How to Eliminate Ground-Loop Hum in Live Event Productions

Alternatives

If you can use wireless mics, that can often help avoid mic-grounding issues. If you can operate your gear off a battery, that can help as well. But often, with a bigger show that’s going to be going all day, for several days, you’ll need to use wired receivers and multiple mixers, and that’s when the grounding issues start to appear.

Sometimes, if you have one piece of hardware that always buzzes when you attach it to the mixer, such as a consumer video player, you can try running a “ground line” between that piece of equipment and the mixer—usually by finding an unpainted screw in the metal enclosure of both items and connecting a thin copper wire (such as speaker wire) between them. This gives the excess energy a path to travel that is not your audio path, similar to a grounding strap for working on computers.

I’ve had this happen with a laptop—I connected the headphone out to the rest of my gear and got a buzz regardless of whether the laptop was running off its own battery or plugged in. But when I connected a wire between the screw hole for the VGA video out, and my audio mixer, suddenly the buzz was gone. It doesn't have to be thick wire; it just needs to give the electricity a different path around your audio chain.

I hope these techniques and solutions will help you conquer the vast majority of grounding issues you’ll encounter. It’s important to remember that the ground loop hum you’re experiencing could arise from any number of individual possibilities, at different stages in the audio path. Don't limit yourself to bringing only a ground lift and assume you’ll have it licked. Sometimes a new development can trip you up where you least expect it.

I recently did audio for a two-DSLR shoot. I used a battery-powered mic, a battery-powered mixer, and a battery-powered audio recorder, and the audio sounded good. Then the producer decided that he wanted me to feed the audio out of the recorder into the battery-powered Canon 5D DSLR. No problem, I thought. All seemed well and good, but in post he reported that there was a little buzz on both channels on the DSLR. Thankfully, the audio in to the audio recorder was clean.

Nevertheless, I’m now buying and adding another audio isolation transformer to my gear bag to isolate my audio recorder from whatever it feeds after me (Figure 5, below).

Figure 5. An Mpow 1/8" Ground Loop Noise Isolator

There's always something new to learn and adapt to. Good luck!