Here's a good place to start, using two 'stock' algorithms from the H9 package. I described a "voice-switching" technique for the PitchFactor in this thread. That used an ADR III to split a mono signal to stereo with an autopanner. Here, the panning follows the stereo pitchshifting. Note that many stereo combinations can be summed to mono before and/or after the 'MetaEffect', and still retain the combined characteristics.
Pitchshifted trills alternate between channels at the set Speed. Changing the Shape parameter defines the transition smoothness from side to side. Complex patterns can be created with S-Mod and D-Mod. Pitch intervals can be delayed. Scale-constrained trills are possible by substituting a Diatonic or QuadraVox algo for the H910 H949.
Preset A
Preset B (in series)
