advice: electromagnetic induction and hum

[Eldad Tsabary <tazberry_docs@xxxxxxxx>]

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