JPH08111849A - Magnetic recording and reproducing device - Google Patents

Abstract

PURPOSE: To prevent inversion by using an equalizer characteristic switching pulse to cover reduction in an envelope to switch an FM equalizer characteristic so as to suppress a reproduction FM signal lower side band. CONSTITUTION: A dropout detection circuit 5 detects a part below a threshold level of an envelope of a reproduced FM signal and generates a dropout pulse Pd. Since intervals of zero points of the envelope are identical to each other in the case of a constant search speed, a delay circuit 9 is used to produce a characteristic switching pulse P1 of 1 to 2H width just before a succeeding pulse Pd and a characteristic switching pulse P2 just after the pulse Pd and they are fed to an FM equalizer 1. The characteristic of the equalizer 1 is switched for only the part where the envelope of the reproduced signal is reduced by using the pulses P1, P2 to improve the S/N and to prevent inversion. Furthermore, the signal is replaced only in the vicinity of the zero point of the envelope through dropout compensation, no mosaic noise bar takes place and a high definition search image is obtained without inversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an azimuth recording type VTR (video tape recorder) having a normal reproducing head used in a standard mode and a normal reproducing head used in a long time mode. The present invention relates to a magnetic recording / reproducing device.

[0002]

2. Description of the Related Art Conventionally, in a VHS type VTR head structure, a standard mode head and a triple mode head form a double azimuth 4 head. FIG. 4 shows a VTR head structure having this structure.
Minus azimuth head 21 for audio and double azimuth head 2 for video at positions equally divided into 60 degrees.
2. A dummy head 23 for rotation balance, a plus azimuth audio head 24, a double azimuth head 25 for video, and a rotary erase head 26 are arranged in this order.

The double azimuth head 22 comprises a minus azimuth image head 22a and a plus azimuth image head 22b, and the double azimuth head 25 comprises a plus azimuth image head 25a and a minus azimuth image head 25b. . Further, the minus azimuth head 22a and the plus azimuth head 25a, and the plus azimuth head 22b and the minus azimuth head 25b are arranged at positions facing each other by 180 degrees.

Four image heads 22a, 22b, 25
a, 25b in the standard mode, the video heads 22a, 2b
5a, in the triple mode, the video heads 22b and 25b
Used for both recording and normal playback. During special reproduction, these heads are used in combination as needed. The track width of each head is 58 μm and 46 μm for the standard mode and 26 to 33 μ for the triple mode.
It is common to select in the range of m.

By the way, the video track pitch in the 3 × mode is 19 μm, whereas the track width of the 3 × mode head is 26 to 33 μm. Therefore, during normal reproduction, crosstalk from adjacent tracks causes edge noise and chroma. There is a problem that flicker occurs and the quality of the reproduced image quality deteriorates.

In order to solve this, the present applicant has proposed to add a head having a track width of 19 μm exclusively for the triple mode (Japanese Patent Laid-Open No. 3-192509). In Figure 5,
A head configuration according to this method is shown. In the figure, on the rotary drum 20, a minus azimuth audio head 21, a double azimuth head 22 for image at a position rotated by 52 degrees, a dummy head 23 at a position further rotated by 49 degrees, and a position further rotated by 27 degrees. Double azimuth heads 31 for images are sequentially arranged in the. Then, at a position facing them at 180 degrees, a plus azimuth audio head 24 and a video double azimuth head 2 are provided.
5, a rotary erase head 26, and a double azimuth head 32 for video are arranged respectively.

The double azimuth head 31 is composed of a minus azimuth image head 31a and a plus azimuth image head 31b.
2 includes a plus azimuth image head 32a and a minus azimuth image head 32b. Then, the minus azimuth head 31a and the plus azimuth head 3
2a, the plus azimuth head 31b and the minus azimuth head 32b are arranged at positions facing each other by 180 degrees.

In this configuration, the video heads 22a and 25a in the standard mode and the video head 22 in the triple mode are
b and 25b are used for both recording and normal reproduction, respectively, and at the time of special reproduction, the video heads 31a, 32a,
31b and 32b are used in combination as required. Since the video head for special reproduction is provided separately from the video head for normal reproduction in this way, the track width of the video head for normal reproduction can be set without considering the effect of special reproduction. Video head 22 for double mode
The track widths of b and 25b were set to be equal to the video track pitch of 19 μm in the triple mode.

