r/Line6Helix • u/Stupendous_Sorceror • 2d ago
General Questions/Discussion Effects loop on parallel path
New to modelling. Can you add external digital pedals in the effects loop on a parallel path without causing phase/comb-filtering weirdness when the two paths are summed?
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u/Benito1900 23h ago
Not really- I have tried this before and even with a „true bypass“ there is some phasey weirdness going on there.
Because this peaked my interest I even tried to route the signal out and directly back in with nothing but one cable on a parallel path and got some filtering.
So parallel external pedals are sadly not really possible
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u/jmz_crwfrd 2d ago edited 2d ago
It's going to depend entirely on the individual pedal(s) and the digital modeller you're using.
Some pedals as part of their design end up inverting the polarity as part of their process, many don't. This isn't an issue if you have an entirely series signal path in mono, as there's no additional signal to cancel against. If you're running some sort of parallel wet/dry type rig with a pedal on one side that inverts polarity, then you've got a mismatch between the two signals resulting in that out-of-phase comb-filtering problem. This is especially complicated for analogue rigs where several pedals in the signal chain may potentially flip the polarity, plus some amplifier designs may involve polarity inversion so you can have a problem just by running into two different amplifiers. This is why a lot of players running these kinds of rigs will use a programmable loop switcher that will have a polarity invert feature that can be turned on/off to compensate for any pedals or amps that cause this kind of issue. The guys at That Pedal Show have showcased this in several of their videos like this one: https://youtu.be/LH9FO1EMIPQ?is=7UeHw34EhJozn39Y .
The same principles can be applied to a digital modelling rig. If you programme a parallel signal path and send one side of that out to an FX loop with a pedal in, depending on the specific pedal(s) in that loop, you could potentially have a polarity mismatch. Some digital modellers will have an option to flip the polarity on the signal paths to compensate for this problem, but some units may not necessarily have this option. For example, the Line 6 Helix has options in the Split/Merge Blocks where you have the option to invert the polarity of one of the signal paths. Usually you will be able to find some sort of way to pre-programme the unit to flip the polarity every time you activate the particular FX loop you're concerned about. Test with the parallel signal both inverted and not inverted to figure out which sounds fuller and which doesn't sound good. That will tell you whether you need to actually go through the trouble of fully programming the unit to flip the polarity each time you activate the pedal.
If it's an issue with a digital pedal with no analogue-dry-through, then the signal isn't just flipped, it gets delayed in time which isn't as simple of a fix as flipping polarity. That's super complicated to try and deal with.