Volvo Trucks North America, Inc. Date Group No. Page
Service Bulletin 4.2004 392 08 25(47)
Compact Disc
A compact disc contains digitally encoded music which
is read by a laser beam. The data is read as a change in
laser light intensity. Since no stylus ever touches the disc
surface, there is no disc wear from playing. Thus, digital
storage, error protection and disc longevity create a high
fidelity audio medium.
Compact Disc Player
CD (Compact Disc) players are somewhat similar to
conventional record players. The disc is rotated by a
motor, just like record is. However, the CD plays inside to
outside unlike the record player which plays outside to
inside. The speed of a record player does not change,
but the rotation speed of a disc does change to maintain
the same velocity as the spiral diameter changes. The
speed slows down as the laser moves from the inside
to the outside of the disc.
A CD player reads the information as digital electronic
signals, whereas a phonograph reads the information
as mechanical signals. An optical pickup (laser beam)
performs the same function as that of the record player’s
mechanical stylus. Nothing mechanical ever touches the
disc. The light beam emitted from the pickup carries the
data. This signal is converted into an analog signal which
is filtered to achieve the final audio signal which can be
processed by a home stereo or a vehicle system.
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