[mustang67408]

Yup, I think Toyotatech is right
Page 215 of your owners manual:
Adjusting the Automatic Sound Levelizer (ASL)
When ASL is selected, turning to the right turns on the ASL,
and turning to the left turns off the ASL.
ASL automatically the volume and tone quality according to the vehicle
speed.
Mode
displayed
Sound quality
mode Level Turn to the left Turn to the right
“BAS” Bass* -5 to 5
Low High
“MID”
(if
equipped)
Mid-range* -5 to 5
“TRE” Treble* -5 to 5
“FAD”
Front/rear
volume
balance
F7 to R7 Shifts to rear Shifts to front
“BAL”
Left/right
volume
balance
L7 to R7 Shifts to left Shifts to right
“SURROUND”
(if
equipped)
Surround ON/OFF OFF ON