Dtura

Hey there! I use to play with a drummer, just me and him, and with the Helix I do two guitars and the bass. But I have an issue... I don't know how I can play a chord with the guitar and make that the bass line just make the lower note, not the entire chord. I tried with a fliter, eq... and the result isn't great. Isn't there a monophonic octave? Does anybody know how I can get it? Thank you very much for you time!