Method and apparatus for the copy protection of optical discs
View Patent ↗The present invention relates to a method of copy protecting optical discs, such as CD-ROMs. Instead of encoding data onto the CD-ROMs in a manner which ensures balanced dc content, for copy protection the digital data is encoded and recorded onto the optical disc such that it is arranged to give some of the recorded digital data unbalanced dc content. Thus, for example, the DSV value of the encoded data may be changed rapidly in less than (100) frames to (FIG. 9 ). For an area of digital data on the optical disc in which the DSV has been caused to rise steeply (FIG. 10 a ), heavy distortions in audio arise (FIG. 10 c ) during an attempt to copy an audio track including the single segment of unbalanced dc content.
1. A method of copy protecting an optical disc on which encoded digital data is recorded, the method comprising the steps of:
encoding and recording the digital data onto the optical disc in a manner which is arranged to give some of the recorded digital data unbalanced dc content;
wherein the recorded digital data on the optical disc is given the unbalanced dc content by encoding selected areas of the digital data to have poor DSV characteristics; and
wherein each said selected area given the unbalanced dc content has a DSV having an absolute value in a range of 3000 to 4000, or a rate of change of DSV in a range of 60 to 225 per frame.
2. The method of copy protecting an optical disc according to claim 1 , wherein the DSV of the recorded digital data has substantial low frequency components.
3. The method of copy protecting an optical disc according to claim 1 ,
each selected area contains about 100 frames of data, each frame including 24 bytes of data.
4. The method of copy protecting an optical disc according to claim 1 , further comprising predetermining the selected areas of the recorded digital data which are to be given the unbalanced dc content.
5. The method of copy protecting an optical disc according to claim 1 , further comprising randomly selected the selected areas of the recorded digital data which are to be given the unbalanced dc content.
6. The method of copy protecting an optical disc according to claim 1 , further comprising recording the digital data onto the optical disc in frames arranged into sectors each having a plurality of frames, and providing that each selected area having the unbalanced de content contains less than 2 sectors.
7. The method of copy protecting an optical disc according to claim 6 , wherein each sector contains 98 frames.
8. The method of copy protecting an optical disc according to claim 1 , wherein some of the recorded digital data is given the unbalanced dc content by providing the recorded digital data with poor DSV characteristics.
9. The method of copy protecting an optical disc according to claim 1 , wherein the recorded digital data on the optical disc is given the unbalanced dc content by encoding the selected areas of the digital data to have poor DSV characteristics.
10. The method of copy protecting an optical disc according to claim 9 , wherein the DSV of the recorded digital data has a rapid rate of change.
11. The method of copy protecting an optical disc according to claim 9 , wherein the DSV of the recorded digital data has high absolute values.
12. The method of copy protecting an optical disc according to claim 1 , wherein the digital data is encoded using EFM encoding where merge bits chosen during the encoding are inserted between successive channel bits, and wherein the merge bits are chosen to give poor DSV characteristics to the selected digital data.
13. The method of copy protecting an optical disc according to claim 1 , wherein the digital data is encoded using EFMPlus encoding where each 8 bit data word is encoded into one of a choice of four 16 bit channel words, and wherein the 16 bit channel words are chosen to give poor DSV characteristics to the selected digital data.
14. A copy protected optical disc having data comprising encoded digital data recorded thereon, wherein some of the recorded digital data have unbalanced dc content, wherein the unbalanced dc content is given to selected areas of the digital data to have poor DSV characteristics; and wherein each said selected area given the unbalanced dc content has a DSV having an absolute value in a range of 3000 to 4000, or a rate of change of DSV in a range of 60 to 225 per frame.
15. The copy protected optical disc according to claim 14 , wherein each selected area contains about 100 frames of data, each frame including 24 bytes of data.
16. The copy protected optical disc according to claim 14 , wherein the selected areas of the recorded digital data which have the unbalanced dc content have been predetermined.
17. The copy protected optical disc according to claim 14 , wherein the selected areas of the recorded digital data which have the unbalanced dc content have been randomly selected.
18. The copy protected optical disc according to claim 14 , wherein the digital data recorded onto the optical disc has been arranged into sectors with each sector containing a plurality of frames, and wherein each said selected area having unbalanced dc content contains less than 2 sectors.
19. The copy protected optical disc according to claim 18 , wherein each sector contains 98 frames.
20. The copy protected optical disc according to claim 14 , wherein a DSV of the recorded digital data has a rapid rate of change.
21. The copy protected optical disc according to claim 14 , wherein a DSV of the recorded digital data has high absolute values.
22. The copy protected optical disc according to claim 14 , wherein a DSV of the recorded digital data has substantial low frequency components.
23. The copy protected optical disc according to claim 14 , wherein the optical disc is a CD and has been subjected to EFM encoding.
24. The copy protected optical disc according to claim 14 , wherein the optical disc is a DVD and has been subjected to EFMPlus encoding.
25. The copy protected optical disc according to claim 14 , wherein the digital data recorded on the optical disc is one or more of audio data, video data, graphics data, visual data, animation data, numerical data, program data, control and access data, and/or any other data.