Treating Ground Loop problems :(

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nalmeth
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I'm fairly certain this isn't OS specific, but since I'm running GNU/Linux, and only effectively using Ardour for audio, I think this is where I should post.

My System:
3.0 GHz Hyperthreading CPU, Gigabyte motherboard, Intel Integrated Video and Sound, Nvidia FX 550, 1.5 Gigs of RAM

The rundown:
I've been constantly and continually fighting this ground-loop problem with my system.

Basically, a device in my PC is causing a noise/feedback effect to be injected into the input in my Intel Integrated sound card.

It affects all input audio, jack and non-jack alike. Output is fine.

To be able to record ANYTHING without triggering an INTENSE AND ALARMING feedback/noise effect, I have to disable the 20db boost in my alsamixer.
The problem here, is that the noise is still there, only reduced. I also still get a BLAST of feedback and noise occasionally, like when many track are open (recycling the feedback), or just opening a project.
On top of that, I have to turn my instruments up much too loud to get a clean sample.

I've grounded every piece of hardware to the tower, but only by screwing in all loose devices. My HD and CD-ROM were loose, but this did not help at all. After hearing bad video cards can cause this, I removed my Nvidia card, and reverted to the onboard Intel i910 card. No difference, unfortunately.

So, at this point, I'm at my wits end.

I've followed the links at the bottom of my post, but most of the advice is too advanced for my knowledge of hardware. Ultimately it suggests tracking down the bad device, grounding it with some sort of calibrator, to drown or kill the looping noise/feedback.

As you must understand, as a person simply trying to enjoy and use all this Free Software, this stupid problem is very debilitating and frustrating. I'm documenting the whole process so I can write some documentation for others to use in the future, but I'm having a lot of difficulty sorting out what could be wrong.

Does anyone have any resources to share on hardware problems of this nature?

I know I should have a better sound card, but trying another sound card only worked temporarily, the noise spread to that card too. A new card won't solve the problem, I have to find the underlying problem to advance anywhere.

Please share any thoughts or ideas or resources you may have, I am greatly appreciative for ANY help right now :)

And here are the resources I have been following:
http://www.maudio.co.uk/index.php?do=support.faq&ID=12cfebbf1c694ee8664859cfd004577c
http://www.epanorama.net/documents/groundloop/
http://www.epanorama.net/documents/groundloop/mains_connectors.html
http://www.epanorama.net/documents/groundloop/example_systems.html

Thank you Dear Ardour enthusiasts!

sampo
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Ground / hum problems are at at 50 or 60hz depending on the type of electricity used in your country. The hum also has some harmonics to 50/60. If you hear a loud, high pitched feedback like sound it's most probably feedback, not ground hum.

When you record with an open mic, is the mic in the same space as the monitoring setup? This sounds like the culprit is software monitoring, and maybe "auto-input" which monitors track inputs automatically when Ardour is not playing / recording.

If this does not help, you should post an audio sample of the hum or feedback for analysis. It's a lot easier deciphering the problem when you hear it.

seablade
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Hmm seems to be a bug with login routines here, anyways...

Sampo, in straight audio connections you are absolutely right, you will hear primarily 50 or 60Hz interference.

However ground loops in between the computer and another piece of equipment show up in a very different way. In general it will sound like digital noise, and get modified based on several factors, your HD spinning up or down, mouse movement, etc.

However like you, I have not seen proof that this occasion is a group loop. For instance, does this problem exist if you plug in a piece of equipment to your mic in, that is not plugged in(For instance a portable CD player, a cheap mic, or one that has been switched to an unbalanced connection?)

If the sound still exists with a device that does not get plugged in and grounded via its own power supply, chances are you are dealing with a completely different problem.

What effects the sounds? Is there anything you are doing to make it better or worse?

My first response when reading your post, is you are using an onboard sound card. That automatically makes me suspicious. They tend to be very noisy themselves.

