JP2502886B2 - VTR - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a VTR capable of variable speed reproduction such as high speed search and slow reproduction.

[0002]

2. Description of the Related Art When performing special reproduction with a helical scan type VTR, a reproducing head is scanned across a number of tracks.

Therefore, the reproduced video signal is reproduced in a form in which a part of each track is cut out. Therefore, if the relationship between the reproduced signal and the track position is accurately grasped, the image quality of the special reproduction image is high. Can be realized.

For this reason, one horizontal period in the video signal
Alternatively, a signal indicating a recording track position (hereinafter referred to as a track ID signal) may be added to each track.

By adding such a signal, the track position of the reproduction signal at the time of special reproduction can be detected.

However, during special reproduction, the reproduction envelope has a shape in which diamonds are arranged like an abacus ball, the SN ratio is worse than in normal reproduction, and the above-mentioned track ID signal cannot always be detected. Sometimes deteriorated.

Particularly, in the case of the multi-track recording system, there has been a big problem. Therefore, when the track ID signal cannot be detected, or in the case of a VTR in which the track ID signal is not recorded, there is a track jump when the reproduction envelope level drops by utilizing the fact that the reproduction envelope level changes. Is used to detect the track position.

FIG. 2 shows the configuration of a VTR having the track jump detection circuit described above. However, the audio signal processing circuit is omitted.

In FIG. 2, 31 is a video signal input terminal,
32 is a video signal recording processing circuit, 33 and 34 are magnetic heads, 35 is a magnetic tape, 36 is a video signal reproduction processing circuit, 37 is a reproduction envelope level slice circuit, 38
Is a pulse width expansion circuit, and 39 is a video signal output terminal.

FIG. 3 is a diagram showing the relationship between the track pattern and the scanning direction of the head during special reproduction. Further, FIG. 4 is a diagram showing signal waveforms of the respective parts of FIG. The operation of each block in FIG. 2 will be described.

During recording, the video signal is a video signal input terminal 31.
It is further input, processed by the video signal recording processing circuit 32 into a signal suitable for recording, and recorded on the magnetic tape 35 through the magnetic head 33.

At the time of reproduction, the signal recorded on the magnetic tape 35 is reproduced through the magnetic head 34. Magnetic head 34
The signal reproduced in (1) is reproduced into a video signal in the video signal reproduction processing circuit 36 and output to the video signal output terminal 39. During special reproduction, the reproduction envelope (FIG. 4A) of the signal reproduced by the magnetic head 34 is detected by the reproduction envelope level slice circuit 37. Then, the set slice level is compared with the reproduction envelope level, and when the reproduction envelope is equal to or lower than the set level, a pulse is output.

In the vicinity of this slice level, since the level of the reproduction envelope is unstable due to the influence of crosstalk from the adjacent tracks, many pulses are likely to occur (FIG. 4 (b)).

Therefore, using this pulse as a trigger signal, the pulse width expanding circuit 38 expands the pulse width to perform pulse shaping (FIG. 4 (c)) to obtain a track jump detection signal.

The track jump detection signal is input to the video signal reproduction processing circuit 36 and used for signal processing of special reproduction, and the reproduced video signal is output to the video output terminal 39.

[0016]

However, as shown in FIG.
As shown in FIG. 4A, if dropout occurs during special reproduction, there is a drawback that an erroneous detection pulse is output (FIG. 4C).

Further, in the conventional track jump detecting method, it is difficult to set the time constant for expanding the pulse width because the shape of the reproduction envelope greatly changes when the tape feeding speed is changed.

In view of the above point, the present invention has an object to provide a VTR which accurately detects a track jump during special reproduction.

[0019]

In view of the above problems, the present invention outputs a pulse when the reproduction envelope level drops below a set value during special reproduction, and expands the pulse width by a pulse width expansion circuit. Has a track jump detection circuit configured to output a track jump detection signal when the pulse width of the pulse width detection circuit is equal to or more than a certain value, and the pulse width expansion circuit and the pulse width detection circuit. Is controlled by using the speed information of the tape feeding speed.

