Some notes about the audio equalizer.

Version 0.6.2 adds an audio equalizer (available in the menu Audio). 

Users of the normal (official) mplayer will need to click on the "Apply"
button so the changes in the controls of the equalizer could take effect.

It's possible though that changes take effect immediately while moving the
controls. For that it's necessary to patch mplayer. The patch was sent to
the mplayer-dev-eng mailing list:
http://lists.mplayerhq.hu/pipermail/mplayer-dev-eng/2008-June/057970.html

You can also download it from the smplayer svn:
http://smplayer.svn.sourceforge.net/viewvc/smplayer/mplayer-builds/patches/patcheq.diff

That patch adds a new slave command for mplayer (af_eq_set_bands).