Phase issues when using "fx" loops (Out4/In4)

[fuzzyoctaves]

This template is a WiP - my end state goal is to use Mixer 1 to blend my dry signal with multiple wet paths. I have run into a snag and would appreciate any advice:

Out4 > In4 are going through an external stereo pedal with no effects on. So In4 is essentially the same signal as Out4, which is essentially the same signal just after the Cab.
If I set Row 6 to 50% and Row 3 to 50%, I get a signal that sounds like a flange effect - I am assuming that this is a phase issue? I have tried reversing the Out4/In4 cables and my next step is to simply route a pair of cables from Out4 to In4. Before I get that deep, I wanted to check to see if I am missing something obvious or if there is some limitation in the Axe that I am unaware of.

 

[mr_fender]

It's D/A and A/D Conversion latency from the loop. This is unavoidable in all digital gear. Wet/dry blends between analog and digital are difficult at best. Unless you can match the latency on all signal paths exactly, it's really only usable for delay based effects.

 

[fuzzyoctaves]

It's D/A and A/D Conversion latency from the loop. This is unavoidable in all digital gear. Wet/dry blends between analog and digital are difficult at best. Unless you can match the latency on all signal paths exactly, it's really only usable for delay based effects.

Well at least I learned something. Thanks so much for saving me a ton of time!

 

[mr_fender]

What effects are you trying to blend? There's often more than one way to skin a cat.

 

[fuzzyoctaves]

I am using Out/In4 to a Helix FX using time based FX. I am thinking that a solution could be to add some % of dry signal to the HXFX out. Digging in to the midi block to figure out how to send messages based on scene changes. Any other approaches I could consider?

 

[mr_fender]

You have to either run the full signal through the HXFX like a series effect or run it 100% wet only. Blending any dry signal through the loop will cause phase issues. Instead of bypassing the HXFX when not in use, you'll have to either mute it or bypass the loop itself on the grid.

 

[lair]

Is there a standard approach to accurately measuring and compensating for latency when using outboard gear?

@Admin M@ - in reference to the GP-100, any tips to get a signal in phase with an amp block on the grid? For the GP specifically I think the signal path is “inA-D48k-outA-inD44.1k-outA-inD48k”, plus whatever blocks add on the grid - and bit rates and oversampling etc. That math is way above my pay grade!

 

[fuzzyoctaves]

You have to either run the full signal through the HXFX like a series effect or run it 100% wet only. Blending any dry signal through the loop will cause phase issues. Instead of bypassing the HXFX when not in use, you'll have to either mute it or bypass the loop itself on the grid.

Yeah - I got it figured out by running the HXFX in series and sending MIDI CCs to the HXFX to switch between snapshots (which are analogous to AxeFx scenes) that sets the wet/dry mix. I guess I could also do this with fine control by using an expression connected to the HXFX, but I already have 6(!) expression controllers connected to the Axe!

On a related note, does anyone know the dB offset when doubling a signal? For example solve for y: Signal_A = x dB, Signal_A*2 - y = x dB

 

[VittorioAngelo]

Hello @fuzzyoctaves;

I, too, struggled with phase issues whilst running through an external Hologram Microcosm pedal:
https://forum.fractalaudio.com/threads/external-pedal-and-delay-compensation.178693/#post-2187956

In the post above, I almost solved the issue using a delay block and a compression block painstakingly dialed in to delay the AxeFX signal path to account for the external pedal latency. This was far from ideal.

What I find that works better is to disable the Out4 block when the external pedals are not being used, and to enable Out4 when the pedal is being used. Necessarily, this means that Out4 should be configured as a parallel block.

I've accomplished this in two ways:

1. Via the FC 12:
   The external pedal is always on, and Out4 is enabled and disabled via a Control Switch.
2. Via a MorningStar midi controller:
   I can enable/disable Out4 and simultaneously control the external pedal.
   In the case of the Microcosm, I enable Out4 and start loop recording at the same time.
   When I'm done recording my loop, I can disable Out4 and start playback at the same time.

 

[GlennO]

I am using Out/In4 to a Helix FX using time based FX. I am thinking that a solution could be to add some % of dry signal to the HXFX out. Digging in to the midi block to figure out how to send messages based on scene changes. Any other approaches I could consider?

I suspect the phasing isn't caused by your effects loops at all. Assuming you're running those 100% wet and they are time based effects, that shouldn't cause any phasing.

However, the way you're using send/return blocks will almost certainly cause phasing issues.

 

[mr_fender]

Yeah the Send and Return blocks are not really needed. If you reorient things a bit they can all be eliminated and simplify things.

 

[Rumbletone]

I am using Out/In4 to a Helix FX using time based FX. I am thinking that a solution could be to add some % of dry signal to the HXFX out. Digging in to the midi block to figure out how to send messages based on scene changes. Any other approaches I could consider?

It could be the latency, it could be polarity issues. But as a practical matter though (and potential solution) - why not just use the AxeFX for those effects instead of the Helix?

 

[rzjd]

I would try your tests with the the loop cable idea. I suspect the latency is ithere.

 

[fuzzyoctaves]

Yes, the 2nd set of Send/Return was just a quick routing test. My current preset is using serial routing so that all the signal comes through in In4 and I am using the HXFX to change the Wet/Dry mix. Here is the current:

 

[fuzzyoctaves]

It could be the latency, it could be polarity issues. But as a practical matter though (and potential solution) - why not just use the AxeFX for those effects instead of the Helix?

My base kitchen sink template (in the post above) is running at ~82% CPU and that is with running reverbs in economy and leaving a lot of FX out. The HXFX is in there for a few more crazy effects that I could probably replicate on the Axe, but Helix makes super easy to dial in (pattern trem, particle reverb, etc). I also use the HXFX Send/Return to act as a switcher for another external pedal.

 

[rzjd]

My base kitchen sink template (in the post above) is running at ~82% CPU and that is with running reverbs in economy and leaving a lot of FX out. The HXFX is in there for a few more crazy effects that I could probably replicate on the Axe, but Helix makes super easy to dial in (pattern trem, particle reverb, etc). I also use the HXFX Send/Return to act as a switcher for another external pedal.

do you still have the same phasing issues with this setup? did it get worse or better?

 

[fuzzyoctaves]

I suspect the phasing isn't caused by your effects loops at all. Assuming you're running those 100% wet and they are time based effects, that shouldn't cause any phasing.

However, the way you're using send/return blocks will almost certainly cause phasing issues.

Hmmm. I actually was running the dry signal through the loop just as a test. Maybe I should go back and just make sure my wet paths are 100% wet.

 

[Rumbletone]

My base kitchen sink template (in the post above) is running at ~82% CPU and that is with running reverbs in economy and leaving a lot of FX out. The HXFX is in there for a few more crazy effects that I could probably replicate on the Axe, but Helix makes super easy to dial in (pattern trem, particle reverb, etc). I also use the HXFX Send/Return to act as a switcher for another external pedal.

Thanks - that must be quite the preset if it’s pushing the AxeFXIII to capacity. I just have an FM3 and I guess I always assumed - apparently incorrectly - that AxeFXIII users never run out of CPU!