Iphone good equalizer app?

I just got the iphone and I love to work with the song mix, sometimes boosting the bass, other times upping the mid, ect. what I want is an app that lets me change up the mix, nothing too complicated, ideally just mid, treble, and bass, though if they get a little more complicated, its not too bad. Another big thing is that a lot of eq apps force you to play the music through the app, and don't passively equalize the ipod player on the phone, Ideally I want one that will equalize my ipod music, and allow me to use the app while listening and mess with the mix. I don't know if an app like this exists but if anyone knows of one your input would be greatly appreciated.