Red Panda Particle granular delay / pitch shifter doing a reverse delay sound. 50% blend with some feedback.
The blend, delay (time), and feedback knobs work as you would expect. The chop knob controls how long each reversed segment is, which allows you to fine tune the effect for the particular instrument and frequency range. The reversed segments (grains) go through the feedback path, so they will alternate between forward and reverse.
In reverse delay mode, the param knob sets the probability of each grain playing either forward or reverse (grain size set by the chop knob mentioned above). It ranges from 100% reverse to 100% forward, and in the middle you can get random glitchy sounds where it is occasionally flipped. With an expression pedal, you can switch from forward to reverse delay whilst playing.