Optical disc authentication using alternate data modulation encoding schemes

An optical disc readback system configured to read data from an optical disc, comprising:

• a primary decoder configured to decode primary data previously encoded in accordance with a first modulation encoding scheme in which the primary data are modulated as a series of data symbols on the disc having nominal symbol lengths over a first range of symbol lengths, the primary data having an informational content used by a user of the optical disc readback system;
• a secondary decoder configured to decode secondary data previously encoded in accordance with a second modulation encoding scheme different from the first modulation encoding scheme in which the secondary data are modulated as a series of data symbols on the disc having nominal symbol lengths over a second range of symbol lengths so that, for a given set of input data, the second modulation encoding scheme provides a different set of data symbols as compared to the first modulation encoding scheme, wherein each symbol length of the second range of symbol lengths appears in the first range of symbol lengths, and wherein the secondary data include a leading synchronization pattern which, when detected, allows remaining portions of the secondary data to be decoded using the second modulation encoding scheme, the secondary data having an informational content used to authenticate the optical disc as an authorized copy;
• and
• a transducing head which transduces a readback modulation signal from the disc, wherein the readback modulation signal is concurrently provided to the primary and secondary decoders, wherein the primary decoder operates upon the readback modulation signal to output the primary data, and wherein the secondary decoder searches the readback modulation signal for the leading synchronization pattern and, upon detection, outputs the secondary data.