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Active or Passive? HDMI/DVI to VGA conversion


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#1 jjitter

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Posted 16 August 2016 - 01:45 PM

Hello All. 
I am looking to connect my PC with a Asus H-97 Pro motherboard, which has a HDMI out, DVI out to a Dell monitor with VGA input. VGA out on the CPU is already connected to the first monitor. Now I read that since HDMI, DVI are digital signals and VGA is analog, there is no way a passive 'converter' can be used to connect. 
But then I always read such mixed reviews of such passive cables where one says it doesn't work, while the other says its perfect! Couple of videos where passive cables worked to connect HDMI out to VGA input. So I wonder how is it working for them? Where is the conversion happening for them? When and what exactly is this passive HDMI to VGA cable used for? Do they work for gaming stations and not CPUs?

What is the trick to figuring out active or passive when connecting digital out to analog in? Is it safe to assume that it definitely requires an active circuitry? 
Coming back to my situation, what type of adapter should I buy? I have a HDMI out, DVI-D dual link out on my CPU and a VGA input Dell Monitor.

Thank you!



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#2 mjd420nova

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Posted 16 August 2016 - 02:08 PM

The newer monitors are active in that they handshake with the video circuitry to determine  the mode it needs to be it to match the input.  Driving more than two displays is dependent on the video hardware and not software.  I drive three, the main display on VGA, then extended display on DVI and the HDMI can display either but not a third source.  Audio is confined to stereo or surround but only one source.



#3 jjitter

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Posted 16 August 2016 - 02:21 PM

Hi. Thanks for the reply.

 

But all your monitors have VGA inputs right? What cable do you use to convert DVI/HDMI to VGA?

 

I am assuming my MB has the ability to drive more than one display since it has VGA, DVI and HDMI out.



#4 smax013

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Posted 17 August 2016 - 10:28 PM

It will depend on the DVI output. There is both digital and analog DVI...DVI-D and DVI-A. And then there are DVI-I output/cables that can handle both analog and digital. You can see what the different connections will look like on this Wikipedia page for DVI:

https://en.wikipedia.org/wiki/Digital_Visual_Interface#Connector

So, it will depend on what you DVI output supports. From looking up that motherboard, it appears that it is just a DVI-D output meaning it will only support digital output.

So, assuming your motherboard integrated graphics supports multiple displays (more on that in a moment), you would either need a monitor that has a DVI-D (or DVI-I since it will support DVI-D) or HDMI input for your second monitor OR get a active DVI-D to VGA converter box. Here is an example of such a DVI-D to VGA converter (not necessarily recommending it as I have never used it and have no clue how well it works, but rather an example hopefully showing what to look for...i.e. generally it will be powered by a power plug that either goes to a wall plug or a USB port to supply power to the "active" part):

https://www.amazon.com/StarTech-com-DVI2VGAE-1920x1200-Adapter-Converter/dp/B00C93JQXS/ref=sr_1_7?ie=UTF8&qid=1471490801&sr=8-7&keywords=dvi-d+to+vga+converter

If your computer had a DVI-I output, then you could have just used a DVI to VGA adapter cable or a DVI to VGA adapter with either a DVI cable or a VGA cable (not a converter...converter tends to imply that it is "actively" converting the signal).

Your graphics system also then need to support more than one monitor. According to the specs on the following page (I assuming I have the right motherboard), your graphics system can support up to three displays (last line under the Graphics section of the specs):

https://www.asus.com/Motherboards/H97PRO/specifications/

#5 jjitter

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Posted 18 August 2016 - 06:18 AM

Thanks a lot BC advisor! 

 

I forgot to mention my graphics card. I have Intel HD graphics 4600, which does support multiple displays. The manual says Multi-VGA support, 1x DVI, 1x HDMI.

 

Dont understand what exactly are these passive adapters, where one end is digital and the other analog. The only answers I get are it wont work, or it will work from manufacturers of passive adapters. They even say we use them to connect our projectors. How is it working for them? Are they just lying for sales? Does something like a passive DAC exist? Or are these products just a scam? 

 

Dont understand who to trust. I am just tired of buying a product and returning it.

 

Thank you BC



#6 smax013

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Posted 18 August 2016 - 07:24 AM

As I explained, DVI can be analog or digital. The analog DVI connection was a hold-over from the era when DVI connectors first came out.

As a result, there are two possible issues that must be dealt with to get a DVI output to work with a VGA input.

The first issue is the connector. This of this as fitting a round peg into a square hole type problem. You have two different connectors, so you need an "adapter" to make the transition from the one connector to the other. This issue will happen whether the DVI signal output is analog or digital.

The second issue is nature of the output signal. Think of this as "converting" or translating a language. If you have someone who only speaks French and you only speak English, then you need an "active" "converter" (aka a translator). Same basic concept here. If the DVI signal is only output in digital, then that signal need to be "converted" into an analog signal. This requires an "active" device...this would be a chipset that is basically acting as the translator. This issue will ONLY happen if the DVI signal is only digital...if it can also send out an analog signal (as a DVI-I connection can), then this issue is not an issue.

As I kind of implied, those that use a DVI to VGA adapter cable (aka "passive") and have it work have a DVI-I (or maybe even a DVI-A, although those are relative rare on computers...I have encountered monitors that were DVI-A input only) output on their computer. In other words, their computer can supply an analog output through the DVI output port. Many computers, especially older ones, do this (most of my computers have a DVI-I output which can support both digital and analog output). In this case, there is no need to "convert"/"translate" the signal from digital to analog. It is purely a matter of "adapting" the connector type from DVI to VGA (i.e. making the round peg fit in the square hole).

