| 摘要 |
<p>The ability of a data reader to access, extract, or otherwise read the data on a CD DA 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. Therefore, errors are deliberately introduced into the encoded data, these errors being of a type which are generally transparent to an audio player but which will interfere with the extraction or reading of the audio data by a data reader. The data on a CD is encoded into frames by EFM (eight to fourteen modulation), and each frame includes 24 bytes of audio data. There are 8 sub code bits contained in every frame which enable 8 different subchannels, P to W, to be formed. The P and Q subchannels incorporate timing and navigation data for the tracks on the disc, and generally are the only subchannels utilised on an audio disc. It is the timing and or navigation data in the P and Q subchannels which is rendered incorrect or inaccurate to provide the copy protection.</p> |