FIG. 6 is a circuit block diagram of a conventional reproducing system. The reproduced FM signal input from each video head is balanced by the FM equalizer 11 in the upper and lower sidebands, demodulated by the FM demodulation circuit 12, and deemphasized by the deemphasis circuit 13. The low-pass filter (LPF) 14 removes carrier components,
It is output from the switch circuit 16 directly from F14 or after being delayed by 1H by the delay circuit 15 by 1H (H is one horizontal scanning period).

At the same time, the dropout detection circuit 17 detects the presence or absence of dropout at the level of the FM signal before demodulation, and the switch circuit 16 is switch-controlled by the dropout pulse, and there is no signal loss during dropout 1H.
The output is switched to the output of the delay circuit 15. The frequency characteristic of the FM equalizer 11 can be set by the external DC voltage, and the dropout detection circuit 17 can also be set by the external DC voltage.

The disadvantage of this method is that the cost increases due to the increase in the number of heads. In order to solve this inconvenience, 3 of the conventional double azimuth 4 head
By setting the track width of the double mode head to 19 μm, the dedicated single head can be abolished, and the cost has been reduced while realizing the high image quality of the triple mode.

[0012]

In the above-described head configuration (FIG. 5) in which the track width of the triple azimuth 4-head triplex mode head is set to 19 μm, the video search (double speed reproduction) in triplex mode is performed. However, since the track width is narrow, the noise bar becomes thick, and inversion phenomenon easily occurs, so that the quality of image quality is deteriorated.

The reason is that when a video search in triple mode is performed with a head having a track width of 19 μm, as shown by the solid line in FIG. 7A, since the head width is narrow, it is turned on as compared with the wide head shown by the broken line. This is because the tracked area becomes narrow. Therefore, as shown by the solid line in FIG. 7B, the envelope of the reproduced signal from the head becomes small, and there is a portion where the level becomes almost 0, and this portion becomes a noise bar. Compared to the maximum output even if it does not reach 0 level-
The portion of 4 dB or less exists for a considerable period. When the envelope is small, C / N is deteriorated, so that sidebands and noise level components are larger than carrier components,
Inversion phenomenon occurs.

Generally, the amount of on-track where the reversal phenomenon does not occur needs to be about 60% or more in consideration of the reproduced image quality. Therefore, the period of -4 dB or less is a period in which the inversion phenomenon may occur. The occurrence of the inversion phenomenon can be suppressed by suppressing the lower sideband of the reproduced FM signal.
In that case, the frequency characteristic after demodulation deteriorates. Further, if the portion where the envelope is lowered is determined to be the dropout portion and the signal before 1H is replaced, as shown in FIG. 7C,
Will be replaced by the same signal over 5H,
The noise bar part becomes a mosaic and the quality of the image is degraded.

Therefore, it is conceivable to replace the noise bar portion with the signal of the on-track portion by operating a dropout compensation circuit (hereinafter referred to as DOC). However, if the sensitivity of the DOC is increased, specifically, if the threshold level of the dropout detection circuit 17 is increased, the same signal is replaced for about 7H in the case of the 15 × search, the noise bar becomes a mosaic, and the image quality deteriorates. To do.

Conversely, if the sensitivity of the DOC is lowered, specifically, the threshold level of the dropout detection circuit 17 is lowered, the quality of the signal itself is degraded. This is the best DO
It is difficult to set the C sensitivity. Further, if the DOC is not used, a part of the horizontal sync signal is lost, and in some TV receivers, vertical sync loss occurs, which is inconvenient.

Therefore, the present invention suppresses the noise generated during the video search in the long time mode when the track width of the long time mode reproducing head is set to be substantially equal to the video track pitch in the long time mode. The purpose is to improve the quality of playback image quality.

