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Video captured with ground loop hum (analog interference)

Jul 14, 2012 1:37 PM

Tags: #bar #loop #composite #progressive #interlaced #ground #bone #interference #roll #hum #analog #herringbone #herring

A client brought me this clip on showsite last week. Before I had this video imported in my system, I only saw it in a 5-inch capture window and thought it was an interlacing issue. Turns out it is actually analog interference, caused by the composite feed from the MOTU HDX-SDI. The feed was sent out over a VGA-to-5-wire fanout cable on GREEN and must have picked up some interference along the way. When captured, it was assumed that was just the preview and that the video lookeed fine...

 

I am wondering if there is any way to remove a diagonal (herringbone) ground-loop hum from video. There seems to be a pattern to it, as it slowly rools up, then down a bit then back up and off the screen - only to start all over again... I will attach some a video of what it looks like.

 

https://www.dropbox.com/s/nesri9s7ngg5mq3/BChil%20Interference%20Sampl e%20-%20saved%20as%20DV%20codec.avi

 

This was recorded at 720x486, 29.97i in Apple Pro Res initially, but this uploaded clip is a 720x480,29.97i DV codec file. Should I de-interlace it first, or try to do something with it interlaced? Seems it would be easier to deal with frames than fieldsx2 when trying to isolate this interference, but not sure... Any help would be greatly appreciated!

 

-BC

 

Here is a still (with logo blacked out)
herringbone analog video interference.jpg

1002 Views   10 Replies   Latest reply: BChilcher, Jul 17, 2012 4:16 PM
 
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  • Jim Simon
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    1. Jim Simon,
    Jul 14, 2012 2:53 PM   in reply to BChilcher
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    This is not the kind of thing you can fix in post.  You need to fix it on site before you record it.

     
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  • BChilcher
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    2. BChilcher,
    Jul 14, 2012 4:17 PM   in reply to Jim Simon
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    Figured as much, but figured since there is a distinct pattern to it, maybe it could be intelligently analyzed and at least reduced. I will let you know if I have any luck with it, but will likely tell them there is nothing I can do to fix it.

     

    Thanks.

     

    -BC

     
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  • Charles VW
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    3. Charles VW,
    Jul 14, 2012 7:34 PM   in reply to Jim Simon
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    sure you can.  this can be done with an FFT plug-in.

     

    Heres an example of a Photoshop plug-in doing a similar job:

    http://video.google.com/videoplay?docid=2621356841303406132

     
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  • shooternz
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    4. shooternz,
    Jul 15, 2012 1:40 PM   in reply to Charles VW
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    You think that can be done over multiple video frames?

     
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  • Charles VW
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    5. Charles VW,
    Jul 15, 2012 7:33 PM   in reply to shooternz
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    Probably not with that particular Photoshop plug-in's workflow, but I know they're out there in the video world.  My point is to show that periodicity is a solvable problem.

     
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  • BChilcher
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    6. BChilcher,
    Jul 16, 2012 3:18 PM   in reply to Charles VW
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    Charles,

     

    Thank you for reopening this case (in my mind) and getting me to try harder - I just bought the Pro version of Neat Video ($99) - I have it looking pretty good, albeit less than perfect - it's just a matter of playing around with the settings. I may not get it perfect, but it will be much better.

     

    Does anyone know of any similar plugins?! i.e. a "smart filter" that analyzes the clip for repetitive noise and fills it in? Re:VisionFX has a Fill plugin that looks like it might be a good 2nd-stage fix for this - or maybe SmoothKit

     

    -BC

     
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  • Bill Hunt
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    7. Bill Hunt,
    Jul 16, 2012 4:23 PM   in reply to BChilcher
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    Though I use Neat Video fairly often, it's mainly for working with video noise, from underexposed footage (often ripped from old VHS material), and it's analysis is usually a good starting point, but as you point out, it does take some tweaking to get really good results. It's analyzer would be better, if the videographer had just shot a gray card, in the same lighting (oh, and also added some light to begin with, but that's another story).

     

    I find that just a hint of Sharpen, after Neat Image, improves things too. "Just a little dab'll do ya."

     

    Render and Export times DO go up.

     

    I have not looked at alternatives in too long, to be of use, but maybe others will have some favs.

     

    Good luck,

     

    Hunt

     
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  • BChilcher
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    8. BChilcher,
    Jul 16, 2012 5:49 PM   in reply to Bill Hunt
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    Too bad this interfence changes direction. I think Neat Video would be perfect if not for that...

     
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  • Bill Hunt
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    9. Bill Hunt,
    Jul 16, 2012 7:19 PM   in reply to BChilcher
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    Ugh, THAT is tough. Hope that you can get close, though.

     

    Good luck,

     

    Hunt

     
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  • BChilcher
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    10. BChilcher,
    Jul 17, 2012 4:16 PM   in reply to Bill Hunt
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    Well, after very limited playing with the settings in Neat Video and this clip, I am already here - without losing really any of the detail. I am thinking of working with luminance mostly after this, as it now seems to be a "pulsing" in the highs and possibly mid-tones... Any suggestions?!

     

    https://www.dropbox.com/s/thr505xogdlfrdb/AVID_Orlando_AFTER_first-pas s.mpeg

     

    This a huge sigh of relief for my client already. I showed him this and it is now acceptable. Less than ideal, but acceptable. Being a perfectionist, I still want to make it better - i.e. some of the diagonol lines still rear their ugly head in the flesh tones and lectern...

     

    Thanks again Charles for making me second-guess myself. Jim, any thoughts?

     

    Please keep in mind that THIS is where we started! - https://www.dropbox.com/s/bt8ev7c2xcpb3zq/AVID_Orlando_BEFORE.mpeg

     

    -BC

     
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