Toyota Prius 2011 Manual page 332

3-2. Using the audio system
Adjusting the Automatic Sound Levelizer (ASL)
■
Type A
When "ASL" is selected, turning
and turning
ASL automatically adjusts the volume and tone quality according to the
noise level as you drive your vehicle.
Type B
When "ASL" is selected, turning
ASL level in the order of "LOW", "MID" and "HIGH".
Turning
ASL automatically adjusts the volume and tone quality according to vehi-
cle speed.
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to the left turns ASL off.
to the left turns off the ASL.
to the right turns ASL on,
to the right changes the