While mainly designed for bass guitar, the BBBO can also be used with other instruments for low, dynamically controlled distortion.
VOLUME: controls output
DRIVE: sets the amount of distortion and sustain, as well as the type of distortion. Lower settings give dynamically controlled overdrive, the unit distorts more the harder you strike the strings and there is no definite clipping point, but rather different shades of distortion as the amplitude changes.
Higher settings will give more compressed sounds.
A good starting point with most basses is fully CCW, turn the knob until you find the overdrive level that suits your playing. Lower settings are good for old school tube amplifier tone, while higher settings gives denser distortion.
NATURE: is a tonecontrol for filtering and to control what register distorts. Turning CCW gives more lowend and also distortion in the lower registers. Turning CW gives an emphasis in the upper midrange for more protruding solo bass tone.