RF interference on recordings

Advertise with us
shop deals on amazon
Shop deals on ebay
GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Herec

Herec

Member
Joined
Oct 27, 2009
Messages
18
Location
Boston
    I'm having trouble with some random RF (a local radio station) getting picked up by something in my recording chain in my apartment. I think it's worse with a particular SDC I use (a modded MXL 603), but its still there. A friend of mine who does bedroom recordings a few streets away says the area is pretty bad, and we are on top of a large hill on the edge of the city. i'm moving soon, so hopefully it won't be an issue at the new place.

My chain is just Mic -> Motu UltraLite -> firewire -> MacBook. Any tips on getting rid of the interference? I don't really want to put a simple LC low-pass on the output of the mics (with a -3db of 1MHz or something), but that's the only solution I can think of.
 
Rectification of RF occurs when circuitry is not fast enough to keep up with RF, or the RF is not effectively filtered out.

It is generally easier to filter it out than speed up you path to pass RF.

Mic input filters often use series inductors with shunt capacitors that have little effect at audio frequency but knock down the RF.

RF when large enough can even sneak into outputs and cause rectification in drivers but that is less common than for input stages.

JR
 
As JR says, it can get in on either the inputs or outputs.

MOTUs have little or no RFI proofing.  Check if you still have problems with a 'male XLR plug with 150R across p2&3' replacing your microphone.

Your microphones are susceptible too.  Some expensive famous name mikes are terrible.  Try a Schoeps mike and see if the problem goes away.  IMHO, RFI/EMI immunity is one to factors that separates truly great mikes from the toys.

It's not trivial to solve.

I pontificate on this in LNprimer.doc in my MicBuilders Yahoo Group directory.  You have to join.

Google 'Pin 1 problem'.

Some possible quick fixes ..

http://www.neutrik.com/fl/en/audio/204_1603252336/EMC-XLR_Series_productlist.aspx
http://intermark-usa.com/products/emc/emi-ferrite-emi-ferrite-cores/  You need these at both ends
 
I'm a little late but:
Jim Brown spends a great deal of time solving RFI problems.  Don't let the title of this paper fool you,  it started out as a audio system paper then he added the Ham information.

'A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing'
by Jim Brown K9YC
Audio Systems Group, Inc.
http://audiosystemsgroup.com
http://www.audiosystemsgroup.com/RFI-Ham.pdf

Other Jim Brown papers and PowerPoints:
http://www.audiosystemsgroup.com/publish.htm
 
Herec said:
    I'm having trouble with some random RF (a local radio station) getting picked up by something in my recording chain in my apartment. I think it's worse with a particular SDC I use (a modded MXL 603), but its still there. A friend of mine who does bedroom recordings a few streets away says the area is pretty bad, and we are on top of a large hill on the edge of the city. i'm moving soon, so hopefully it won't be an issue at the new place.

My chain is just Mic -> Motu UltraLite -> firewire -> MacBook. Any tips on getting rid of the interference? I don't really want to put a simple LC low-pass on the output of the mics (with a -3db of 1MHz or something), but that's the only solution I can think of.
Click to expand...
I would suggest you connect two 0.01uf ceramic caps across each leg to shield. This will low-pass the signal at about 150kHz. Can you live with that? Since you don't know for certain if it's the preamp or the mic (or both) that suffer the problem, you may have to experiment at what end to put these caps.
 

Similar threads

pucho812
Pucho's 2012 aes report
2
Replies
20
Views
7K
fazer
F
pucho812
2011 AES report. add anything I missed.
Replies
1
Views
3K
zayance
zayance
livingnote
Neumann odyssey
2 3
Replies
47
Views
10K
tv
T
W
microphone buzzing with RF interference
Replies
15
Views
13K
CJ
CJ
K
BEHRINGER MODS / UPGRADES - MY FINDINGS (T1953-Centric)
2 3
Replies
46
Views
60K
scott2000
scott2000

Latest posts

Back
Top