Electrical Interference Diagnosis

S

SteveGlen

New member
Hi HomeRecording.com Forum Readers,

I have an issue with my recording space and I hope you can hep me diagnose the problem, and maybe even suggest some solutions.

The problem is that I am picking up hum or a "buzz" into my system. The sound is not audible to ears, only through the recording equipment, which has me assuming that this is electrical interference. Overall, the sound is variable, so some days it's unnoticeable, but one occasion has ruined a day's take. During troubleshooting, the sound is louder when the microphone is nearer to "the source", or orientated in certain directions.

The source is the ceiling in the basement. There are pot lights installed which shouldn't be on any dimmer switches (the wall only has I/O switch), and when the lights are off, the sound persists. We've also been able to recreate the problem from the floor above by putting the microphone closer to the floor.

The sE v7 picks up the hum louder than the AT-2040. I wonder if it's a shielding issue or a difference in their output impedence.


Equipment chain:
sE v7 or Audio-Technica-2040 or Rode NTG-2
6ft XLR cable (I'm 90% sure shielded)
Rodecaster Pro mki
Recording media (micro SD card) or Monitoring headphones

I've attached a short recording of the buzz the variation in the amplitude of the buzz is me moving the microphone around (if the position is static, the sound is consistent). Treatment on the recording is 4:1 compression and gain increase.

What do I need to do? Do I need to get an electrician and find the source? Can I make a makeshift barrier with coil springs from an old mattress and several rolls of aluminum foil?

Thank you,
Steve
 

Attachments

  • Troublshooting Buzz v1.mp3
    2 MB
SteveGlen said:
Hi HomeRecording.com Forum Readers,

I have an issue with my recording space and I hope you can hep me diagnose the problem, and maybe even suggest some solutions.

The problem is that I am picking up hum or a "buzz" into my system. The sound is not audible to ears, only through the recording equipment, which has me assuming that this is electrical interference. Overall, the sound is variable, so some days it's unnoticeable, but one occasion has ruined a day's take. During troubleshooting, the sound is louder when the microphone is nearer to "the source", or orientated in certain directions.

The source is the ceiling in the basement. There are pot lights installed which shouldn't be on any dimmer switches (the wall only has I/O switch), and when the lights are off, the sound persists. We've also been able to recreate the problem from the floor above by putting the microphone closer to the floor.

The sE v7 picks up the hum louder than the AT-2040. I wonder if it's a shielding issue or a difference in their output impedence.


Equipment chain:
sE v7 or Audio-Technica-2040 or Rode NTG-2
6ft XLR cable (I'm 90% sure shielded)
Rodecaster Pro mki
Recording media (micro SD card) or Monitoring headphones

I've attached a short recording of the buzz the variation in the amplitude of the buzz is me moving the microphone around (if the position is static, the sound is consistent). Treatment on the recording is 4:1 compression and gain increase.

What do I need to do? Do I need to get an electrician and find the source? Can I make a makeshift barrier with coil springs from an old mattress and several rolls of aluminum foil?

Thank you,
Steve
Click to expand...
First thing I would ask you is if the basement is carpeted. Because concrete floors make that sound when cable connections are touching them. Also, the mic stand can do this if the pole in the center is touching the concrete floor.
As far as electricity, I would get a nicer power supply. I would normally suggest a bench power supply but now these days I would suggest something like a battery pack so you can record anywhere. Like this one: https://a.co/d/bzY1txE .
 
Troubleshooting 101 is a process of eliminating causes.

Start by setting up the Rodecaster as stand alone with nothing but the power supply and a microphone connected. If you still have noise, swap the mic cable. Still have noise, it's either the Rodecaster or outside electrical noise.

Something electrical could be dimmers, cheap LED fixtures and so forth. If able, you can turn off electrical panel breakers one at a time to see if something on a particular circuit is causing the issue. If so, then it is a matter of figuring out what on that circuit is the noise maker.
 
I'd guess that's switch mode power supply, but it is NOT locked to the AC mains frequency, which is a bit odd. Looking at the 0-1K area, you can easily see the harmonics stacking up, but at 42.5Hz and then 85 etc. As Folkcafe says, next step is to isolate which AC circuit, then locate the dodgy device, or devices. It's possible it's some kind of dimmer system that has long feed lines - and if the ceiling is rebar dense concrete the steelwork could be working a bit like a Faraday shield, but in reverse, actually enabling the interference to propagate through the entire structure? I've never heard this as distinct as what you've captured. If your mic is so good at capturing it, it would be a good tool to track down the offending device. Good luck - it is not going to be an easy one.
 
Thanks drtechno, Folkcafe, and rob! This was helpful. After performing more troubleshooting, including powering the Rodecaster from a battery pack, I decided the best way to maintain our recording schedule was to use different microphones. I rented a 2 mics to try, a condenser and the SM7b, neither had any interference issues.
 
This has become a very useful topic - you tried all sorts with the Rodecaster, but the conclusion was that it was the mic - which none of use really expected it to be. Great you fixed it.
 
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