CDR-RW Digital Audio Media

Digital Audio for Consumers is a term used in connection with CD recorders that form a part of a home audio stereo system, connecting to amplifiers, tuners, cassette decks, CD players and the like through standard RCA jacks. Whilst their appearance is similar to any other hi-fi component, their function has more in common with that of a PC CD-R drive – the recording of audio onto CD recordable or rewritable media.

For this they use specifically designed audio-only CD media. Fundamentally these are no different from conventional recordable/rewritable CD media. However, between them the audio-only CD recorder and media implement a copy protection scheme known as SCMS, designed to limit unauthorised copies of intellectual property – music owned by recording companies or musicians.

Basically the aim of SCMS is to allow consumers to make a copy of an original, but not a copy of a copy. It achieves this by using a single bit to encode whether or not the material is protected, and whether or not the disc is an original. For originals which are subject to copyright protection, the copy bit is continuously on, for originals that contain unprotected material the copy bit is continuously off and for an original which has itself been copied from a copyright-protected original, the copy bit is toggled every 5 frames between on and off.

Originally the cost of audio-only media was significantly more than conventional media. Whilst the differential is no longer as great as it was, it will always exist as a consequence of licensing agreements under which the disc manufacturer pays a royalty the recording industry for each disc sold on the assumption that everything recorded to this type of media is pirated copyrighted material.

Professional versions of audio-only CD recorders, capable of using both audio-only and conventional media – and thereby of by-passing SCMS – are also available. These units offer a wider set of features and input/output connectors than their consumer counterparts and are a lot more expensive.

It is also important to note that the expression of CD-R/CD-RW disc capacity in terms of minutes rather than megabytes does not imply that the media are audio-only. Some manufacturers simply choose to express capacity as 74/80 minutes as an alternative to 650/700MB.