a noise band 8 is generated at the bottom of the playback screen 7 as shown in FIG. The same applies to the case of 1/3x speed.

As shown in the above example, the conventional method has a drawback in that it is impossible to avoid the appearance of noise bands at the edges of the screen when performing odd-multiple or odd-multiple reproduction.

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording/reproducing apparatus which eliminates the drawbacks of the prior art described above and is capable of reducing noise bands even in odd-numbered and odd-numbered 1x speed reproduction.

To achieve this objective, in the present invention both rotating heads are made approximately 15-35% wider than the recording track pitch.
A required amount of head output can be obtained at both the start and end of the head trace locus, and noise bands occurring at the upper and lower ends of the playback screen can be reduced.

Embodiments of the present invention will be described below with reference to FIGS. 10 to 14 in comparison with the cases described in FIGS. 1 to 9.

In FIG. 14, 41 is a magnetic tape, 42 is a rotating cylinder, 43 is a rotating head having a head width approximately 25% larger than the recording track pitch, 44 is a tack head, 45 is a cylinder motor, 46 is a cylinder servo circuit, and 47 is a reference. 48 is a capstan, 49 is a capstan motor, 50 is a control head, 51 is a capstan servo circuit, 52 is a tracking adjustment circuit for delaying the output of the reference oscillator 47, and 53 is a variable speed command circuit.

A case where triple speed playback is performed with the above configuration will be explained. First, a triple speed command is issued from the variable speed command circuit 53 to the capstan servo circuit 51 to run the magnetic tape 41 at triple speed, and a signal from the control head 50 is input to the capstan servo circuit 51. On the other hand, the reference oscillator 47
The signal is supplied to the tracking adjustment circuit 52, and is delayed by the variable speed command circuit 53 according to the variable speed ratio so as to achieve the optimum tracking state, and is also input to the capstan servo circuit 51, so that the phases of the two coincide. Perform servo control like this.

Further, a signal from the same reference oscillator 47 and a signal detected by the task head 44 and corresponding to the rotation of the cylinder are input to the cylinder servo circuit 46, and servo control is performed so that the phases of the two coincide. In the manner described above, optimal tracking control at three times the speed as shown in FIG. 10 is realized.

In FIG. 10, A1 and A2 are recording tracks by the A head, B1 and B2 are recording tracks by the B head, and 31 and 32 are the scanning loci of the rotary head 43 when running at three times the speed. In this case, the B head that scans the trajectory 31 and the trajectory 32
As mentioned above, both the A head for scanning the recording track pitch have a head width approximately 25% larger than the recording track pitch.

When such a wide balanced head is used, it is possible to pick up half the amount of the head output at the beginning and end of the head trajectory, so each head output 33, 34 at this time is equal to the 11th head output.
The envelope becomes symmetrical as shown in Figure a, and the dropout output b also becomes almost zero. However, in this case, at the start and end of tracking, approximately the same amount of adjacent (equal azimuth) signals as the regular signal are picked up, resulting in a noise band. Such a noise band also occurs in an unbalanced head, and the greater the degree of imbalance, the greater the amount of noise band generated at one end.

Because of this adjacent interference, even the balanced type cannot be unnecessarily widened. Visually, between the noise band caused by adjacent interference and the noise band caused by dropout, the noise band width caused by dropout is generally wider and the degree of disturbance is more significant. This situation can be seen by changing the width of the head and obtaining the total noise bandwidth (the sum of the noise due to adjacent interference and the noise due to dropout).
Figure 13 shows what was experimentally determined. It can be seen from this that the optimum head width is about 125%, and good results can be obtained in the range of 115-135%.

The above explanation has been given using 3x speed playback as an example, but the total noise band is also the same for 1/3x speed and -1x (reverse) playback, with the total noise band being at its minimum at a head width of approximately 125%, and 115 to 135%. Within this range, the level is almost tolerable on the screen.

Further, although the case where the azimuths of the A-head and B-head types are different during reproduction has been described, the above-mentioned tendency regarding the noise bandwidth is exactly the same when reproduction is performed using heads with the same azimuth only during reproduction.

Further, although the case where a balanced head is used has been described above, it goes without saying that an unbalanced head may be used as long as the head width is within the range of 115% to 135%.

As explained above, according to the present invention, it is possible to reduce noise bands at odd-number times and odd-numbered speeds, so 3x quick and 1/2 speeds have greater variable speed effects than conventional 2x and 1/2x speeds. It is possible to obtain good reproduced images even in 3x slow motion and even in reverse.

[Brief explanation of the drawing]

Figure 1 is a plan view showing the trajectory of the recording track and rotating head when playing back at double speed with the same head width as the track pitch, Figure 2 is a waveform diagram showing the head output and dropout output in that case, and Figure 3 is a waveform diagram showing the head output and dropout output in that case. The playback screen for the case shown in Fig. 1, Fig. 4 is a plan view showing the trajectory of the recording track and rotating head when playing back at double speed with an unbalanced head, and Fig. 5 is a waveform diagram showing the resulting head output and dropout output.
Figure 6 is the playback screen in the case of Figure 4, Figure 7 is a plan view showing the recording track and trajectory of the rotating head when triple speed playback is performed with an unbalanced head, and Figure 8 is the resulting head output. 9 shows the playback screen in the case of FIG. 7, and FIG. 10 shows the recording track and trajectory of the rotary head when performing triple-speed playback using the wide head according to the present invention. FIG. 11 is a waveform diagram showing the head output and dropout output, FIG. 12 is a playback screen in the case of FIG.
FIG. 3 is a characteristic diagram showing the noise band width when the degree of width of the head is changed, and FIG. 14 is a block diagram showing an embodiment of the present invention. 41... Magnetic tape, 42... Rotating head, 4
3...Magnetic head, 46...Cylinder servo circuit, 47...Reference oscillator, 51...Capstan servo circuit, 52...Tracking adjustment circuit, 5
3...Variable speed command circuit.

Claims (1)

[Scope of Claims] 1. In an azimuth recording rotary two-head helical scan type magnetic recording and reproducing device having a variable speed reproduction mechanism of an odd number or a fraction of an odd number, the degree of width of each head for each recording track is 15. A magnetic recording/reproducing device characterized by being set at ~35% increase. 2. The magnetic recording and reproducing apparatus according to claim 1, wherein the two heads are of a wide balanced type.