Input Lag with different connections

Everything about latency. Tips, testing methods, mouse lag, display lag, game engine lag, network lag, whole input lag chain, VSYNC OFF vs VSYNC ON, and more! Input Lag Articles on Blur Busters.
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AllenPCarlson
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Input Lag with different connections

Post by AllenPCarlson » 04 Feb 2018, 21:19

About 2 years ago you guys helped me choose the BenQ xl2411. When I bought it I tested the difference between HDMI and DVI and DVI was way faster. The way I did this was through a reflex tester website, with DVI I was near .12 seconds. With HDMI I was near .25 seconds. Which is a HUGE difference.

Now everything that I had at the time is basically toast, long story, but I'm in the market to buy a new. So I'm probably going to go with a laptop with which I'll connect to a monitor, keyboard, etc. But laptops don't usually use DVI... or ever use DVI, so which is fastest? Displayport? USB type C? Mini-displayport? VGA? Am I going back in time to VGA?

When I look up the difference between the connection methods everyone says, "There's no difference." Which is absolute BS from my own experience. So which is the fastest and why is that?

Sparky
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Re: Input Lag with different connections

Post by Sparky » 04 Feb 2018, 23:25

The way I did this was through a reflex tester website, with DVI I was near .12 seconds. With HDMI I was near .25 seconds. Which is a HUGE difference.
That is 130ms, which is about 8 frames at 60hz. Uncapped vsync can make a difference that big in extreme situations, but I don't see how HDMI can. I'd be surprised if the change in interface alone made more than 1ms difference on the same gpu and monitor. Most likely something else was going on.

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Chief Blur Buster
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Re: Input Lag with different connections

Post by Chief Blur Buster » 05 Feb 2018, 00:29

Lag difference of HDMI and DVI isn't that big, unless the monitor is defective.

Are you sure HDMI was set to the same refresh rate?

Cause #1
The screen refresh rate often automatically changes with different video inputs. Different refresh rates have different input lag (especially VSYNC ON), and when I move video cables, to switch from DVI to HDMI, my refresh rate automatically goes back to 60 Hz.

Cause #2
Also, if you have two monitors connected, Two monitors, one at 60Hz, one at 144Hz -- the dual-monitor can cause the 144Hz to have more lag. This is often noticed in TestUFO that often gets slowed down to 60fps even when displayed on the 144Hz monitor whenever a second monitor is set to 60Hz.

So:
(A) Verify your refresh rate did not change when you switched video cables. Go to Control Panel and reset it back to 144.
(B) Make it the primary monitor
(C) All multi monitors at the same refresh rate

If your lag differential is still that high, please report back.
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lexlazootin
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Re: Input Lag with different connections

Post by lexlazootin » 05 Feb 2018, 03:08

Like what everyone else is saying, i've personally tested ports with a 1000fps camera and a mouse i mounted with a LED and i was getting pretty identical performance with HDMI/DP, 1 millisecond to Sub millisecond performance.

There is a CHANCE that your monitor that you had or something at the time was doing something funky to add that much latency but it's still a EXTREME amount. It's so much that moving the mouse would be unbearable.

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RealNC
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Re: Input Lag with different connections

Post by RealNC » 05 Feb 2018, 09:58

I don't know about this monitor, but some monitors (mine included) use a different scaler module when using HDMI. So there can be different amounts of processing going on when you use HDMI, and thus different input lag values.

The "native" port of PC displays is almost always DVI or DisplayPort, if they have it. The HDMI port in these cases might be going through another scaler, which is there just for compatibility, and thus not optimal. Now I don't know how scalers actually work, so this might be BS, but I thought about that maybe the HDMI module is doing processing on its own, then convert the signal and pipe it to the DVI module, which then does its own processing on top of that? Someone who actually knows what they're talking about might be able to shed some light here :mrgreen:

In my case, the HDMI port goes through the monitor's scaler, while the DP port goes to the gsync module. It stands to reason that the HDMI scaler is not as good as the gsync module when it comes to processing overhead. Worst case scenario would be that the HDMI scaler might be doing full-frame buffering. We don't really know though. Review sites that do latency tests don't test HDMI.
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AllenPCarlson
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Re: Input Lag with different connections

Post by AllenPCarlson » 05 Feb 2018, 10:29

Thanks for the responses. I think I've worked it out.

