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Digital time-base corrector for special motion reproduction by helical-scan VTR
| Details |
Inventors: Mizukami, Mineo; Konishi, Tatsuo;
Assignee: Nippon Electric Co., Ltd. (Tokyo, JP)
Primary Examiner: Konick; Bernard
Assistant Examiner: McElheny, Jr.; Donald
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak and Seas
A time base corrector (TBC) for a special-motion video reproduction system employing a helical-scan VTR generates write-in address data synchronized to the reproduced digital data and stores the digital data in a digital memory in accordance with the generated write-in address. When the reproducing head jumps vertically, i.e. perpendicular to the data track, the currently-generated write-in address is latched. In response to a reference signal, the latched data is transferred to a read-out address counter for generating a read-out line address, and the stored video signal is then read out of the digital memory under control of the read-out address data. |
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DETAILED DESCRIPTION OF THE INVENTION Referring to FIG.
1, a digital TBC 10 according to one embodiment of this invention is for use in a special-motion reproduction system accompanied by a helical-scan VTR.
In the helical-scan VTR, a magnetic tape 11 is wrapped around a guide drum 12 and transported by tape transporting means 13 consisting of a capstan 14 and a pinch roller 15 in the direction of arrow B.
The guide drum 12 has a pair of drum portions 16 and 17 between which is provided a rotary magnetic head 18 rotating in the direction of arrow A at a vertical scanning rate.
The movement of the head forms a plurality of video tracks 11a, 11b, 11c and 11d, as shown in FIG.
2, each containing video information of one field.
The video tracks are formed diagonally with respect to the longitudinal direction of tape 11.
The actual magnetic tape also contains a plurality of other tracks (audio track, control track, and cue track) formed parallel to the lengthwise direction of the tape 11.
These tracks form no part of the instant invention and accordingly are omitted for purposes of this description.
When the magnetic tape 11 is transported for play back at a speed equal to normal transport speed in the record mode, the rotary head 18 achieves perfect tracking of the video track.
The center of the rotary head 18, which starts scanning at point P (FIG.
2) on the video track 11a, scans the track 11a while depicting the path following by the dashed line PQ and completes scanning at point Q on the same video track 11a.
Since the magnetic tape 11 moves one pitch of video track in the period of one scanning, the rotary head 18 passes the point Q almost concurrently with the next rotary head (for a dual-head system) or the same head (for a single-head system) passing point R on the adjacent video track 11b.
In the next scanning period, the rotary head 18 scans the video track 11b from point R to point S depicting the path shown by the dashed line RS.
Thus, the magnetic head 18 achieves perfect tracking of the video track in normal tape transportation
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TV Signal 
