- CD pirates beware - the music industry has a new weapon
up its sleeve. It is called the Cactus Data Shield, and it is designed
to add noisy garbage to all copied CDs. The trouble is, it could also damage
the hi-fi and loudspeakers of people who play pirated CDs.
- Sony is already evaluating the Cactus system through
its music division, which has been secretly testing it in Eastern Europe.
The system was developed by Midbar Tech, a company based in Tel Aviv. Midbar
Tech refuses to comment on how its system works, but New Scientist has
dug out its American patent (US 6208598) - which reveals all.
- Midbar's anti-piracy technology follows on the heels
of a similar system from Macrovision of California, which recently launched
its SafeAudio system ( New Scientist , 14 July, p 22). This adds uncorrectable
errors to the digital music on a CD, so CD writers on PCs can't copy it.
But Macrovision admits SafeAudio doesn't work with consumer disc-to-disc
- However, Eyal Shavit of Midbar Tech claims, "We
can stop all kinds of copying, even on domestic CD recorders."
- Code and control
- Midbar's patent points out that all music CDs store bursts
of music code and control information. The music data is marked with "flags"
which tell the CD player to decode it and send it to the amplifier and
loudspeakers. The control information is not decoded.
- When burning the original CD, Midbar's idea is to replace
some of the music with false data and label it as control information.
While CD players do not decode this, they are designed to disguise the
gap by bridging it with guessed data. So the original CD plays acceptably,
according to Midbar.
- "There is little or no net difference in audio quality,"
it claims in its patent, though the company will not identify the "golden-eared"
listeners who have tested the system.
- If the CD is copied, however, the copier machine (a PC
or disc-to-disc copier) sees the fake control data as music. So when the
copied disc is played, there are bursts of distortion as the player tries
in vain to decode the garbage. It not only sounds bad, says Midbar, but
it is "potentially damaging" to the player's circuitry if the
added noise has a suitable wave shape.
- Square wave
- It is well known in the audio industry that feeding large
"square wave" pulses to sensitive circuitry - particularly loudspeakers
- can cause damage because high-frequency harmonics in the steeply rising
and trailing edges cause rapidly repeating high-energy peaks in the speaker
- Sony has secretly tested Cactus by treating several thousand
CDs sold recently in the Czech Republic and Slovakia, but the system was
not set to cause damage on this occasion.
- "We have had no problems with loudspeakers,"
Shavit says. While acknowledging that it may seem "unacceptable"
to harm consumers' equipment deliberately, he adds, "It's 'sweat engineering'.
We can add extra lines of defence as people use new attacks."
- Midbar will not identify the affected CD titles sold
in Eastern Europe, so no independent listening tests are possible.
- Related Stories from New Scientist:
- Anti-piracy CD system raises distortion fear http://www.newscientist.com/news/news.jsp?id=ns9999998