Video disc encoding and decoding system providing intra-field track error correction

DETAILED DESCRIPTION FIGS.
1 and 2 provide a comparison of a field-by-field track error correction method (FIG.
1) with the line-by-line correction method (FIG.
2).
In FIG.
1, five adjacent tracks of a disc record are shown along with the locus (path) of travel (dark arrow) of a signal recovery stylus.
The term "track", as used herein, means an information conveying path on a disc and may be formed in a spiral or in concentric circles.
The stylus is initially in track number N of field A at time t-0 and is lofted from the disc at time t-1 upon encountering a particle of dirt spanning tracks N-2, N-1 and N.
AT time t-2 the stylus lands in track number N+2 and continues in that track until the beginning of the next field (field C).
Since the stylus has been radially translated by two tracks, the true tracking error amounts to a total skip of sixteen fields in a disc system where there are eight fields per disc convolution.
To correct the tracking error, the DAXI field number code recovered in the vertical interval of field B is compared with the code for field C which is recoverd at time t-3.
A kick pulse is applied to the stylus at time t-4 which, for illustrative purposes, results in an overkick in the interval t-4 to t-5 to track number N-1.
The overkick is corrected in a similar fashion in field D until the stylus is again tracking the correct track N.
As seen, in this hypothetical example, the total time lost during track error correction amounts to about two fields.
Even if the overkick had not occurred in field C, the disruption in the video signal would amount to about one field which would be visible in the displayed video image and audible in the reproduced sound.
It is desirable to reduce the duration of the disruptions and thus increase the "fidelity" of the recovered image.
FIG.
2 illustrates the improvement which may be obtained when track error correction is provided on a line-by-line basis in accordance with the invention using information specially encoded on the player sound carriers