Can an active Display Port --> DVI adapter retain 100% image quality?

NeilF · 17 Aug 2021 at 15:11

I'm looking to update my graphics card from an NVidia 1070 to a 3070. However, my current setup uses an Aten 1782a KVM using DVI. The 30000 series only have display ports and HDMI connections.

Been looking at various solution, but it seems one simple one is to just get Startech Display Port to DVI active adapter (DP2DVID2) for about £100.

So my two issues/questions with this are:-
1) Will the image quality suffer? Because if I get any image quality reduction, it's just not worth it.
2) I have a second monitor directly connected to my main PC (extending the desktop), so my understanding is, if EDID is not supported, then when I flick the KVM away from that machine, windows will think it's lost the monitor and redisplay the desktop. Which obviously I do not want. The adapter in question states "EDID pass-through" which I would hope means all will be ok?

The alternative to this is to get a whole new HDMI KVM, with all the possible issues with that, along with my other PC not having an HDMI connection, so would need to use a DP-->HDMI lead. Would that create EDID issues? Note: I'd also ideally have to get a 3070 with two HDMI ports to, meaning me getting an ASUS one instead of a preferred MSI.

Armageus · 17 Aug 2021 at 15:17

Assuming you have enough PCI-E slots and space, another option you have is to retain the 1070 as a second graphics card purely to drive the 2nd screen?

NeilF · 17 Aug 2021 at 15:48

Armageus said:
Assuming you have enough PCI-E slots and space, another option you have is to retain the 1070 as a second graphics card purely to drive the 2nd screen?

We're talking about the primary screen on the KVM.

The primary screen is on the KVM, and a small second HDMI monitor is also plugged into the gaming PC (extending its desktop) purely for a status display.

Armageus · 17 Aug 2021 at 16:09

Is it the monitor in your sig (PB278QV)?

I personally wouldn't spend £100 on an adapter (it's better spent on a KVM or updating your monitor for example)

Additional isn't your KVM limiting you to 60hz anyway?

Worst case you could directly connect the new GPU to the monitor (and switch inputs on the monitor), and still use the KVM just to switch Keyboard and Mouse

NeilF · 17 Aug 2021 at 18:03

Armageus said:
Is it the monitor in your sig (PB278QV)?

I personally wouldn't spend £100 on an adapter (it's better spent on a KVM or updating your monitor for example)

Additional isn't your KVM limiting you to 60hz anyway?

Worst case you could directly connect the new GPU to the monitor (and switch inputs on the monitor), and still use the KVM just to switch Keyboard and Mouse

Yes, a Asus PB278QV. (Supposed max refresh is 75hz)

It's hard to find a KVM that does above 60hz, and I'm not super bothered about high hz.

EDIT: I don't believe I could resort to just swapping keyboard and mouse with the KVM. If I switched away from my main PC to the other one via the monitor, the main PC would see the main monitor has gone, and I fear would then try and move the desktop over to the secondary monitor still plugged into it. Making a desktop mess!

LuckyBenski · 17 Aug 2021 at 18:12

DisplayPort can passively split (i.e. £5 cable or dongle) to HDMI or DVI-D. only up to 60Hz on the DVI though. Have you given this a try? It's worth a punt for £5 if you just want to keep a display running.

Spudgun · 17 Aug 2021 at 19:21

LuckyBenski said:
DisplayPort can passively split (i.e. £5 cable or dongle) to HDMI or DVI-D. only up to 60Hz on the DVI though. Have you given this a try? It's worth a punt for £5 if you just want to keep a display running.

Passive adapters are limited to 1080p and 60hz, so be aware of that if you go down this route

NeilF · 17 Aug 2021 at 19:23

Spudgun said:
Passive adapters are limited to 1080p and 60hz, so be aware of that if you go down this route

Tried a number of devices <£20. None of them can handle DP->DVI at above 1080p. Ie: I'm at 1440p.

The Startech unit in the op can do it by all accounts. If it can do it with no image quality issue, and retain EDID support, bingo.

My concern is DP doesn't seem to support EDID. At least no DP KVM offers it. My hope would be the Startech unit does offer/supporr it, so like the DVI port now, makes the Display Port think the monitor is attached when the KVM has moved the monitor to the other PC.

NeilF · 17 Aug 2021 at 20:26

Aten do an HDMI USB3 version of my old DVI USB2 KVM, the CS1822, but it's well over £300! - https://www.aten.com/global/en/products/kvm/desktop-kvm-switches/cs1822/

So with that I'd need top ensure I get an NVidia 3070 with TWO HDMI ports (eg: an Asus one not an MSI), so one HDMI lead to the new KVM and one to second monitor. And with my other PC, hope a DVI-->HDMI lead works OK (it only has DP and DVI ports).

NightSt@lk3r · 18 Aug 2021 at 06:03

NeilF said:
EDIT: I don't believe I could resort to just swapping keyboard and mouse with the KVM. If I switched away from my main PC to the other one via the monitor, the main PC would see the main monitor has gone, and I fear would then try and move the desktop over to the secondary monitor still plugged into it. Making a desktop mess!

Switching inputs on the monitor won't change anything on the main computer, it will only do that if you physically disconnect the port from the GPU, if it acted the way you think it does it would think the monitor has been disconnected just by turning it off.

And yes an active DisplayPort to DVI adaptor will retain 100% quality, i've used the StarTech mdp2dvid2 for years.

VersionMonkey · 18 Aug 2021 at 12:07

NightSt@lk3r said:
Switching inputs on the monitor won't change anything on the main computer, it will only do that if you physically disconnect the port from the GPU, if it acted the way you think it does it would think the monitor has been disconnected just by turning it off.

