Wobble frequency
Optical discs with the exception of the DVD-RAM have their data encoded on a single spiral, or a groove, which covers the surface of the disc. In the case of recordable media, this spiral contains a slight sinusoidal deviation from a perfect spiral. The period of this sine curve corresponds to the wobble frequency. First of all, it is used as a synchronization source to achieve constant linear velocity while writing a disc. The frequencies quoted all assume that the disc is being written at the 'x1' speed. The frequencies are appropriately higher for faster writing speeds.
CD-R and CD-RW discs, use a frequency modulated wobble of 140.6 kHz to encode some information, such as Absolute Time in Pregroove (ATIP) into the groove.[1]
DVD-R and DVD-RW have a constant wobble frequency of 140.6 kHz relying on data 'pits' beside the groove to convey information (Land pre-pit).[2]
DVD+R and DVD+RW have a constant wobble frequency of 817.4 kHz, but encodes its addressing information by periodically inverting the phase of the wobble signal (bi-phase modulation) to encode an exact address of the location on the spiral track (Address in Pregroove).[3] The practical upshot of this arrangement is that the recording drive can navigate to an exact location on the DVD+R(W) disc whereas it cannot do so with the DVD-R(W).
BD-R and BD-RE discs utilise Address in Pregrove.
HD DVD-R and HD DVD-RW uses the land pre-pit system of the common or garden DVD-R(W).