the center position (128), so as to be compatible with other drivers.
The equalizer is enhancement only, and the values < 128 don't take
any effect.
Yeah, this causes spec change....
For equalization.treble and equalization.bass, the relation between
old and new value is
new_value = (old_value / 2) + 128.
(Note this does not apply to equalization.surround.)
2. Support ++ and -- of mixerctl(1) for stepping volume variables.
3. Fix problem where the chip is not powered up
when the mic input is unmuted.