My monitor (a Dell P2415Q) does exactly that - it disconnects the inactive inputs so the PC on the other end behaves as if the cable was removed (and the soft power button on the front does the same for the active input).

Apparently that's normal for Dell monitors (according to an old post on their community site at least). Don't know if it applies to the OP's Asus monitor as I don't have one.

NeilF · 18 Aug 2021 at 13:11

VersionMonkey said:
My monitor (a Dell P2415Q) does exactly that - it disconnects the inactive inputs so the PC on the other end behaves as if the cable was removed (and the soft power button on the front does the same for the active input).

Apparently that's normal for Dell monitors (according to an old post on their community site at least). Don't know if it applies to the OP's Asus monitor as I don't have one.

Are you using Display Port?

NeilF · 18 Aug 2021 at 13:18

NightSt@lk3r said:
Switching inputs on the monitor won't change anything on the main computer, it will only do that if you physically disconnect the port from the GPU, if it acted the way you think it does it would think the monitor has been disconnected just by turning it off.

Testing this on my monitor, using HDMI, DP and DVI, if I switch the monitor between those sources, the HDMI and DVI retain connection - ie: The PCs do NOT redisplay their desktops. HOWEVER, the Display Port connection immediately loses its desktop when the monitor's source is moved away. This seems to backup my understanding that DP just does not offer EDID support at all?

So if I were to go down the manual selection route for my PCs via the monitor, then:-

Display Port = PC 1
HDMI = PC 2 (with a second HDMI lead to it's extended desktop on a second monitor).

This would sort of work, albeit clunky to change, and moving off PC 1 on the monitor shouldn't cause a problem as the monitor is it's only display.

HOWEVER, currently my work PC is connected into that Display Port, so during working days, I just use the monitor as an extension of it. So I have a conflict there of two PCs wanting to use that Display Port input into the monitor.

NightSt@lk3r said:
And yes an active DisplayPort to DVI adaptor will retain 100% quality, i've used the StarTech mdp2dvid2 for years.

Ooooooooooooooooooh!

So that's the exact unit I'm looking at, except it's mini-DP instead of normal sized DP. You believe it doesn't reduce image quality or introduce (noticably) lag? If that's the case, then that would be fab to know!

My only technical question then would be if the unit passes EDID through back to the PC from the KVM. Given DP doesn't seem to handle EDID normally, this is the question mark. ie: I don't want to find switching the KVM input (or changing the monitor source) screws up the display on the PC using the Startech adapter (DP --> DVI)... Worse case I buy, try, return.

VersionMonkey · 18 Aug 2021 at 14:54

NeilF said:
Are you using Display Port?

I am for the two PCs. I have an RPi on the HDMI input (which doesn't recognise the monitor presence on boot, if the input isn't selected; but doesn't care if I then switch away).

NeilF said:
This seems to backup my understanding that DP just does not offer EDID support at all?

Some quick further reading suggests it is down to the way that DP specifies the Hotplug Detect feature. It seems many people with many different makes of monitor experience the same switching behaviour; although a few monitors apparently don't do it. So I might have been a little harsh calling out Dell specifically.

Display port is supposed to support EDID. I think the EDID emulators that are sometimes used with KVMs must be providing correct hotplug signals, as well as an EDID to inform the connected PC of the display resolution/frequency.

NightSt@lk3r · 18 Aug 2021 at 17:28

NeilF said:
My only technical question then would be if the unit passes EDID through back to the PC from the KVM. Given DP doesn't seem to handle EDID normally, this is the question mark. ie: I don't want to find switching the KVM input (or changing the monitor source) screws up the display on the PC using the Startech adapter (DP --> DVI)... Worse case I buy, try, return.

I have 2 PC's connected to the monitor which is connected to my main PC via the StarTech adaptor and the monitor is never lost when switching to my secondary PC.

NeilF · 18 Aug 2021 at 18:20

NightSt@lk3r said:
I have 2 PC's connected to the monitor which is connected to my main PC via the StarTech adaptor and the monitor is never lost when switching to my secondary PC.

Excellent. Thanks!

So it seems the clear toss up is between:-

£100 for the Startech DP-->DVI adapter - Use this to simply allow my PC to use an Nvidia 3070's DP to fit into my existing DVI KVM.
Or £330 CS1822 HDMI KVM - Future proof mysetup by moving over to HDMI. ie: If I replace my other PC, it's unlikely to have a DVI port, so I'll be back in the same situation again!

Armageus · 18 Aug 2021 at 19:44

What about a software screen sharing/kvm solution?

Spudgun · 18 Aug 2021 at 20:15

NeilF said:
Excellent. Thanks!

So it seems the clear toss up is between:-

£100 for the Startech DP-->DVI adapter - Use this to simply allow my PC to use an Nvidia 3070's DP to fit into my existing DVI KVM.

Or £330 CS1822 HDMI KVM - Future proof mysetup by moving over to HDMI. ie: If I replace my other PC, it's unlikely to have a DVI port, so I'll be back in the same situation again!

The Dell bizzlink active adapter could do the same job as the starlink and can be had for around £40 on the bay

NeilF · 18 Aug 2021 at 22:22

Armageus said:
What about a software screen sharing/kvm solution?

Alas, the server is on virtually all the time (the single screen PC), and my gaming PC (with two screens) is far less often on.

So using one to reach the other makes no real sense?

NeilF · 18 Aug 2021 at 22:29

Spudgun said:
The Dell bizzlink active adapter could do the same job as the starlink and can be had for around £40 on the bay

Yeh, seems a lot of folks report issues with that one? And I don't know if it supports EDID etc? ie: If I when it's used with my KVM, if switch to the other PC will make it think the monitor is turned off so screw up the desktop.