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FDP Forum / Home Recording Forum / RFI in my recording--solved!

tiller2
Contributing Member
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Washington DC

Dec 7th, 2017 06:47 AM   Edit   Profile   Print Topic   Search Topic

I've often complained about unwanted radio signals that are picked up by my amps and especially my condenser mics and get added to my recordings. My attic studio within a couple of blocks of radio stations and transmission towers seems to be prone to this issue.

Working intensively on an album project, I recently was able to improve things by swinging the boom of my mic stand around to find the position where the RFI is quietest.

Then yesterday, I made another discovery: When I attach my pop filter--a Stedman Proscreen XL--to the stand of my condenser mic and adjust it so the metal screen is precisely 3 inches from the face of the mic, practically all the RFI signals disappear. If I move the screen closer or farther, or remove the gadget, the signals are back.

This is a real breakthrough for me in home recording, so I wanted to pass it along. Can anyone provide a scientific explanation?


thumbpicker
Contributing Member
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St. Louis

"Thumbpicks don't slide into soundholes"
Dec 7th, 2017 09:00 AM   Edit   Profile   Print Topic   Search Topic

I was playing in a bar one night and had a dodgy mic cable. We were on break and two truckers were talking about something and the whole conversation on their CB radios was being simulcasted over the PA. In government test facilities they used to line the entire building with a copper mesh material to keep radio signals in or out so no one could monitor test data etc. . I would imagine your situation is similar.

gdw3

LA-la-land, CA

Insert clever comment here
Dec 7th, 2017 04:49 PM   Edit   Profile   Print Topic   Search Topic

That's a new one on me!

I've definitely had CB radios cut thru during a gig multiple times. Always very disconcerting, but not a whole lot you can do about it!

thumbpicker
Contributing Member
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St. Louis

"Thumbpicks don't slide into soundholes"
Dec 8th, 2017 09:55 AM   Edit   Profile   Print Topic   Search Topic

I did forget to mention that the it was a small town and let's just put it this way..... they were speaking pretty plainly about another guys wife and the guy and his wife were in the bar were in the bar.
Funny but not funny.

Te 52

Laws of Physics

strictly enforced
Dec 8th, 2017 10:55 AM   Edit   Profile   Print Topic   Search Topic

Sounds like your metal screen pop filter is acting as a partial Faraday cage around the mic. A Faraday cage can be a mesh or have holes in it as long as the width of the holes is no larger than around 1/10 of the wavelength of the interfering radiation.

tiller2
Contributing Member
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Washington DC

Dec 8th, 2017 01:33 PM   Edit   Profile   Print Topic   Search Topic

"pop filter is acting as a partial Faraday cage"

Yes, I think so, Te 52. The filter is sturdy and the mesh is pretty fine.

Peegoo
Contributing Member
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Close

but no guitar
Dec 13th, 2017 01:43 PM   Edit   Profile   Print Topic   Search Topic

Either the Faraday effect--or changing the relationship of (distance between) the pop filter and mic is akin to tuning an antenna.

RF works in strange ways.

Roly
Contributing Member
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Whitehorse Canada

I don't get out much
Dec 14th, 2017 01:42 AM   Edit   Profile   Print Topic   Search Topic

My understanding of a Faraday cage is....it (the cage) does nothing unless it is connected to the chassis of the audio gear.

Why, in your situation, proximity makes a difference is interesting.

"I recently was able to improve things by swinging the boom of my mic stand around to find the position where the RFI is quietest."
Seems a lot like what one would encounter with a single coil guitar pickup.
Are all your cables balanced?...Have you tested them to ensure they are balanced?

Ohm out the pop screen to chassis with mic connected, and report back.
cheers



Cal-Woody

USA/California

Why do I keep fixing things that work?
Jan 29th, 2018 03:06 PM   Edit   Profile   Print Topic   Search Topic

Because the pop filter is usually attached with a plastic clip, run a grounding strap from the metal bracket to the mic stand.
Maybe this will help to create a ground and bleed off the signal.
Just a guess but what the heck....

FDP Forum / Home Recording Forum / RFI in my recording--solved!




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