This post is about a little audio issue I have been experiencing whilst recording and streaming. I am glad to say I now know what the issue is and have found a solution.
My Behringer Xenyx X1204USB mixer takes audio feeds from my RØDE PodMic Dynamic Podcasting Microphone, PC and Mac. I don’t actually broadcast the PC signal, but use it to monitor the audio in my headphones whilst streaming.
At high volume, you can notice an audible electrical interference type sound that was really irritating. The noise came in on both my PC and the Mac channel but was worse on the Mac.
After asking for advice on twitter a few people ( @StuRobson , @02DClarke and @pete_codes) suggested it might be to do with an electrical issue and that was enough to help me discover the issue of Ground Loop interference.
The following Hackaday article helped me diagnose the issue. It defined the exact issue I had and explained why it was happening:
The ground loop in a nutshell is what happens when two separate devices (A and B) are connected to ground separately, and then also connected to each other through some kind of communication cable with a ground, creating a loop. This provides two separate paths to ground (B can go through its own connection to ground or it can go through the ground of the cable to A and then to A’s ground), and means that current may start flowing in unanticipated ways.Hackaday article
To test the theory it suggested that devices that are running on battery will not cause this issue since they are not connected to ground via mains electricity.
I, therefore, unplugged my mac and had it run directly off the battery, sure enough, the hum disappeared like smoke in the wind.
So my issue was temporarily solved. However, I wanted to keep my Mac plugged into power whilst I am streaming and so I ordered two ground loop isolators, One for my Mac and one for the feed coming from my PC.
They solved the issue 100% on the PC and the Mac. However, I was using an HP dock that takes all the feeds over USB 3 and then has a headphone output. I found even when I use the ground loop isolated on this port there is still a very small amount of noise on the input.
I wonder if there is a similar ground loop issue with the audio being carried over USB3. My solution is to simply have two cables feeding into my mac rather than one, and not to use the HP dock for audio.
So there you have it, a simple £10.99 product solved my issue. These little devices are simple, the cable from your computer goes in one end then a cable (that is supplied with the device I bought) leaves the device and plugs into the mixer. The device is very small and requires no external power.