A few specific questions about input delay when locking FPS to 60 on high refresh rate monitor

[Cifer]

Hello everyone,

I hope the questions below haven't been answered before, but I couldn't find a direct answer on the forums or in the articles.

I'm trying to figure out the input latency difference between a specific 4K 60Hz Monitor and a high refresh rate 1440p monitor when running games at 60 FPS because they either don't support higher frame rates, or because they have issues at higher frame rates and I have to lock them (through vsync or through a direct lock).

The two models I want to compare are the Dell 2721QS and the Dell G2724D. I cannot link to rtings, so you'll have to open the comparison page there yourself if you want to help.

There are several input latency measurements shown for high refresh rate monitors: max refresh rate, 120 FPS, and 60 FPS.

How exactly do I figure out the input delay difference between the 60 Hz monitor and the high refresh monitor running at max refresh rate when playing a game locked to 60 FPS?

According to rtings, the input latency shown applies to when the monitor is "set to" 60 Hz, but it also says that it applies when a source's output is 60 Hz - a console for example. Are those two the same thing? Does running a game from a console whose output is limited to 60 Hz or 120 Hz make the monitor run at that Hz even if I don't change the monitor's refresh rate?

And do I understand it correctly that this isn't related at all to the monitor's input latency when a PC game is inherently locked to 60 FPS or when I limit a game to 60 FPS which supports unlocked framerate? Is it possible at all to figure out from the rtings measurements how much latency I would get?

Thanks a lot!

[RealNC]

According to rtings, the input latency shown applies to when the monitor is "set to" 60 Hz, but it also says that it applies when a source's output is 60 Hz - a console for example. Are those two the same thing?

Yes. When the source outputs 60Hz, that's the same as saying the monitor is set to 60Hz. (The console sets it.)

Does running a game from a console whose output is limited to 60 Hz or 120 Hz make the monitor run at that Hz even if I don't change the monitor's refresh rate?

You cannot change the monitor's refresh rate yourself. You need to configure the source to set it. Whether that's on PC or console doesn't matter. Even monitors that come with some refresh rate change button, what that button really does is communicate to the PC that it should set a different refresh rate.

And do I understand it correctly that this isn't related at all to the monitor's input latency when a PC game is inherently locked to 60 FPS or when I limit a game to 60 FPS which supports unlocked framerate? Is it possible at all to figure out from the rtings measurements how much latency I would get?

The monitor's latency doesn't change, regardless of the frame rate. If a monitor runs at 120Hz, you can ignore the 60Hz latency data. Keep in mind that the total input latency will increase when going from 120FPS to 60FPS. But that increase comes from the game's side. The monitor's latency stays the same. Which is why total latency is a bit lower when running 60FPS@120Hz compared to 60FPS@60Hz. This is true for VRR as well (g-sync/freesync.) With VRR, the monitor should be set to its highest refresh rate (not just for better latency, but also for much better LFC.)

[Cifer]

Thanks a lot!

So if I understand correctly this means that a) for PC gaming only the highest refresh rate data will matter, and b) I can't know from the rtings data what exactly the latency will be when running a 60 fps game on the 144 or 165 monitor, correct?

How big do you presume the difference will be between the two monitors?

And would the added latency from using vsync and locking frame rate slightly below refresh rate be roughly the same on both monitors? Does vsync add proportionally more latency depending on the latency of the monitor, or is it essentially a fixed amount that's largely the same on all monitors when running at 60 fps?
I hope the way I worded it is comprehensible.

I currently have the 2721QS monitor and was planning to get a monitor for games, but realized that almost everything I was planning to play in the next year are older games locked to - or unplayable correctly above - 60 fps. So now I am considering using the monitor I already have here to play those, and by the time I start playing more modern games again there might be better monitors available anyway.

However, I'm sensitive too put latency, so I'm curious how much worse it would be on the 2721QS compared to high refresh rate monitors.

[RealNC]

So if I understand correctly this means that a) for PC gaming only the highest refresh rate data will matter, and b) I can't know from the rtings data what exactly the latency will be when running a 60 fps game on the 144 or 165 monitor, correct?

How big do you presume the difference will be between the two monitors?

And would the added latency from using vsync and locking frame rate slightly below refresh rate be roughly the same on both monitors?

You can't know the exact total input latency anyway from these tests. There's a lot of factors that contribute to the total latency and it really isn't something that a review site can test. With one game and a certain mouse and a certain GPU and CPU, you might have 140ms total latency, with another game, a different mouse and different GPU and CPU you might have 40ms. Even at the exact same FPS!

The latency tests performed by rtings serve one purpose only: to make it possible to compare different displays to each other. If display A has 2ms lower latency than display B, this will translate to a 2ms lower overall latency for A compared to B.

Note that the tests performed by review sites are different, and they give different results. You can't compare displays by using rtings data for one display and, say, PC Monitors for another display.

Vsync and FPS caps don't matter in the comparison. No matter what you do, monitor A will always have a 2ms advantage over the other when both are used in the exact same way. This is what rtings tests are useful for.

Does vsync add proportionally more latency depending on the latency of the monitor, or is it essentially a fixed amount that's largely the same on all monitors when running at 60 fps?

Vsync lag does not affect the monitor's latency. It all happens before the signal even enters the cable. It's caused by the PC, not the monitor. The monitor doesn't care about vsync (it doesn't even actually know what vsync is - vsync is a GPU feature, not a display feature.)

However, I'm sensitive too put latency, so I'm curious how much worse it would be on the 2721QS compared to high refresh rate monitors.

When going from a 60Hz display to a high refresh rate display like 144Hz or higher, you will actually see a big latency decrease if you use VRR (freesync/gsync.) Not because of the monitor itself, but because of the huge latency decrease VRR gives you when you are not reaching the vsync cap.

