# Ground hum from hell...



## Andrew Aversa (Apr 6, 2017)

I've been trying to figure out the source of some terrible 60hz hum in my RME Fireface interface for over a year. The hum is on both mic input channels and scales proportionately with gain. This is LOUD, distorted hum with 40+ harmonics. I've tried different mics, different cables, different outlets. I currently have the RME hooked up into its own outlet running through an Ebtech Hum-X. None of this makes any difference at all.

Could it be the unit itself that's faulty?


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## Nick Batzdorf (Apr 6, 2017)

It could definitely be the unit.

Is it the Fireface that uses a power transformer? If so, I'd try a different one, because those things can go bad.

If it's one with an internal transformer, does the hum go away if you lift the ground (i.e. use a 2-prong adapter)? You're not supposed to do that, of course, but it will tell you whether the unit has a grounding issue.

Also, does the hum stop when you disconnect the FireWire cable? It could be a ground loop with your computer.


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## Andrew Aversa (Apr 7, 2017)

I can't remember exactly when it started. It may have to do with the house we're in now. There are some dimmer switches on the same circuit (this whole part of the house has them, despite my office being a floor above) which I've heard can cause problems.

I have it connected to the computer via USB as opposed to FW - no FW connection on this PC. I could remove USB, but then how would I test if the hum is still happening?

I'll try borrowing my wife's Onyx Blackjack to see if that makes a difference.

No hum over monitors/phones.


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## dtcomposer (Apr 7, 2017)

I had a similar issue and I ended up having to use 2 hum-X boxes . One between the Interface and the Subwoofer, and another between the sub woofer and Speakers. I have no idea how or why this worked. When I used one in either chain location only I still had a hum. If you haven't tried this I'd give it a shot.

https://www.amazon.com/Ebtech-HE-2-XLR-Eliminator-2-Channel-Jacks/dp/B00101WA4C/ref=pd_sim_267_1?_encoding=UTF8&pd_rd_i=B00101WA4C&pd_rd_r=KJCPK2CHFE1273YWN3Z0&pd_rd_w=Cl5nu&pd_rd_wg=Bx1VC&psc=1&refRID=KJCPK2CHFE1273YWN3Z0 (This is what I used)


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## patrick76 (Apr 7, 2017)

I had an issue also with my babyface. The issue was with usb. Try connecting via different usb ports if possible. On my computer some were terrible and only a couple of the usb ports work fine.


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## wst3 (Apr 7, 2017)

I'll try to keep it brief, I promise...

There are a couple common ways that power line noise can get into an audio system. Ground Loops are probably the most popular with the press, but the dreaded "Pin 1 Problem" is really the most common. And USB is a frequent culprit of Pin-1 problems, as are any single-ended connections.

Current flowing in a ground conductor is also common, and it is the reason you should NEVER defeat the safety ground. If there is a sizable potential difference, resulting in ground current flowing, you'll get zapped. You could be killed if the potential difference is large enough. (And current flowing in the ground is the aggressor - see below - in the pin q problem.)

You mention over 40 harmonics - that suggests significant unwanted energy above 2 kHz, and that is really unusual, it suggests that 60 Hz power is not the source of the noise problem, or at least not the only source, some higher frequency energy is "mixing" with the 60 Hz and its harmonics to create sidebands. This sort of noise is often generated by inexpensive lighting dimmers, motor controllers, and the like.

The trick here is to identify the aggressor (the part of the system creating the noise) or the victim (where the noise is getting into the system) or both. It is the only way to solve the problem once and for all.

In that vein - what happens if you short circuit the inputs of the interface? If the noise goes away then there is a problem with the Fireface.

Next up, plug in any other USB audio interface and see if the problem persists, if it does short those inputs too.

Finally (and I apologize in advance) plug both (all) interfaces into all your USB ports. On most computers the physical interface differs between groups of ports ,depending on how they've implemented the bridges.

Without answers to those it is difficult to figure out where to look next, so we'll stop troubleshooting until you get a chance to do those tests.

In the meantime there is a solution that is 100% guaranteed to work in any environment. Balanced sources feeding balanced inputs with very high common mode rejection ratio (CMRR) with a twisted pair in between (shielding is not required for power line noise problems, it is required for RF noise problems). It used to be that only transformer balanced inputs were guaranteed to work, but advances with active balanced circuits (and especially the InGenius(tm) chip from THAT Corp) have changed that. Both transformer and transformerless inputs work well, and each has benefits, and disadvantages.

Any other solution involves trade-offs, and might work in one space but not another. Or at one time of the day and not another (ask me sometime about that nightmare!)

I should also note that the inexpensive transformers sold as HumBusters are good enough for troubleshooting, but you should never subject your music to their innards. ESPECIALLY if you do anything that has a lot of information in the bottom couple of octaves. There is a reason a good transformer costs upwards of $100 and the Ebtech doesn't.


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## Nick Batzdorf (Apr 7, 2017)

Andrew, if the problem is in the unit, you'll hear hum with USB disconnected.

