Electrical hum?

Question

The Issue Getting a hum in audio recording (ACX) When I move the mic around in the room it gets stronger or weaker in certain areas (where I know a power cable runs to a plug or through the wall) I can hear it when monitoring and when listening to the recording but only after doing the amplification for ACX

Equipment Behringer Xm8500 mic Scarlet solo 3rd gen interface Asus ROG laptop hooked to 2 hdmi monitors (3 total including laptop monitor)

The Room My studio is built in the basement its 5.5ft X 9ft its sound treated but not professionally, I record mostly in evenings so outside noise isn't an issue

I have set myself up in a way where if my mic is in a certain spot I can record and I don't have the electrical hum, however its not the most comfortable for long recordings. Also in doing this and getting rid of the steady hum, I have somehow now gotten a slight whine, I only notice it here and there. I want to think it is maybe the way I moved the cording around.

I have tried a electric conditioner, it didn't do anything. would the steady hum be RMI/EMI? would copper meshing on the walls help filter that and prevent it?

I can't change rooms, its where I have to live with. and I can't take wires out of the walls either so ya.. I also have a deadline on a book and ya its stressing me out.

Answer 1

There are two ways to tackle this - the proper way & the easy way.

The proper way is to identify & isolate your source of interference. 'Hum' is going to be something at mains frequency. You're going to have to chase round the room seeing where it's loudest, whether rotating any piece of equipment 90° changes the pickup.
It might be a wire in a wall, but it could also be a display, or a light, or a computer, or just a bad cable…

Once isolated, then you can either try building Faraday cages around the affected parts, or see if correct earthing/grounding has any effect.
This is a faff, to say the least, and may not be entirely succesful.

While your spending time & effort [both physical & mental] on this, your job isn't getting done… so method two

The easy way.
This comes in two flavours.

1. de-noising software like Izotope's RX De-hum module. Buy once, run everything through it 'forever'.

2. Adobe's [still free for limited use, with paid options] Podcast Enhance AI.
   Throw a finished file at it, marvel at the result.

Answer 2

When using a dynamic mic, switch off phantom power. It is not supposed to do anything with modern microphones, but the generation of the phantom power can produce noise.

Instead of trying different locations in the room, you can try different orientations of the microphone.

Make sure you have a good balanced XLR cable and use XLR from microphone to soundcard, without any adapters.

It's also worth checking whether you have 100 Hz hum or 50 Hz hum: the former means something in/near your room is humming mechanically, the latter means you have a magnetic field picked up somewhere (change to 120/60 Hz in U.S. and its similarly frequented electric cousins).

The microphone may pick up magnetic fields. The only way to shield that is with a cage/hull of mu-metal around the microphone, and that's sort of impractical.

Answer 3

The Behringer Xm8500 is a dynamic mic (basically a speaker working in reverse) and has a coil of wire internally. From what you describe, it sounds like this coil is picking up the magnetic field produced by the wiring in the walls and generating hum. Try using a mic that isn't dynamic like a pure condenser or electret condenser mic and see if the hum goes away. If not, as Tetsujin says, there could be quite a bit of work ahead getting to the root cause.

I was a little lazy/sloppy with my reference to "wiring in the walls" and wanted to add more information. I fully agree that properly installed wiring has very little chance of creating a magnetic field of any consequence, but improper wiring (among other things) certainly can. From your description of the problem it occurs only near the wall and nowhere else, and this suggests that one of the possible causes is a magnetic field in that area. You mention that there is a garage on the other side of the wall. Check to see what's there. Maybe an electrical panel, a piece of equipment with a power transformer, even a water pipe can cause problems if it's carrying stray current. Hope you have some luck.