But you can do that already though. If you run a 60FPS game on a 60Hz display, you better cap your FPS to something like 58 or 57 when using VRR. If you use a 144Hz display, you can cap to whatever you want though (if the game is fine with it.) You can cap to 70, 84, up to about 140 (to avoid 144Hz vsync cap.) Give it a try and see how it goes. Usually all you have to do is:

• Enable vsync
• Enable g-sync (or freesync on AMD)
• Cap your FPS to 57 (or 58 might also work)

A high refresh rate display though will give you way more freedom in your choice of FPS. You can cap to whatever you want. 60, 64, 77, 91, whatever arbitrary value you want. Up to a limit of course, to avoid reaching the vsync limit. It will also lower latency a bit more, because with VRR, even if you run a 60FPS game, if the monitor runs at 144Hz (or whatever its max is) you will still get 144Hz scanout speed for each frame. At 144Hz, each frame takes 10ms less time to be scanned out compared to 60Hz, which translates to 5ms less average latency.

Of course you could apply this FPS cap even without VRR, but then you'd get stutter because of FPS/Hz mismatch, which is the main problem VRR was invented to fix.

[Cifer]

Thanks again!

I am aware that other peripherals as well as the PC itself contribute to latency as well, but since those will be the same, I'm only interested in the monitor differences - in case I wasn't clear enough.

I've been using Vsync and capping my frame rate below refresh rate for years, and that's also what I would do with both displays, and it's also the scenario in which i'd like to compare the performance of the two monitors.

The latency difference you mention between 60 Hz with Vsync and 60 fps Vsync on a high refresh monitor is exactly what I was trying to figure out. I've read the old article about how everything works, but I don't quite understand how I could figure out the difference between these two specific monitors with only the data on rtings.

What do you estimate the difference would be, very roughly? I'd really just like to know if it would be closer to the 9 ms at 60Hz/60fps or to the 3ms at max refresh rate and high fps.

Another quick question on the side:
I just realized that 60 fps on 144 Hz or 165 Hz monitors would perform badly because 60 is not a divisor of 144 or 165, meaning that it would likely not be a good idea to use the monitor in question either way.

Is there actually a way around this issue on monitors with those refresh rates, or is the only solution to buy a 180 Hz, 240 Hz Monitor, etc.?

[RealNC]

What do you estimate the difference would be, very roughly? I'd really just like to know if it would be closer to the 9 ms at 60Hz/60fps or to the 3ms at max refresh rate and high fps.

The signal processing delay difference between the two monitors appears to be 0.3ms, so that's negligible. It also means that as you raise the refresh rate to 165Hz, input lag at the top of the screen stays virtually the same, improves by 5ms in the middle of the screen, and improves by 10ms at the bottom of the screen. So average input lag improves by 5ms.

This is a simple refresh rate frame scanout time calculation. 1000 / Hz gives you the frame scanout time in ms.

60Hz: 1000 / 60 = 16.7ms
165Hz: 1000 / 165 = 6.1ms.

So that's difference of 10.6ms of input lag at the bottom of the screen. The average is half of that, so that's about 5ms of an improvement. Normally you add the two monitor's processing lag difference on top of that, but since it's only 0.3ms, we ignore it.

What all of this means is that if your 60FPS game has an average input lag of 70ms currently, you can expect it to have about 65ms in the 165Hz monitor.

Obviously with games where you can reach high FPS and they're not locked to 60, the input lag improvement is going to be much, much better (like dropping from 65ms to 30ms.)

I just realized that 60 fps on 144 Hz or 165 Hz monitors would perform badly because 60 is not a divisor of 144 or 165, meaning that it would likely not be a good idea to use the monitor in question either way.

Is there actually a way around this issue on monitors with those refresh rates, or is the only solution to buy a 180 Hz, 240 Hz Monitor, etc.?

This is solved by VRR (freesync or g-sync.) This also requires the monitor's VRR and the GPU's VRR to work correctly though. I've seen people still have stutter issues with low FPS, but most of the time this happens when you approach 40FPS. At 60, it's usually fine.

[Cifer]

Thanks a lot!

So just to sum it up, because I'm really quite new to this topic since I have not played 60 fps limited titles in decades:

If I simply play those games at 60 fps - with V-Sync and framerate capped to minimize input lag - then the difference will likely be about 5 ms between both monitors, and there isn't any setting or tweak that will change that number even further in favour of the higher refresh rate one. Correct?

If that is true then it's probably indeed better to simply use the 4K/60Hz monitor for now and buy a higher refresh monitor later when - if ever - I actually play modern games again. 5 ms even in action games isn't a huge deal compared to the overall system latency, I feel.

[RealNC]

If I simply play those games at 60 fps - with V-Sync and framerate capped to minimize input lag - then the difference will likely be about 5 ms between both monitors, and there isn't any setting or tweak that will change that number even further in favour of the higher refresh rate one. Correct?

With vsync, you can't play at 60FPS on a 60Hz monitor. There will be way more of a lag difference than just 5ms. More like 30ms or even more. You need to cap to about 58FPS to avoid vsync lag.

(This extra latency has nothing to do with the monitor. It's simply a side effect of vsync called "vsync backpressure." Capping to 58FPS should avoid it on a 60Hz display, but without VRR this will result in some animation jitter. If you're on an nvidia GPU, this 58FPS cap is performed automatically by the driver if you have gsync enabled and also set "low latency mode" to "ultra" in the nvidia control panel. This effect is not specific to 60Hz. The same thing would happen if you played a game at 144FPS vsync on a 144Hz monitor. To avoid vsync backpressure, you'd need to cap the game lower than 144FPS; the nvidia driver in this case would auto-cap to 138FPS.)