[0020]

According to the present invention, with the above configuration, it is possible to accurately identify whether the output reduction of the reproduction envelope during special reproduction is due to dropout or due to a track jump. Therefore, even if the track ID signal added to the reproduction signal cannot be detected, the relationship between the reproduction signal and the track position can be identified, so that a high quality special reproduction image can be provided.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a circuit in an embodiment of the present invention. However, the audio signal processing is omitted.

In FIG. 1, 1 is a video signal input terminal, 2
Is a video signal recording processing circuit, 3 and 4 are magnetic heads, 5
Is a magnetic tape, 6 is a video signal reproduction processing circuit, 7 is a reproduction envelope level slice circuit, 8 is a pulse width expansion circuit, 9 is a pulse width detection circuit, 10 is a reference clock generation circuit, 11 is a frequency dividing circuit, and 12 is a servo. The circuit, 13 is a video signal output terminal.

FIGS. 5 to 7 are diagrams showing operation waveforms of the respective portions of FIG. 1 at various reproduction speeds. First, the operation of each block in FIG. 1 will be described.

During recording, a video signal is input from the input terminal 1, converted by the video signal recording processing circuit 2 into a signal suitable for recording, and recorded on the magnetic tape 5 through the magnetic head 3.

At the time of reproduction, the signal recorded on the magnetic tape 5 is reproduced through the magnetic head 4. The magnetic heads 3 and 4 may be shared for recording and reproduction. The signal reproduced by the magnetic head 4 is reproduced into a video signal by the video signal reproduction processing circuit 6, and the reproduced video signal is reproduced by the re-video signal output terminal 1.
4 is output. On the other hand, the signal reproduced by the magnetic head 4 is input to the reproduction envelope level slicing circuit 7 to be compared with a certain set reference level and the reproduction envelope level, and a pulse is generated in a period below the reference level. .

The pulse width expanding circuit 8 expands the pulse width by using this pulse as a trigger signal to perform waveform shaping, and is input as a gate signal of the next pulse width detecting circuit 9. The pulse width detection circuit 9 counts clocks while the gate signal is being applied, and when the count value reaches the set value of the counter of the pulse width detection circuit 9, it is discriminated as a track jump, and the video signal reproduction processing is performed. It outputs a pulse to the circuit 6. If the count value does not reach the set value, it is processed as dropout.

The clock supplied to the counters of the pulse width expanding circuit 8 and the pulse width detecting circuit 9 is supplied by dividing the output of the reference clock generating circuit 10 by the frequency dividing circuit 11. Speed information is input to the frequency dividing circuit 11 from the servo circuit 12 that controls the running system of the magnetic tape 5, and the frequency dividing ratio is determined according to the tape feeding speed. That is, when the number of track jumps is high, such as during high-speed search, the division ratio is lowered to increase the clock frequency to increase resolution, and conversely, when the number of track jumps is low, such as during slow playback. Increase the ratio and lower the clock frequency.

In this way, the track jump can be easily detected by changing the clock frequency following the speed information. The above operation will be described in detail based on the waveform of each part.

FIG. 5 is a diagram showing signal waveforms of the respective parts of FIG. The reproduction envelope shows the case where the recording track pattern on the magnetic tape shown in FIG. 3 is reproduced at each reproduction speed.

In FIG. 5A, the cycle of the head switching signal is 1
This shows a reproduction envelope in the case where the reproduction is performed at 6.67 ms at a tape feeding speed three times as high as that in the normal reproduction and the signals are alternately read by the heads having different azimuth angles.

The reproduction envelope is unstable in the portion where the output is reduced due to the linearity of the recording track and the crosstalk from the adjacent track. For such a playback envelope, set the slice level to the peak value −
When the output level of the envelope level slice circuit 7 is 10 dB, a number of pulses are generated as shown in FIG.

