Capturing EM interference with a microphone

jh · 2005-11-04T06:58:05+00:00

Hi,I was hoping somebody here might be able to help me with a question. First, some background. A couple of months ago I was trying to record the sounds of the insides of my computer for an experimental sound project. I first tried it with a cheap, crappy lapel mic that came with a pocket voice recorder. It worked just fine. Then I borrowed a fairly nice, high quality microphone and tried it again. Sure enough, this microphone picked up a lot more sounds... in fact, it recorded all sorts of beeps, buzzes, and hums that weren't even there, apparently some sort of electromagnetic interference. I was amused to find that this high-quality microphone was much more prone to picking up this interference than the cheap one I tried earlier.The thing is, the interference sounds were much more interesting than the real sounds. Holding the microphone near the graphics card, it recorded different noises depending on what was being displayed on screen. The fans sounded like something out of a science fiction movie. My personal favorite sound came from the power cord while the computer was asleep: it made a bizarre sequence of changing pitches that repeated every couple of seconds.The only problem is, all of these great interference-caused phantom sounds were almost drowned out by the actual normal sound produced by the fans, hard drive, etc. in the computer. Needless to say, the microphone was quite adept at recording these sounds.So my question is this: is it possible to build a device, or modify a microphone, so that it picks up ONLY the electromagnetic interference, but no actual sound?Thanks,Joshp.s.: I hope people don't mind that I'm not including my real email address. It's probably bad etiquette, but I'm kinda paranoid about spam.

Nov 04, 2005 20 Replies

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Marc Noon 20 years ago

Here's a good link.

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Also try and put a radio real close to your computer and see if it slows down any processes. Start at 100Mhz transmitters and work up.

I guess the experiment would be like a counter for 10 second... see if it counts the same number after 10 seconds has elapsed. Then try to scale the distances.

Marc

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