[0018]

A magnetic recording / reproducing apparatus according to the present invention comprises a reproducing head group having a long time mode reproducing head having a track width substantially equal to a video track pitch of the long time mode, and a reproducing head group from the reproducing head group. An FM equalizer that balances the upper and lower sidebands of the reproduced FM signal, a dropout compensation circuit that detects dropout from the output of the equalizer and compensates the dropout of the reproduced FM signal, and a dropout is detected by the dropout compensation circuit. A delay circuit for delaying a dropout pulse generated at a predetermined time for a predetermined time and generating first and second characteristic switching pulses immediately before and immediately after the dropout pulse.
And the characteristic of the FM equalizer is switched by the second characteristic switching pulse to further suppress the lower sideband of the reproduced FM signal.

In this case, the reproducing head group includes a first normal reproducing head for performing normal reproduction in the standard mode, a second normal reproducing head for performing normal reproduction in the long time mode, and the above-mentioned 2
And a special reproduction head for performing special reproduction in one mode, and the track width of the second normal reproduction head is set to be substantially equal to the track pitch in the long-time mode.

In this case, the dropout compensation circuit has 1 to 2 before and after the zero point of the envelope of the reproduced FM signal.
The sensitivity is set so as to generate the dropout pulse for the horizontal scanning period.

[0021]

In the structure of the present invention, when a video search (double speed reproduction) is performed using a head having a track width almost equal to the video track pitch in the long mode as a long mode reproducing head, dropout pulse is generated. Before and after the zero point of the envelope of the reproduced FM signal 1
The sensitivity of the dropout compensation circuit is set so as to occur for about 2H period, and the dropout pulse is delayed to create an equalizer characteristic switching pulse that covers the lower portion of the envelope before and after the next dropout pulse.
This pulse switches the characteristics of the FM equalizer.
This suppresses the lower sideband of the reproduced FM signal to prevent the inversion phenomenon.

[0022]

1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention. In the present embodiment, the reproduced FM signal from the reproducing head described above is made to have a constant amplitude by an AGC (not shown), and then the FM equalizer 1 balances the upper and lower sidebands, and the FM demodulation circuit 2, After passing through the emphasis circuit 3, the LPF 4 removes the carrier component and outputs it. The FM equalizer 1 uses an equalizer with good phase characteristics that can control frequency characteristics with an external DC voltage.

At the same time, the dropout detection circuit 5 detects a portion of the reproduced FM signal below the threshold level of the envelope and generates a dropout pulse Pd. This threshold level can be controlled by an external DC voltage. In this embodiment, the mode signal from the microcomputer 6 further lowers the detection sensitivity as compared with the conventional one, that is, the threshold level is lowered, and 1 to 2H before and after the envelope becomes 0 level.
It is set to a degree. FIG. 2A shows the envelope of the reproduced FM signal, and FIG. 2B shows the dropout pulse P.
Indicates d.

The dropout pulse Pd switches the switch circuit 7, and when the envelope of the reproduced FM signal exceeds the threshold level, the through signal from the LPF 4 is selected,
If it is below the threshold level, the delay signal from the 1H delay circuit 8 obtained by delaying the output signal of the LPF 4 by 1H is selected.

The dropout pulse Pd is delayed by the first delay circuit 9 for a certain period of time and further delayed by the second delay circuit 10 for a certain period of time, and output as characteristic switching pulses P1 and P2 of the FM equalizer 1, respectively. .

When the search speed is constant, the intervals of the 0 points of the envelope become equal, so that the first delay circuit 9 causes 1 to 2 immediately before the generation of the next dropout pulse.
Generate a first characteristic switching pulse P1 having a width of about 2H,
The second delay circuit 10 causes the second characteristic switching pulse P2 to be generated immediately after the next dropout pulse. Figure 2
This relationship is shown in (c).

The characteristic switching pulses P1 and P2 cover the portion below the threshold where the envelope is lowered and the inversion phenomenon occurs. Specifically, in the FM equalizer 1,
By passing a system such as a band-pass filter centering on the carrier component to the reproduced FM signal, the influence of sliding noise generated from near the carrier frequency to high frequencies is reduced, and the lower sideband that increases as a characteristic of magnetic recording is reduced. The suppression suppresses the occurrence of the inversion phenomenon.