Therefore, in the pulse width expansion circuit 8, FIG.
Is used as a trigger signal to expand the pulse width, and the pulse trains that are generated repeatedly are shaped into one pulse as shown in FIG. 5C. The pulse width expansion circuit 8 is composed of a digital circuit. When a pulse is input, the counter is reset and starts counting, and when the count value reaches the set value, the counting is stopped and H during the counting period.
The i level is output, and the pulse width is expanded as a result.
Therefore, the pulse width expansion circuit 8 operates as a retrigger type monostable multivibrator, but the pulse width generated changes according to the input clock frequency and the set value of the counter.

Next, in order to discriminate the width of the waveform-shaped pulse, this pulse is used as the gate signal of the pulse width detection circuit 9, and counting is started by the clock common to the pulse width expansion circuit 8.

When the count value reaches the set value, that is, the track jump determination pulse width, it is determined that there is a track jump, and the track jump detection signal is shown in FIG.
It is output as shown in (d).

Therefore, when dropout occurs in the reproduction envelope, if the pulse width of the erroneous detection pulse due to dropout is smaller than this set value, it is determined as dropout, and the output of the pulse width detection circuit 9 ignores it. Further, if the width of the dropout becomes large, an erroneous detection pulse is output, but in this case, the interval of the output pulse train of the pulse width detection circuit 9 changes greatly with respect to the steady state, and therefore it is possible to detect from the preceding and following pulse intervals. Yes, it can be interpolated.

Similarly, FIG. 6 shows the signal waveform of each part in the case of still reproduction and FIG. 7 in the case of -3 × speed reproduction. Since FIGS. 5 to 7 show the concept of the present invention, the time axis is slightly incorrect.

In this embodiment, the reference clock frequency is 12.288 MHz. Further, the frequency division ratio is set so that about 1/100 of the interval at which the track jump occurs becomes one clock cycle.

Table 1 shows the set values in this embodiment. It should be noted that these values need to be changed appropriately depending on the VTR format used.

[0039]

[Table 1]

As is clear from (Table 1), even if the shape of the reproduction envelope changes due to the difference in reproduction speed, the clock frequency changes accordingly, so that the pulse width expansion circuit 8 and the pulse width detection circuit 9 The optimum pulse width can be generated without frequently changing the set value of the counter.

[0041]

As described above, according to the present invention, the track jump information can be accurately detected by controlling the track jump detection circuit based on the speed information from the servo circuit. Therefore, particularly in the special reproduction of the VTR of the multi-track recording system, the relationship between the reproduction signal and the track position can be accurately grasped, so that a high quality reproduced image can be provided and its effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of a VTR according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a conventional example.

FIG. 3 is a diagram showing a signal waveform of each part of FIG.

FIG. 4 is a schematic diagram showing a recording pattern of tracks on a magnetic tape.

FIG. 5 is a diagram showing signal waveforms at various parts in FIG. 1 during 3 × speed reproduction.

FIG. 6 is a diagram showing signal waveforms of various parts of FIG. 1 during still reproduction.

FIG. 7 is a diagram showing signal waveforms at various parts in FIG. 1 during -3 × speed reproduction.

[Explanation of symbols]

 1 video signal input terminal 2 video signal recording processing circuit 3 magnetic head 4 magnetic head 5 magnetic tape 6 video signal reproduction processing circuit 7 reproduction envelope level slice circuit 8 pulse width expansion circuit 9 pulse width detection circuit 10 reference clock generation circuit 11 frequency division Circuit 12 Servo circuit 13 Video signal output terminal

Claims (1)

(57) [Claims] 1. A helical scan type VTR in which tracks are formed adjacent to each other on a magnetic tape, and adjacent tracks have different azimuth angles, and a reproduction envelope level drops below a set value during special reproduction. In this case, a pulse jump is performed, the pulse width is expanded by a pulse width expansion circuit to shape the waveform, and the track width detection circuit outputs a track jump detection signal when the pulse width exceeds a certain value. A VTR having a detection circuit, wherein the pulse width expansion circuit and the pulse width detection circuit are controlled by speed information of a tape feeding speed.