JPH0153830B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for more accurately detecting the timing at which a reproducing head jumps onto a recorded video track or returns to a previously recorded video track in a magnetic recording/reproducing apparatus such as a VTR. It is.

Generally, a helical scan video tape recorder (hereinafter referred to as VTR) has a rotating head.
In this case, various inconveniences occur during special playback such as search playback and still playback.

For example, depending on the value of the number of deviations in H (αH) between adjacent recording video tracks on a magnetic tape, (1) horizontal skew phenomenon due to discontinuity of horizontal synchronization may occur during the above special playback.

(2) As described in Japanese Patent Application No. 56-195685 (Japanese Unexamined Patent Publication No. 58-97990), in the PAL system, the phenomenon of no coloration due to disturbances in the color synchronization section of the receiver.

occurs. Also, regardless of the number of deviations of H (αH), (3) Noise band on the playback screen.

This may cause other inconveniences.

These problems occur when the playback head jumps forward or backward one track to play. This will be briefly explained.

FIG. 1 shows an example of a recorded video track pattern on a magnetic tape and a trace pattern of a playback head during search playback. In the figure, the recording video tracks are recorded at two heads with different azimuths, and A ₁ , A ₂ , A ₃ . . . and B ₁ , B ₂ , B ₃ . . . have different azimuths. Also,
Reproduction head A is a head that reproduces video tracks A ₁ , A ₂ , A ₃ . . . Reproduction head B is a head that reproduces video tracks B ₁ , B ₂ , B ₃ . As shown in the figure, after playback head A plays video tracks A ₁ , A ₂ , and A ₃ ,
Reproducing head B reproduces tracks B ₄ , B ₅ , and so on.
An example of the envelope characteristic of the reproduction head output in this case is shown in FIG. 3a. As shown in the figure, the reproduction output constricts, for example, at the so-called track jump point, where the reproduction head A transitions from track _A1 to track _A2 . This constriction indicates that the reproduction output level is low, and becomes a noise band. Furthermore, at the track jump point mentioned above, a line jump of 2αH occurs. Therefore, for example, when 2αH is not an integral multiple of H, a horizontal skew phenomenon occurs. Furthermore, when 2αH is an integral multiple of H and is not an odd multiple, a phenomenon occurs in which no color is added to the playback screen in the PAL system.

On the other hand, FIG. 2 shows an example of a recorded video track pattern on a magnetic tape and a trace pattern of a playback head during still playback. In this example, playback head A plays track A ₃ and playback head B plays track B _2. An example of the envelope characteristic of the playback output in this case is shown in FIG. 3B. As shown, the reproduction output constricts at the point where each head reproduction transitions from track A ₃ to track B ₂ . The point of this transition from track A ₃ to track B ₂ is that in normal playback, track B ₃ should be played after track A ₃ , but by jumping just one track, track B ₂ is played.
To return to this point, we call it the track jump point. This track jump point is caused by the noise band and horizontal skew phenomenon, as in the case of search playback described above.
This may cause colors to not appear in the PAL system.

Next, an example of suppressing such inconvenience will be described.

First, (1) one example of a method for suppressing the horizontal skew phenomenon due to discontinuity in horizontal synchronization is to correct discontinuity in horizontal synchronization at a track jump point using a delay line. For example, when 2αH=1.5H (where 1H represents one horizontal period), a horizontal synchronization discontinuity of 0.5H occurs at the track jump point, and a horizontal skew phenomenon of 0.5H occurs on the playback screen. Therefore, using a 0.5H delay line,
By alternately switching between the reproduced signal that passes through a 0.5H delay line and the signal that does not pass through the delay line at the track jump point, jumps at the track jump point can be prevented.
2αH±0.5=1H or 2H. That is, since it is an integral multiple of H, horizontal synchronization is continuous and the horizontal skew phenomenon is suppressed.

Next, (2) In the PAL system, as a method to suppress the phenomenon of no coloring, as described in Japanese Patent Application No. 56-195685 (Japanese Unexamined Patent Publication No. 58-97990), there is a 1H delay at the track jump point. One example is switching between a regenerated chroma signal and a regenerated chroma signal that is not delayed.

Next, (3) as a method for suppressing image quality deterioration due to noise bands on the playback screen, one example is to force the noise bands into a vertical blanking period during still playback so that they do not appear on the playback screen. Furthermore, during search playback, by fixing the noise band at a fixed position on the playback screen, it is possible to obtain a screen that is less unsightly than when it is not fixed. In this case, the noise band corresponds to the track jump point as described above.

