The MIX BAL knob on the front panel of the FCA1616 and FCA610 will control the sound you hear from headphones attached to the front panel (or speakers attached to the 1/4 jacks on the back panel). If you turn the knob to the far left you will only hear the direct sound of any microphone or instrument plugged into the FCA1616 inputs. If you turn the knob all the way to the right, you will hear only the output sound of the software you are using. Midway will blend the two signals.