[Reader-list] CD-Audio Protection System

[Jaswinder Singh Kohli]

 The World's No.1 Science & Technology News Service



Anti-piracy CD system raises distortion fear

16:03   16  July  01
Barry Fox

Anti-piracy compact discs that cannot be copied by a computer have gone
on sale in California. The first CD title has already sold 100,000
copies, but it is causing concern among audio experts because they fear
that the music may be audibly distorted.


 Photo: FPG
The SafeAudio system was developed by Macrovision, a California-based
company best known for its anti-piracy video systems. The technology
stops people "ripping" music CDs to create high-quality digital copies
on a computer hard disc or for downloading to a portable player.

The system also prevents people creating digital files from the CD to
swap over the internet or copying music onto a blank CD - although it
would still be possible to make a poor quality copy by converting the
analogue output into digital code.

SafeAudio works by degrading the digital code. The CD will still play on
an ordinary player or through a computer's speakers or headphones. But
it cannot be copied. Macrovision says that the changes made to the music
are not discernible.


Bursts of hiss


Macrovision is reluctant to discuss how SafeAudio works, but has told
New Scientist that it is based on work done by TTR Technologies of
Israel. Patents filed by TTR describe how a "copy-protected audio
compact disc" works.

The patents say the system deliberately gives some of the digital code
on the CD "grossly erroneous values", adding bursts of hiss to the audio
signal. In addition, the error-correction codes on the CD, which would
normally correct such errors, are distorted. So error correction fails,
leaving tiny gaps in the music.

When this happens, a consumer CD player bridges the gaps. It looks at
the music on either side of the gap and interpolates a replacement
section. A computer does the same when playing CDs for listening.

But the computer's CD drive cannot repair the digital data going to the
hard disc. So the hard disc copies nothing, or a nasty noise. TTR says
the repairs made by a music CD player are not audible. Macrovision has
improved the TTR system, says David Simmons, managing director of
Macrovision's British subsidiary.


Golden ears


The company says it has spent six months playing discs to consumers, and
to professional listeners - known as "golden ears" - at two major record
companies. None detected any distortion.

An as yet unidentified album with SafeAudio copy protection has also
gone on sale in California. "There was no increase in return rate or
complaints," says Macrovision's Heinz Griesshaber.

But this doesn't placate hi-fi buffs. "It's a dreadful, dreadful thing
to contaminate the sound deliberately, says Martin Colloms, a British
hi-fi expert whose columns are syndicated around the world. "We all hate
piracy but the idea of mucking up the sound of a recording is
reprehensible. It's like slashing paintings in a gallery to stop someone
stealing them."


16:03   16  July  01


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Regards
Jaswinder Singh Kohli
jskohli at fig.org
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The Uni(multi)verse is a figment of its own imagination.
In truth time is but an illusion of 3D frequency grid programs.