Mazda MX-5 Miata 2004 Owner's Manual page 141

Interior Comfort
Audio System
NOTE
About 5 seconds after selecting any
mode, the volume function will be
automatically selected. To reset bass,
mid-range, treble and balance, press
the audio control dial for 2 seconds.
The unit will beep and "CLEAR" will
be displayed.
6-20
Automatic Level Control (ALC)
The automatic level control is a feature
that automatically adjusts audio volume
and sound quality according to the vehicle
speed.
The volume increases in accordance with
the increase in vehicle speed, and
decreases as vehicle speed decreases.
The following seven modes are available.
Select the desired mode according to use.
Mode
Volume
Use
change
ALC does
No change
not operate.
Minimum
Use when
the
convertible
top is open. Medium
Three levels
are
available.
Maximum
Use when
Minimum
the
convertible
top is
Medium
closed.
Three levels
are
Maximum
available.