GMC Sierra 2008 Owner's Manual page 267

Playing a CD (In Either the DVD or
CD Slot)
Insert a CD partway into the slot, label side up.
The player pulls it in and the CD should begin playing
(loading a disc into the system, depending on media
type and format ranges from 5 to 20 seconds for a CD,
and up to 30 seconds for a DVD to begin playing).
If the ignition or radio is turned off, with a CD in the
player, it stays in the player. When the ignition or radio
is turned on, the CD starts playing where it stopped, if it
was the last selected audio source. The CD is controlled
by the buttons on the radio faceplate or by the RSA unit.
See Rear Seat Audio (RSA) on page 3-129 for more
information. The DVD/CD decks, (upper slot is the DVD
deck and the lower slot is the CD deck) of the radio
are compatible with most audio CDs, CD-R, CD-RW,
and MP3s.
When a CD is inserted, the text label DVD or CD
symbol displays on the left side of the radio display.
As each new track starts to play, the track number
displays.
The CD player can play the smaller 3 inch (8 cm)
single CDs with an adapter ring. Full-size CDs and
the smaller CDs are loaded in the same manner.
Care of CDs
If playing a CD-R, the sound quality can be reduced
due to CD-R or CD-RW quality, the method of recording,
the quality of the music that has been recorded, and the
way the CD-R or CD-RW has been handled. Handle them
carefully. Store CD-R(s) or CD-RW(s) in their original
cases or other protective cases and away from direct
sunlight and dust. The CD or DVD player scans the
bottom surface of the disc. If the surface of a CD is
damaged, such as cracked, broken, or scratched,
the CD does not play properly or not at all. Do not touch
the bottom side of a CD while handling it; this could
damage the surface. Pick up CDs by grasping the outer
edges or the edge of the hole and the outer edge.
If the surface of a CD is soiled, take a soft, lint free
cloth or dampen a clean, soft cloth in a mild, neutral
detergent solution mixed with water, and clean it.
Make sure the wiping process starts from the center
to the edge.
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