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I have to run a 10ft cable to reach a VGA cable which is another 6ft. The source is DVI, the destination is VGA. Would there be any signal difference if I...

  • Used a DVI>VGA adapter and then a 10ft VGA cable, or
  • Used a DVI>VGA cable to run the 10ft without the adapter.

Edit: This is for a small 7" touchscreen display, native resolution is 800x480, resolution in use is 1024x768. The DVI>VGA adapter is passive. Converter was the wrong work to use.

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What resolution displays are you looking at? What refresh rate? DVI-D should cope well with WUGXA (1920x1200@60Hz) up to 15ft, further with a lower resolution, whereas analogue cables can show significant ghosting with even 1024x768 at that distance, even with good quality cables. –  Mark Booth Sep 5 '11 at 10:27
Also as suggested in the answers, are you talking about a passive DVI-A/DVI-I to VGA converter like this, or an active DVI-D to VGA converter like this? –  Mark Booth Sep 5 '11 at 10:40
I've updated my answer to be more clear, thanks. –  Josh M. Sep 5 '11 at 16:34
Any particular reason why you are sending a 1024x768 signal to an 800x480 device? You would probaly get a much better quality display if you scaled your application to the screen rather than relying on the screens internal re-scaling. –  Mark Booth Sep 5 '11 at 17:20
The display is listed as "High Resolution Display 800x480 up to 1024 x 768." And 800x480 is not a "normal" resolution so it doesn't show up as an option unless you use a 3rd party app to add it as a value. I'd rather just go the easy route - the display supports it and it looks good. Thanks. –  Josh M. Sep 5 '11 at 18:09
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3 Answers

Assuming the quality of both cables is the same and that the quality of the internal DVI-to-VGA converter of the source and of the external converter are the same, no.

But still, the best idea is to run a 16ft DVI cable and then place the converter at the very end, so that the signal is digital along most of the path.


By "converter" I assume that you mean a device to convert the DVI-D signal to a VGA signal, and not just a connector that peels the analog signals from a DVI-I source.

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Sorry I was unclear, it is a simple passive DVI>VGA adapter. –  Josh M. Sep 5 '11 at 16:30
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If its a passive converter, you MUST put the converter first then the cable - the physical connector configuration is used to switch between DVI A and DVI D - otherwise there's no real difference, since the output is analogue anyway.If its an active converter, using the digital signal, then switching to analogue at the last possible time is a smarter idea - since digital signals degrade less.

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I must somewhat disagree with Ignacio Vazquez-Abrams. Since no DAC is mentioned in the question, I'll assume that there isn't any.

In that case, backward compatibility of DVI is used (there's the DVI-A mode). Some (I'd say most) DVI connectors can send analog signal through the cable to work with analog receivers. Then the signal goes through the DVI->VGA converter that is just a mechanical converter which provides a VGA plug at the end of the line and the signal is actually analog the whole way.

In that case, I'd say that the difference would mostly be in the type of particular cable used and in forward compatibility needed at the end of the cable.

The DVI cable itself may be better than a VGA cable, but there's no guarantee of that. On the other hand, if you plan to switch to digital later on, than DVI may be better option.

Also be sure to check if the source can provide analog signal through the DVI port. If it doesn't, then you'd need an active converter, which can cost a lot more than passive, but you'd have digital signal up to the point at which the DVI cable ends.

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Thanks for your explanation, it helps to know that the DVI>VGA adapter is simply grabbing the analog signal from the line, I wasn't sure how it worked. That makes it clear that the type of cable doesn't matter as much as the quality. Yes, the source does provide an analog signal as well, I'm running about 12ft now and the picture is good. Before I was using a 25ft VGA cable and the picture was dismal. I just need a couple extra feet so I can "hide" the cable. –  Josh M. Sep 5 '11 at 16:33
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