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Wurlitzer
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Joined: 11/12/02
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My monitors are interfering with my monitors! new
      #477041 - 23/06/07 10:46 PM
Like in many DAW-based home studios, I have two TFT monitors on a desk roughly between (though slightly in front of) my Event TR8 speakers.

The TFTs make a terrible audible mid-range buzz come through the speakers. I know that they are the cause because when they automatically turn off, after I haven't done anything on the computer for a while, the buzz immediately stops.

What can I do about it?


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seablade



Joined: 21/11/04
Posts: 3999
Re: My monitors are interfering with my monitors! new [Re: Wurlitzer]
      #477048 - 23/06/07 11:24 PM
Get new LCDs

I have two Samsung 19" LCDs I love right between my two Event TR8s with no problem whatsoever.

Now question, does the buzz go away when you turn the monitors off, but still wave the mouse? Reason I ask is I wonder if the problem might be with yoour video card instead of the monitors. While I suppose that the LCDs could be it if their power supply is going bad, I certainly can't say I have had that problem with a good LCD, or my CRTs before that.

Seablade


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Evie McCreevie



Joined: 06/09/04
Posts: 1028
Loc: Dublin
Re: My monitors are interfering with my monitors! [Re: seablade]
      #477051 - 23/06/07 11:44 PM
It might be worth screening your speakers from the computer screens with successive layers of tinfoil (around the speakers).

It won't look very sexy, and I don't know how many layers you'll need - but it may well work.


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Wurlitzer
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Re: My monitors are interfering with my monitors! new [Re: seablade]
      #477059 - 24/06/07 12:21 AM
Curiouser and curiouser...

Quote seablade:

Now question, does the buzz go away when you turn the monitors off, but still wave the mouse? Reason I ask is I wonder if the problem might be with yoour video card instead of the monitors. While I suppose that the LCDs could be it if their power supply is going bad, I certainly can't say I have had that problem with a good LCD, or my CRTs before that




The sound appears to have three components, which could be due to multiple unrelated sources: a low-pitched hum (which is VERY faint, so much so that I think it's not so much a fault as just the ordinary kind of background sound you get with even properly functioning gear); a mid-range hum (less faint) and a crackly buzz (bloody irritating!).

I'll try and describe as best I can what happens:

If Windows auto-switches off the monitors, according to its timed power management, both the mid-range hum and the buzz stop. And the remaining low hum is so faint that I can't even really hear it from a short distance away.

If I switch off the monitors from their front-panel switches, nothing changes. The sound continues exactly as before. I don't even need to move the mouse.

One of the LCDs is a little 14" jobby with an external power supply. If I switch it off by pulling the cable out of the power supply, the LOW hum appears to stop, but the rest (including the buzz) keeps going (at least that is what I think is happening - the sound seems to lose its depth or something).

The other LCD does not have an external power supply. If I switch it off by pulling the cable out of it, the low hum also seems to stop, and the mid-hum keeps going but CHANGES PITCH! (gets slightly lower) The buzz also keeps going.

It would appear that the LCDs definitely cause the low hum, but really that isn't a problem. The buzz and mid-range hum go away when Windows auto-switches them off, but are unchanged when they are switched off at the front panel. When the power cables are disconnected they also continue, but in one case the hum appears to change pitch.

Your analysis?


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Mevi



Joined: 06/10/05
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Loc: UK
Re: My monitors are interfering with my monitors! new [Re: Wurlitzer]
      #477066 - 24/06/07 01:06 AM
Here's a test. If you move the events well away from the monitors, does the sound continue?

Can you plug in headphones anywhere on your rig? Same buzz on the phones?

Going by the symptoms you describe, I'd go with Seablade and his video card theory. That or it's an earthing problem in your PC. What soundcard do you have? Is it PCI and how close is it installed to your video card?

The onboard sound in my Shuttle PC is unuseable due to being able to hear the screen refresh through the audio out!! When I googled it, I discovered that it's down to an earth loop in the circuit board design!!!

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http://www.mevi.co.uk


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Hugh RobjohnsAdministrator
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Re: My monitors are interfering with my monitors! new [Re: Wurlitzer]
      #477068 - 24/06/07 01:19 AM
If the buzz doesn't change when you physically unplug tha monitor mains feeds, then it can't be coming fromthe monitors PSUS, which would have been my first suspect.

If it goes when Windows shuts off the video card output, then that would imply it is computer based noise, or possible something nasty radiating from the video cables connecting the LCD monitors.

So, you could try re-routing the video cables well away from the audio cables. I assume the monitors are being fed with a proper balanced output adn balanced cables?

It could also be mains-carried noise from the computer getting back into the monitors. Try plugging the computer and LCDs into a different power outlet from the rest of the audio gear to see if that helps.

Hugh

--------------------
Technical Editor, Sound On Sound


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steveman



Joined: 17/03/02
Posts: 1142
Loc: London - UK
Re: My monitors are interfering with my monitors! new [Re: Wurlitzer]
      #477071 - 24/06/07 01:27 AM
Quote:

If I switch off the monitors from their front-panel switches, nothing changes. The sound continues exactly as before. I don't even need to move the mouse.



