MAM Technical Papers

	Digital Audio CD-R for Consumers

"Digital Audio for Consumers" is the term used to describe CD-R media and recorders that incorporate a copy protection scheme known as SCMS (see below). The idea is to limit unauthorized copies of "intellectual property", i.e., music owned by recording companies or musicians. CD-R discs that are recorded with these drives can not be copied with another drive that complies with SCMS. --You can't make a copy from a copy. CD recorders that comply with these requirements use built in software that looks for information on the CD-R and either rejects or accepts it. If it finds the copy protection coding, the recorder identifies it as "Digital Audio for Consumers" and recording begins If the CD-R is not coded, the disc is rejected. This system was adopted by manufacturers at the insistence of the Recording Industry Association of America (RIAA). Royalties are paid by the manufacturers to the recording industry for each CD-R sold.

Serial Copy Management System (SCMS)

SCMS prevents the illegal production of multiple generations of digital copies from a copyright-protected original. Making a single copy for personal use by owners of the Digital Audio Home Recorders is permitted. The SCMS status of an original is indicated by a copy bit which is present on an original CD and is placed on a recording at a frequency of 75 frames per second. For originals which are subject to copyright protection, the copy bit is continuously ‘on’ (high state). For so-called ‘copy free’ discs, to which no copyright restrictions apply, the copy bit is continuously ‘off’ (low state). 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’ (high and low states). SCMS distinguishes between three possible copying situations, and provides appropriate copying strategies in each case:

Copyright-free originals: copy bit continuously ‘off’ (low state). No restrictions on copying. A copy is also recorded with copy bit continuously ‘off’. Normal copyright-protected commercial CDs and all analogue originals: copy bit continuously ‘on’ (high state). A single copy is allowed to be made for personal use only. A copy is recorded with copy bit that toggles every 5 frames between ‘on’ and ‘off’ (high and low states). The copy is an SCMS original. SCMS originals, i.e. copies of copyright-protected originals: copy bit toggles every 5 frames between ‘on’ and ‘off’ (high and low states). No further digital copying is allowed.

RID (Recorder Unique Identifier)

The RID is a 97-bit code which is recorded every 100 frames on all discs made with the Digital Audio Home Recorders. It comprises a brand name identifier, a type number and the drive number which, together, uniquely identify the recorder on which any specific disc was recorded. The RID is a further measure to prevent unauthorized copying by enabling the source of any recording to be identified.

Use of Audio CD-R and CD-RW discs

To comply with copyright legislation in various countries, Digital Audio Home Recorders will only make recordings on CD-R and CD-RW discs bearing the appropriate ‘audio’ logo. These discs are subject to levies which are payable to the relevant copyright protection associations.

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