SCMS is the Serial Copy Management System
. The record companies
forced manufacturers of CD
recorders and any other digital audio devices to include SCMS to prevent the unlimited copying of prerecorded digital audio.
SCMS works by including data in the digital audio stream subcodes. The subcodes contain the following information:
- Track start positions
- Audio source (CD, DAT, minidisc, analog source, etc.)
- Audio is original or a copy
- Audio is copy-protected or not
SCMS allows a copy of a CD or other prerecorded format, but does not allow a copy of this copy. The idea is that to prevent piracy, one can make an archival copy of a CD they own, but that copy cannot be copied again.
SCMS applies only to the consumer-grade digital audio standard, S/PDIF. SCMS can be defeated by using the professional digital audio standard, AES/EBU, which does not support copy management. It can also be defeated by recording to a computer first, or by using an "SCMS copybit killer," a fairly simple electronic circuit. The European electronics magazine Elektor has included such circuits in the past.