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Little DV cams + big rigs=video troubles


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#1 Charles Papert

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Posted 25 July 2004 - 01:22 PM

Here's the thing:

I flew an XL1s on my PRO last year and discovered that looping video out of the rig from anywhere (including the BNC on the TB6) for checking lighting on the broadcast monitor during setup was problematic. The image was dark in a "double terminated" fashion. The transmitted video was the same. The image on the rig was fine. We even tried cabling direct from the camera to the broadcast monitor, then looping back to the rig, which should have definitely worked, but it still double-terminated. We tried using a T out of the camera, didn't work either. Any available termination switches were thrown and re-thrown. Different cables were tried. All obvious techniques failed.

This week I saw Erwin's Ultimate do the same thing with a DVX100. So, two different DV cameras, two different sleds (and of course the Ultimate having a built in video d.a. to boot).

What's going on here??
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#2 RonBaldwin

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Posted 25 July 2004 - 06:12 PM

Charles,
I've had the same problem, but with an SR-3. While searching for the problem I flipped off my monitor and everyone at video villiage yelled "that's better!" Nice. Break out the paralax cross-hairs!

As I was reading your post I was thinking to myself "ahhh, that's what Greg Bubb is talking about." Then when you said Erwin's sled did it too...hmmm.

I have the older style Pro sled with the bnc at the bottom, the image is much better when I put a terminator on that connector (not sure which ohm -- 50 or 75). Having a playback recorder also makes a difference on my sled (with some taps). Seems like voo-doo to me

Ron
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#3 Mitch Gross

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Posted 26 July 2004 - 10:45 AM

Sounds like a small video distribution amp (VDA) is in order.
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#4 Charles Papert

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Posted 26 July 2004 - 01:09 PM

Mitch, I thought so too. Sort of really annoying, since that means it has to be powered...ugh. The real question is, why is this happening? And why, since the Ultimate has a DA in it, would this still be happening under these circumstances?
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#5 JasonMcKelvey

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Posted 26 July 2004 - 01:14 PM

Could it be that both DV camcorders were set to 0 setup intstead if 7.5 IRE setup?
Jason
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#6 RobVanGelder

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Posted 26 July 2004 - 08:57 PM

Jason, please explain as some of us video-nono´s don´t have a clue what you are talking about! Including me and I dare say I know a little bit about video.

Rob van Gelder, Bangkok, Thailand :blink:
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#7 PeterAbraham

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Posted 26 July 2004 - 09:16 PM

Charles,

I own a VERY small video D/A that can be powered by your sled, or a 9volt battery. I'll be glad to send it to you, to try out and see if that fixes the problem. It takes a video in, and delivers 5 separated 1 volt peak to peak video outs.

Worth a try. You want to try it?

Peter Abraham, E.M.T. for the time being.....
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#8 PeterAbraham

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Posted 26 July 2004 - 09:18 PM

Jason, if that were the case the recorded images would be pulled down badly as well. It does not sound as though this is the case.
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#9 JasonMcKelvey

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Posted 26 July 2004 - 09:28 PM

The broadcast standard for video sets limits to how bright the brightest whites are and how black the blacks are. NTSC standards state that the blackest you want blacks to be on a waveform is 7.5 IRE. Japan uses 0 IRE for true black. So, with DV products coming out of Japan, it's no wonder that there are standards problems. I know for a fact that the dvx100 and the pd150 have the option to set setup to 0 or 7.5 IRE. It would make sense to me that if the picture looks dark, the camera is set to 0. If some has access to one of these cameras, you could hook it up to your rig and switch it back and forth to 0 and 7.5. Also check it on playback back and forth. As a side note, this will affect your editing system and final output. It might look good on your rig, but the final product might have double setup (15 IRE) and look washed out when recorded out of the NLE to another DV deck (which might boost the black yet again by another 7.5).

I don't know if this is your problem though, usually it just looks really contrasty because the blacks are too low... not necessarily the whole picture looks dark.

Hope this helps.
Jason
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#10 Lawrence Karman

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Posted 27 July 2004 - 11:27 AM

I've been flying a Millenium XL these past couple of weeks and have been experiencing a dark picture when in interiors. The video guy was also complaining about a dark transmitted picture. Also I always seem to run my TB6 monitor at or near peak brightness and contrast for the best picture. Anywhere near the middle range is just too dark and flat to be usable. This prompted a call to Greg Bubb, the maker of the TB6. He felt that my sled, a PRO, had video distribution that was triple terminated and this would contribute to the dark picture. Greg suggested that I get one of those small video DA bricks (coincidentally the same one that Peter was offering to Charles). Well I got one and it made absolutely no difference. Of course the only place I could put it in line was directly out of the camera before the video input went into the sled. Yesterday with too much time on my hands I started fooling around with the switched on the video tap and found a gain switch which gave me a much brighter picture. Wahoo!