In your case, you KNOW you ONLY have a DVI-D (aka ONLY digital) output for your DVI output. An "active" converter is required. You need to "convert" the digital signal to an analog signal if you want to use that VGA only monitor. If you just use an adapter cable (i.e. "passive"), it WILL NOT work. Of course, you also need to "adapt" the connector type too.

#7 jjitter

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Posted 18 August 2016 - 07:37 AM

Thanks! Thats what I thought. Will get an active converter. 

 

Though I was wondering if there is a way to get an extended display with the multi-VGA out?



#8 smax013

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Posted 18 August 2016 - 07:47 AM

Thanks! Thats what I thought. Will get an active converter. 
 
Though I was wondering if there is a way to get an extended display with the multi-VGA out?


Based upon the way the manual and specs state "multi-VGA", I interpret in the most basic way...i.e. "multi-video graphics adapter", not VGA as in the analog 15 pin VGA output port. In other words, it is appears to refer to the ability to support multiple screens by way of the VGA, DVI-D and HDMI port.

The end result is that you should be able to use extended mode in Windows as opposed to only mirroring the displays.

I will note that because it is integrated graphics, with more than one display connected, the graphics "power" will be even more limited as you will be using more of the shared memory for graphics just to drive the two monitors. So, while integrated graphics systems typically don't do well with gaming, it will be even worse when driving two monitors. If you are only doing basic computer stuff such as email, browsing, word processing, spreadsheets, etc, then you should have few, if no, problems. If you start to do something that is more graphically intense, then you might have more problems than when you were only driving one screen.

#9 Platypus

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Posted 18 August 2016 - 07:55 AM

Dont understand what exactly are these passive adapters, where one end is digital and the other analog. The only answers I get are it wont work, or it will work from manufacturers of passive adapters. They even say we use them to connect our projectors. How is it working for them? Are they just lying for sales? Does something like a passive DAC exist? Or are these products just a scam?


They adapt the cable type, not the output signal type. In an emergency it lets you use an analog (VGA) cable to carry a digital signal or vice versa.

For example, at my church we have an old installation with a long throw projector fed via a VGA cable run under the control desk, in the wall up to the roof mounting. We haven't updated it because we hope to move to another building. The projector was expensive but the optic engine is slowly dying - we hope to get another 12 months out of it. Suppose the projector's VGA input failed, it would not be worth fixing it, but we wouldn't want to spend thousands just now on another long throw projector. Neither would we want to re-run a long digital cable so we could change to use the projector's DVI input. But we could get 2 cheap DVI-VGA adapters, and run the DVI signal over the existing VGA cable, until we move or the projector completely fails.

Edited by Platypus, 18 August 2016 - 07:56 AM.

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#10 mjd420nova

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Posted 18 August 2016 - 09:34 AM

There are a number of mfgrs of splitter boxes for video.  I am not a fan of adapters or converters, it seems to be more trouble than it's worth.  The Lenovo i5 desktop has those three outputs, VGA, DVI and HDMI.  But I only have two ways to display.  Of course, a larger display lets you have more tabs open so it could look like another separate display.



#11 smax013

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Posted 18 August 2016 - 09:43 AM

There are a number of mfgrs of splitter boxes for video.


A pure splitter will only mirror the image, however.

The original poster stated they want an extended desktop, not mirrored displays. This would require something along the lines of DualHead adapter like the following (which are not cheap...the original poster could buy a new monitor with a HDMI or DVI-D connection typically for what they cost if they wanted to avoid adapters/converters) rather than a splitter:

http://www.matrox.com/graphics/en/products/gxm/dh2go/analog/

#12 jjitter

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Posted 19 August 2016 - 07:42 AM

 

Dont understand what exactly are these passive adapters, where one end is digital and the other analog. The only answers I get are it wont work, or it will work from manufacturers of passive adapters. They even say we use them to connect our projectors. How is it working for them? Are they just lying for sales? Does something like a passive DAC exist? Or are these products just a scam?


They adapt the cable type, not the output signal type. In an emergency it lets you use an analog (VGA) cable to carry a digital signal or vice versa.

For example, at my church we have an old installation with a long throw projector fed via a VGA cable run under the control desk, in the wall up to the roof mounting. We haven't updated it because we hope to move to another building. The projector was expensive but the optic engine is slowly dying - we hope to get another 12 months out of it. Suppose the projector's VGA input failed, it would not be worth fixing it, but we wouldn't want to spend thousands just now on another long throw projector. Neither would we want to re-run a long digital cable so we could change to use the projector's DVI input. But we could get 2 cheap DVI-VGA adapters, and run the DVI signal over the existing VGA cable, until we move or the projector completely fails.

 

 

Thank you. But I dont understand what good will adapting to the cable type do without adapting/converting the signal type?

I have a feeling you are talking about DVI-I which carries analog too. Hence just the adapter will suffice. In case of DVI-D which is pure digital, will need an adapter which also has a converter inside.



#13 jjitter

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Posted 19 August 2016 - 07:49 AM

Thanks for the help everyone.

 

I think I will go ahead with a good converter. HDMI monitors are a little out of budget as of now.

And on the bright side, will always have options with a converter.



#14 Platypus

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Posted 19 August 2016 - 08:21 AM

But I dont understand what good will adapting to the cable type do without adapting/converting the signal type?


They let you use the cable you've got, even if it has the "wrong" connectors. If you've already got a $60 cable but it's the wrong one (e.g.VGA), instead of throwing it away and buying another $60 cable (e.g. DVI-D), you can buy two adapters for $10 and use the one you've got. Likewise someone who does video work can have a handful of adapters in their toolbox for emergencies and patch up a lead if they hand you the wrong one and say "sorry this is all we've got".

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#15 jjitter

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Posted 19 August 2016 - 05:04 PM

Thanks.

 

Getting an active connector. Hope all connects well...


Edited by jjitter, 19 August 2016 - 05:10 PM.





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