Whether you’re using your PC for conference calls, audio recording or online multiplayer video gaming with a headset, both USB and analog audio, you quite likely stumbled across that issue. Since your computer normally isn’t set up to output your own voice, other people participating in your calls are first to complain about background noise from your side. If that background noise sounds like a constant buzzing or humming, it’s a ground loop (Wikipedia: Ground Loop). An easy way to find out if you got a ground loop is to disconnect your laptop from the power outlet. The noise should be gone immediately and those people on the other end should be fine.
There are hardware solutions to that problem and I absolutely recommend sticking to those if you like to properly record from your microphone. Usually, they involve a certain setup, cables and more often than not, patience and luck. For instance, you can touch any grounded part like USB ports or metal surfaces of your laptop with your fingers and the noise is reduced as well. I like to talk without touching my devices all the time.
Sometimes, you can neither choose the quality of your local electric grid nor the grounding of your USB headset as well as your laptop, leaving only software solutions. Right now I’m changing my location once in a while and although I’m lucky in finding WiFi hotspots even in a jungle, I didn’t encounter a stable electric grid including properly grounded devices too often in South America. I’m using a run-of-the-mill Logitech USB headset and an Asus Zenbook.
Microphone recording with ground loop noise (use headphones to listen):
There is a simple solution that works with any device:
- Install a microphone equalizer
- Filter out ground loop noise
After applying the filter:
Detailed Instructions (USB Headset, Windows 10)
- Install EqualizerAPO (Sourceforge: EqualizerAPO)
- When installing and running the first time, EqualizerAPO will ask you to choose the device that you’d like to have an Equalizer installed to in the Configurator. Choose your headset microphone from the Capture devices tab and click OK:
- Download this ZIP archive and unzip the included filter file (.txt) to a location of your choice: filter-ground-loop-noise-60Hz.zip
- Start the Configuration Editor and configure EqualizerAPO to use the filter file using the existing Include section:
That’s it! You can use the default voice recording app or do a Skype test call to check if the noise is gone, or temporarily enable “Listen to this device” in your Windows recording devices system settings.
Please leave a comment if you have any questions, something didn’t work as expected or in case you got an easier solution.
If you are interested in how and why that filter works, read on. If not, enjoy your day and talk to people!
Additional Information
The filter set strongly dampens parts of the frequency spectrum in your microphone’s recordings, more specifically only those frequencies that constitute the ground loop noise, leaving other frequencies untouched. It works best with power grids that run at 60 Hz, like basically all grids on the American continent. Filtering out only 60 Hz itself isn’t sufficient because the ground loop noise includes a lot of harmonic frequencies (or overtones) above 60 Hz, more specifically multiples of 60 Hz. Actually, 60 Hz is not an issue since most audio/video calling systems filter out frequencies that low anyway. The most annoying parts of that noise are 180 Hz and a lot of overtones between 420 Hz and 720 Hz.
The spectrum before and after the filter illustrate how dirty that noise is:
The filter removes those frequencies: 60 Hz, 120 Hz, 180 Hz, …, 780 Hz, 840 Hz. Its frequency response looks like this:
I encountered some power grids whose frequency is fluctuating a lot (+- 5 Hz) around 60 Hz so that filter isn’t perfect. Since it also removes essential parts of your voice, I tried to keep the damage low and used a set of peak filters with a very high slope.
You can easily adapt that to other frequencies, like for instance 50 Hz in Europe: filter-ground-loop-noise-50Hz
Filters for some higher overtones are disabled (commented out) because my call partners weren’t that annoyed by those sounds. It should work sufficiently well for you but if it doesn’t, play a bit with that filter set.
Thanks for reading!
Johannes Ghiletiuc 
Hi Johannes, thanks for that article, with which you pressed a button with me. Well, yes, using a multi-band notch filter is an appropriate ‘first aid’ method to dim that annoying humming noise that (mostly) unbalanced audio connections are ‘contaminated’ with. Here are a few suggestions in order to improve the resulting audio signal, although it’s not that easy to achieve that in realtime. But it’s possible.
Though, there’s a prerequisite to it in order to make it work properly, namely the fact the fundamental frequency of that noise is stable and constant. Otherwise you might get ugly comb filter effects that sound like from silly 1960’s sci-fi movies.
Anyway, the basic idea is to record an isolated sample of that humming noise, let’s say 2 seconds, whereof he humming noise must not be in superposition with any other signal. Use an audio editing software tool like Audacity to inverse the polarity of that short audio sample. Mark the polarity-inverted audio clip and make an infinite loop out of it. Now, create a 2nd audio track in Audacity and switch on its record enable mode and its input monitoring mode on. Define your headset or whatever source as an input device. If nothing goes wrong then the humming noise induced by a ground loop and the polarity-inverted clip of that humming noise should cancel each other out to zero, which should result in a clean audio signal. It must be mentioned that this method is not the best one and needs some attempts to get both signal’s phase in line, i.e. both signals – the recorded humming noise and the one that comes in via Audacity’s input monitor being switched on – must have the same initial signal phase in order to result in a total annihilation of that humming noise. Furthermore take into account that this method will definitely produce an audible latency in the signal path, but for the most of the applications this is acceptable, depending on the CPU performance of the host computer and the audio buffer settings of the audio hardware that’s in use.
And yes, before I forget this: It’s also highly recommended to use a low cut filter as well to get rid of any low frequency rumbling noise. For recording the human voice the low cut frequency can be set to something like between 80 – 150 Hz. And also keep in mind that a humming noise induced by a ground loop can consist of even and odd harmonics. Under some inconvenient circumstances it can happen that not all of these ‘spikes’ can be fully removed by applying simple notch filters. Then it needs some more sophisticated algorithms, such as you can find in Izotope’s RX audio restoration suite, which is quite pricey but ass-kicking amazing in terms of flexibility and results you can achieve with this ‘beast’. Hope that helps. If not then forget about it and keep on enjoying the beach and all the other nice things that life has to offer. 🙂
Best regards and Happy Easter,
Marcus
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Hey Marcus, thanks for your extensive answer! Actually, I started with just a low cut filter and later wanted to record the humming noise to cancel that out completely. It’s hard to get a clean recording of that humming noise, especially because it’s frequency is changing over the course of about 15 seconds (yes, the grid here is really bad). It’s a great idea anyway, I’m going to check in the next city if that humming noise is roughly the same.
Latency is not a big issue right now because the base latency for most audio calls is pretty high already but of course I’m trying to keep that as low as possible. Speaking of latency: Haha, I recognize that comb filter from old movies. I guess they found a simple way back then to do it in hardware and everybody was crazy about how “spacey” that sounds :-).
Regarding balanced connections: I’m spoiled by PA systems which feature balanced connections. That’s one issue less to worry about. Getting consumer electronics devices with balanced connections is really hard. For now, I need to stick to a simple USB headset/mic but maybe I find something. Most people got a studio (at home or at least close) when they’re really into audio recording but that doesn’t fit a backpack.
Happy Easter as well!
Johannes
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