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Goal

We have a Behringer X32. Everything in the mixer sound great. We try to bring its sound to a PC so we can record and stream it.

Problem

The audio in the PC is noisy. In indescribable, outrageous, scandalously unbearable levels. It is only noise. The speech is barely audible and it sounds like hoarse aliens. Theoretically we have separate power phase for PCs, light and audio.

Attempted solutions and results

  • Mixer's main -> XLR -> 3,5 jack -> tower PC's (Win 7 and Kubuntu 18.04) line in. Result: Horrible noise.
  • Mixer's XUSB card -> USB2 -> tower PC (Kubuntu 18.04). Essentially using the mixer as an audio interface. Result: No noise, but the sound quality wasn't good and it was super quiet even with everything turned up.
  • Mixers main -> XLR -> Steinberg UR22 audio interface -> USB2 -> tower PC (Kubuntu 18.04). Result: Horrible noise.
  • Mixer's main -> XLR -> Focusrite iTrack Dock that has an iPad on it running GarageBand -> 6,3 jack -> XLR -> Steinberg UR22 audio interface -> USB2 -> Acer laptop (Win 10, plugged to power). Result: GarageBand recording is crystal clear, it is mixer grade. Laptop recording is just slightly worse but still really good.
  • Mixer's main -> XLR -> Focusrite iTrack Dock that has an iPad on it running GarageBand -> 6,3 jack -> XLR -> Steinberg UR22 audio interface -> USB2 -> tower PC's (Kubuntu 18.04) line in. Result: Good sound but there was a small-moderate ground loop buzz.
  • Mixer's main -> XLR -> Focusrite iTrack Dock that has an iPad on it running GarageBand -> 6,3 jack -> XLR -> Behringer ULTRA-DI DI20 (ground lifter enabled, 0db attenuation, power from 9V battery) -> 6,3 jack -> XLR -> Steinberg UR22 audio interface -> USB2 -> tower PC's (Kubuntu 18.04) line in. Result: Good sound with negligible ground loop-like buzz.
  • Mixer's main -> XLR -> Behringer ULTRA-DI DI20 (ground lifter enabled, 0db attenuation, power from 9V battery) -> 6,3 jack -> XLR -> Steinberg UR22 audio interface -> USB2 -> MacBook Pro (Ubuntu 16.04, running from battery). Result: Ranging from horrible to good sound. Once it is just plain noise with barely audible speech, the next minute noise is gone and only a slight hum is there with speech sounding good. When there was only noise, the laptop's/USB cable's position affected the amount of noise. Getting closer to power cord cables increased the amount of noise. Then this behavior was gone and there was a fixed amount of noise which increased when I touched the laptop (running from battery) and an electric cable.
  • Shure SM58 -> XLR -> 3.5 jack -> tower PC's (Kubuntu 18.04) line in/mic in. Result: Horrible noise.
  • Plain 3.5 cable without anything on the other end -> tower PC's (Kubuntu 18.04) line in. Result: Horrible noise?!

Solution

I tried to change cables, remove UPSs, swap PCs and laptops, using different audio embeders, turning lights off (movement of the DMX controller's faders add buzz). Nothing affected the setup. Then in the end I plugged the X32 to a UPS (connected to the same PDU the PCs use) and it fixed everything. Only a slight buzz remained which was coming from the ULTRA-DI ground lifter (?!). After removing that and connecting the mixer straight to the Steinberg UR22 the audio became good on every device. I wouldn't say that it was as pure as the GarageBand recording (maybe some software stuff going on there) but it was pretty good.

Question

What on earth is going on? How did the PSU fixed everything and why is everything so noisy? I'm sure it is coming from the power system, but how? How can I eliminate this? Why is buzz picked up from the movement of the faders of the DMX controller (Showtec SM-8/2) for the lights? Why was the GarageBand recording so good?

  • I count six questions in here. It might be a good idea to condense this down to a single question that can be succinctly answered. – Mark Apr 19 at 1:03
  • @Mark My question is "How can the power system mess up the audio?". I clearly described the goal and problem as well. The end just summarizes what I don't get. All of them are on the same specific issue: what was the problem, what fixed it and how should I fix it properly? – totymedli Apr 19 at 2:34
  • Research Ground Loops. – Mark Apr 19 at 7:55
  • I'd also research isolating 1:1 transformers, especially if you know you have 3 phases in one installation. I'd have avoided that myself. I can only assume you have US 110v if you have to resort to that type of structure. – Tetsujin Apr 19 at 8:45

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