 Sometimes you'd like to have the audio input that goes into the aux in Guide your key and scale or your natural play, but you don't necessarily want it going out into the Main outs to the audience You may also want a metronome going into there or some other thing and you just don't want the audience to hear it Hear it. So because the overall mix gets sent out through the instrument out to the PA You need to basically block that signal. So all you're going to do is you're going to hold down the headphone button While you plug in the aux cable like this and that's going to set it up so that it won't send that audio signal out to the mains It will not remember this setting. So every time you power up Unplug the aux and plug it back in it's going to forget that setting So just make sure that you remember to do that every time This is specifically so that if people forget that they did that and it got stuck that way It'd be really hard for them to understand what was basically going on and undoing it So every time you want that to happen Just make sure that you hold down the headphone and plug that in while you're powering up And of course the unit needs to be on while that's happening