JPH07122967B2 - Digital VTR - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a digital VTR in which tracking control is performed so that a head scanning position follows a track, and in particular, a screen produced when a track is switched during variable speed reproduction. It is related to the improvement of disorder.

[Outline of Invention]

According to the present invention, in a digital VTR in which tracking control is performed so that the head scanning position follows a track, a reproduction signal is written in a memory and the error state of the reproduction signal is discriminated so that the signal is previously written in the memory. By selecting and outputting one of the reproduction signal which has been written and the reproduction signal which is written in this memory, the disturbance of the screen does not occur even when the tracking is not correctly performed during the variable speed reproduction.

[Conventional technology]

In a digital VTR, dynamic tracking is used in which the scanning position of the head is made to follow a track by changing the position of the head during reproduction, for example, by a piezoelectric element. This dynamic tracking detects the level of the reproduction RF signal while slightly vibrating (wobbling) the head, detects the tracking error by the level of this RF signal, and reduces the tracking error amount. Tracking control is performed by changing the position.

[Problems to be solved by the invention]

By performing such dynamic tracking, good tracking control is performed during steady reproduction. However, during variable speed reproduction, in the conventional digital VTR using dynamic tracking, tracking could not be achieved when tracks were switched, and the screen might be disturbed. In other words, if the head is made to follow the track by dynamic tracking during variable speed playback, the tape transfer speed will be different from that during steady playback, so scan of one track will end and scanning of the next track will start. Then, the start position of the next track becomes unknown. Therefore, the starting position of the next track is predicted based on the tape transfer speed, and the head scanning is started from this predicted position. However, if the tracking interval at the editing point deviates from the regular one, the predicted position will not match the position of the next track, and tracking will not be complete. Therefore, error data occurs in the reproduction signal during this period, and snow noise occurs in the reproduction screen.

Therefore, an object of the present invention is to provide a digital VTR in which the playback screen is not disturbed even when tracking is lost when the tracks are switched during variable speed playback.

[Means for solving problems]

According to the present invention, in a digital VTR in which a head scanning position is controlled to follow a track, a read signal is written in a memory, and the error state of the read signal to be written in this memory is discriminated. Digital that selects and outputs one of the playback signal written in the memory and the playback signal written in the memory
It is a VTR.

[Action]

Playback signal is field memory 8A and 8B for each field
Are stored alternately. The error in the reproduction signal supplied to the field memories 8A and 8B is a tracking detection circuit.
If it is determined in step 17 that there are not many errors, the outputs of the field memories 8A and 8B are alternately output for each field. When many errors occur, the reproduction signal of the field in which many errors occur is not used, and the reproduction signal of the previous field is continuously output.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which FIG.
And 1B are rotary heads. The rotary heads 1A and 1B are arranged on the rotary drum 2 at the same position as shown in FIG. The tape 3 is wound around the rotating drum 2 by omega. During recording, when the rotary drum 2 is rotated once, two tracks T1 and T2 are formed on the tape 3 by the rotary head 1A and the rotary head 1B, as shown in FIG. The rotary drum 2 is rotated twice in one field, and four tracks of tracks T1 and T3 formed by the rotary head 1A and tracks T2 and T3 formed by the rotary head 1B correspond to digital video signals for one field. The recording signal to be recorded is recorded.

During reproduction, reproduction RF signals from the rotary heads 1A and 1B in FIG. 1 are supplied to the reproduction circuit 5. In the reproducing circuit 5, the data divided and recorded on the tracks T1 to T4 of the tape 3 are converted into continuous data, and the clock signal is extracted and the synchronizing signal is detected. The output of the reproduction circuit 5 is supplied to the tracking control circuit 6, and the tracking control amount is obtained by the tracking control circuit 6 according to a conventionally known method such as a wobbling method according to the level of the reproduction RF signal. Based on this tracking control amount, the positions of the rotary heads 1A and 1B are changed by the piezoelectric element, and dynamic tracking control is performed.

The output of the reproducing circuit 5 is supplied to the field memories 8A and 8B via the switch circuit 7. Field memory
The outputs of 8A and 8B are taken out from the output terminal 10 via the switch circuit 9.

These field memories 8A and 8B are used for playback RF during steady playback.
It is used to remove the time base fluctuations in the signal. That is, the switch circuit 7 is supplied with the field pulse synchronized with the reproduction signal from the terminal 11 via the AND gate 12 and the flop-flop 13. The switch circuit 7 is alternately switched for each field of the reproduction RF signal by the field pulse synchronized with the reproduction signal. On the other hand, the switch circuit 9
Is supplied with a reference field pulse from a terminal 14 via an AND gate 15 and a flip-flop 16. With this reference field pulse, the switch circuit 9 is alternately switched for each reference field. Further, although not shown, the field memories 8A and 8B are written by a write clock synchronized with the reproduction RF signal, and the field memories 8A and 8B are read by a reference read clock.

