Noisy mics

[Jen12345678]

I’m having ongoing issues with static and interference noise when using any microphone in my shed studio — except for my Soyuz, which is completely silent. It seems like it might be an electrical or interference-related issue, but I haven’t been able to pinpoint it.

Here’s what I’ve tried so far:
Power conditioner
Multiple audio interfaces
Different mics (both with and without their own power supplies)
Various XLR leads and power supplies
Changing inputs, checking gain levels, adjusting mic placement
Ferrite beads on cables
DI boxes (when testing with guitar)
Running power from the house directly via an extension cable (no improvement)

Some mics seem more sensitive than others, and a couple have exhibited clicking noises, which may or may not be related to the interference.

My Soyuz mics are the only ones that remain clean and silent, which makes me wonder if they're better shielded or transformer-isolated, and simply less susceptible to whatever is going on?

I also read about potential sample rate mismatches between the interface and DAW causing noise — but wouldn’t that affect the Soyuz as well?

My laptop fan does emit a bit of noise, but I’ve tested with it positioned elsewhere, and the interference issue persists regardless.

Is this sounding like a grounding issue? Any suggestions on what else I could try would be hugely appreciated.

Thanks in advance!

[Wonks]

Yes, sounds just like a lack of a solid ground in your system. Laptops rarely have a mains ground/earth connection from their PSU, so you need something in your recording chain that does.

You don't say which Soyuz mics you have, but if they are valve/tube mics, you are giving the recording system a good ground/earth via the power supply.

If this is the case and you can spare an input, you could keep the Soyuz power supply permanently connected. It won't need to be switched on or the Soyuz mic plugged in. But the mains ground will be carried through the XLR cable screen and provide the system with a solid ground path.

You should then find that your other mics perform as they should.

[Jen12345678]

Thanks, this sounds like it could be a reality 'Laptops rarely have a mains ground/earth connection from their PSU, so you need something in your recording chain that does'.

The mics that are silent are the Soyuz 013 FET (phantom powered). The mics with their own power supplies have the biggest issues with noise e.g. Rode K2. But also some of the phantom powered ones; NT5's. Sontronics ARIA was the same. I think the SM57's were actually ok.

If I was recording 4 mics, 2 Soyuz and 2 rodes (or whatever) the 2 Soyuz were fine and the 2 others were bad.......

[Hugh Robjohns]

There are lots of possibilities for the differences between mics, largely depending on the mics' physical and electrical constructions.

But I would suggest the very first thing to do is ensure your interface (and thus the computer) has a solid ground connection to the mains safety earth.

That alone often cures all manner of weird noises and interferences.

With that in place you'll be in a better position to track down whether the problem is related to external interference or something else.

[Jen12345678]

Great thank you. What does this actually mean? Both the MacBook Pro and the Apollo X4 are currently plugged directly into the wall. My brother is an electrician and he came out and said there was no problem but I don't know if he's right of course. I've just bought this: Kewtech KEWCHECK103 from amazon as I think this might be what is being suggested? Thanks

[Wonks]

Both the laptop and the Apollo X4 are powered from external PSUs. Yes, the PSUs are plugged into the wall, but certainly the Apollo (and it's highly probable that the MacBook) won't connect the DC 0v rail from them directly to ground. Sometimes on Macs there is a high resistance connection to ground through a resistor within the PSU, but whilst this stops the 0V from floating too far away from the ground reference, it's too high a resistance for dumping noise through.

Without a connection to ground, the '0v' reference voltage floats. It's perfectly safe in the context of using the system without risk of shock, but it's not great for audio applications where you need a good ground/earth.

So there is a very high probability that neither the Apollo or the MacBook have a a proper ground reference.

So you are then reliant on something else in your system having a good ground connection.

I won't say it's true in every case, but the power supplies for valve mics that have an IEC mains connection will certainly earth the casing, and this is probably carried through to the input and output screen connections. Though there may be a ground lift switch on the output side back to the interface as this could cause a ground loop if you are using a desktop or tower computer which will already have a solid ground reference. So if you have a valve power supply with a ground lift switch, make sure that it's not in the lift position.

If that's connected, then the other mics should behave themselves.

Otherwise you need to work out a way of connecting the system 0v to ground/earth.

You can modify something like this (other makes are available) with the snap-on connector removed and the end of the wire soldered to the sleeve or a TS or TRS jack (nothing else connected) or pin 1 on an XLR connector and pushed into an unused input or output on the Apollo.

https://www.amazon.co.uk/Durable-Ground ... r=8-6&th=1

[Hugh Robjohns]

If you brother is a trained electrician then I'm sure he's right about the presence of the safety earth in the shed.

The issue is getting that ground to the computer/interface so that it can play its role effectively in providing interference shielding.

Wonks has suggested some ways of doing that by connecting other grounded equipment to the interface. An alternative is a pukka grounding connection like the one I described here:

https://www.soundonsound.com/reviews/gr ... ction-plug

... or Wonk's version which is probably a much better price! Either way, there's a little bit of DIY modification to do, though

The often confusing issue with grounding is that you can get unwanted noises both when you have too many ground connections (as in ground-loops) and when you don't have any (as in the situation with laptops and double-insulated power units).

[Sam Spoons]

I have a couple of MacBooks, 2011 and 2020 and in both cases the PSU adapter plug (UK spec) has a metal earth pin but is OC to earth. Using the extension lead instead of the adapter gives a high resistance path to earth (~1kΩ) but as Wonky and Hugh say, that's not adequate as an audio system earth.

[Jen12345678]

Ok I think I'll pass this info. to my brother, DIY and me don't really go together, but this is great info. I should note, just incase it's helpful that the worst offender is the Rode K2 when plugged into the Apollo, it has it's own power supply and the noise is bad with/without the ground/lift moved. All the mics with their own power supply are worse but def. some of the phantom power mics do have a lesser issue but an issue. Thanks for the info!

[Hugh Robjohns]

A sample of the unwanted noise might help to identify the problem.

[Jen12345678]

Yes great idea, I'm home next week so will upload, thank you