The following will allow you to operate the GDI21 to its full potential:1.  Connect your guitar to the IN jack using a 1/4" cable.2.  Connect the GDI21 to your mixer using the balanced XLR output.3.  Connect the GDI21 to your amplifier (if one is being used) with a 1/4" cable connected to the Out jack.4.  Activate the GDI21 by pressing the footswitch.  The GDI21 acts as a standard DI box when deactivated.5.  Use the Drive control to adjust the amount of gain and overdrive of your signal.6.  Use the Treble and Bass controls to adjust the frequencies of your tone.7.  Use the Level control to adjust to overall volume of the signal.8.  Adjust the Amp switch to change among the three amp models - Tweed, British, and Californian.9.  Adjust the Mod switch to change among the three gain settings - Clean, High Gain, and Hot.10.  Adjust the Mic switch to change among the three mic placements - Classic, Center, and Off Axis11.  Adjust the Gnd Lift switch to On if you are experiencing a hum in your signal.As always, experiment with your settings to find the tone that sounds best to your ears.