Introduction A television programme may be impaired by a lack of synchronism@ that is a relative timing error@ between the sound and picture signals. Loss of time relationship between sound and picture can occur in two principal areas: - in equipment used for studio effects or interconnect and preemission processing; such as video digital production effects units@ synchronizers@ standards converters and audio digital encoding equipment. This equipment will of necessity be different for the sound and picture signals and therefore may introduce appreciable differential delay between these components. Although the amount of differential delay introduced by individual items of equipment may be relatively small@ the cumulative effect occurring when such equipment is cascaded in the programme path may be significant. -where sound and picture are sent over separate circuits@ particularly if one circuit is terrestrial and the other satellite.