Sudden hum in my Mic channel

I’m hours away from recording my first interviews for a new podcast. I tested my set up by recording a conversation with a friend via Skype and all went well.

Today I suddenly have a loud constant hum in my Mic channel. I’ve done all I know to isolate it but it’s still there. Here is the setup…

I’m running a mix-minus setup. 2013 Mac Book Pro, MXL V63M mic into a Behringer Xenyx 1002FX mixer. I’m using the aux feed (FX Feed) back into a a Griffin iMic and then coming out of the mixer thru the main out into a Tascam DR05 audio recorder. Everything works wonderfully except for this sudden constant hum.

To troubleshoot, I turned off my AC, hum still there. I have disconnected everything but the mic from the mixer and the hum is there. I’ve plugged the mic into the other XLR input, hum is still there. I’ve changed mic cables, hum is still there. I’ve plugged the mixer into a different outlet/power circuit in the room, hum is still there. I’ve shut down the computer, hum is still there. The only other mic I have (besides the computer’s on-board mic) is a USB mic (Rode Podcaster) but I don’t have the cabling or adapters to route it into my mixer.

I’m at a loss what to do - I can’t really afford to go out and buy another mic just to troubleshoot this one. I have the mic mounted to my desktop with a collapsible boom. I do note that when I touch the boom, the volume of the hum increases some, if I touch the base of the mic’s shock mount the hum doubles or even triples in volume in my Bose headphones.

Here’s a shocker - as I’m writing this, I reached out and wrapped my hands around the top (condenser/windscreen) of the mic and the hum is virtually gone. Now it is a higher pitched hum that sounds almost like a fan, possibly the same harmonic but with far less roar. This is much better than just before - well, it’s the lesser of evils, and at this level might be virtually eliminated by Noise Reduction in Audacity - but I don’t have a clue what’s going on and I worry the loud hum might pop up again at any time, like right in the middle of an interview.

Any ideas? Could it be the mic… It’s been sitting unused for a year or more but I don’t recall having this issue when I used it before.

Oops - curiouser and curiouser - I found the fan noise - it was a fan. My MBP sits on an angled riser that has a fan in it runing to keep the computer cool. I shut that down and voila, all quiet. But, I moved the mic back in front of me and again a bit of hum, by moving it around a bit in its shock mount I got the hum to go away, for now. Do I possibly have a bad XLR connector or something else wrong with the mic???

Help please!

Grounds. Has to be grounds. Are you in the US? Does it sound like this?

I guess in the UK it would just be lower pitch.

If you can touch things or wave your hands around and the hum comes and goes you have lost a protective shield or ground connections somewhere.

The Desperation Method is wiggle and/or unplug everything and plug it back in firmly several times. It helps if you’re sweating as you do this. Cursing optional. Start with the microphone and work back toward the computer. The digital links may get confused if you start replugging them, so if you get that far, you should shut down.

I would have to play your system description several times to build your system in my head. The last time I had a live performance and found a bad cable, I changed out three cables before I found the problem and fixed it — all in about four seconds. I attribute my success entirely to my military experience with naughty words.


Griffin iMic

My old amigo.

I’m not a fan of the Griffin iMic. The one I had was such a bad performer I put it in a box in the garage. It may still be there. The box, not the garage. They keep insisting you can easily switch between Microphone and Line-Level. Mine would do both jobs equally badly. The phrase: “This thing is terrible,” kept falling from my lips.

Wiggle the connections around the iMic.