• Registered: 2022-06-20
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Topic: Hum with Shure SM57+Fireface UCX II

Hi,

I'm recording speech with a Shure SM57 connected to my RME Fireface UCX II. At some point I noticed there is a slight hum. It is not loud at all, but if there is silence in the recording and you turn up the volume it is noticeable. Looking at a spectrogram, the hum is around 50 Hz so I wonder whether it might just be a ground loop. I only observe the hum when recording the microphone, but not when playing back music.

I have unplugged all unneeded electronics, I have even disconnected the USB cable of the interface, I have tried with a different SM57, a different interface, and a different cable, but some hum was always audible.

Any idea why this might be the case and how to get rid of it? My understanding is that dynamic microphones always exhibit a bit of a hiss, but no hum.

Thanks!

2 Reply by waedi (edited by waedi 2023-01-19 06:30:37)

  • waedi
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Re: Hum with Shure SM57+Fireface UCX II

For the cleaning between the vocals you simply can ad a gate effect to the track in the DAW.
On the mic input phantom power is off ?
Even with a different interface ?
Do you record a noise from a fan or from a machine ?
Is your computer connected to the house electricity ? Has it 50Hz AC ?
May you try a Notebook computer with Akku ?

M1-Sequoia, Madiface Pro, Digiface USB, Babyface silver and blue
  • cyrano
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Re: Hum with Shure SM57+Fireface UCX II

Have you tried it in another location?

Just because I used to have a spot in my previous workspace where some strange interference came in from outside. Drove me nuts for months until I noticed even my DMM behaved strangely in that spot.

It was solved by moving my desk 2 meters. Later, walking around with a DMM I found another spot in the same house that had that same interference. Never really found the source, but I suspect it were the VFDs driving sewage pumps in front of the house in combination with some very old wiring.

In your case it's pure 50 Hz hum, but it could be from some transformer near cabling or interface. What's next door?

We have also had hum trouble in one of our venues, but there's a very! big! old! transformer for the tramway across the street. IIRC it's something like 500 kVA. That was solved by inserting an isolation transformer into the power feed for that venue.

Also don't forget the mic preamps are capable of >60 dB of gain. Some hum might always be present if you turn them to max. gain.

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  • Registered: 2022-06-20
  • Posts: 5

Re: Hum with Shure SM57+Fireface UCX II

Thanks a lot for your detailed answers! Please find my comments below.

On the mic input phantom power is off ?

Yes, phantom power is off.

Even with a different interface ?

Yes, and the other interface was not bus-powered, either.

Do you record a noise from a fan or from a machine ?

I don't hear any noise that the microphone might record.

Is your computer connected to the house electricity ? Has it 50Hz AC ?

I'm note sure what you mean by house electricity? The interface is just plugged into a normal power strip that's plugged into the wall socket.

May you try a Notebook computer with Akku ?

The hum already occurs when I don't connect the interface to a computer at all.

Have you tried it in another location?

Yes, I've now moved the interface and the microphone to two different rooms but the hum was still there in both cases. There are also no tram transformers outside. ;-)

Also don't forget the mic preamps are capable of >60 dB of gain. Some hum might always be present if you turn them to max. gain.

That makes sense, for the test I'm using 72 dB of gain. Maybe given the high gain, it is normal to have such a kind of hum?

I'm wondering whether a power conditioner might help in this case?

5 Reply by waedi (edited by waedi 2023-01-23 23:37:26)

  • waedi
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Re: Hum with Shure SM57+Fireface UCX II

With 72 gain you will have a lot of noise when nothing is connected to the preamp, but with a mic connected that noise should be very low.
Can you use Digicheck to measure the noise (hum) ?
I would not spend money for a power conditioner, the power supply from RME is already a power conditioner, serves the unit with proper DC.

M1-Sequoia, Madiface Pro, Digiface USB, Babyface silver and blue

6 Reply by estragon (edited by estragon 2023-01-26 23:07:24)

  • Registered: 2022-06-20
  • Posts: 5

Re: Hum with Shure SM57+Fireface UCX II

I would not spend money for a power conditioner, the power supply from RME is already a power conditioner, serves the unit with proper DC.

This is really helpful, thank you!

With 72 gain you will have a lot of noise when nothing is connected to the preamp, but with a mic connected that noise should be very low.
Can you use Digicheck to measure the noise (hum) ?

That's a good idea. I've made a screenshot when nothing is connected to the preamp: digicheck_no_mic.png, and another one when the mic is connected: digicheck.png.

There is indeed more noise when nothing is connected. But with the microphone connected, there is a clear peak at 50 Hz, as well as two other peaks at 25 Hz and 150 Hz, which seem to correspond to the hum.

What might cause the hum to occur when the mic is connected?