Geschlossenes Informationssystem mit Kopierschutz

摘要

Playback apparatus for a record carrier on which information is recorded 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 recovery circuit recovers the information from a detection signal produced by the transducer. The record carrier also exhibits a variation of a second physical parameter, which differs from the first physical parameter but is of a type which is detectable by the same transducer. A detection circuit detects the presence of the second variation on the basis of a further detection signal produced by the transducer. A circuit controlled by the detection circuit enables the information recovery circuit in the event that the presence of the second variations is detected. Since copying recorders of the usual type only copy variations of the first physical parameter, representing the recorded information, and do not copy variations of the second physical parameter, such copiers cannot copy the information recorded on the described record carrier.