GMC 2005 Safari Owner's Manual page 154

Setting the Tone (Bass/Treble) Radio with CD
BASS: Slide this lever up or down to increase or to
decrease bass.
TREB (Treble): Slide this lever up or down to increase
or to decrease treble. If a station is weak or noisy,
decrease the treble.
Adjusting the Speakers (Balance/Fade)
BAL (Balance): Turn the control ring behind the
upper knob to move the sound toward the left or the
right speakers.
FADE: Turn the control ring behind the lower knob to
move the sound toward the front or the rear speakers.
3-44