|What is SCMS?||SCMS stands for Serial Copying Management System which was forced on the hardware developers by the software manufacturers (i.e. record companies) to prevent unlimited digital copying of CD's and other prerecorded media.|
|How does it work?||A
digital audio signal in the S/PDIF format (Sony/Philips
Digital Interchange Format) which is used by all home
equipment (professional equipment uses the similar EBU
format) contains audio data and subcode data. The subcode
contains information about:
Basically, you are allowed to copy a CD or a prerecorded tape (i.e. an original) to another tape, but you're not allowed to copy a tape that already is a copy of such a copy-protected source (by default, all CD's and prerecorded media are copy-protected, even the ones that were made before SCMS was invented).
However, you _can_ copy a tape indefinitely if it's your own recording, including analog copies of copy-protected media (the issue was about digital copies of prerecorded work, right?) or if it was recorded from a digital source that has the "copying allowed" bit enabled in subcode. Of course it is also possible to make as many copies of an original as you want (even simultaneously if you have some kind of digital signal splitter) but not from a copy.
Interesting note: I have a CD (CD-maxisingle of "Children" by Robert Miles, pressed by EOD in Tilburg, the Netherlands) that has the copy-allowed bit set to ON (probably because of a mistake with the mastering) but CANNOT be recorded with either of my DCC recorders; it appears the "copy allowed" bit (which is encoded slightly differently on a CD from what I hear) is misinterpreted by the DCC as a second-generation CD.
By the way, it is relatively easy to make a digital copy of an audio CD if you have a CD-recorder: all CD-recorders (and many CD-ROM drives) can read audio CD's digitally to harddisk. See the CD-R FAQ for more details on Digital Audio Extraction (DAE).
|Can I buy a DCC deck without SCMS?||No. All manufacturers of digital audio recording equipment agreed they would implement SCMS in every new machine. However, there are some DAT recorders (early generations before SCMS was invented and professional DAT recorders) that don't have SCMS.|
|Is there a way to defeat SCMS?||The
SCMS system is very well-documented. Technically,
defeating SCMS is as easy as flipping some bits in each
frame of the serial S/PDIF signal. The Dutch
international electronics magazine Elektuur (a.k.a.
Elektor) published several circuit descriptions for
SCMS-defeating devices (unfortunately there are no online
addresses to order kits of these):
There are other more elaborate ways around SCMS. For example, if you record audio to harddisk using the DCC175 + PC-link you can copy it back to another tape no problem. Also there are ways to copy from a digital source to a computer and back using a digital audio card such as the CardD (See the CD-R FAQ).
Last updated: November 23, 1997.
Author: Jac Goudsmit (jacg a xs4all.nl)
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