Controls:

Mid Boost

Sets the gain of the input stage, and is set to boost mids rather than full range boost. Gives you more aggression, gain, and compression but keeps the bass TIGHT. If you want more headroom and cleanness, this is what you'll want to turn down first. This is your hot, sustaining pre-amp gain control.

Tightness

(A subtle control) Dials in the amount of low mids going into the fuzz section, to give you a light, sparkly attack clockwise, or add swampy saturation and beefy chug counter-clockwise, or keep it neutral in the middle. This control is somewhat interactive with the Mid Boost control as it affects its frequency range.

Fuzz

Sets the gain of the overdrive section and takes you from clean through touch-sensitive overdrive all the way to sustaining, cranked-amp fuzz. Gives you greasy, chimey, huge-sounding power-tube type distortion.

Presence

Lets you get a lot more brilliance and bite or make it darker and smoother, to suit your amp and taste. A lot of treble boost is available; you might want this turned down when the other controls are cranked up. I usually keep it at noon.

Volume

Passive humbucker pickups should achieve unity gain between noon and 2:00 o'clock. Passive single coil pickups should find unity gain around noon. Active humbuckers might take 3:00 o'clock to reach unity gain volume.

Unity Gain: Since any dirt pedal will compress your signal, you'll get roughly the same volume no matter how hard you hit the strings, when it's on, yeah? So here's how you figure what constitutes "unity gain" with the HFD pedal: switch it to bypass and hit a chord LOUDLY. Now switch the pedal on and do the same thing. Adjust the volume of your HFD until it roughly matches your bypassed volume while you are hitting a loud chord.