No definite duration is recommended by the CCITT for the preparatory period. This duration is determined by the broadcasting organizations, but a typical duration is 15 minutes. During this period, the tests to be made are also left to the iscretion of t
ITU-T N.54-1988 history
1988ITU-T N.54-1988 DEFINITION AND DURATION OF THE LINE-UP PERIOD AND THE PREPARATORY PERIOD