CD-Text

CD-Text is an extension of the Red Book standard for audio CDs. It allows for storage of additional information (e.g. album name, song name, and artist) on a standards-compliant audio CD. The information is stored in the lead-in area of the CD (there is roughly five kilobytes space there), or in the Subchannels R to W on the disc, which are not used on Red-Book compliant CDs. About 31 megabytes of information can be stored there. The text is stored in a format usable by the Interactive Text Transmission System (ITTS). ITTS is also used by Digital Audio Broadcasting or the MiniDisc.
Note that other extensions such as CD+G also use those subchannels to store graphics in.
Copy protection
The Red Book audio specification does not include any copy protection mechanism. Ripping is the process by which the contents of an audio disc is copied out verbatim to a duplicate disc or re-encoded into some other format, such as MP3.
An error-correcting code is included with Red Book audio to deal with small scratches or defects on the disc media. Where error correction fails on larger defects, audio CD players are expected to apply interpolation algorithms to conceal the loss of audio data.
Starting in early 2002, attempts were made by record companies to market "copy-protected" compact discs. Some of these deliberately introduced error patterns into audio tracks severe enough to defeat the error-correcting code (and hence defeat most CD-ROM drives attempting to copy the tracks as data), but not so disruptive as to prevent interpolation from working (hence allowing the same tracks to be played in audio mode without overly affecting fidelity).
Another copy protection method places a data track (usually containing bonus software for computer users) at the end of the disc and gives it an invalid size in the disc's table of contents. This is intended to prevent the data track from being ripped, but can be defeated by ignoring the table of contents and reading the disc sector by sector.
Philips has stated that such discs are not permitted to bear the trademarked Compact Disc Digital Audio logo because they violate the Red Book specification. It also seems likely that Philips' new models of CD recorders will be designed to be able to record from these "protected" discs. However, there has been great public outcry over copy-protected discs because many see it as a threat to fair use.
Other systems developed are Macrovision CDS-200 and Mediamax CD-3.
In any case, even if a disc cannot be directly ripped, it can still be played in audio mode, and the audio thence captured. Any loss of sound quality caused by this method is generally considered negligible. This is commonly referred to as the analog hole.