Unwanted noise (again - sorry)

[Gronow]

Hi everybody, apologies as this has been covered to death and thank you to Hugh Robjohns and Martin Walker for all they have written but I've still got an annoying noise (electrical crackle / old modem noise) and I can't get rid of it I must be missing something.
Inta audio music PC, Focusrite Scarlett 2i4 interface, two Tascam VLX5 monitors ie not a complicated setup).
The monitors and PC are plugged into one extension.
ART isolator at either end makes things worse.
Cutting the screen at the monitor end doesn't help.
I've swapped every cable one by one.
The monitors are silent when no audio cables are connected.
The noise goes away completely when I unplug the USB cable from the interface.
The noise isn't present in headphgones plugged into th einterface.
If I draw this, then there is an obvious loop from PC earth to interface to monitor to monitor earth but attempting to break this by cutting the shield doesn't break the loop and fix the noise (makes me think it's not an earth loop).
This has followed me round three house moves, at least three PCs and at least three interfaces and the only common component is the monitors.
In the past I've used a cheap Behringer DI20 between the interface and the monitors with ground lifted but this introduces loads of hiss.
The system is acceptably quiet, although the noise is still present, if I use my PA speakers instead (Evolution RZ12A V3 ie not expensive speakers).
I am completely out of ideas and if someone has any suggestions, I'd love to hear them:)

[Murray B]

Are you using TRS cables between the interface and the monitors?

[Gronow]

Hi thanks for your reply, yes I am although switching to TS cables doesn't make much difference.

[Hugh Robjohns]

If the DI box fixes the unwanted noises, then the ART isolator should too, and without the hiss.

So there's some critical detail here that you've left out of your description.

Which ART boxes are you using? How — exactly — are the various units wired together? Where are you placing the ART boxes? What else is connected to what?

[Sam Spoons]

If you've swapped every component (cables, computer, interface, house, even the speakers, for the PA cabs) then the noise must be caused by something else*. Does it happen with nothing plugged into the interface or only with a guitar/keyboard/mic plugged in. Is it always the same instrument/mic?

The next step is to work out what else you have around your studio space, microwave oven, mobile phone, central heating controller, fridge, WHY?

Then is it there on headphones? with the monitors connected or disconnected, switched off etc.?

Then try to borrow some different monitors (local music shop may help if they have something used) or hire some for a few days.

* Are you sure you haven't forgotten anything, an old HDD that has you old projects on that you've transferred from PC to PC or something else like that?

[Gronow]

Thank you for taking the trouble to reply.
If I put the ART DTI at the interface or the monitor end of the cable, the noise gets worse (lots). If I connect the interface to the DI20 using TS 1/4" patch cables then the DI20 to the monitors using TRS to XLR balanced cables, the noise reduces significantly and when I use the ground lift switch on the DI20, the noise disappears. I've just done this and I'm not getting the hiss I got earlier today so I'm dismissing the hiss part. This is a solution I've used for years but I don't like my audio going through a cheapo Behringer DI box as I've no idea what it does to the audio. The DI box behaviour makes sense to me in terms of ground loops but the ART DTI part is a mystery and I might have broken physics. Is there a way of attaching recordings of the noises on here?
OK so what's causing noise? There is nothing else in here in here that is switched on apart from two displays and the light (no dimmer). I suspected power line internet adaptors but unplugging that makes no difference. Plugging guitars or mics into the interface makes no difference, plugging USB keyboards into the PC makes no difference. The noise does not appear in headphones plugged into the interface and it does not record (thank you Gods for this). The only thing I haven't changed is the monitors but, as they are silent when I unplug the USB cable from the interface or the audio cables from the monitors, I'm not convinced it is them. Borrowing a pair from somewhere is something I must try, thank you.
Thank you for your kind attention.

[Hugh Robjohns]

If I put the ART DTI at the interface or the monitor end of the cable, the noise gets worse (lots).

Difficult to diagnose remotely, but if the noise gets worse with a transformer in the signal path it's usually because the equipment on one or both sides is actually lacking a solid ground reference.

So the problem might be an absent ground rather than a ground loop.

If I connect the interface to the DI20 using TS 1/4" patch cables then the DI20 to the monitors using TRS to XLR balanced cables, the noise reduces significantly and when I use the ground lift switch on the DI20, the noise disappears.

I'm confused here.... why TRS to XLR? Are you not using the XLR outputs?

Is there a way of attaching recordings of the noises on here?

No... but you can put them on Soundcloud, for example, and then paste a link to the file back here.

The noise does not appear in headphones plugged into the interface and it does not record (thank you Gods for this).

This suggests the computer/interface is clean, and the issue is somewhere between the interface, speakers and/or their cabling...

The only thing I haven't changed is the monitors but, as they are silent when I unplug the USB cable from the interface or the audio cables from the monitors, I'm not convinced it is them.

I'm much less convinced...

[Gronow]

Thank you Hugh, I appreciate your time and trouble. The interface doesn't have XLR outputs unfortunately and I don't have TRS 1/4" cables (but could easily get some). It seems to me that if the issue has travelled between houses, it must be equipment. If we pursue the lack of ground reference idea then I understand it but I'm not sure what to do about it and would appreciate any help.
Thank you again.

[Hugh Robjohns]

The interface doesn't have XLR outputs unfortunately and I don't have TRS 1/4" cables (but could easily get some).

Ah... I see some light at the end of the tunnel!

Please get some — either TRS-TRS or TRS-XLRm — so that you're running fully balanced signals directly from the interface to the speakers.

There's a very good chance all your problems will then disappear. This should definitely be your no. 1 change.

When you were writing before about cutting cable screens I assumed you meant on balanced cables. You can't use that technique on unbalanced cables! It will always make things worse.

[Gronow]

Thanks Hugh and sorry to confuse matters but...if I use TRS to XLR from interface to monitors I have the noise, unsoldering the screen in these cables does not help. The DI20 has 1/4" inputs and XLR outputs, the interface has 1/4" outputs so to put the DI20 in the signal path I have to use 1/4" from interface to DI20 (these are TS as I don't have any 1/4" TRS) then balanced XLRs from interface to monitors. This setup allows me to ground lift the DI20 which removes the noise. This is curing the symptoms but not the cause which I would love to do.
Thanks again.

[Hugh Robjohns]

Sorry. Very confused over what you have tried...

As I said, it's quite hard to diagnose remotely.

Perhaps some audio samples might shed more light.