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-   -   Audio monitoring problem (http://www.dvinfo.net/forum/all-things-audio/495221-audio-monitoring-problem.html)

Vincent Oliver April 29th, 2011 01:44 AM

Audio monitoring problem
 
I recently invested in a PreSonus Firestudio Mobile external device (Firewire) and linked it up to two Yamaha speakers using mono leads with 1/4 jacks (not TSR).

The problem I am having is that when I play video I hear a sound that sounds like an old movie projector, but quieter. This sound can also be heard when I move windows about on the screen. The interference does not come out on any final production, but it is just annoying when I am trying to edit sound.

Any ideas how to cure/fix the problem?

Gary Nattrass April 29th, 2011 03:24 AM

Re: Audio monitoring problem
 
Its noise from the computer being induced onto the speakers, sometimes I get this from my ext hard drives and it can be very annoying. I think balancing the feed to the speakers may cure this but I tend to just live with it as it never goes onto the final audio track.

Paul R Johnson April 29th, 2011 04:12 AM

Re: Audio monitoring problem
 
In my audio studio I get the same problem - and was determined to track it down. I bought an 8 way rack mount DI and this cleaned up the bulk of the problem with sound from the audio interface getting into the audio mixer. It was still there to a degree, though, and it got more annoying as these things do when you're not happy. One day I noticed that the puttering changed when I moved the mouse, then on fiddling it also changed depending on what windows were doing on the screen. So a window with a moving display had a putter in sync with the window. I turned the monitor off, and the noise vanished totally. I'm not certain how the monitor was getting back into the computer, and then leaking out of the audio interface - on the surface these things are not linked? Switching to another monitor totally cured the problem. I suppose I could have experimented with ferrite rings and all sorts, but a swap cured my audio interference - could be worth a go?

Gary Nattrass April 29th, 2011 06:24 AM

Re: Audio monitoring problem
 
In balancing a transformer buffer will probably be the best way to get rid of this altogether, that is what the DI box is doing but as Paul says it may not go altogether.

Greg Miller April 29th, 2011 06:46 AM

Re: Audio monitoring problem
 
I always try to rule out possibilities, one by one.

1.) Power supply. Your problem sounds like noise in the power buss, which might occur if the PreSonus is being powered from the computer power supply. Are you using the PreSonus factory 12V supply, or powering over the Firewire cable? One point of using a device like the PreSonus is to get you away from all the noise inside the computer. Using computer power, via the Firewire cable, seems like a bad idea.

2.) Ground loops. Is any or all of your equipment rack mounted, which could cause ground loops between the various metal chassis? Or is everything electrically isolated?

3.) Speaker wiring. There's a fairly slim possibility that the speaker wiring is picking up electromagnetic radiation from the monitor or monitor wiring.

I'd check this by plugging headphones into the PreSonus. Do you hear the same noise on the headphones that you hear on the speakers? If so, disconnect the speaker cables from the PreSonus. Does that get rid of the noise in the headphones? If so, have you tried shielded speaker cables?


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