In this way, in order to suppress the inconvenience during special playback, it is sufficient to detect the track jump point and use the detection signal to use, for example, the above-mentioned compensation means.

SUMMARY OF THE INVENTION An object of the present invention is to provide a means for more accurately detecting the track jump point, which is used to suppress the above-mentioned disadvantages.

In order to achieve the above object, in the present invention, four types of pilot signals having different frequencies are selected for each field in a predetermined order, multiplexed with the video signal and recorded, and adjacent tracks are recorded with different azimuth angles. A playback head that reproduces a plurality of pilot signals along with a video signal by drawing a playback locus spanning a plurality of recording tracks on a magnetic tape having a large number of tracks, and a plurality of playback pilot signals obtained from the playback head. from,
There is an extraction means for extracting a reproduction pilot signal multiplexed with the reproduction video signal that is reproduced by the reproduction head, and as the reproduction head moves along the reproduction trajectory, the reproduction pilot signal obtained from the extraction means is attenuated and other frequencies are detected. Detection means are provided for detecting the alternation of the regenerated pilot signal with the regenerated pilot signal, thereby detecting the track jump point.

As an embodiment of the present invention, a case will be described in which four frequencies are used as pilot signals recorded on each video track.

Here, the four-frequency pilot signals are _{1 and 1} , respectively.
₂ , ₃ , and ₄ , and select their respective frequencies so that the following relationship holds.

₂ − _{1 4} − ₃ k・_H …(1) ₃ − _{1 4} − ₂ m・_H …(2) k≠m …(3) However, _H is the frequency of one horizontal period, and k and m are positive values. It is. Also, select pilot signals ₁ and ₄ to be recorded on the channel A track, and select pilot signals ₂ and ₃ to be recorded on the channel B track.

As an example of a pilot signal that satisfies the above relational expression, let k = 1, m = 3, ₁ = 6.5 _H , ₂ =
There are 7.5 _H , ₃ = 9.5 _H , and ₄ = 10.5 _H. Also, as another example, let k = 1, m = 3, = 6.88 _H ,
You can also choose ₂ = 7.80 _H , ₃ = 9.75 _H , and ₄ = 10.64 _H.

FIG. 4 shows an embodiment of a circuit for recording the pilot signal on each video track. In FIG. 4, 1 is an input terminal for the FM-converted luminance signal, 2 is an input terminal for the low-frequency converted chroma signal,
3 is an input terminal for pulses synchronized with head switching, 4
1 is a first mixer, 5 is a second mixer, 6 is a recording amplifier, 7 is a recording head, 8 is a pilot signal generation circuit, and 9 is a selection circuit. The luminance FM signal and the low frequency converted chroma signal are mixed in the first mixer 4 and guided to the second mixer 5. On the other hand, pilot signals ₁ to ₄ from the pilot signal generation circuit 8 are led to the selection circuit 9, and are sequentially selected by pulses synchronized with head switching, for example, in the order of ₁ → ₂ → ₄ → ₃ , and then 2 mixer 5. However, in this case, pilot signals ₁ and 4 are sent to the channel A head, and pilot signals 1 and ₄ are sent to the channel B head.
₂ and ₃ shall be selected. Second mixer 5
Then, the luminance FM signal, low-frequency chroma signal, and pilot signal are mixed together, guided through a recording amplifier 6 to a recording head 7, and recorded on a magnetic tape.

The recorded video track pattern diagrams in FIGS. 1 and 2 show an example of the recording pattern of the pilot signal recorded in this manner.

FIG. 5 shows an embodiment of the track jump point detection circuit in the above example. In FIG. 5, 10 is an input terminal for reproduction pilot signals ₁ to ₄ , 11 is an input terminal for pulses synchronized with head switching, 12 is a frequency converter, 13 is a first tank circuit, and 14 is a second tank circuit. , 15 is a differential amplifier, 16 is a limiter circuit, 17 is an output terminal for a JP signal indicating a track jump point, and 18 is a selection circuit.

The principle by which the track jump point during the 6x speed search playback shown in FIG. 1 is detected by an embodiment of the detection circuit shown in FIG. 5 will now be described with reference to FIG.

