JP2522253B2 - Magnetic playback device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is for reproducing a magnetic tape in which a signal obtained by FM-modulating a carrier wave of first and second frequencies with a video signal is continuously recorded. The present invention relates to a magnetic reproducing device that is suitable for application.

[Outline of Invention]

In the present invention, the carrier wave of the reproduction signal from the magnetic tape is the first.
By controlling the DC level of the reproduced video signal from the FM demodulator depending on whether the frequency is the second frequency or the second frequency, a signal in which the carrier waves of the first and second frequencies are FM-modulated with the video signal is generated. Even when the magnetic tape recorded continuously is reproduced, the DC level of the reproduced video signal is made continuous.

[Conventional technology]

Low-pass converted carrier color signal C _L and FM modulated luminance signal
In a VTR that records a composite signal with Y _FM , it has been proposed that the FM modulation frequency be made higher than usual to widen the band of the luminance signal to improve the image quality.

Fig. 3 shows the frequency spectrum when the FM modulation frequency is normal (low band mode). The FM is adjusted so that the sync signal tip is 3.8MHz and the white peak is 5.4MHz.
It is modulated. The carrier color signal of 3.58MHz (NTSC system) is converted to a low frequency of 688KHz. On the other hand, FIG. 6B shows the frequency spectrum when the FM modulation frequency is made higher than in the normal case (high band mode),
FM modulation is applied so that the tip of the sync signal is 4.8MHz and the white peak is 6.4MHz.

When editing and recording the signal in the high band mode on the magnetic tape on which the signal in the low band mode is recorded, or vice versa, the signal in the low band mode and the signal in the high band mode are consecutive. A recorded magnetic tape will be formed.
FIG. 4 shows an example of such a magnetic tape track pattern, which is an example of a rotary two-head type VTR. When the magnetic head is HA, HB, the recording track TA,
TBs are alternately formed for each field by the magnetic heads HA and HB, respectively.

[Problems to be solved by the invention]

As described above, when reproducing a magnetic tape on which a signal in the low band mode and a signal in the high band mode are continuously recorded by a VTR, assuming the characteristics of the FM demodulator, for example, as shown in FIG. Playback signal from the head
For Y _FM , the reproduced luminance signal Y from the FM demodulator is output according to this characteristic. Therefore, the reproduction luminance signal Y
As shown in FIG. 6, the DC level becomes discontinuous at the switching point from the low band mode to the high band mode. Therefore, when this reproduction luminance signal Y is supplied to the monitor and observed, there are disadvantages such as image disturbance due to malfunction of the sync separation circuit and a momentary white peak of the image. I couldn't do it. This is the same at the switching point from the high band mode to the low band mode, and also at the still reproduction and the variable speed reproduction.

In FIG. 6, the direct current level of the reproduction luminance signal Y returns after a predetermined time from the switching point because the direct current is cut off in the VTR transmission system.

In view of the above, the present invention aims to make the DC level of a reproduced video signal continuous even when reproducing a magnetic tape on which a signal in a low band mode and a signal in a high band mode are continuously recorded. To aim.

[Means for solving problems]

The present invention relates to a magnetic reproducing apparatus which obtains a reproduction signal by scanning a track obliquely recorded on a magnetic tape with a plurality of reproducing magnetic heads to obtain a reproduction signal. The plurality of magnetic heads are arranged at intervals at which at least two magnetic heads are in sliding contact, and the next switching target among the at least two magnetic heads in sliding contact with the magnetic tape before the switching of the magnetic heads. Based on the reproduction signal from the magnetic head, the carrier wave of the reproduction signal has a first frequency or a second frequency.
A detection circuit for detecting whether the frequency is, a DC level shift circuit for correcting the DC level of the reproduced video signal from the FM demodulator and outputting it as a reproduced video correction signal, among the reproduced video signal and the reproduced video correction signal. And a selection circuit for switching the signal according to the detection result from the detection circuit at the time of switching the magnetic head.

