The equaliser is solely based on modifying the gain of the mp3 subbands. That means that it is a very crude beast. The first band already covers 690 Hz, so don't expect too much fine grained detail. The equalizer can be modified per song. To do so, open the song segment, then click on the button.
The first 32 bands are the 32 mp3 subbands. The last band, marked with a V is the replay gain, which can be modified separately
The clear button will clear the spectrum modifications
It is possible to make all tracks in the mix have a more similar sound color. This option is found in the menu Mix|Equalize songs to average profile