Seablade

nalmeth
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Joined: 2006-11-09
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I live in Canada, I'm not sure how to measure the signal noise in Hz though. It seems to be a hum that is usually independent of computer activity, though something must be triggering it, I used to not have this problem at all.

Anyway, the fact that its a hum seemed consistent with the description of ground loop, and I have seen times where it WAS affected by computer activity.

~A week ago, I tried playing with Ardour running Beryl on my Nvidia Card. When any animations occurred, the sound/hum changed noticeably. This is what triggered me to remove the Nvidia Card, but the noise was still there after doing so.
I've since put it back in, but haven't noticed anything similar.

nalmeth
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The worst part about this is how enabling the 20dB in my alsamixer causes a severe noise level, it seems to magnify the hum to a much more intense level.

I've made a recording showing the hum effect, the 20dB boost effect (blasts hum noise right to 0 on meter), and the effect of adding tracks (simply adding incrementally to the noise, not unexpected). There is no mic plugged in during the recording.
Is there a way of posting it to the forum here?

Seablade, I do indeed just have an onboard card, and realize that is probably the central weakness of my system :)
That would probably be better if I found it is just the Intel sound to blame, maybe I can find a way to blacklist it or prevent it from operating.
I have another Realtek card or something similar, but the noise is present using that card aswell.
I plugged a discman into the mic input, and it seemed to play OK, the 20dB boost didn't overwhelm or destroy the signal, only boosted it. I'm not sure but maybe the Discman just covered up the hum?

SK
User offline. Last seen 6 years 49 weeks ago. Offline
Joined: 2007-01-23
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You could use baudline to analyse your problem.
http://www.baudline.com/

Anyways internal soundcards and especially on motherboards integrated soundcards are a pain. With my onboard sound i can hear the CPU activity and other things and that is output. Input with activated boost is hell ;-)

When you want quality, you should buy a good (external) soundcard that does what you need. In my case a USB UA-25 from edirol does quite well.

Then the next step is to address the humming. Connect everything connected to the PC from one power source (by _one_ big outlet, if possible don't cascade them). Unplug everything you can and selectively plug in the devices until humming starts. Then you know the bad boy. Try to reverse the plug (don't know if this is possible in canada, in germany it is). Sometimes reversing reduces hum a great deal.

seablade
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[quote]
I plugged a discman into the mic input, and it seemed to play OK, the 20dB boost didn’t overwhelm or destroy the signal, only boosted it. I’m not sure but maybe the Discman just covered up the hum?
[/quote]

What happens when you have the boost on, and just have the discman paused?

Seablade

nalmeth
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What happens when you have the boost on, and just have the discman paused?

No noise at all!
I just tried Audacity, Jokosher and Rezound, and under Jack, Rezound picks up NO NOISE at all, either!
Rezound is the only app that doesn't pick up anything. Audacity, Jokosher, Ardour all have problems.
It's bizarre. I think this may be something application level, because I'm getting different results with different programs. Though, I have tested another install and it has the same problems.

Audacity has a high-pitch distortion when recording.
Ardour blasts the noise when 20db boost is enabled, and if I mute the mixer, the excess noise goes away, but I can still see the hum. It alternates levels between L & R, and has a marked R tendency.
I tried changing HW/SW monitoring, but it didn't help.
Noise exists when only one track exists.

SK, that is a cool application (or group of applications), I love to checkout different visualization techniques, but this looks very advanced. And probably perfect for this. Thats great that it supports JACK :)

I tried unplugging every external device - monitor, speakers, even USB devices - No change in the hum though.
I can't reverse plug, we have three-pronged power cord, while Germany it's just the 2, correct? I think thats what you meant in reversing the plug.

Thanks for your suggestions, I think I understand things a bit better now. I haven't ruled out this ground-loop possibility, but there seems to be a host of other things that could be at fault, like the noisy onboard card :)

I think something might be amiss with Ardour, as it has the most severe problems, so I'm going to try to install Ardour2 to see if there is a difference. At least, until I track down the problem, Rezound seems to be working great :]

SK
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We have a symmetric design in germany:
http://de.wikipedia.org/wiki/Schuko

If you had unplugged everything which didn't change anything and one application has no problems with the noise, it is unlikely to be a grounding problem.