In FIG. 6, 6a corresponds to the envelope waveform of the head reproduction signal during search reproduction in FIG.
This is the envelope waveform of a pilot signal played back from a video track recorded at the same azimuth angle as the playback head. 6b is an envelope waveform of a pilot signal reproduced from a video track recorded at an azimuth angle different from that of the reproduction head.
Generally, pilot signals ₁ to ₄ are selected to have a frequency lower than that of the low-frequency conversion chroma signal, around 100 KHz, so no azimuth effect can be expected. Therefore, the reproduced pilot signal introduced to the input terminal 10 in FIG. 5 is a signal obtained by combining the envelope waveforms 6a and 6b. The reproduced pilot signals 6a and 6b are led to a frequency converter 12, where they are frequency-converted with the pilot signals ₁ to ₄ from the pilot signal generating circuit 8. Here, in the above equations (1) to (3), k = 1, m = 3 as conditions for the pilot signal.
An example of the case will be explained. Frequency converter 12
The above pilot signal ₁ led with the carrier signal of
_.about.4 are switched for each channel by the selection circuit 18 by a pulse such as 6h from the input terminal 11 synchronized with head switching. Here, as a carrier signal, as shown in 6c, when the head of channel A is reproduced, the pilot signal ₂ or ₃ recorded on channel track B is used, and when the head of channel B is reproduced, the pilot signal 1 or ₃ recorded on channel track A is used. Select ₄ . In this case, among the outputs of the frequency converter 12, the difference frequencies between the reproduced pilot signal and the carrier signal are 6d and 6e. However, 6d is the difference frequency between the envelope waveform 6a of the reproduced pilot signal and the carrier signal, and 6e is the difference frequency between the envelope waveform 6b and the carrier signal. First tank circuit 13 and second tank circuit 1 in FIG.
If the tank frequencies of 4 are chosen to be _H and 3 _H , respectively,
The output of the differential amplifier 15 is as shown in 6. In order to detect the zero cross point of the output 6 of this differential amplifier 15, it is passed through a limiter 16, and the 6
A JP signal indicating the track jump point as shown in g is obtained.

In the example in FIG. 1, the order in which the pilot signals are recorded is selected in a cycle of ₁ → ₂ → ₄ → _3. In this case, during special playback, the selection circuit 18 in FIG. By selecting the order in which ₁ to ₄ are switched for each channel in a cycle of ₂ → ₁ → ₃ → ₄ , the JP signal indicating the track jump point can be detected regardless of the search speed.

Furthermore, in the example shown in FIG. 1, the order in which the pilot signals are recorded may be selected in a cycle of ₁ → ₃ → ₄ → _2. In this case, during special playback, the order in which the pilot signals are switched by the selection circuit 18 may be selected. By selecting ₂ → ₄ → ₃ → ₁ in one cycle, the JP signal can be detected.

The above search playback describes a method for detecting a track jump point in frame playback, in which playback heads with different azimuth angles are switched for each channel. This makes it possible to detect a track jump point in, for example, field reproduction using a reproduction head with the same azimuth.

That is, when reproducing the carrier signal input to the frequency converter 12 of FIG. 5 at the same azimuth angle as the recording head of channel track A, the pilot signal ₂ or ₃ recorded on channel track B is Conversely, if you want to play back at the same azimuth angle as the recording head of channel track B, select pilot signal ₁ or ₄ recorded on channel track A and always keep the same frequency without switching the carrier signal for each channel. By using , the JP signal can be obtained in the same manner as shown in FIG.

The above has explained the case during search playback. Next, it will be explained with reference to FIG. 7 that a track jump point can be detected according to the present invention even during still playback shown in FIG. 2.

In FIG. 7, 7a corresponds to the envelope waveform of the head reproduction signal during still reproduction in FIG.
This is the envelope waveform of a pilot signal played back from a video track recorded at the same azimuth angle as the playback head. 7b is an envelope waveform of a pilot signal reproduced from a video track recorded at an azimuth angle different from that of the reproduction head.
As in the case of search reproduction described above, a signal obtained by combining the envelope waveforms 7a and 7b of the reproduced pilot signal is led to the input terminal 10 of FIG. The carrier signal 7c guided to the frequency converter 12 is similar to the search playback described above, when the head of channel A is reproduced, the pilot signal ₂ or ₃ recorded on the channel track B is used, and when the head of channel B is reproduced, the carrier signal 7c is used as the pilot signal 2 or 3 recorded on the channel track A. Pilot signal ₁ or ₄ recorded in Here, the pilot signal conditions are the same as for search playback, k = 1, m
=3, of the output of the frequency converter 12, the difference frequency between the envelope waveform 7a of the reproduced pilot signal and the carrier signal is 7d, and the difference frequency between the envelope waveform 7b of the reproduced pilot signal and the carrier signal is 7e. It becomes like this. Therefore, the output of the differential amplifier 15 in FIG.
By passing the limiter 16,
At the output terminal 17, a JP signal such as 7g indicating the track jump point is obtained.

