So first I have to say these are amazingly good, way better than what I came up with. Have a couple questions/comments if you don't mind indulging me.
Just re-watched the Keeley video and he says that the modulation cross fades between the two channels. Is that what's happening in your blocks? Both the first and second delay block have LFO1 set to target Both with a phase of 90 deg. Would you not want to use both LFO 1 and LFO 2 with each targeting a different channel and a 90 degree phase shift between them?
Regarding diffusion, I feel like this gets mentioned in passing on some of the Halo videos. I liked the sound of a small amount of diffusion with Diffusion Time around 70% and a bit of modulation. The blocks guide says that adding modulation to the duffuser gives a chorus-like effect, which Andy mentions in the Keeley video.
Last is just a comment that I liked the EQ settings you used much better than what I had. I was using a Memory Man like EQ curve with a sharp roll off. I was finding it difficult to make the first delay repeat sit correctly in the mix. You used the 6 dB slopes which are the default on the tape delays. Any idea if the actual pedal is doing something similar?
EDIT: threw this on a patch with a few different variations. I dialed this in in a Strat, neck pickup with the volume rolled off a bit. Scene 1 is the blocks just as above except mix turned up. Scene 2 used LFO1 and 2 as described above. Scene 3 adds a bit of diffusion with modulation to the mix.
I think the issue here is that the Dual Delay is defining one delay time as either the L or R channel. The cross feedback ends up feeding back into the dotted 1/8th, which isn't what happens in the real pedal (or the old Memory Man setup). There was "too much" going on there, which is I think why I started throwing diffusion at it.
Not that I'm doubting what you're saying, but do you have more info on how the phase offsets work? I've found that things like the Blocks Guide and the Wiki tend to be pretty short on technical details, especially on more advanced parameters like this. The way I was interpreting this, it is applying a 90 phase offset to "both" channels. You're saying that there's an additional 90 already baked in there on the R channel? To my ears at least, when I set LFO1 at 90 deg targeting L and LFO2 at 180 deg targeting R, I heard a much wider sound.
Re: diffusion...after using the stereo blocks in series, I no longer felt the diffusion sounded right. I think it was just a Band-Aid I was using on a poor solution.
Regarding the LFO crossfade: When Robert Keeley says that in the video, I'm pretty sure he just means that the modulation isn't the same for left and right. IOW, a phase offset.
When a LFO is assigned to "both" on a stereo delay in the Axe-Fx, the phase parameter only controls the modulation for the right side delay. When using a phase offset of 45-90 degrees, you get this almost panning illusion of the repeats, since one side of the delay is always chasing the other in terms of modulating to a longer or shorter delay time (which is what modulating a delay does). This affects our perception of where in the stereo image it sits. It's more obvious with a chorus, but you can hear it on the Halo too. The repeats "cross" the stereo image at intervals consistent with the modulation rate. So yeah, the LFO "crossfade" is baked into my blocks the way they are set up.
I'm fairly certain that the Halo uses only one LFO for everything (so no secondary LFO modulating at a faster rate, for instance). That LFO might have two or four outputs. In the case of two, both left side delays are modulating in unison, and both on the right side are modulation in unison, but with a phase offset in relation to the left side. If the LFO has 4 outputs, it might be something like 0, 90, 180, and 270 degrees. Since we can't sync the LFOs in two delay blocks in the Axe-Fx anyway, it's kinda pointless to go to far down that particular rabbit hole.
Regards the diffusion: Yeah, I'm totally onboard with your final conclusion: There is no diffusion on the Halo. Some describe diffusion as sounding a bit like a reverb, and some a bit like a chorus. I would say it's both, and neither. Diffusion is a transient schmear, and it does this by adding microdelays to diffuse the sound. It can sound like anything from a static flanger, to a big washy grainy reverb. When done like Lexicon does it (the most famous example of diffusion I can think of is the PCM70 Circular Dlys), it sounds almost fluffy. If a normal delay repeat is a bare fisted punch, adding just the right amount of diffusion is akin to covering the same fist in a big bag of cotton. FWIW, diffusion this way is normally done with the mix at 100 %, and the only control is the diffusion time.
EQ: 6 dB/octave was the closest I could get with that particular delay type. As I mentioned in a previous post, there is something more going on with the EQ that's just missing from the stereo tape type. The high cut is very shallow, and there is probably some EQ going on that's not part of the feedback loop. Like a static low mid bump or something outside of the feedback loop.