Editing Serial Copy Management System (section)

==Technical details==
SCMS copy protection looks for bits written in the subcode data in a digital link.<ref>{{cite web |title=IS/IEC 60958-3 |url=https://archive.org/details/gov.in.is.iec.60958.3.2003/page/n3 |website=Archive.org |publisher=Bureau of Indian Standards |accessdate=26 March 2019}}</ref> There are two bits which are relevant:
* Bit 2 in the Channel Status subchannel is the "Cp" bit indicating whether the source signal is copyrighted or not: 0 means copyrighted, 1 means not copyrighted
* Bit 15 in the Channel Status subchannel is the "L" bit indicating whether the source signal is an original medium (such as an audio CD<ref>{{cite web |title=What is SCMS |url=https://www.sweetwater.com/insync/scms/ |website=Sweetwater |access-date=8 December 2021 |date=1997}}</ref> or a prerecorded DCC tape) or "not determined". For audio CDs and laser optical media, 0 means original and 1 means "not determined"; for other digital sources the values of this bit are reversed.

Copying is only allowed if the source signal for the recording is not copyrighted, or is copyrighted and is an original. If the source signal is a copyrighted recording, the recorder must set the "L" bit to "not determined" when it plays the copy, so that the copy cannot be copied digitally again.

{| class="wikitable"
|-
! Source Cp !! Source L !! Copying allowed !! Copy L || Copyable Copy
|-
| "Copyrighted" || "Original" || Yes || "Not Determined" || No
|-
| "Copyrighted" || "Undetermined" || No || N/A || N/A
|-
| "Not Copyrighted" || (any) || Yes || (same as source) || Yes
|}