| 摘要 |
A method of copy protecting optical discs uses the differences in capability between the encoder associated with a laser beam recorder and that in currently available CD writers. Digital sum value (DSV) is a property of the encoded data on CDs and, in order to maintain good DSV characteristics, the encoder often has a choice of the merge bits to insert between the symbols which carry the data. An encoder, which controls a laser beam recorder may be able to choose a pattern of merge bits which result in the overall DSV having optimal properties. During mastering of a CD, data patterns are added to the disc to provide an authenticating signature. These data patterns are chosen to cause DSV problems. However, the encoder of the laser beam recorder is able to write the authenticating signature accurately to the glass master. When a CD writer is used to make a copy of the original disc it is provided with user data from the disc, but as this user data is the product of decoding, the information about the pattern of merge bits will have been discarded. Currently available CD writers have been found to have difficulty writing an authenticating signature of the type described without producing a resulting CD which has severe readability problems. Thus, the copy disc written by the CD writer will result in a CD reader returning corrupted data or information signalling a read error.
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