[Action]

In the magnetic reproducing apparatus according to the present invention, first, a magnetic reproducing apparatus having a plurality of magnetic heads, of which a reproducing signal is obtained through a magnetic head that is in sliding contact with a magnetic tape, There is. Specifically, the reproduction signal is obtained by switching the magnetic head connected to the reproduction system to the magnetic head that is currently in sliding contact with the magnetic tape.

Then, in the present invention, before the magnetic head is switched in the detection circuit, it is reproduced next time based on the reproduction signal from at least the magnetic head to be switched next time (the magnetic head which is in sliding contact with the magnetic tape this time) in advance. It is detected whether the carrier frequency of the signal to be transmitted is the first frequency or the second frequency. That is, this detection circuit detects which frequency the next reproduction signal has before being fetched as a valid reproduction signal.

Further, in the present invention, in the selection circuit at the subsequent stage, the reproduction video signal from the FM demodulator and the reproduction video correction signal from the DC level shift circuit are switched to the signal corresponding to the frequency detected by the detection circuit. However, since this switching time point is just the switching time point of the magnetic head, the above-mentioned signal switching is performed at the stage when a valid reproduction signal is fetched.

Therefore, the carrier wave of the first and second frequencies is a video signal.
When reproducing a magnetic tape on which FM-modulated signals are continuously recorded, the DC level of the reproduced video signal becomes continuous, and it is possible to prevent image disturbance and image quality deterioration due to changes in the DC level. Become.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This example is an example applied to a reproducing system of a rotary two-head type VTR. FIG. 1 shows only the luminance signal reproducing system.

In the figure, HA and HB are rotary magnetic heads arranged at an angular interval of 180 ° from each other, and have two fields (1
One rotation is made in the frame period. Also,
Reference numeral (1) is a magnetic tape, which is obliquely wound around the peripheral surface of the tape guide drum (2) at a winding angle of a little over 180 ° so as to run at a predetermined speed.

The rotary magnetic heads HA and HB sequentially scan the tracks TA and TB on the magnetic tape (1), and the head HA and
The reproduction signal (FM signal) obtained from the HB is supplied to the fixed terminals on the A side and B side of the changeover switch (4) via the reproduction amplifiers (3A) and (3B), respectively. A so-called RF switching pulse P _RF is supplied from the terminal (5) to the changeover switch (4), and during the one field period during which the magnetic heads HA and HB scan the magnetic tape (1), the A side and the B side, respectively. Is switched to.

The reproduction signal Y _FM obtained from the switching switch (4) is supplied to the FM demodulator (7) via the limiter (6) and the luminance signal Y is demodulated. The luminance signal Y from the FM demodulator (7) is supplied to the fixed terminal on the A side of the changeover switch (8), and the luminance signal Y from the FM demodulator (7) has a predetermined value X.
The voltage is supplied to the fixed terminal on the B side of the switching switch (8) via the DC level shift circuit (9) that lowers the DC level only.

Further, the predetermined value X is determined from the DC level of the luminance signal Y from the FM demodulator (7) when the reproduction signal Y _FM is a signal in the high band mode and when the reproduction signal Y _FM is a signal in the low band mode. It is made equal to the difference voltage obtained by subtracting the DC level of the luminance signal Y from the FM demodulator (7).

Further, the output terminal (10) is led out from the changeover switch (8).

Also, the output signal of the limiter (6) is the switching switch (1
It is supplied to the fixed terminal on the A side of 1), and this switching switch (1
The output signal of the reproduction amplifier (3B) is supplied to the fixed terminal on the B side of 1) via the limiter (12). The output signal of the switching switch (11) is supplied to the mode detection circuit (13). This detection circuit (13) is a circuit that detects whether the reproduced signal Y _FM is a signal in the low band mode or a signal in the high band mode, and pays attention to the fact that the carrier frequency (modulation frequency) differs in each mode. Detection is done. A specific method of this detection is disclosed in, for example, JP-A-60-169294.
It is described in detail in the publication.

