Synchronisation of television picture sources is a necessary prerequisite for modem programme production methods. Within a studio centre, this is normally achieved by permanently arranging the timings of the signals within the centre to be synchronous. However, this method is not possible for peripatetic remote sources such as outside broadcast units and very difficult even for fixed remote sources.nTwo methods are available which can synchronise such sources, at least to with¬in an acceptable error range. The first, used in the BBC 'Natlock' system, relies on a comparison of the timings of the remote source and the reference to generate an error signal which can be used to alter the timing of either the source or the reference in such a way as to reduce the error to an acceptable value. The second method uses a variable delay, usually in the source signal chain, to alter the relative timing between source and reference. This variable delay and its associated (automatic) controls are usually referred to by the collective title of 'afield (or picture or frame )-s tore synchroniser。
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