Optical record carrier inscribed with read-out control data and apparatus for reading such record carrier in conformity with such control data

DETAILED DESCRIPTION It is an object of the invention to provide means enabling the signal-processing circuit to be adapted simply to the strength of the applied signals.
To this end, in accordance with a first aspect of the invention, the record carrier is characterized in that control data is recorded as a preformed information structure in a predetermined area in the track, which control data is indicative of the magnitude of said optically detectable change in reflection.
In accordance with a second aspect of the invention the read apparatus is characterized in that it comprises control means for causing the predetermined area of the track to be scanned prior to the actual read-out of the information recorded in the information-recording area, means for deriving from the detected electric signal a control-information signal which is representative of the recorded control data, and adjustment means which are responsive to the derived control information signal to adjust the signal-processing circuit.
If the record carrier is intended for recording EFM signals, for example a standard CD signal, it is advantageous to include the control data in the Q subcode channel of an EFM signal to be recorded by means of the preformed information structure.
In that case the control data can be recovered simply by means of the subcode demodulator, which is needed anyway for controlling the process of reading the EFM signal recorded in the information-recording area.
In the Q-channel signal predetermined bit groups are employed to indicate the type of information represented by the subsequent bit groups.
Thus, the position of the required control data can be indicated very simply by including a unique code in said predetermined bit groups.
The control data thus recorded can be readily recovered by read apparatus which is characterized in that the signal-processing circuit includes an EFM-subcode demodulator for deriving the Q-channel signal from the electric signal, and in that the adjustment means comprise detection means for detecting the unique code in the Q-channel signal, which code indicates the position of the control data, and for extracting the control data from the Q-channel signal upon detection of the unique code