I get the feeling it's a combination of rolling off the treble and octave pedal but I'm not entirely sure and figure someone else out there would be much more informed than I am on this kind of thing.
Active 3 years, 2 months ago
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That's an Envelope Follower or Envelope Filter. Probably an Auto-Wah.
These pedals basically make a smoothed-curve signal using the (high-)frequency (or amplitude after a band-pass) of the input signal, and then use that as a control parameter, usually for tone/eq/compression attack etc.
For modern pedal simulator software, a single envelope follower can be assigned to multiple parameters on multiple effects: such as simulating a univibe by adjusting wet/dry Dopler Speaker, auto-wah intensity, and phaser modulation speed all at once based on how loud the input signal is.
See, for example: https://en.wikipedia.org/wiki/Envelope_detector