Troubleshooting Radio Interference

Any hints or tips on how to get rid of radio interference when recording something, specifically via the line-in port on an iMac?

Seriously, I'm getting some sort of talk radio station faintly in the background when I record things. Faintly, until I use any kind of compression, then it's like listening to air traffic control. It's come and gone in the past (unless it was always there and I only started noticing it), but seems to be here to stay for the time being. It's also been consistent despite living in two different apartments. It's also consistent despite the cord or instrument. The instrument doesn't even need to be plugged in! Any plug, even size converters alone with no cord attached, once inserted into the jack, attracts interference. Without an input, there is no line-in signal.

posted by not_on_display (3 comments total)

It's not uncommon for cables, even very short ones, to act as antennas - the fact that you're getting noticeable interference even with a tiny adapter suggests that whatever station you're picking up is putting out a really strong signal into your place.

Idea 1 would be to make sure the outlets you're plugging your power into are grounded, and that you're not using one of those "3-to-2 ground adapters". If you're not properly connected to electrical ground, you could be reducing the efficiency of whatever EM shielding is in the Mac, if there is any.

Idea 2 would be to physically move the computer - a pain in the ass, probably, but radio waves are at such high frequencies (and therefore short wavelengths), that just putting your computer in a different place could take it out of the exact positioning needed to pick up the radio signal.

Idea 3 would be to clamp an "RF choke" (also known as "ferrite bead" or "ferrite choke") around your input or instrument cables, maybe also around your Mac's power cable and the power cables of any audio interfaces you're using, if they don't already have one. Link to an example from Radio Shack. Wikipedia article. Might take a little trial-and-error for how many and where on the cable to put them, but usually one anywhere on the audio cable does the trick.

Idea 4 would be to start getting kinda weird and diving into shielding your computer and/or components and cables inside. But that would be a last-resort kind of thing if nothing else works.
posted by soundguy99 at 8:23 AM on April 26, 2016 [1 favorite]

Since you hear it even when its just an adapter plugged in, I doubt the interference is actually coming from the input port (when nothing is plugged in to the port the input is disabled so you wouldnt hear anything at all). So adding a filter or choke at the port likely wont help.

Unfortunately its probably the front end amplifier that is demodulating the signal. If so, its unlikely to be something that you can easily fix. It Doesnt hurt to try some of the shielding ideas above but I wouldnt get your hopes up.

The good news that decent DAW interfaces are pretty affordable. I have this one and have been pretty happy with it.
posted by jpdoane at 7:44 PM on April 27, 2016

Thanks! Out of all the ideas, moving the computer around actually sounds like the best plan for me now, just in case it's just too close to routers or lines in the wall, etc. I'm also a cheep bastahd.
posted by not_on_display at 6:34 PM on April 30, 2016