I use a TC Helicon Voice Live Touch in a live application. Current configuration. Plug mic in - out to PA and use some harmonies here and there. I know it can do much more and can auto tune if I plug in the various keys to all our songs but that is unrealistic for live. We play to mp3 backing tracks. I know if I played guitar and plugged in then it would recognize my chords and harmonies and pitch correction would be based off that - would the same be true if I plugged my mp3's into the TC? If so where? Would I plug into the guitar in and thru out to my board? Would I use the aux in? I know that is for mp'3 but I'm not sure its routed through the unit to identify the keys of the songs. Thanks in advance - I always get great information here.