Microphone hum when plugged into interface


I have 2 brand new Lewitt 550 LCT microphones plugged into the RME Fireface UC audio interface using XLR cables. The interface is plugged into a MacBook via USB cable. There is a constant humming sound in both playback and during recording. I've tried the following tests:

  • I plugged in 2 Neumann mics into the interface with no humming issues on any laptop.
  • When I plug the Lewitt mics into a Zoom handheld recorder there is no hum.
  • When I touch the Lewitt mics while plugged into the interface, the hum quiets down slightly.
  • I've tried using the Lewitt mics and the interface with the following laptops: 2 Lenovos (it produces no hum), 2 ASUS (it produces hum), and the MacBook (it produces hum).

Here is a short clip of the humming sound: http://vocaroo.com/i/s0FPE1nDasAJ

EDIT: The above clip is when the MacBook is on battery power. When the MacBook is plugged into the wall, the hum is greatly reduced but it is still there.

I would greatly appreciate any tips that will help me get back to recording. Thank you very much.


Posted 2017-03-26T08:26:34.120

Reputation: 11

You used the same cables for the Neumanns, eliminating the cable as the cause? Does it do the same whether the Mac is on battery or mains power? – Tetsujin – 2017-03-26T11:09:52.153

I did use the same cables for both the Neumanns and the Lewitts. The humming is really loud when the Mac is on battery power. When I plug in the Mac the humming is greatly reduced, but it's still there if you listen closely. Thank you for any help! – Aelin – 2017-03-26T11:36:50.343

I found out that when I plug the interface directly into the wall and plug the laptop into a power strip that's also plugged into the wall but turned off, there is no hum... so long as the strip stays off... – Aelin – 2017-03-28T14:11:31.790

1Earthing issue then, by the sound of it – Tetsujin – 2017-03-28T14:49:06.233

No answers