When playing stills above, the pilot signal
₁ to ₄ are switched for each channel, and the switching order depends on the recording order and is the same as in search playback.

Furthermore, in still playback, for example, a method for detecting a track jump point in the case of frame playback has been described in which playback heads with different azimuth angles are switched for each channel. Detection of track jump points in the case of regeneration is also possible.

That is, as carrier signals input to the frequency converter 12 in FIG. 5, ₂ and ₁ , ₂ and ₄ , ₃ and
By alternately switching ₁ or ₃ and ₄ , for example ₂ and ₁ , for each channel, a JP signal indicating the track jump point can be obtained.

As described above, by using one embodiment of the present invention, a track jump point can be easily detected. By using the JP signal detected in this way as a control signal for the above-described means for suppressing failure during special playback, image quality deterioration can be suppressed.

Next, a description will be given of means for improving the above-mentioned effect of suppressing image quality deterioration.

FIG. 8 shows an embodiment in which the tracking jump point detection signal according to the present invention is used to improve image quality during special playback.

In FIG. 8, 19 indicates the detected track jump point obtained at the output terminal 17 in FIG.
JP signal input terminal, 20 is the first frequency dividing circuit, 2
1 is a phase detection circuit, 22 is a second frequency dividing circuit, 23
is an input terminal for a control signal synchronized with head switching, 2
Reference numeral 4 indicates an input terminal for a control signal to switch the magnetic tape feed speed, 25 indicates an input terminal for a control signal indicating whether or not to reproduce still images, and 26 indicates a track jump point.
JP signal output terminal 27 is an output terminal led to the capstan servo circuit, and 28 is a control circuit. In this embodiment, the capstan servo circuit is controlled by a signal obtained by comparing the phase of the JP signal from the input terminal 19 and the control signal synchronized with head switching from the input terminal 23 to control the magnetic tape feeding speed during search playback. By doing so, by locking the phase to the field or frame period, the noise band can be almost fixed on the playback screen, and the visual quality of the image can be improved.

Also, during still playback, for example, the input terminal 25
The control circuit 28 uses the control signal from the phase detection circuit 21 to control the JP signal to be located near the vertical synchronization signal using the above detection signal, thereby driving the noise band to the edge of the playback screen, thereby improving the visual appearance. Image quality can be improved.

In addition, the JP signal, which is used as a control signal to correct the horizontal skew phenomenon described above and the lack of coloration in the PAL system, and the signal synchronized with head switching from the input terminal 23 during still playback, are
Otherwise, by using the JP signal from the input terminal 19, it is possible to improve the above-mentioned correction accuracy, especially during still playback. 29 is a switch circuit that switches the JP signal in this way.

FIG. 9 shows another embodiment in which the present invention is used during special playback to improve image quality.

In FIG. 9, 30 is a phase detection circuit, 31 is a voltage controlled oscillator (hereinafter referred to as VCO), 32,
33 is a frequency dividing circuit, and the other parts are the same as those shown in FIG.
In this embodiment, the JP signal obtained from the input terminal 19, for example, in the embodiment shown in FIG. By stabilizing it, the effect obtained in FIG. 8 can be further improved. Although not shown in the embodiment of FIG. 9, as a control signal for correcting the horizontal skew phenomenon and the non-coloring phenomenon in the PAL system,
By using the output signal of the VCO 31, the correction effect can be improved.

FIG. 10 shows another embodiment using the present invention.

In FIG. 10, 33 is an input terminal for a JP signal indicating a track jump point detected by the present invention, 34 is an input terminal for a capstan FG pulse,
35 is an input terminal for a control signal, 36 is an output terminal to a capstan motor drive circuit, 37 and 39 are frequency dividing circuits, 38 is a phase detection circuit, and 40 is a capstan servo circuit. In this embodiment, the magnetic tape feeding speed is controlled by comparing the phases of the FG pulse indicating the speed of the capstan motor and the JP signal. In this case, by switching at least the frequency dividing ratio of the frequency dividing circuit 37 or 39 using a control signal from the input terminal 35, the magnetic tape feeding speed during special playback can be easily changed.

In the above invention, the pilot signals ₁ to ₄ are recorded over the entire video track, but the pilot signals may be recorded intermittently, for example, during the front porch period of the horizontal synchronizing signal. You may do so.

Furthermore, although the present invention has been described only for search playback and still playback, it is not limited thereto and can be used in other modes as well.

Furthermore, although the present invention has been described only with respect to the case where the pilot signal is used during special playback, it is also possible to use the pilot signal also as a pilot signal used for auto-tracking.