From the detection circuit (13), when the reproduction signal Y _FM is a signal by the low-band mode and the high-band mode, the signal of each low level "0" and the high level "1" is output. The output signal of this detection circuit (13) is A of the changeover switch (14).
Supplied to the fixed terminal on the side. The output signal of the detection circuit (13) is supplied to the input terminal D of the D flip-flop (15), and the clock input terminal CK of this D flip-flop (15) is supplied with the RF switching pulse P _RF from the terminal (5). To be done. Then, the signal obtained at the output terminal Q of the D flip-flop (15) is supplied to the fixed terminal on the B side of the switching switch (14).

The output signal of the switching switch (14) is supplied to the switching switch (8) as a switching control signal. When the output signal of the switching switch (14) is low level "0" and high level "1", the switching switch (8) is on the A side and the B side, respectively.
Switched to the side.

Further, when the terminal (16) of the normal reproduction mode high level "1", signal S _C to a low level "0" is supplied when the special reproduction mode such as still or speed reproduction, the signal S _C is switched It is supplied to the switches (11) and (14) as a switching control signal. When the signal S _C is low level “0” and high level “1”, the switching switches (11) and (14) are switched to the A side and the B side, respectively.

In the above structure, in the normal reproduction mode, the signal S _C supplied to the terminal (16) becomes the high level "1" and the changeover switches (11) and (14) are changed over to the B side.

2A and 2B are reproduction signals obtained from the heads HA and HB, respectively. Since the winding angle of the magnetic tape (1) is 180 °, these reproduction signals are partially overlapped. . Further, FIG. 6C shows an RF switching pulse supplied from the terminal (5).

When the reproduction signal obtained at the head HB from the time point t ₁ becomes a signal in the high band mode, the output signal of the detection circuit (13) becomes higher than the low level “0” at the time point t ₁ as shown in FIG. 2D. The level becomes "1". Then, at time t ₂ , the RF switching pulse P _RF rises, so the D flip-flop (15)
The output signal of, a high level "1" from the low level "0" at time t ₂ as shown in FIG E. Therefore, the switching switch (8) is switched to the B side from the time point t ₂ , and the FM demodulator (7)
The luminance signal Y obtained from the DC level shift circuit (9)
Through the output terminal (10).

When the reproduction signal Y _FM is a signal in the high band mode, the DC level of the luminance signal Y obtained from the FM demodulator (7) is increased by a predetermined value X, but as described above, this luminance signal Y is DC level. Since the direct current level is reduced by the predetermined value X through the shift circuit (9), the luminance signal Y direct current level derived to the output terminal (10) is a signal in which the reproduced signal is in the low band mode to a signal in the high band mode. It will be continuous even if switched to. Although detailed description is omitted, conversely, when switching from the signal in the high band mode to the signal in the low band mode, the switching switch (8) is switched to the A side, and the brightness obtained from the FM demodulator (7). The signal Y is directly output to the output terminal (10). Therefore, the DC level of the luminance signal Y derived to the output terminal (10) is continuous even if the reproduction signal is switched from the signal in the high band mode to the signal in the low band mode.

The example in FIG. 1 is an example in which the signal switching always starts from the reproduction signal obtained from the head HB, and the output signal of the reproduction amplifier (3B) is sent to the detection circuit (13) via the limiter (12). It is configured to be supplied. However, when the signal switching starts from the reproduction signal obtained from the head HA, it is necessary to supply the output signal of the reproduction amplifier (3A) to the detection circuit (13) via the limiter, and the signal switching is also performed. When it is unclear which of the playback signals obtained from the head HA or HB starts, the output signals of both playback amplifiers (3A) and (3B) are detected via the limiter (13).
Need to be supplied to.

Then, when the special reproduction mode, signal S _C that is supplied to the terminal (16) is low level "0", the switching switch (11) and (14) is switched to the A side.

