|Anti-piracy system could damage loudspeakers
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. 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 CD copiers.
However, Eyal Shavit of Midbar Tech claims, "We can stop all kinds of copying, even on domestic CD recorders." 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.
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 output. 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.