Compact disc

Compact disc (or CD) is an optical disc used to store digital data, originally developed for storing digital audio. It is the standard playback format for commercial audio recordings today.

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.

Related Topics:
Red Book - Copy protection - MP3

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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).

Related Topics:
2002 - CD-ROM - Fidelity

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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.

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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.

Related Topics:
Trademark - Fair use

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Other systems developed are Macrovision CDS-200 and Mediamax CD-3.

Related Topics:
Macrovision CDS-200 - Mediamax CD-3

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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.

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