Re: advice: electromagnetic induction and hum

[Peter Lennox <P.Lennox@xxxxxxxxxxx>]

You could just check that the lead actually is properly balanced - it's
not uncommon for them to have been altered. SM58s are normally quite
robust in terms of hum rejection - the mic's not damaged, is it?

Dr. Peter Lennox
S.P.A.R.G.
Signal Processing Applications Research Group
University of Derby
http://sparg.derby.ac.uk  
Int. tel: 1775

>>> Eldad Tsabary <tazberry_docs@xxxxxxxx> 15/06/2006 14:59 >>>
Hi list,

I ran into a Hum problem in my home studio being picked up by my SM58
mic.

The mic is connected (balanced) to a USB M-Audio (Fast Track Pro) and a
very
audible hum is generated (and also transferred to the recording... not
only
on the monitoring part).  I shut everything off including the monitors
and
used headphones to limit the possibilities.
 
Disconnecting the mic from the cable while keeping the input and output
at
max kills the hum, so it is not picked up by the cable it's definitely
from
the mic.

I tried this mic and cable somewhere else and they work fine.

Moving the mic around the room the hum level changes and I finally
discovered that the strongest spot is a line running in the ceiling -
I
could imagine a cable's position just by following the hum line with
the
mic.  

My conclusion at that is that there's some kind of strong
electromagnetic
induction being generated by a single cable; however it is pretty
strong,
the hum is picked up by the mic in the entire studio room and outside
as
well.

Any ideas of how to get rid of it? (short of moving my studio
somewhere
else).  

Also, I tried my condenser mic with my minidisk and it has no problem
with
this induction; do condenser mics less prone to picking up
electromagnetic
induction (since they work on the electrostatic principle?) 

Best

Eldad
www.yaeldad.com 


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