According to the present invention, track jumps of the playback head during special playback such as search playback and still playback can be easily and more accurately detected.
It is possible to improve the image quality during special playback. Furthermore, the present invention can also be used as a pilot signal used for auto-tracking during normal playback, thereby reducing costs.

[Brief explanation of drawings]

Figure 1 shows the recorded video track pattern and the trace pattern during search playback. Figure 2 shows the recorded video track pattern and the trace pattern during still playback. Figure 3 shows the playback envelope waveform during search and still playback. 4 is a circuit diagram showing an embodiment of a pilot signal recording circuit, and FIG.
The figure is a circuit diagram showing an embodiment of a detection circuit for a JP signal indicating a track jump caused by a pilot signal.
FIG. 6 is a waveform diagram showing an embodiment of the present invention during search playback, FIG. 7 is a waveform diagram showing an embodiment of the present invention during still playback, and FIG. 8 is a waveform diagram showing an embodiment of the present invention during search playback. A circuit diagram showing one embodiment, FIG. 9, is as follows:
Circuit diagram showing another embodiment using the present invention, 1st
FIG. 0 is a circuit diagram showing another embodiment using the present invention. Explanation of symbols 5...Mixer, 8...Pilot signal generation circuit, 9...Pilot signal selection circuit, 12
...Frequency converter, 13, 14...Tank circuit, 15
... Differential amplifier, 16 ... Limiter circuit, 19 ... JP signal input terminal, 20, 22 ... Frequency divider circuit, 21 ... Phase detection circuit, 23 ... Signal synchronized with head switching,
30... Phase detection circuit, 31... VCO circuit, 32,
33... Frequency dividing circuit, 37, 39... Frequency dividing circuit, 38...
Phase detection circuit, 40...servo circuit.

Claims (1)

[Scope of Claims] 1. Four types of pilot signals with different frequencies are selected for each field in a predetermined order, and are multiplexed with the video signal and recorded, and there are many recording tracks with different azimuth angles between adjacent tracks. A playback head that reproduces a plurality of pilot signals along with a video signal by drawing a playback trajectory spanning a plurality of recording tracks on the formed magnetic tape; and a playback head that reproduces a plurality of pilot signals obtained from the playback head. Extracting means for extracting a reproduced pilot signal multiplexed with a reproduced video signal reproduced by the head; and an extracting means for extracting a reproduced pilot signal multiplexed with a reproduced video signal reproduced by the head, and a reproduced pilot signal obtained from the extracting means attenuated as the reproduction head moves along a reproduction locus, and reproduces other frequencies. 1. A truck jump detection device comprising: detecting means for detecting alternation of a regenerated pilot signal with a pilot signal. 2. The extraction means includes a carrier signal source that generates a carrier signal of a frequency equal to the pilot signal recorded on a recording track adjacent to the recording track on which the reproduced video signal is recorded, from the reproduction head and mixing means for mixing a reproduced pilot signal from a carrier signal source and a carrier signal from a carrier signal source; and a means for mixing tank frequency components using a tank circuit whose tank frequency is set to the difference frequency between pilot signals recorded on mutually adjacent recording tracks. filter means for extracting from the output of the filter means, and the detection means comprises envelope detection means for detecting a change in the envelope waveform of the tank frequency component extracted by the filter means. The track jump detection device described above. 3. The filter means has first and second tank circuits to which the output of the mixing means is supplied, and the envelope detection means subtracts the output of the second tank circuit from the output of the first tank circuit. 3. The track jump detection device according to claim 2, further comprising a subtraction circuit. 4 First, second, third and fourth pilot signals having different frequencies are selected for each field in this order and multiplexed with the video signal to generate two rotations having first and second azimuth angles. A large number of recording tracks are formed which are alternately recorded by the heads, and one of the first and third pilot signals is multiplex recorded on the recording tracks recorded by the rotating head having the first azimuth angle, and the second For a magnetic tape on which either the second or fourth pilot signal is multiplex recorded on a recording track recorded by a rotating head having an azimuth angle,
a reproducing means for reproducing a recorded signal recorded on a recording track by two reproducing heads having first and second azimuth angles; 4
generates a carrier signal of a frequency equal to the frequency of one of the pilot signals of the first and third pilot signals when the reproducing head having the second azimuth angle is in the reproducing state; a carrier signal source for generating a carrier signal; mixing means for mixing a reproduced pilot signal from the reproduction means and a carrier signal from the carrier signal source; 4. A truck characterized in that it consists of an extraction means for extracting from the output of the mixing means a component with a frequency equal to the difference frequency with the pilot signal, and a detection means for detecting a change in the envelope of the output of the extraction means. jump detection device.