The field memories 8A and 8B are controlled so that the writing state and the reading state are alternately switched for each field during steady reproduction, and when one of the field memories 8A and 8B is in the reading state, the other is in the writing state. The reproduction RF signal output from the reproduction circuit 5 is supplied via the switch circuit 7 to one of the field memories 8A and 8B which is in the written state. An output signal is taken out from the other field memory in the read state via the switch circuit 9. Since the switch circuit 9 is switched by the reference field pulse, the output signal taken out from the output terminal 10 is synchronized with the reference field pulse.

Further, the field memories 8A and 8B are used to realize various variable speed reproductions. Called shuttle playback
When performing high speed reproduction of 10 to 60 times, the transport speed of the tape 3 is set to a high speed, and the rotary heads 1A and 1B scan across a plurality of tracks. For this reason, data for one continuous field cannot be obtained by one scan. Therefore, one field memory out of the field memories 8A and 8B stores data obtained by a plurality of scans to obtain data for one field and reads the data.

When reproducing a still image called freeze reproduction, the field memories 8A and 8B are not rewritten for each field, and the data stored in the field memories 8A and 8B are continuously read over several fields. It controls the switch circuits 7 and 9. As a result, data in the same field is continuously read.

When performing reverse playback called program play and variable speed playback up to 3 times speed, the transfer speed of the tape 3 is changed while tracking control is performed by the dynamic tracking control, and the control of the switch circuits 7 and 9 is performed in the same manner as during steady playback. Done. That is, in a certain field, the terminals 7A and 7B of the switch circuit 7 are connected, and the switch circuit 9
Assume that the terminal 9C and the terminal 9A are connected, the field memory 8A is in the write state, and the field memory 8B is in the read state. Terminals 7A and 7C of the switch circuit 7 are generated by the field pulse of the reproduction RF signal and the reference field pulse supplied via
Are connected, the terminals 9B and 9A of the switch circuit 9 are connected, the field memory 8A is set to the read state, and the field memory 8B is set to the write state.

In this program play, since the tape transfer speed is different from that during steady reproduction, tracking may not be performed correctly when the tracks are switched. The reproduction RF signal is supplied from the terminal 18 to the tracking detection circuit 17, and it is detected from the envelope of the reproduction RF signal whether or not the tracking is correctly performed. If tracking is performed correctly, the tracking detection circuit 17
Output is high level. When tracking is not performed correctly, the output of the tracking detection circuit 17 is set to low level.

When the output of the tracking detection circuit 17 becomes low level, the field pulse of the reproduction RF signal and the reference field pulse from the terminals 11 and 14 are not supplied to the switch circuits 7 and 9. Therefore, the switch circuit 7 and the switch circuit 9 are held in the same state even if the field is changed, and the data of the previous field is continuously output from the output terminal 10.

It should be noted that the detection as to whether or not the tracking is correctly performed may be performed depending on whether or not the synchronization signal or the address signal can be correctly detected. It is also possible to detect an error in the reproduced data by an error correction code and detect from this error rate whether or not the tracking is correctly performed.

〔The invention's effect〕

According to the present invention, the reproduced signal is stored in the feedback memory, the error state of the reproduced signal stored in the field memory is discriminated to detect whether or not the tracking is correctly performed, and the tracking is correctly performed and an error occurs. If not, the reproduced signal is output, and if tracking is not performed properly and many errors occur, the reproduced signal of the previous field is output. In this way, after determining the error of the playback signal, it is determined whether or not to output this playback signal.If many errors occur, the playback signal of the previous field is output without using the screen of this field. Therefore, even if the tracking is not performed correctly during the variable speed reproduction and many errors are included in the reproduction signal, the reproduction screen is not disturbed. As described above, since the screen for one field is once stored in the field memory regardless of the prediction, it is judged whether or not this data contains many errors, so that the operation is reliable.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram of a tape head system of a VTR to which the present invention is applied, and FIG. 3 is an explanation of recording tracks in a VTR to which the present invention is applied. It is a schematic diagram used for. Description of main symbols in the drawings 1A, 1B: rotary head, 6: tracking control circuit, 7, 9: switch circuit, 8A, 8B: field memory, 17: tracking detection circuit.

Claims (1)

[Claims] 1. A digital VTR in which a head is movable in the track width direction and tracking control is performed by causing the scanning position of the head to follow the track, and tracking detection means for detecting the tracking control state and reproduction. First and second memories for storing signals, first and second switch means for controlling inputs and outputs of the first and second memories, and control for the first and second switch means Switch control means, wherein the switch control means alternately switches the first and second switch means for each field in a steady state, and alternately outputs a reproduction signal from the first and second memories. When the output of the tracking detecting means detects that the tracking is not performed correctly, the first and second Digital VTR which is adapted either from the memory continuously reproduced signal to output of the memory.