Record carrier having first variations of a first physical parameter corresponding to information recorded thereon and second variations of a second physical parameter relating to recovery of the information

Abstract

A record carrier, a playback apparatus and a system including the record carrier and the 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 a predetermined property of the second variations (e.g., that the second variations exhibit a modulation pattern representing a code) 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 predetermined property of the second variations is detected, causing it to recover the information.

Dependencies are inferred from the claim text.