What RealNC is saying makes some sense to me. Incidentally I've been talking to some retro gaming enthusiasts who say something similar about cheap upscalers producing input lag.

Keep in mind, this test was about 2 years ago and my memory isn't perfect. The take away, at the time was, VGA and DVI good, HDMI bad. If I remember corrected I tested VGA and HDMI from my laptop which has a gtx 660m, but it has that weird BS feature where the onboard GPU is in control of the desktop, while the 660m should(but rarely does) take over for gaming. Which has me wondering if there's something going on there.

Along with that, I think I had it hooked up to my old cheap flat screen TV. I'm not entirely sure if I did the same test with the gtx 970 with the BenQ XL 2411. I think I did, but I know I did the laptop test.

In any event, for my case, what you guys are essentially saying is, if I buy a laptop with a gtx 1060 and hook it up to a BenQ XL 2411 it won't matter if I use the HDMI or mini Displayport, right? It'll both be the same and fast. Right?

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Re: Input Lag with different connections

Post by Chief Blur Buster » 05 Feb 2018, 12:55

RealNC wrote:I don't know about this monitor, but some monitors (mine included) use a different scaler module when using HDMI. So there can be different amounts of processing going on when you use HDMI, and thus different input lag values.
Yes, the G-SYNC module is almost always lower lag than a default monitor scaler.

If any display has 2 separate processing units for different inputs -- then there could be major lag differentials (especially for terrible internal scalers) between the two.

Also switching inputs can automatically switch modes (e.g. enable HDR, enable 10-bit, enable improved television picture scaling algorithms) which may add lag for a specific input (e.g. HDMI).
AllenPCarlson wrote:In any event, for my case, what you guys are essentially saying is, if I buy a laptop with a gtx 1060 and hook it up to a BenQ XL 2411 it won't matter if I use the HDMI or mini Displayport, right? It'll both be the same and fast. Right?
If the laptop lid is closed and the external display is now the primary display -- then correct, the lag difference should only be approximately 1ms if the ports are designed correctly, for exactly the same resolution/color depth/settings.

Do not keep the laptop opened when playing on external displays higher-Hz than the laptop screen. Otherwise, the limited-Hz laptop screen can unintentionally add lag when playing on your high-Hz external display.

The desktop window manager (Windows compositor) often gets bottlenecked by the lowest common denominator refresh rate on a multiple-Hz multi-display setup.
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AllenPCarlson
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Re: Input Lag with different connections

Post by AllenPCarlson » 05 Feb 2018, 21:35

Chief Blur Buster wrote:
AllenPCarlson wrote:In any event, for my case, what you guys are essentially saying is, if I buy a laptop with a gtx 1060 and hook it up to a BenQ XL 2411 it won't matter if I use the HDMI or mini Displayport, right? It'll both be the same and fast. Right?
If the laptop lid is closed and the external display is now the primary display -- then correct, the lag difference should only be approximately 1ms if the ports are designed correctly, for exactly the same resolution/color depth/settings.

Do not keep the laptop opened when playing on external displays higher-Hz than the laptop screen. Otherwise, the limited-Hz laptop screen can unintentionally add lag when playing on your high-Hz external display.

The desktop window manager (Windows compositor) often gets bottlenecked by the lowest common denominator refresh rate on a multiple-Hz multi-display setup.
Great, thanks!

I just realized the BenQ XL 2411 doesn't have display port... what if I buy a DP to DVI adapter, would that produce any sort of lag?

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Re: Input Lag with different connections

Post by Chief Blur Buster » 06 Feb 2018, 00:41

Yes, electronic adaptors can add lag. Not much, but they do.
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