Auto Wah Envelope Filter. Yes, there was a time when "Auto Wah" might have been a label on an envelope filter. The shortest answer is that they are effects used mostly in funk music for a "quack" or "bow wow" sound on the bass, guitar, or keyboards.
DOD GFX25 Extreme Envelope Filter Auto Wah Xtreme Effects ... (Jesse Morgan)
I tend to me more aligned to the more compact pedals. I think not so much anymore. This funky, tripped-out circuit has been a decade in the making.
What is an envelope filter or a wah pedal?
In the bass world, it remains especially popular with.
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They are often called auto-wahs or auto-filters to distinguish them from conventional foot-operated pedals. Envelope Filters are things like the Q-Tron (which is what you're probably after). The 'Envelope' from MOOER is a pocket sized 'envelope filter'/'dynamic auto wah' pedal with big tone and lots of versatility.