Copy protection of digital audio compact discs
View Patent ↗The ability of a data reader, such as a CD-ROM drive, to access, extract, or otherwise read the data on a digital audio compact disc provides a problem for the music industry. A user can use his CD-ROM drive to read the data from an audio disc into a computer file, and then that data can be copied. To provide copy protection, errors are deliberately introduced into the data on a CD, but these errors are of a type which are generally transparent to an audio player but which will interfere with the reading of the audio data by a data reader. According to the standards, the data on a CD is encoded into frames by EFM (eight to fourteen modulation). Each frame has sync data, sub-code bits providing control and display symbols, data bits and parity bits, and includes 24 bytes of data, which is audio data for a CD-DA. The standard requires that 98 such frames are grouped into a sector. To provide copy protection, each is provided with a non-standard number of frames, for example, has 99 rather than 98 frames. Then the S 0 and S 1 sub-code synchronisation patterns are placed one frame later than they otherwise would be, but the data within each frame remains the same. An audio player would divide the 24 bytes of data from each frame of the sector into 4 byte samples and continue playing the disc, albeit with an inaccurate time display. However, a data reader used to read audio data from the CD-DA to enable a copy to be made, would produce a copy having a degraded quality of sound.
1. A method of copy protecting a digital audio compact disc which has audio data and control data encoded thereon, the control data being arranged to facilitate playing and/or reading of the audio data on the line compact discs and the copy protection method comprising the steps selecting control data which is to be encoded onto the digital audio compact disc and rendering the selected control data incorrect and/or inaccurate in a manner such that the incorrect and/or inaccurate control data encoded on the compact disc interferes with the reading of audio data from the compact disc whilst not interfering with the playing of audio data from the compact disc, wherein the data is encoded on the compact disc in data sectors, and wherein the control data encoded on the compact disc which has been rendered incorrect is the structure of a data sector on the compact disc.
2. A method of copy protecting a digital audio compact disc according to claim 1 , wherein the incorrect and/or inaccurate control data is arranged such that it cannot be corrected by the error correction arrangements of available data readers.
3. A copy protection method according to claim 1 , wherein the data on the compact disc is encoded into frames which are grouped into a sector, and wherein the number of frames grouped in each sector is changed from the standard.
4. A copy protection method according to claim 1 , wherein the control data encoded on the compact disc has been altered prior to mastering of the disc.
5. A copy protection method according to claim 4 , comprising the step of changing the parameters of an encoder used in the mastering process to change the frame structure of the mastered disc.
6. A copy protected compact disc having audio data and control data encoded thereon, the control data being arranged to facilitate playing and/or reading of the audio data on the compact disc, wherein selected control data encoded on the compact disc has been rendered incorrect and/or inaccurate prior to its encoding onto the compact disc, the incorrect and/or inaccurate compact data being arranged to interfere with the reading of audio data from the compact disc whilst not interfering with the playing of audio data from the compact disc, wherein the data is encoded on the compact disc in data sectors, and wherein the control data encoded on the compact disc which has been rendered incorrect is the structure of a data sector on the compact disc.
7. A copy protected digital audio compact disc according to claim 6 , wherein the incorrect and/or inaccurate control data is arranged such that it cannot be corrected by the error correction arrangements of available data readers.
8. A copy protected digital audio compact disc according to claim 6 , wherein the data is encoded on the compact disc in frames, and the frames are grouped in sectors, wherein there is a non-standard number of frames in each sector.
9. A copy protected digital audio compact disc according to claim 6 , wherein the compact disc has non-standard sectors only.
10. A copy protected digital audio compact disc according to claim 6 , wherein the compact disc has non-standard sectors, and additionally has other control data which is incorrect and/or inaccurate.
11. A method of copy protecting a digital audio compact disc which has audio data and control data encoded thereon, the control data being arranged to facilitate playing and/or reading of the audio data on the compact disc and the copy protection method comprising the steps of selecting control data which is to be encoded onto the digital audio compact disc and rendering the selected control data incorrect and/or inaccurate in a manner such that the incorrect and/or inaccurate control data encoded on the compact disc interferes with the reading of audio data from the compact disc whilst not interfering wit the playing of audio data from the compact disc, wherein the data on the compact disc is encoded into frames which are grouped into a sector, and wherein the number of frames grouped in each sector is changed from the standard.
12. A copy protected compact disc having audio data and control data encoded thereon, the control data being arranged to facilitate playing and/or reading of the audio data on the compact disc, wherein selected control data encoded on the compact disc has been rendered incorrect and/or inaccurate prior to its encoding onto the compact disc, the incorrect and/or inaccurate control data being arranged to interfere with the reading of audio data from the compact disc whilst not interfering with the playing of audio data from the compact disc, wherein the data is encoded on the compact disc in frames, and the frames are grouped in sectors, wherein there is a non-standard number of frames in each sector.