This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
SCMS is the Serial Copy Management System. The goal is to allow consumers
to make a copy of an original, but not a copy of a copy. Analog recording
media, such as audio cassettes and VHS video tape, degrades rather quickly
with each successive copy. Digital media doesn't suffer from the same
degree of generation loss, so the recording industry added a feature that
has the same net effect.
SCMS will affect you if you use consumer-grade audio equipment.
Professional-grade equipment and recorders that connect to your computer
aren't restricted. See section (5-12) for more about the differences
between these types of devices.
The system works by encoding whether or not the material is protected, and
whether or not the disc is an original. The encoding is done with a single
bit that is either on, off, or alternating on/off every five frames. The
value is handled as follows:
- Unprotected material: copy allowed. The data written is also marked
- Protected material, original disc: copy allowed. The data written
will be identified as a duplicate.
- Protected material, duplicate: copy not allowed.
There are hardware "SCMS strippers", primarily used in conjunction
with a DAT deck, that strip the SCMS bits out of an S/PDIF connection.
Some of these reportedly introduce unacceptable artifacts into the audio.
It's possible to "wash" the audio by converting it to and from analog
format, but again the quality will suffer.
If you're using a consumer audio CD recorder, SCMS will prevent you from
making copies of copies of protected material. It will not prevent you
from making a copy of an original disc you have purchased, and it won't
stop you from copying unprotected discs.