Disc wobble, also called wobble groove, is a technology developed by Royal Philips Electronics NV. This technology together with digital watermarking could ensure that only authentic discs would be played on the next generation players that will respect these proposed forms of copy protection (see also Digital rights management).
This technique encodes hidden protection data onto the lead-in groove along the inner edge of a disc in a difficult-to-duplicate manner. Normally, discs' grooves form a smooth spiral, with the data encoded as reflective and absorptive spots along the path. Disc wobble reshapes the groove by wiggling the path back and forth ever so slightly in a pattern that conveys the ons and offs of digital data.
The wobble is too fast for the laser pickup head to physically follow, but the error signals that keep the head’s lens on track move in step with the wobble. This allows the protection data to be read by an appropriately equipped player, entirely separate from the normal data recorded in the track. If a decryption or authentication key is encoded in the wobble, then only discs which reproduce the wobble will be playable. Due to the sophisticated technologies needed to manufacture such discs, counterfeiting authentic wobbled discs would be next to impossible.
To assure copy protection of original discs, the initial problem is to detect whether the recording device is playing read-only discs or (re)writable discs. For this reason Phillips has presented the pregroove-wobble. This technology only exists in (re)writable discs and together with pregroove-wobble detectors present in recording devices will prevent original discs from being copied. If the recording device does not detect the disc as a (re)writable disc, that is, a read only disc, the device will not be able to copy the data from that disc. Therefore recording devices will only work with (re)writable discs, which are not original discs.
Read-only discs, as said before, will also use wobble technology. In this case, an authentication key will be encoded in the wobble and only devices that use this technology will be able to play these discs. With the above said it is ensured copy-protection by using the wobble disc technology and just adding a pregroove-wobble detector to devices, this turns out to be a very low additional cost for the devices and a strong copy protection system.
- Marc Rosenthal, IEEE Spectrum. "Special Report on Copy Protection, May 2003". Retrieved 2008-12-14.
- Maurice Maers & Joop Talstra. "Inexpensive Media Recognition for Optical discs, CPTWG November 28th 2001.". Retrieved 2008-12-14.