Mon, 7 Apr 1997 01:02:57 +0200 Hello DAT-Heads ... > >1) Are all commercially produced CDs bought from our local music store > >(HMV, SAM the record man, TOWER Records, Sunrise or whatever) able to be > >digitally transferred to DAT with NO PROBLEMS? > > Almost all CDs have the SCMS code 11, which means 1 more copy, so you > can copy them digitally to a consumer dat deck (but you'll get a tape > with 10, which cannot be copied digitally to a consumer deck). (The > scms code for CDs was defined that way, which explains the unintuitive > numbering scheme. CDs don't really have SCMS, but they have a > "copyright asserted" bit (which is the first bit of their "scms"), and > a "generation" bit (which is always 1, since CDs aren't masters) > (which was used as the second bit of their "scms").) An interesting way to see the CD copy bit. In fact, there is only a single copyright bit in each 1/75 sec frame of a CD (the 3rd bit in the "Q data block"). 0 means "copy deny" and 1 means "copy permit". Nearly all CDs have this bit set to "0". Together with the "CD" category code in the CDs S/P-DIF data stream, this is interpreted by an SCMS-compliant DAT recorder as "copyright asserted, (one) copy permitted" and leads to an SMCS "10" tape. If the bit is "1", it is interpreted as "no copy protection" and should give a SCMS "00" tape. To implement copyright protection on CDs done with (consumer) CD recorders, a SCMS-compliant DAT recorder has to check whether the CD copyright bit is alternating with 4 to 10 Hz. In this case, the DAT recorder is not permitted to record the CD, since it was made with a (consumer) DAT recorder an is not an "original" like a CD bought in a shop ... I havenīt yet checked whether this mechanism is really implemented in some comsumer DAT recorders ... (if I only had more time ... ;-) Another note ...: The DAT SCMS codes 00 Unlimited digital copies 10 No digital copies can be made 11 One digital copy can be made (those you see when pressing "mode" and "6" on a Sony DAT) refer to the "ID-6" field in the PCM header on the DAT tape. The way "SCMS" is encoded in an S/P-DIF stream is a bit more complex: There is a "copyright" bit: 0=copyright asserted 1=no copyright asserted and a "generation" bit: 0=1st generation/unkown 1=original/prerecorded The meaning of the "generation" bit is reversed for CD and digital tuners ... For more information on this topic, check: "An Understanding and Implementation of the SCMS Serial Copy Management System for Digital Audio Transmission", Clifton W. Sanchez 94th AES Convetion, Berlin, March 1993, Preprint #3518 (reprinted in "Crystal Semiconductor Audio Databook 1994") "The art of digital audio", John Watkinson. 2. ed. Oxford : Focal Press, 1994. - XIV, 685 p. ISBN 0-240-51320-7 "RDAT" [Rotary head digital audio tape (RDAT)], John Watkinson. Oxford : Focal Press, 1991. - xi, 244 p. ISBN 0-240-51306-1 Happy listening ... Heiko ---------------------------------------------------------------------- Dipl.-Ing. Heiko Purnhagen Isernhagener Str. 51 D-30163 Hannover mailto:purnhage@tnt.uni-hannover.de home: +49-511-624449 http://www.fet.uni-hannover.de/purnhage/ work: +49-511-762-5033 http://www.tnt.uni-hannover.de/~purnhage fax: +49-511-762-5052 "Theatre is life, film is art, television is furniture."