In the special reproduction mode, the heads HA and NB scan across the recording tracks TA and TB on the magnetic tape (1) diagonally. Therefore, in the vicinity of the boundary between the track recorded with the signal in the low band mode and the track recorded with the signal in the high band mode on the magnetic tape (1), the head HA, HB
Thus, these two types of recording tracks are alternately scanned.

In this case, the output signal Y _FM of the switching switch (4) is supplied to the detection circuit (13) via the limiter (6),
When the heads HA and HB scan the track recorded with the signal in the low band mode and the track recorded with the signal in the high band mode, the output signals of the detection circuit (13) are low level "0" and high level "1", respectively. "It becomes. And
The switching switch (8) is switched to the A side and the B side, respectively.

Therefore, when the reproduction signal Y _FM becomes a signal in the low band mode, the luminance signal Y obtained from the FM demodulator (7)
Is fed directly to the output terminal (10), while the playback signal Y _FM
Is a signal in the high band mode, the signal Y obtained from the FM demodulator (7) is led to the output terminal (10) via the DC level shift circuit (9). Therefore, even in the special reproduction mode, the DC level of the luminance signal Y used at the output terminal (10) is continuous.

As described above, according to this example, when reproducing the magnetic tape (1) on which the signals in the low band mode and the signals in the high band mode are continuously recorded, the DC level of the luminance signal Y is continuous at the switching point. Becomes

When the DC level shift circuit (9) increases the DC level by a predetermined value X, the switching of the switching switch (8) is controlled in the opposite manner to the above example. In addition, the recording signal in the above-mentioned embodiment is an example, and the present invention provides the first and second recording signals.
It can be similarly applied to reproducing a magnetic tape in which a signal obtained by FM-modulating a carrier wave having a frequency of 1 is modulated with a video signal.

〔The invention's effect〕

According to the present invention described above, FM is reproduced depending on whether the carrier wave of the reproduction signal from the magnetic tape is the first frequency or the second frequency.
Since the direct current level of the reproduced video signal from the demodulator is controlled, even when reproducing the magnetic tape in which the signals obtained by FM-modulating the carrier waves of the first and second frequencies with the video signal are continuously recorded, The DC level of the reproduced video signal can be continuous. Therefore, according to the present invention, it is possible to prevent image disturbance and image quality deterioration due to a change in DC level.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation thereof, and FIGS. 3 to 6 are diagrams for explaining a conventional example. (1) is a magnetic tape, (7) is an FM demodulator, (8) is a switching switch, (9) is a DC level shift circuit, (10) is an output terminal, and (13) is a mode detection circuit.

Front Page Continuation (72) Inventor Ichitaro Sato 6-7-35 Kitashinagawa, Shinagawa-ku, Tokyo Within Sony Corporation (56) References JP 61-88678 (JP, A) JP 53- 20309 (JP, A) JP-A-60-169294 (JP, A)

Claims (2)

(57) [Claims] 1. A magnetic reproducing apparatus for obtaining a reproduction signal by scanning a track obliquely recorded on a magnetic tape with a plurality of reproducing magnetic heads so as to obtain a reproduction signal. The plurality of magnetic heads are arranged at intervals such that at least two magnetic heads are in sliding contact with each other, and before the switching of the magnetic heads, the next switching among the at least two magnetic heads in sliding contact with the magnetic tape is performed. Based on the reproduction signal from the target magnetic head, the detection circuit that detects whether the carrier of the reproduction signal is the first frequency or the second frequency, and corrects the DC level of the reproduction video signal from the FM demodulator. A DC level shift circuit for outputting as a reproduced video correction signal according to the detection result from the detection circuit among the reproduced video signal and the reproduced video correction signal. Magnetic reproducing apparatus characterized by having a selection circuit for switching the switching time of the magnetic head. 2. The plurality of reproducing magnetic heads are arranged on the rotary drum so as to face each other by 180 °, and the winding angle of the magnetic tape with respect to the rotary drum is slightly over 180 °. The magnetic reproducing device according to the item.