A Roland Dimension D is going to be difficult to recreate with a single pedal or existing algorithm. I've never owned one; just heard it. It remains a mystery effect. As I understand it, there's all manner of processing going on there. It may help to do some of this sound shaping before/after it gets to to the H9:
Compander (noise reduction) circuit with some distortion added
Bass boost on just the dry signal
High pass filter before the delay signals (bass cut)
(No doubt) a low pass filter after the delays for the clocking frequency
Out-of-phase flattened triangle modulation of the L & R delays
Flipping of the stereo image on most switch positions
Then you add in the four switch options and combinations of each. I've heard between 5 and 15 ms. of delay time; depending on the switch selected. I don't know if any delay signal was fed back. Modulation depth varies with each switch setting, and I'd stick with 0.25 – 0.50 Hz. for the modulation speed changes. Very slow … almost imperceptible modulation rates.
That said, I've experimented with many of the H9 algorithms to this end. Oddly enough, I never thought the Chorus variations were going to cut it (and I've yet to data-mine the PitchFactor algorithms for this). Vintage Delay and Tape Echo have some advantages, but Mod Delay may be your best bet for coming close.
Here's something that I tossed together during the 5-minute demo at the Store. It's a starting point that will need some serious tweaking.
Dimension D SW 1
Wet Mix = WET: 50
Delay Mix = A10+B10
Delay A = A: 5 ms.
Delay B = B: 6 ms.
Feedback A = 0 ms.
Feedback B = 0 ms.
(encoder) = Mod Delay / TMP: OFF
Mod Shape = ATRI B 180TRI
Mod Depth = 5
Mod Speed = 0.50 Hz.
Filter = (-) 25
Not too happy with the filtering results. For different switch combinations, try increasing the delay times up to 15 ms. Offset one delay time from the other by a millisecond or two (component variations, and it will sound thicker). Of course, increase/decrease the Mod Depth with the Delay adjustments, and vary Mod Speed. You should be able to emulate Dimension D switch positions with the HotSwitch, aux switches, MIDI, or even an expression pedal.
