Record carrier, playback apparatus and information system comprising a record carrier and a playback apparatus

An information system according to the invention comprises a record carrier (1) and a playback apparatus (20). The record carrier has information marks along a track (11) thereof and exhibits first variations caused by existence and nonexistence of the information marks along the track. The first variations represent an information signal recorded on said record carrier. The record carrier further exhibits second variations (W) caused by variations associated with the information marks. The phase of the second variations is coupled to the phase of the first variations. A playback apparatus (20) according to the invention includes a transducer unit (20A, 20B, 20C) for scanning said record carrier (1). The transducer unit is adapted to detect said first variations and said second variations. The apparatus further includes a first recovery unit (22) coupled to the transducer unit (20A, 20B, 20C) for recovering a clock signal (CL) from the first variations and a second recovery unit (23) coupled to the transducer unit (20A, 20B,20C) for recovering an information signal (Sout) from the first variations. The apparatus further includes a detection unit (24) for detecting whether said second variations exhibit a predetermined variation pattern on the basis of at least one signal (SA), which is at least indicative of said second variations, originating from said transducer unit. The detection unit (24) using the said clock signal (CL) generated by the first recovery unit (22) for detecting. Further an enabling unit (25) is included for enabling said second recovery unit (23) to recover the information signal (Sout) when said detection unit detects (24) said predetermined variation pattern.