The Keeley uses two delays in series. That usually means you have to use the Filter Pong algorithm in an H9. I wasn’t satisfied with the ‘rhythm’ it created. I suspect the cross-FEEDBACK path(s) differ from Filter Pong.
All is not lost. I got roughly the same ‘Halo’ results in many of the other parallel delay algorithms. (As an aside, the UltraTap *pedal* format – with FEEDBACK – seemed perfect for this application).
It will take some fine-tuning, but I was getting good results with Spacetime, MultiTap, even PitchFuzz (no ‘fuzz’ & arp delays). Tape Echo, if the Keeley saturation is important to you. Vintage Delay for the bucket brigade mode, etc.
It’s all in the feedback looping path, & diffusion on the repeats (SLUR-M). I was working those almost with 2 FEEDBACK alternatives.
Other than that, the examples I’ve heard are cascading dotted eighths & quarter notes. 375 ms. and 500 ms. at 120 BPM.