In order to suppress the inversion phenomenon, it is effective to suppress the lower sideband in this way, but the frequency characteristic after demodulation deteriorates. Therefore, as shown in FIG. 3, the characteristic indicated by the solid line a during normal reproduction, and the characteristic indicated by the broken line b for further suppressing the lower sideband by switching the characteristic with the characteristic switching pulses P1 and P2 in the portion where the envelope is lowered during the search. Switch to. In this way, the occurrence of the inversion phenomenon is suppressed only in the vicinity of the noise bar at the time of search without degrading the image quality at the time of normal reproduction.

In this way, only the portion where the envelope of the reproduction signal is lowered by the characteristic switching pulses P1 and P2 is FM.
The characteristics of the equalizer 1 are switched to improve the S / N and suppress the occurrence of the inversion phenomenon. Since this signal is replaced only in the vicinity of the zero point portion of the envelope by the dropout compensation, the noise bar does not become mosaic and a high-quality search image without inversion phenomenon can be obtained. Further, since the DOC is used, there is no loss of the horizontal sync signal, and vertical sync loss does not occur in any TV receiver.

A monostable multivibrator, for example, can be used as the first and second delay circuits. In this case, the output of the first delay circuit may be delayed by a simple integrating circuit instead of the monostable multivibrator as the second delay circuit.

[0031]

According to the present invention, the characteristics of the FM equalizer in the part where the envelope before and after the dropout pulse is lowered are switched based on the dropout pulse to further suppress the lower sideband, and thus the long time mode is extended. When a video search is performed using a head having a track width that is approximately equal to the video track pitch of the mode, specifically, it is of high quality in a low-cost double azimuth 4-head system that uses a 19 μm head for the triple mode. Both normal reproduction image quality and search image quality can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a magnetic recording / reproducing apparatus according to the present invention.

2A to 2C are waveform diagrams for explaining the operation of the embodiment shown in FIG.

FIG. 3 is a frequency characteristic diagram of the equalizer shown in FIG.

FIG. 4 is a schematic plan view showing a head arrangement on a rotary drum of a conventional VTR.

FIG. 5 is a conventional VT in which a head dedicated to the triple mode is added.
It is a schematic plan view which shows the head arrangement on the rotating drum of R.

FIG. 6 is a circuit block diagram of a conventional reproducing system.

7A to 7C are waveform diagrams for explaining the operation of the circuit shown in FIG.

[Explanation of symbols]

 1 FM equalizer 2 FM demodulation circuit 3 De-emphasis circuit 4 Low pass filter (LPF) 5 Dropout detection circuit 7 Switch circuit 8 1H delay circuit 9, 10 Delay circuit

Claims (3)

[Claims] 1. A reproducing head group having a long time mode reproducing head having a track width substantially equal to a video track pitch of the long time mode, and an FM for balancing upper and lower sidebands of a reproduced FM signal from the reproducing head group. An equalizer, a dropout compensation circuit that detects a dropout from the output of the equalizer and compensates a dropout of a reproduced FM signal, and a dropout pulse that is generated when the dropout is detected by the dropout compensation circuit for a predetermined time. A delay circuit that delays and generates first and second characteristic switching pulses immediately before and immediately after the dropout pulse, and the FM is generated by the first and second characteristic switching pulses.
A magnetic recording / reproducing apparatus characterized in that the characteristics of an equalizer are switched to further suppress the lower sideband of the reproduced FM signal. 2. The reproducing head group includes a first normal reproducing head that performs normal reproduction in a standard mode, a second normal reproducing head that performs normal reproduction in a long time mode, and a special reproduction head in the two modes. 2. A magnetic recording / reproducing apparatus according to claim 1, further comprising a special reproducing head for reproducing, wherein a track width of the second normal reproducing head is set to be substantially equal to a track pitch in a long time mode. . 3. The dropout compensating circuit includes 1-2 before and after the zero point of the envelope of the reproduced FM signal.
2. The magnetic recording / reproducing apparatus according to claim 1, wherein the sensitivity is set so as to generate a dropout pulse for about a horizontal scanning period.