Wobble frequency

DVDs and CDs have their data encoded on a single spiral, or a "groove", which covers the surface of the disc. In case the optical medium is recordable, 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 synchronization source to achieve constant linear velocity while writing a disc. However, the slight wobble frequency modulation is used to encode some information, such as Absolute Time in Pregroove (ATIP) on CD-R and CD-RW discs. DVD-R and DVD-RW have a constant wobble frequency, whereas DVD+R also uses frequency modulation in a manner similar to CD-R and CD-RW. DVD+RW has a constant wobble frequency, but encodes its addressing information using phase-modulated wobble addressing.