I believe that is the "Blend" knob. All the way off means no SA effect. "Presence" is more of a treble increase to my ears.I wasn't really a fan of the baked in tone either. It made me feel like my bass and gear sounded like every other bass and rig with an active sansamp in the chain. Felt very vanilla. However, I was under the impression that that tone was more or less dependent on the presence setting, so all the way CC would be minimal to no sansamp tone.