I've got a Moog Mooferfooger filter pedal that does a similar thing (though something's wrong with it as it's very noisy indeed). It's akin to an auto-wah, but a bit more subtle as it doesn't boost a centre frequency, just filters off the higher frequencies above the filter point. It's almost a glorified passive guitar tone control as you can create a similar effect by rapidly moving the tone control knob (though this makes playing the guitar very difficult to do at the same time). I don't know if the Korg has a resonance control, but on the Moog, turning that up high can get the filter to self-oscillate. Just below that, the sound becomes a lot more peaky, and more like a wah sound.