Philips DVDR985 Technical Training Manual page 58

Wobble
A Pre-groove is stamped on writable discs. All
recordable DVD media types feature a micro-
scopic wobble groove embedded in the plastic
substrate. This wobble provides the recorder
with the timing information needed to place the
data accurately on the disc. During recording,
the drive's laser follows this groove to ensure
consistent spacing of data in a spiral track. The
walls of the groove are modulated in a consistent
sinusoidal pattern, so the Wobble processor can
read and compare it to an oscillator for precise
rotation of the disc. This modulated pattern is
called a wobble groove because the walls of the
groove appear to wobble from side to side. This
signal is only used during recording, and there-
fore has no effect on the playback process.
Among the DVD family of formats, only record-
able media use wobble grooves.
Lossless linking describes the need to connect
data streams on a disc without any unused
space between the previous track and the newly
recorded segment. For lossless linking, it is nec-
essary to write data blocks in the correct position
with high accuracy (within 1 micron). For this
purpose, the groove is mastered with a high
Figure 30 - Wobble Tracks
wobble frequency (817kHz), which ensures that
the writing can be started and stopped at an
accurately defined position. The writing clock as
obtained from this groove is very accurate.
ADIP
Address in Pregroove is the name of the process
of knowing how far into a disc the laser position
is during recording. The Wobbles are counted,
and an address location of the section of the
disc is calculated.
The CD HF signal path and the DVD signal path
needs are different. The DVD signals are han-
dled by the Signal Processor IC for DVD
Recording, the SPIDRE. The CD HF signal is
handled by the Decoder, IC 7402.