Bill is absolutely right that you should never lift the ground. I would never do something that bad. Never.


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## Nick Batzdorf (Apr 7, 2017)

Never ever.


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## Andrew Aversa (Apr 7, 2017)

Admittedly a lot of this is over my head...



> In the meantime there is a solution that is 100% guaranteed to work in any environment. Balanced sources feeding balanced inputs with very high common mode rejection ratio (CMRR) with a twisted pair in between (shielding is not required for power line noise problems, it is required for RF noise problems). It used to be that only transformer balanced inputs were guaranteed to work, but advances with active balanced circuits (and especially the InGenius(tm) chip from THAT Corp) have changed that. Both transformer and transformerless inputs work well, and each has benefits, and disadvantages.



This may as well be greek :D What are you suggesting, specifically?

Also, I don't know what you mean by "short circuiting" the inputs of the interface. If you mean turning off phantom power, then yes, the hum goes away (along with the rest of the signal).

As soon as I have the chance to try the other interface, I will.

EDIT: I've tried a totally different interface - no difference. Worth noting, the alternate interface is USB-powered, and it had the same problem. (No wall power.) Also have tried multiple USB ports. Speaking directly into the mic, the hum is about 24dB lower. So, absolutely brutal.

I'm aware that dimmers on the same circuit can cause issues. My office is in an expansion of our house, and the lower floor is on the same circuit, with several dimmers. Unfortunately I can't do anything about that. I'm surprised the Hum-X didn't work as I thought that was what it was supposed to do.

If anyone is curious as to the sound of the hum, here it is (turned up, naturally)

http://impactsoundworks.com/audio/BrutalHum.wav

Also again for emphasis, absolutely no hum or noise whatsoever on the headphone or line outs of either interface.


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## Astronaut FX (Apr 7, 2017)

That sounds very much like a ground hum that I had as well. In my case, twice. In both cases, it was a USB ground loop. The first was caused by the USB connection with an Arturia BeatStep Pro, the second with a Roland JU-06. 

In both cases, the USB cable carried MIDI and powered the device. For the BSP I solved it by using the included Y-connector along with a standalone power supply. For the JU-06, I solved it with a standalone power supply and a standard 5-pin MIDI connection. 

I'd like to get another of the special y-connectors that came with the BSP for use with the JU-06. 







in short, my issues were a result of USB ground hum caused by units that were powered via USB. Is there anything in your set up that draws its power via USB? If so, this may be your culprit.


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## Nick Batzdorf (Apr 7, 2017)

^ That's one of the things I'm suggesting, although it's not necessarily because the devices are drawing power, it's just a ground loop.


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## Andrew Aversa (Apr 7, 2017)

Sure, I have a couple USB keys and a USB hard drive. I'm not sure I understand how those would cause an issue... is the suggestion to just disconnect all of them?


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## Astronaut FX (Apr 7, 2017)

zircon_st said:


> Sure, I have a couple USB keys and a USB hard drive. I'm not sure I understand how those would cause an issue... is the suggestion to just disconnect all of them?



Well, as part of the investigation to determine the offending device, yes, I would try it. Take one element at a time out of your system until you identify the culprit. Once you're able to track it down to the root cause, then you can work towards the resolution.

Your situation may be totally unique from mine. I shared it just to shine a light on some of the types of things that could potentially cause such an issue.


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## Nick Batzdorf (Apr 7, 2017)

No, the idea is to break the connection between the interface and the computer to see whether having two paths to ground is causing the hum.


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## Nick Batzdorf (Apr 7, 2017)

Crossed posts, but I say unplug the USB cable and see whether the noise goes away. If so, you'll know what the next step is.


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## Andrew Aversa (Apr 7, 2017)

I'm still confused - am I disconnecting USB devices that are *bus powered*, or USB devices that are connected to the wall?


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## Nick Batzdorf (Apr 7, 2017)

You're breaking the connection between your interface and the computer by unplugging the USB cable.

It's just for troubleshooting.


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## Andrew Aversa (Apr 7, 2017)

Now I'm even more confused! How would I tell if I'm still getting hum if I have no means of recording to the computer? It has no monitoring capabilities as far as I can tell, all of that loopback stuff is done with the TotalMix software. And furthermore, my other interface (Onyx Blackjack) is bus-powered, so I _can't_ disconnect that without losing power to the interface.


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## Nick Batzdorf (Apr 7, 2017)

I figured your speakers are connected to your audio interface, and you were hearing hum in your speakers! You wouldn't need to record to hear whether that went away.

So now I'm confused. I'm also a little confused that you have an RME Fireface with no FireWire but with USB. I didn't know they made one.


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## wpc982 (Apr 7, 2017)

fwiw, I too had a bad RME hum (RME HDSPe AIO, PCIe audio card). It's still there, though I've worked around it; so even though the card works flawlessly, in some ways, I can't use the direct analog output nor the headphone output. Interesting reading all the stuff about USB, since I never methodically got into disconnecting USB things (none of the audio in the computer uses USB).


