How the heck does he do the filter sweep at the end of this video? https://www.instagram.com/p/BxfYp3WHzXg/ I see him reach behind for something, but then it looks like he's going for the tone knob (or switch where the tone knob would be). What is that? I know pedals can achieve this, but I want the onboard effect if it exists! I can't find any info anywhere.... any ideas?