GMC Hummer H3 2008 Owner's Handbook Manual page 75

Instrumentation and Controls
Display Control
Press DISP to recall the frequency
of the station being played or to
display the clock.
If the ignition is off, pressing this
knob will display the clock.
To change what is normally shown
on the display (station or time),
press DISP to recall the desired
display, then hold DISP in for two
seconds.
You will hear one beep.
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Automatic Volume Control
This feature automatically
compensates for the increase in
road noise levels at higher speeds.
Adjust the volume to the desired
level by rotating the upper knob.
Press AUTO VOL to turn the auto-
matic volume control feature on.
Press AUTO VOL repeatedly to
scroll through four volume
compensation levels.
You may choose between LOW,
MEDIUM, HIGH and AVOL OFF.
With this feature activated, the
sound system will automatically
adjust the volume so that it always
sounds the same to you.
If the sound system is unable to
determine the vehicle's speed,
NONE will appear on the display.
If this happens, adjust the volume
manually.
To turn this feature off, press
AUTO VOL until AVOL OFF
appears on the display.