Subaru 2004 Legacy Owner's Manual page 219

Audio
Power switch and volume/bass/treble/fader/
balance control (PWR/VOL)
The dial (1) is used for both power (ON/OFF) and vol-
ume control. The radio is turned ON and OFF by push-
ing the dial and the volume is controlled by turning the
dial.
This dial is used for bass/middle/treble controls when
the "AUDIO" button (2) is in the depressed position. It
is also used for fader/balance controls when the "BAL"
button (3) is in the depressed position.
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