One thing comes to my mind now, what could be the problem in ardour. There could really be a loop inside ardour. This happened to me lately but i don't remember the setup correctly. Some of the sound in ardour got fed back to an input and there was humming. Maybe hardware monitoring was part of that as the monitor outputs are input channels, too. So there could be a loop inside your PC, inside ardour, inside your soundcard.

To check if it is this, turn up the volumes in the mixer in ardour and check if one or more levels raise abnormally when having a low volume input. First turn main volume up, then the others. For me it resulted in a strange noise and for a bit higher volume the signal clipped.

The high pitch distortion in audacity might be a problem with realtime/xruns as signal gaps lead to level-jumps which have a broad spectrum.
Another possibility could be a characteristic CPU/GPU utilization. Try to run a 3D-Application like glxgears in parallel.

nalmeth
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I've installed ardour2, but the situation is exactly the same.

I tried tuning the mixers as you pointed out, but it didn't affect the noise like it does for you. Probably a different problem altogether :P

Running glxgears had no effect on the noise either.

You might be right about audacity, I don't know what else could be at fault.

It's a wonder that Rezound doesn't have any of the problems that the other applications do, I wonder if there is some loop effect within Ardour itself causing the noise, like you said.

Does it rule out anything given that Rezound works fine? As in no noise/feedback on input?

EDIT: Nevermind, the noise isn't as visible in its mixer, but there is a strong fuzz when playing back a recorded track. Rezound is afflicted afterall.

seablade
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Lets go to usenet style quoting since apparently there is no BB code here;)

>If you had unplugged everything which didn’t change anything and one application has no problems with the noise, it is unlikely to be a grounding problem.

SK is dead correct. If you are picking up the noise and the only ground your computer is connected to is through its power supply, it is highly doubtful you have a ground loop(As that by its nature requires at least two electrical grounds)

If you have nothing hooked up to the computer, and can record that noise, the noise is coming directly from your soundcard. The reasons for this can be numerous, onboard sound cards are not known for quality componets and a sound like white noise will generally indicate low quality amplification(Or pre-amplification). That +20 switch in alsamixer you keep referring to is probably just for mic pre-amplification, thus why it makes such a difference.

If instead it sounds like clicks, pops, etc, then you are probably picking up interference from other componets in your computer. Not much you can do about this with an onboard sound card.

My suggestion is see if you can borrow a sound card you know works in linux and see if switching sound cards makes a difference. Unlike what was noted above you can get decent signals from an internal sound card, but you do need to be careful about where it is in the case and what it is near. My RME for instance was susceptible to video card interference when located directly next to the card, but moving it down to the last slot in my case got rid of that problem rather quickly.

But yes right now I am still leaning strongly towards you are running into quality limitations of an onboard card. At least if I am understanding you correctly.

Seablade

nalmeth
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>If you have nothing hooked up to the computer, and can record that noise, the noise is coming directly from your soundcard.

Alright! So it's probably not ground-loop. I don't experience the clicks and pops that others do, but I can see how low quality amplification might cause this kind of sound. It's like amplified white-noise :)

I have another cheap old sound-card from another PC, and I managed to use it for a couple weeks, noise & hum free. Finally it succumbed aswell, but this is also a really cheap card. Probably from around 1999 or so. The thing that struck me is that it was the same type of noise between the two, so I thought it must be something system-wide.

Anyway, I've had my eye on a couple of M-Audio cards, the 4 input/output card would be perfect for me, but there aren't any dealers in my city, I'd have to have one mailed to me. I have some research to do :)

Thanks for your analysis & interpretation Seablade, Sampo, and SK, hopefully soon I can get back to using Ardour, and get away from fixing awful noises!