So you're saying the sound continues with the monitors switched off? Then the problem obviously isn't the monitors.
Windows 'sleeping' the monitors and the sound stopping - sounds like it's the videocard, I'd presume Windows sleeping the screens means it's no longer driving the video card.
Computer don't directly depower monitors, they just stop driving them, the monitors auto-sleep in the absense of a signal. (I'm pretty sure that's what happens - there's nothing on a VGA connector that sends any sort of signal other than video).
That's my 'analysis' anyway Good luck figuring it out.


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Wurlitzer
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Re: My monitors are interfering with my monitors! new [Re: Hugh Robjohns]
      #477187 - 24/06/07 11:37 AM
Thanks everyone. Hugh's post made me realise I should have given more information about the physical setup, which is probably relevant.

The computer is in a cupboard at the back of the room. The soundcard is connected via balanced leads and connections to a Spirit Compact 4 mixer at the front of the room (about 5 metres away). Although the leads (which are in a 4-way loom) are balanced, to be honest I was suspicious when I got them as they seem to be considerably thinner than most long, balanced leads.

The video card feeds long extension cables that go around the wall and feed the monitors at the other end. These are proper shielded cables made for the purpose, but they might be struggling to do their job as there is a little bit of ghosting on the monitors, which I'd never got around to doing anything about.

The video extension leads DO run parallel to the audio loom along the long wall, though encased in a separate piece of plastic trunking. Could this be the issue? I know there is a problem with power cables in a situation like that, but I didn't imagine data cables would be such an issue.

From the posts above, it sounds like it's clearly either the video card within the computer, or the leads leading to the mixer that causing the problem. Unfortunately investigating those things further will take a bit of physical digging around and experimenting, which I don't really have time for at the moment.

Quote Hugh Robjohns:

So, you could try re-routing the video cables well away from the audio cables. I assume the monitors are being fed with a proper balanced output adn balanced cables?




Just to clarify the above: The computer has a Soundscape mixtreme soundcard which actually has a coaxial spdif out, leading via proper 75ohm digital cable to an M-Audio Flying Calf A/D converter. This has balanced outputs which feed balanced leads in a four-way loom (2 in and 2 out - though as I said they seem to be poor quality or surprisingly thin - to balanced inputs on the mixer, which has balanced outputs feeding balanced leads to balanced inputs on the speakers.

I don't know if the spdif/phono part of the equation could be a weakness, or the quality of the balanced loom. I suppose I'll just have to experiment with moving and replacing things.

Quote:

It could also be mains-carried noise from the computer getting back into the monitors. Try plugging the computer and LCDs into a different power outlet from the rest of the audio gear to see if that helps.




The computer's on a completely different mains circuit at the back of the room. The LCDs are on the same circuit as the mixer and speakers, but different wall plugs. What should I do?

Thanks again.


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MikeOates



Joined: 16/01/06
Posts: 387
Loc: Manchester, UK
Re: My monitors are interfering with my monitors! new [Re: Wurlitzer]
      #477208 - 24/06/07 12:50 PM
Quote Wurlitzer:



The computer's on a completely different mains circuit at the back of the room. The LCDs are on the same circuit as the mixer and speakers, but different wall plugs. What should I do?





Now then, how about putting a temporary mains extension lead from the same point where your mixer & monitors are pluged in, to the computer and see if the noise goes, if it does, you may have a ground loop. Its a quick and easy thing to check.

Mike

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Audio Recording Live


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Hugh RobjohnsAdministrator
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Joined: 25/07/03
Posts: 21736
Loc: Worcestershire
Re: My monitors are interfering with my monitors! new [Re: Wurlitzer]
      #477260 - 24/06/07 04:04 PM
Quote Wurlitzer:

The video extension leads DO run parallel to the audio loom along the long wall, though encased in a separate piece of plastic trunking. Could this be the issue?




Quite possibly. Long cables can often act as radiating aerials for all sorts of nasty RF hash from the computer.

I would suggest running some temporary separate balanced cables to your sound desk, keeping them well away from the LCD monitor cables to see if that helps. Poor balancing/screening of the audio cables could well be part of the problem.

Plastic trunking obviously won't help in screening, but maybe you could think about lining one or both trunks with silver foil, earthed at the mixer end.

Quote:

From the posts above, it sounds like it's clearly either the video card within the computer, or the leads leading to the mixer that causing the problem.




Yep. Try connecting the monitors directly to the video card, missing out the long cables. That might give a clue as to whether the cables are the isse, or it is the card itself putting noise on the audio I/O card in the computer.

If the noise is still there, then you might want to think about relocating the audio card further away from the video card inside the machine, in case it is radiated noise. If the problem is internal buss noise, then there's not much else you can do.

Quote:

Unfortunately investigating those things further will take a bit of physical digging around and experimenting, which I don't really have time for at the moment.




Tis always the way!


Regarding the mains supplies, try rinning an extension so that the LCDs are plugged into the same mains supply as the computer at the back of the room. And if that makes no difference, try runningthe extension the other way around so that the computer is running fromthe same supply as the rest of the audio gear.

Ground loops can affect digital signals as well as analogue ones, and you probably do have a loop issue between the cpmputer and the rest of the audio gear. Ground loops with digital connections don't manifest as the familiar low level hums and buzzes. They tend to be much more odd than that, and it could indeed be the problem here.

Hugh

--------------------
Technical Editor, Sound On Sound


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