Mercedes-Benz SLR McLaren. Operator's Manual.

Controls in detail
Audio system
Balance
Regardless of operating mode, press
the AUD key repeatedly until BALANCE
appears on the display.
Press L or R key to shift sound accordingly
to the left or right speakers.
or
Press both L and R keys simultaneously
to reset the Balance to its center level.
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Returning audio functions to factory
settings
Regardless of operating mode, press
and hold AUD key longer than
2 seconds. RESET will appear on the
display.
All settings for bass, treble and balance
are returned to the center level and the
volume is set to a predefined level.
Audio system sound selection (EXT)*
Regardless of operating mode, press
the AUD key.
The sound settings menu appears on
the display.
Press the EXT key.
Press one of the function keys.