Don't really get how to use the auto trim feature. In the tutorial video I watched on line, it shows that you talk or play as loud as you can while in the auto trim mode. Then you go back and set the volume knob for the channel to 0. How do you get the individual volumes for all the vocals/instruments. Some mics are feeding back so you have to turn the volume down on some channels. Am I doing this right? If not give me a step by step please.