True Grit is a switchable low gain or high gain overdrive device. The BOOST footswitch control will toggle the device between the low and high settings. This switch, combined with the GAIN knob will adjust the gain and distortion sound of the device. The tone controls (BASS & TREBLE) have enough range that you can dial in a tone on the amp (ON/OFF footswitch in the OFF position, when True Grit is bypassed) for one sound, then switch the True Grit on for another. By using the BOOST function, you can get a 3rd completely different sound (#1 - effect bypassed, #2 - True Grit on low gain setting, #3 - True Grit on high gain BOOST setting). BASS and TREBLE controls do what you would expect, and GRIT alters the upper midrange frequency (buzz and grit in some amps) for the best tone for any amplifier. VOLUME controls the output level.