GB1327264A - Data recording - Google Patents

Abstract

1327264 Recording and playback BRITISH AIRCRAFT CORP Ltd 26 Nov 1971 [21 Sept 1970] 44904/70 Heading G4C and G5R A recording system maintains a predetermined average data packing density level, in spite of the existence of periods when no data is recorded, by appropriately varying the density at other periods. In the embodiment of Fig. 2, a signal is applied to a control unit 14 whenever a detector 15 (see below) senses a dropout region on a tape, or when a sync. timing unit 16 actuates a generator 17 to produce sync. pulses for recording in the data track instead of normal data; the unit 14 thereupon controls a clock 13 to release data from a buffer 8 at faster than usual rates on either side of the no-data region, as in Fig. 1 (not shown). In the dropout detection system 15, shown in detail in Fig. 3, test signals recorded on the tape 23 by a head 22 are read by a head 24, and a comparison is made at 28 between the signals applied to the write head (these ae obtained from a unit 29) and the signals received from the read head; any difference sensed is used to produce the dropout signal which is despatched to control unit 14 of Fig. 2. In the data buffer 8, as detailed in Fig. 4, data bits in a series of individual stages 35 are gated out by a series of gates 37 which receive address signals from a counter 40. The counter senses any differences between the regular clock-in pulses it receives over line 9 and the occasionally irregular clock-out pulses it receives over line 10 (from clock 13 in Fig. 2), and thereupon changes the addresses it supplies to gates 37. Data is thus read out from a different section of the series of stages 35 to change the packing density level as required.