Patent GB-1407036-A (GB)
Title: Magnetic recording and or reproducing system
IPC: H04N9/86
Filed: 1972-08-10
Abstract: 1407036 Television signal recording SONY CORP 10 Aug 1972 [13 Aug 1971 24 Aug 1971] 37435/72 Heading H4F To improve the utilization of magnetic tape, a video signal to be recorded (or at least a selected portion thereof, such as the chrominance component) is gated so that only every alternate line (or other signal period) is passed to the recording transducer, this gated signal being recorded in parallel transverse tracks along the tape with the signals recorded in one track being aligned with spaces between the recorded signals in adjacent tracks. Specifically each track 24a, 24b, ... Fig. 5A, includes all the signals necessary to complete one television field, and preferably the horizontal sync signals recorded on adjacent tracks are aligned. In one embodiment the luminance component is arranged to frequency modulate a 4À2 mHz carrier and is continuously recorded (i.e. it is not gated at line frequency) on the parallel tracks, and the chrominance components carrier is shifted to 560 kHz and alternate lines thereof are recorded with the luminance component, e.g. lines 1, 3 .. &c. as shaded in Fig. 5A. As shown in Fig. 5A these recorded chrominance component lines are staggered with respect to each other in adjacent tracks. This checkerboard array of recorded chrominance signals enables the space between adjacent tracks to be reduced without consequential interference between adjacent field recording, in fact not only may the guard space between tracks be eliminated but the adjacent tracks may overlap (Figs. 12 and 20, not shown) or be completely interleaved (Fig. 23, not shown). In the recording, whether the same order i.e. odd or even line, intervals of chrominance signals were recorded in the second field as in the first field would depend upon the slant angle and width of the tracks and upon whether the tracks were recorded so that the slant angle was acute (as shown in Fig. 5A) or obtuse (Fig. 5B) with respect to the longitudinal direction of the tape (movement of recording transducers indicated by arrow d, and movement of tape by arrow c). In addition the recording order for the second frame is the reverse of the order for the first frame. Thus in Fig. 5A the sequence through four fields is odd, odd, even, even, whereas in Fig. 5B the sequence is odd, even, even, odd. The air gaps in the recording heads (usually two in a rotating arrangement, each recording alternate fields) may be perpendicular to the track direction or at different angles (azimuth angles) to the track direction (Figs. 11 and 19, not shown). By using heads having different azimuth directions the reproduction of information i.e. interference during playback, is further reduced and enables adjacent tracks to be overlapped. During reproduction the gated signal is delayed by one line period and combined with the non-delay signal. Instead of just gating the chrominance signal the entire video signal may be gated at line frequency (Fig. 16, not shown), the entire video signal being frequency modulated on a carrier. The Specification includes detailed description of recording and playback arrangements in which the correct gating phases for the different tracks are obtained. Instead of passing every alternate line of the video signal to the recording transducer every third or every fourth line may be gated and passed to the recording transducer.