Pehaps sun spot activity could be to blame for your DV cam problems. Or Al Queda.
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#11 Brant S. Fagan SOC

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Posted 28 July 2004 - 08:06 AM

Gents--

The problem here is termination, plain and simple. A video DA will not correct the termination problems.

Just had this problem with a multi camera show last month. The engineer explained the video voodoo to me and this situation seems to be the same problem I had as well. However, my situation was caused by my rig monitor (the Panasonic 7" LCD monitor) being an auto terminate device rather than one which can be selected as terminated or non-terminated; also like some women can accomplish during a relationship, but a video DA here likewise will not help.

While adding a small video DA is a great idea to help sort and spread out the precious little camera images, termination is rather less forgiving, even when compared to women. Definitely a binary world rather than shades of gray.

All video signals must be terminated, just once with a 75 ohm load, either from a device in the signal path, or by adding a 75 ohm terminator.

Happy signalling!

Best,

Brant "Definitely Non-Terminated at home" Fagan
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#12 JimBartell

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Posted 28 July 2004 - 12:22 PM

All video signals must be terminated, just once with a 75 ohm load, either from a device in the signal path, or by adding a 75 ohm terminator.

Actually, this is an extremely common misconception. Termination is required to prevent reflection of the signal. This can only happen when the terminated end is a substantial fraction of one wavelength away from the source. At 10 MHz (typical for video) one wavelength is 66 feet long! So, unless you are running a reeeaaalllllyyyy long super post, termination is not required. Also, many Steadicams don't use 75 Ohm cable for video transmission anyway (PRO, IIIA, EFP, etc.), so termination adds nothing useful.

There is one other effect termination has that can be either good or bad, depending. In order to compensate for the 50% drop in signal amplitude when termination is applied, most video outputs are twice the intended amplitude when unterminated. This can give a signal that is too large for some inputs.

Jim "got a library full of electronics textbooks and not afraid to use them" Bartell
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#13 Charles Papert

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Posted 28 July 2004 - 01:23 PM

OK, so lots of thoughts and ideas, thanks everyone.

Jason: the cameras are indeed set for 0 IRE, which is recommended while in the digital domain. My understanding is that TV's, DVD players etc. will add the setup needed to bring it to the proper 7.5 IRE for the analog world, so we are doing the right thing. I should have added the following: cabling direct from the camera to the monitor worked just fine. Cabling through the rig caused the image to appear double-terminated. And as I described before, cabling from the camera to the monitor (again, fine) and then looping out of the monitor to the rig caused the image to go bad again on the monitor. And I should clarify that the image is not just a setup issue--the whole image drops down, with the appearance of an improperly-terminated signal.

A VDA mini-brick like the one Peter describes and offers (thanks Pete, I've actually got a couple of projects that I'll need these for so I'm about to order a handful) should do the trick...shouldn't it? Will a termination issue on one output of the VDA affect the others? In other words, a clean signal going into the VDA (from the camera) can then be passed on to the monitor, while another output goes to the sled. If the sled somehow terminates or otherwise messes up the video signal, are we saying that this will contaminate the other outputs, including the one to the monitor? I thought a VDA keeps things discrete. But then again--we've been seeing these problems on the Ultimate also, which uses an internal VDA.

keep 'em coming folks, we'll lick this thing yet.

Oh, and if anyone (Peter etc) has a recommendation on a brand/place to get good deals on 3 output VDA, I'm all ears. Doing the research but recommendations are good too.
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#14 JimBartell

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Posted 28 July 2004 - 01:39 PM

Oh, and if anyone (Peter etc) has a recommendation on a brand/place to get good deals on 3 output VDA, I'm all ears. Doing the research but recommendations are good too.

Hey Charles,

Here are two sources I've used before with good results:

VAC

Horita

Both offer solid products at very reasonable prices.

Jim "bargain hunter" Bartell
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#15 Mitch Gross

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Posted 28 July 2004 - 11:55 PM

Take a look at Markertek.com. There are lots of options on small VDAs.
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