[dvd-discuss] How the SCMS spec was manipulated to prevent ALL CD>DAT copying

[John Schulien <jms(at)uic.edu>]

> Honestly.. I don't get SCMS because if you have an MD deck with
> digital out, it is decompressed anyhow, so I wouldn't want it.  I'd
> rather go back to the CD and get the origional form.

> The CD has SCMS as well.

Yes, and SCMS on CD players is another dirty trick by the
recording industry.  They carefully designed the SCMS specs
so that CDs become "exempt" from the requirement to allow
first generation copies.  Let me explain.

In non-professional SPD/IF, there are two bits that control 
SCMS, called the "C" bit and the "L" bit.  These bits are
sent along with every digital audio frame, meaning that 
they are sent exactly 75 times per second.

The "C" bit is supposed to indicate whether copyright has 
been asserted over the recording.  

C = 0:  Copyright asserted
C = 1:  Copyright not asserted or public domain

The L bit is supposed to indicate the recording generation:

L = 1:  Original media
L = 0:  First generation copy or higher

Quoting from the standard:

> For most products, if the L Bit is set as `0', the 
> source is a recording that is first-generation or higher. 
> If the L Bit is set as `1', the source is `original.' 
> There are four specific categories of products which
> indicate generation status differently, as follows:
>
> --Compact disc players compatible with the specifications 
> in IEC 908 (Category Code 10000000) are incapable of 
> controlling the L Bit. These products signal generation 
> status solely by means of the C Bit (Bit 2).

Now think about that for a moment ... back in 1992, there
were exactly two different types of digital audio devices
on the market:  CDs and DATs.  The main purpose of the 
AHRA, as persued by the recording industry, with a remarkable
degree of tunnel vision, was to PREVENT ANY copying of 
CDs onto DATs, at all costs.  This was to prevent the
"Death Of The Recording Industry."

So they told a Big Lie. The recording industry represented 
SCMS to Congress as a system that would allow consumers to 
make first generation copies of CDs, but not copies of copies.  
However, when they delivered the final technical specification, 
the specification noted that CD players did not HAVE an L-bit 
(because there was no such thing as a CD recorder, only a player.)  

Quoting from the standard:

> Compact disc players compatible with the specifications in 
> IEC 908 (Category Code 10000000) are incapable of controlling 
> the L Bit. These products signal generation status solely by 
> means of the C Bit (Bit 2).

So, the only piece of information that the CD player has 
available to it is the 'C' bit, which is under the control
of the publisher, (and you can damn well bet that's ALWAYS
set -- it's the "copyright asserted" bit.)  


The part of the SCMS spec that defines the required behavior 
of a CD player says:

> Compact disc players ... [require that] Where the signal 
> is original and copyright protection has been asserted, the 
> C Bit = `0'. Where no copyright protection has been asserted, 
> the C Bit = `1'. Where the signal is first-generation and 
> copyright protection has been asserted, the C Bit will 
> fluctuate between `0' and `1' at a rate of between 4-10 Hz.

However, with the lack of an L bit in the CD standard, there
is no way to know if a given CD is an "original" or a "first
generation."  The result was that all of the CD player 
manufacturers, in order to protect themselves legally, were
forced to treat ALL CDs as if they were "first generation" 
CDs, even though no "first generation" CDs even EXISTED.

The net effect was that CD players, whenever they play
back ANY CD, toggle the SCMS permissions at a rapid rate,
which breaks every known SCMS implementation.

The recording industry got what they wanted -- on one hand
making the public claim that SCMS permits consumer copying
of CDs, while in reality, the spec was carefully designed
to prevent the making of ANY digital recordings from CDs onto 
DATs or MDs, as anyone who actually tried to use the 
equipment for this purpose instantly discovered.