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

An information system, comprising:

• a record carrier (1) having information marks along a track (11) thereof and exhibiting:
• first variations caused by existence and nonexistence of the information marks along the track, said first variations representing an information signal recorded on said record carrier, and second variations (W) caused by variations associated with the information marks;
• the phase of the second variations being coupled to the phase of the first variations,
• a playback apparatus (20) including:
• a transducer unit (20A, 20B, 20C) for scanning said record carrier (1), said 10 transducer unit being adapted to detect said first variations and said second variations,
• a first recovery unit (22) coupled to the transducer unit (20A, 20B, 20C) for recovering a clock signal (CL) from the first variations,
• a second recovery unit (23) coupled to the transducer unit (20A, 20B, 20C) for recovering an information signal (Sout) from the first variations,
• a detection unit (24) fur 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) for detecting, and
• an enabling unit (25) for enabling said second recovery unit (23) to recover the information signal (Sout) when said detection unit (24) detects said predetermined variation pattern.