System and apparatus for recovering information from a record carrier which exhibits variations of two different physical parameters thereof

摘要

An information system including a record carrier and a playback apparatus. Information has been recorded on the record carrier in the form of variations of a first physical parameter. The playback apparatus scans the record carrier by means of a transducer which is responsive to the variations of the first physical parameter. An information recovering circuit recovers the information from a detection signal received from the transducer. The record carrier exhibits second variations of a second physical parameter, which differs from the first physical parameter but which second variations are of a type that are detectable by the transducer. A detection circuit detects the presence of the second variations on the basis of a detection signal received from the transducer. A circuit responsive to the detection circuit enables the information recovering circuit when the presence of the second variations is detected causing it to recover the information.