Toyota Prius c 2014 Owner's Manual page 288

3-2. Using the audio system
■
Adjusting the Automatic Sound Levelizer (ASL)
When ASL is selected, turning
amount of ASL in the order of "LOW", "MID" and "HIGH".
Turning
ASL automatically adjusts the volume and tone quality according to vehi-
cle speed.
286
to the left turns ASL off.
to the right changes the