what the hell is this noise

[solarbird]

Let’s play everybody’s favourite new game, “what the hell is this noise?”!

It’s captured on a live mic in a quiet recording studio; the sound is not audible in the room itself. I’m really curious if it sounds familiar to anyone, and reminds them of anything other than ground loop:

https://dl.dropboxusercontent.com/s/bxrisd4be9kk70y/what-is-it-noise.mp3

This was picked up on AKG200 microphones, across multiple mics (All AKG200s) and cables, so it’s not am individual microphone or cable problem.

It starts at about 450hz and goes all the way through the floor. There’s something to amplify throughout that signal range. I put a sweep equaliser and found tones to boost throughout that range. Nothing above that, though.

I realise it sounds like a ground loop, but it’s not; I chased the 60hz question for a while, but it’s far wider than that. I have a workaround that reduces it to inaudibility that involves changing nothing connected to any of the equipment – at least, as long as I’m recording other people. That would not be true for a ground loop.

I posted about this a couple of places last night; the link goes to the Facebook link that got a bunch of comments.

Also, if I change out the mic to an Octava 012, it goes away. Also, a Shure SM57. No cable change fixes any part of it.

Whatcha got?

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Comments

[oh6]

Link's slightly busted - there's a stray <br /> hanging off the end. With that taken off, I could download it, and... well, just sounds like PA hum to me, sorry! Hope someone else can help with your mystery.

[solarbird]

Thanks, WordPress to Dreamwidth HTML conversion kind of pooched it. Fixed now.

[mdlbear]

You mention on the facebook page that it goes away when you ground yourself. This, combined with the fact that it only happens with the AKG 200's, suggests that the mics are inadequately shielded. When capacitively coupled to a large non-grounded conductor, their ability to pick up noise is greatly enhanced.

I'm wondering whether the shell of the mic is adequately grounded. A bit of fine sandpaper in the right place might do it.

[solarbird]

It doesn't go away. It goes to inaudible when I'm adequately far away - like, across the room. The recording you're hearing there is with me grounded, but close to it. Close enough that I couldn't record myself. Record someone else, yes; me, no.

Ungrounded, I can't even be on the same floor. Other people can, though. This is why I'm downplaying that part, but I have witnesses, so.