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## Andrew Aversa (Apr 7, 2017)

Sorry, I should have clarified better. The hum is ONLY when recording w/ phantom power. No hum through speakers or headphones. It's whisper-quiet outside of the mic inputs. I actually don't have any dynamic mics so I can't test those, but multiple condensers all have the same issue.

The Fireface UCX does indeed have Firewire out but I don't have a Firewire input on this PC.

Since I've eliminated everything else, the possibilities are that it's my computer (somehow), or the electrical circuit (which does have various dimmers on it). Unfortunately I have no idea how to deal with either problem!


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## Silence-is-Golden (Apr 8, 2017)

zircon_st said:


> dimmers


Oh, that can very well be a source of hum.


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## wst3 (Apr 8, 2017)

So just to clarify - 

phantom powered microphone = hum, 

any line level source = no hum

If that's correct you can rule out the computer. It could be a bad phantom power supply - how many different microphones can you test?


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## Nick Batzdorf (Apr 8, 2017)

Only when recording with phantom power. Does it go away when you switch mic cables or re-route the same ones?

I think if that doesn't do it, it has to be what Bill says: a bad phantom power supply.

It's definitely not an AC issue if it's only with phantom power.


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## Andrew Aversa (Apr 9, 2017)

But this happens with two interfaces, one of which I've tested in another room (and it has no hum there), and also multiple microphones. Also it happens on any mic input, with any mic cable.

I have not tested line in recording, as I have nothing to test with.


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## wst3 (Apr 9, 2017)

well that's the thing about ground loops - they can occur almost anywhere - there could be something that closes a loop when you power a microphone... far fetched, but I've seen stranger things.

Also, are you powering the interfaces over USB or locally?


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## Kardon (Apr 9, 2017)

Astronaut FX said:


> That sounds very much like a ground hum that I had as well. In my case, twice. In both cases, it was a USB ground loop. The first was caused by the USB connection with an Arturia BeatStep Pro, the second with a Roland JU-06.
> 
> In both cases, the USB cable carried MIDI and powered the device. For the BSP I solved it by using the included Y-connector along with a standalone power supply. For the JU-06, I solved it with a standalone power supply and a standard 5-pin MIDI connection.
> 
> ...



Does anyone know where you can buy one of these or similar USB power Y cables like the one Astronaut_FX got with his Arturia?




It can power a USB device using an external power supply and not from the PC, hopefully defeating the ground loop hum like he did. My searches have come up with lots of splitters but nothing that does this.


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## The Darris (Apr 10, 2017)

Just curious, and this is for the ones who understand this issue. If the interface is USB powered, would the wattage of the PC power supply matter? Could this simply be a PC power issue? I mean, applying phantom power adds the hum. Just trying to back track slowly through the issue.


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## Andrew Aversa (Apr 10, 2017)

This happens with both the RME Fireface (wall-powered) and Onyx Blackbird (USB-powered), and the Onyx works fine on another machine in another room...


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## Nick Batzdorf (Apr 10, 2017)

The Darris, I would think that's on the list of possibilities but not very high up.

Andrew - not that I'm being a lot of help here  - it's a matter of isolating the issue. If you bring the offending computer into the next room, you'll know whether the computer is part of the problem. Same with the interfaces, mics, cables (have you tried really short ones?), etc.


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## rrichard63 (Apr 10, 2017)

zircon_st said:


> ... the lower floor is on the same circuit, with several dimmers. Unfortunately I can't do anything about that. ...


Can you replace the dimmers with a different make and model? Not all of them interfere with audio, at least not to the same extent. I've forgotten the details, so you'll have to Google this subject. Also keep in mind that not all dimmers and all types of light bulbs are compatible. You need to learn which type or types work with the bulbs you want to use and, at the same time, don't induce hum in audio circuits. Eventually I need to worry about this myself, just not now.

Another possibility is to add a separate electrical circuit for your office/home studio. That may or may not be possible depending on your existing main breaker box.


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## Andrew Aversa (Apr 10, 2017)

Nick Batzdorf said:


> The Darris, I would think that's on the list of possibilities but not very high up.
> 
> Andrew - not that I'm being a lot of help here  - it's a matter of isolating the issue. If you bring the offending computer into the next room, you'll know whether the computer is part of the problem. Same with the interfaces, mics, cables (have you tried really short ones?), etc.



I appreciate your help and everyone else's! Sorry, I should have been saying that more. Thank you.

It's.... not easy to move my computer from this room. It weighs a ton and it's connected with quite a few other things. But I do have an idea - I can bring a laptop in this room and connect it to the recording setup and see if that makes a difference.

EDIT: OK, now THIS is weird. Very very weird. For some reason, the hum is currently gone (or at least, about 30 dB quieter). As far as I know, nothing has changed on the circuit... I'm going to play around with switches and see what happens!


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