This is a bit of a puzzler for me - Noise coming in on unbal

[alexdingley]

Hey all...

So I've got a lovely home studio space here in the suburbs of Philly and I'm close to public transportation.... REALLY close to public transportation. Outside my apartment window, and about 15 feet away, stand the electric overhead lines for our regional rail system (SEPTA Trains) in the Philadelphia area.

I think this noise might be new... but for several months now I've been noticing a strange high-frequency noise bleeding into my unbalanced audio lines in the studio. So, it's just effecting my guitars... everything else is balanced.

This noise comes in seemingly random bursts, for different lengths of time... they don't seem to line up on either side of when a train is coming by... and they might happen during a train passing or not. What's really interesting is that none of my -10 equipment (record player, home theater) seem to be effected by the noise. it just seems to show up on the guitars that I plug into my amp, and when I plug my acoustic into a DI box and directly into the console. I also did notice this sound showing up on the 1/8th inch unbalanced line coming out of my mac into the console...

So, my microphones aren't getting any of it on their lines, none of my balanced signal sends/returns to or from the console to my converters... no signal in my monitor lines... nothing in my effects sends or returns... just the unbalanced guitar level gear seems to get it... and my computer output.

and recently I heard this same sound momentarily show up on the overhead announce system on a train in a different line of our transit system. it burst in while the announcer was talking... and he didn't know what it was either. I asked and he said it's been around as long as he... (which was only 3 months for him)

here's a sample. it's not supremely loud, but it is ugly sounding.

SEPTA has already gotten back to me to talk about the issue, and they are going to listen to my audio clip and see if they can figure out the source... but I thought I'd throw this to you folks since there tend to be smart, experienced minds on these boards.

[goose134]

Are these electric trains? What kind of power are they using? In Chicago, the L system runs on 600 volt DC lines. EMF is generally not a problem because unlike AC current, the EMF fields tend to be smaller. I'm sure it's not a coincidence. Short term, I'd try to buy one cable of the best shielding you can afford and try it.

[alexdingley]

goose...

solid question, and yes they're electric trains... I will be in contact with our train system's tech team as soon as they write back from the email I sent today. I hope they can give me a clue about the sound once they hear it.