Best to start from what is CMS: here I will use Wikipedia:
The Serial Copy Management System (SCMS) is a copy protection scheme that was created in response to the digital audio tape (DAT) invention, in order to prevent DAT recorders from making second-generation or serial copies. SCMS sets a “copy” bit in all copies, which prevents anyone from making further copies of those first copies. It does not, however, limit the number of first-generation copies made from a master.
SCMS was also included in consumer MiniDisc and Digital Compact Cassette (DCC) players and recorders. With the demise of these formats, SCMS is not in widespread use. However, the concept of SCMS was resurrected in the broadcast flag, a measure (and now defunct) mandated by the Federal Communications Commission (FCC) to limit the copying of digital TV signals.
SCMS was created as a compromise between electronics manufacturers, mainly Sony and Philips, who wanted to make DAT machines available in the United States, and the RIAA, which had previously hampered the availability of DAT machines in the US with the threat of lawsuits. The RIAA did not want low-cost digital recorders readily available, since it felt that such technology would result in widespread piracy. These lawsuit threats resulted in a chilling effect, which prevented DAT decks from becoming readily affordable.
In 1987, a member of the RIAA proposed a system where DAT recorders would have copy protection in them. The copy protection would look for the presence of frequencies in a particular high-frequency band; if there was no audio present in this band, the recorder would assume that the music in question was copy protected, and would not allow recording of the music. The record companies would then release all music with this particular frequency band filtered out. It would be illegal to manufacture a DAT machine with the presence of audio in this frequency band; the RIAA was lobbying Congress to make this the law of the land.
The reaction to this proposed scheme was very negative. The Home Recording Rights Coalition orchestrated a letter writing campaign opposing this scheme. Editorials in musician’s and home stereo magazines attacked this scheme. The proposed law never made it out of committee.
Even after this law was shot down, the RIAA still threatened to sue anyone who released an affordable consumer DAT recorder in the US. No one made such a recorder available.
In 1992, Congress passed the Audio Home Recording Act. In this law, blank digital media (including DAT tapes) would be taxed, with the money going to the RIAA, and a new copy protection scheme, SCMS, would be enforced. Blank analog media, such as cassette tapes, were not subject to the tax. SCMS was compulsory in digital media because there is zero deterioration of quality from copy to copy. SCMS was universally disliked by home musicians who used DAT decks to record their own music; the acronym was pronounced as a derogatory term, “scums”.
The digital signal format audio SPDIF, used in domestic and semi-professional audio systems, in addition to audio data has a digital code containing:
– Information about the beginning of each track – ie. The places where begins each soundtrack;
– information about the type of the source of the recording – CD, DAT, DCC, MD, or other analog source;
– marker to indicate if it is an original or a copy;
– tag specifying whether copying is permitted.
Limitation of copying is to set a marker copy consisting of two bits in the digital code of the original and subsequent copies.
• 00 = unlimited copying
• 11 = one copy allowed
• 10 = Not Copy
Basically you can make a copy of a digital CD or other media, but you can not copy the digital media, which is already a copy of the original (a marker 10 – “lack the ability to copy”).
Of course, you can make an unlimited number of copies of your own recordings (00 bit). You can also make analog copies of the original digital plates, because the system SCMS operates only in digital format.
From me :
Of course, today, in the era of universal digital media security is no longer much meaning, and the security can be regarded as primitive, and having no meaning.
CDs are already “obsolete” by media such as MiniDisc, DAT, or DDC probably no one remembers. But fortunately there is still a group of lovers of such equipment, and the quality of the recording is in the foreground.
There are people who love old audio that just works … for years and does not spoil after 2 years or even earlier.
SCMS – is further included in the digital signal stream.
As described above, the protection used in digital signal is two bits of 192 (384bity for both channels) that they inform the digital receiver if and how is to be considered an input for further copying.
And description of the first 16 bits:
|Bit||Unset (0)||Set (1)|
|0||Consumer (S/PDIF)||Professional (AES3)
(changes meaning of control word)
|2||Copy restrict||Copy permit|
|3||2 channels||4 channels|
|6–7||Mode, defines subsequent bytes, always zero|
|8–14||Audio source category (general, CD-DA, DVD, etc.)|
|15||L-bit, original or copy (see text)|
Thus, the signal should be controlled in order to obtain these bits as control signal is to be interpreted by a receiver in terms of, inter alia copying.
Let’s get to the schema of the device:
The device has two input format SPDIF electrical and optical. Then we need to decode the signal is responsible for IC1- CS8412. The next step is correction of the bit stream in the map-based digital signal. This task is performed by circuits IC2 IC3 IC4 IC5 and IC6. I will not elaborate here on the detailed operation of the decoder, if someone wants to know how to please contact me.
At the end of the signal is re-encoded by means of CS8402 – IC7
bitmap EPROM to IC4 can be downloaded HERE : EPROM
Default configuration for the switch should look like this:
|S1 : S1-1 OFF||S2 : S2-1 OFF||S3 : S3-1 OFF||S4 : S4-1 ON|
|S1-2 OFF||S2-2 OFF||S3-2 OFF||S4-2 OFF|
|S1-3 ON||S2-3 ON||S3-3 OFF||S4-3 OFF|
|S1-4 OFF||S2-4 N.C.||S3-4 OFF||S4-4 OFF|
The printed circuit board contains all components including transformer.
(NOTE!) On the PCB is a voltage of 230 V)
And now at the very end of the enclosures. It was used aluminium enclosure universal.
And finally, the view from the thermal imaging camera 🙂
1 . WIKIPEDIA SCMS – https://pl.wikipedia.org/wiki/SCMS
2. WIKIPEDIA S/PDIF – https://en.wikipedia.org/wiki/S/PDIF
3. S/PDIF Specification 1 – http://www-inst.eecs.berkeley.edu/~cs150/fa01/labs/project/SPDIF_explanation.pdf
4. S/PDIF Specification 2 – SPDIF – spec
6. EAGLE files (sch and brd): PCB SCMS BIT KILLER
7. Elektor FR – 06/2002 ELEKTOR FR 06-2002 art nr F026062