GB857582A - Improvements in methods of recording and reproducing discontinuous signals - Google Patents

Abstract

857,582. Automatic alignment control systems. RANK CINTEL Ltd. Feb. 27, 1958 [Feb. 27, 1957], No. 6590/57. Class 38 (4). In a system for automatically aligning a scan with linear traces of a discontinuous signal record, unmodulated traces provided prior to the commencement of each element of the record are explored by displacing the scan in a transverse direction to produce a signal, indicative of the mean position of the scan, which is used to correct the relative position of scan and record. In Fig. 2 television signals are recorded line-byline on a cinematograph film 3, spot-wobbling producing picture signal traces 4. In recording, the spot-wobble oscillation is eliminated between lines by the blanking pulses and the flyback of the line scanning generator is arranged to terminate before the end of the television signal blanking period so that locally - produced brightening-pulses produce unmodulated portions 5 without spot-wobble, at the commencement of each line to mark the centre lines of the picture signal traces. During reproduction, a light spot scanning the lines is oscillated between positions 7, 7<SP>1</SP>, Fig. 3, while traversing the unmodulated portion 5 so that if the mean position of the spot corresponds to the centre line of the picture signal trace 4, equal signals are produced at positions 7, 7<SP>1</SP>. Any equality in these signals is utilized to correct the relative position of spot and trace automatically as shown in Fig. 6, in which the recorded cinematograph film 25 is scanned by a cathode-ray tube 29 controlled by a line-scan generator 31 synchronized by signals applied at terminal 32. The signals produced from the film by a photo-cell 34 are applied through an amplifier 35 and black-level clamp 36 and are available for external use at terminal 38. A vertical scan generator 39 which produces the oscillation of the spot while traversing the unmodulated portions of the trace is synchronized by applying at terminal 40 pulses which are appropriately timed relatively to those applied at terminal 32. Pulses are also derived from scan generator 39 by a pulse generator 42 when the spot is in each of its extreme positions relative to the unmodulated portion and these pulses are applied to a sampler 43 which is fed with video signals from clamp circuit 36 and produces in a generator 44 a signal indicative of any inequality in the signals at the two positions. From this error signal a filter circuit 45 derives low-frequency components which are applied to a control circuit 46 to correct the mean speed of film drive mechanism 28, and high-frequency components which are applied to a deflection generator 47 to correct the vertical position of the spot.