after a while, I tried to replicate the bug and conduct deeper analysis:
- On an up-to-date Ubuntu 16.04, I can still replicate the problem.
- The problem arises as soon as I connect the "System Capture_1" (or 2) to the input of the guitarix head.
- When I use a synthesizer (zynaddsubfx) and connect it to the guitarix head, the problem does not occur.
- The problem increases the more I push the gain/drive controls to the max (but as I high-gain guitarist, I cannot live with medium drive settings
- A tiny and very silent (-60/-50 db) signal of the jack master output is audible on the input and sent into the guitarix amp again although only the "System Capture_1" is connected to the input.
- I also tested without any external devices connected to the interface, so it's not a wiring issue.
- Direct hardware monitoring of the interface is deactivated.
After considering all these points, the only two reasons for the problem that I can imagine would be:
1. A hardware issue in the input channel of my interface (I should maybe test another interface)
2. A software problem with the guitarix drive simulation. I did not look into the source code so I can only speculate: maybe, for the "overdrive simulation/generation" (or however you call that), there could be a bug that sends a tiny bit of the overall master output into the input. Maybe this only happens with high drive settings or as soon as the signal is louder than 0 db.
I suppose the hardware issue is more likely to be the problem but could you maybe just think about whether the second possibility could be the issue as well? Or do you see a third option that I did not consider yet?
By the way, my interface is a Behringer UCA202. I also have a Behringer Firewire Interface that I could maybe test if I find the time. But until now I never had any issues with the interface (and on Windows and also during recordings without guitarix, the problem did not occur. Also on clean tones with guitarix, I cannot hear the issue (maybe for cleans it's too silent to be audible)).
Thanks for a reply and best regards,