G-SYNC 101: Input Lag & Test Methodology


Test Setup

High Speed CameraCasio Exilim EX-ZR200 w/1000 FPS 224x64px video capture
DisplayAcer Predator XB252Q 240Hz w/G-SYNC (1920×1080)
MouseRazer Deathadder Chroma modified w/external LED
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Nvidia Driver381.78
Nvidia Control PanelDefault settings (“Prefer maximum performance” enabled)
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OSWindows 10 Home 64-bit (Creators Update)
MotherboardASRock Z87 Extreme4
Power SupplyEVGA SuperNOVA 750 W G2
HeatsinkHyper 212 Evo w/2x Noctua NF-F12 fans
CPUi7-4770k @4.2GHz w/Hyper-Threading enabled (8 cores, unparked: 4 physical/4 virtual)
GPUEVGA GTX 1080 FTW GAMING ACX 3.0 w/8GB VRAM & 1975MHz Boost Clock
Sound CardCreative Sound Blaster Z (optical audio)
RAM16GB G.SKILL Sniper DDR3 @1866 MHz (dual-channel: 9-10-9-28, 2T)
SSD (OS)256GB Samsung 850 Pro
HDD (Games)5TB Western Digital Black 7200 RPM w/128 MB cache
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Test Game #1Overwatch w/lowest settings, “Reduced Buffering” enabled
Test Game #2Counter-Strike: Global Offensive w/lowest settings, “Multicore Rendering” disabled

Introduction

The input lag testing method used in this article was pioneered by Blur Buster’s Mark Rejhon, and originally featured in his 2014 Preview of NVIDIA G-SYNC, Part #2 (Input Lag) article. It has become the standard among testers since, and is used by a variety of sources across the web.

Middle Screen vs. First On-screen Reaction

In my original input lag tests featured in this thread on the Blur Busters Forums, I measured middle screen (crosshair-level) reactions at a single refresh rate (144Hz), and found that both V-SYNC OFF and G-SYNC, at the same framerate within the refresh rate, delivered frames to the middle of the screen at virtually the same time. This still holds true.

Blur Buster's G-SYNC 101: Input Lag & Optimal Settings

However, while middle screen measurements are a common and fully valid input lag testing method, they are limited in what they can reveal, and do not account for the first on-screen reaction, which can mask the subtle and not so subtle differences in frame delivery between V-SYNC OFF and various syncing solutions; a reason why I opted to capture the entire screen this time around.

Due to the differences between the two test methods, V-SYNC OFF results generated from first on-screen measurements, especially at lower refresh rates (for reasons that will later be explained), can appear to have up to twice the input lag reduction of middle screen readings:

Blur Buster's G-SYNC 101: Middle Screen vs. First On-screen Reaction Diagram

As the diagram shows, this is because the measurement of the first on-screen reaction is begun at the start of the frame scan, whereas the measurement of the middle screen reaction is begun at crosshair-level, where, with G-SYNC, the in-progress frame scan is already half completed, and with V-SYNC OFF, can be at various percentages of completion, depending on the given refresh rate/framerate offset.

When V-SYNC OFF is directly compared to FPS-limited G-SYNC at crosshair-level, even with V-SYNC OFF’s framerate at up to 3x times above the refresh rate, middle screen readings are virtually a wash (the results in this article included). But, as will be detailed further in, V-SYNC OFF can, for a lack of better term, “defeat” the scanout by beginning the next frame scan in the previous scanout.

With V-SYNC OFF at -2 FPS below the refresh rate, for instance (the scenario used to compare V-SYNC OFF directly against G-SYNC in this article), the tearline will continuously roll downwards, which means, when measured by first on-screen reactions, its advantage over G-SYNC can be anywhere from 0 to 1/2 frame, depending on the ever-fluctuating position of the tearline between samples. With middle screen readings, the initial position of the tearline(s), and thus, its advantage, is effectively ignored.

These differences should be kept in mind when inspecting the upcoming results, with the method featured in this article being the best case scenario for V-SYNC OFF, and the worst case scenario for synced when directly compared to V-SYNC OFF, G-SYNC included.

Test Methodology

To further facilitate the first on-screen reaction method, I’ve changed sample capture from muzzle flash to strafe for Overwatch (credit goes to Battle(non)sense for the initial suggestion) and look for CS:GO, which triggers horizontal updates across the entire screen. The strafe/look mechanics are also more consistent from click to click, and less prone to the built-in variable delay experienced from shot to shot with the previous method.

To ensure a proper control environment for testing, and rule out as many variables as possible, the Nvidia Control Panel settings (but for “Power management mode” set to “Prefer maximum performance”) were left at defaults, all background programs were closed, and all overlays were disabled, as was the Creators Update’s newly introduced “Game Mode,” and .exe Compatibility option “fullscreen optimizations,” along with the existing “Game bar” and “Game DVR” options.

To guarantee extraneous mouse movements didn’t throw off input reads during rapid clicks, masking tape was placed over the sensor of the modified test mouse (Deathadder Chroma), and a second mouse (Deathadder Elite) was used to navigate the game menus and get into place for sample capture.

To emulate lower maximum refresh rates on the native 240Hz Acer Predator XB252Q, “Preferred refresh rate” was set to “Application-controlled” when G-SYNC was enabled, and the refresh rate was manually adjusted as needed in the game options (Overwatch), or on the desktop (CS:GO) before launch.

And, finally, to validate and track the refresh rate, framerate, and the syncing solution in use for each scenario, the in-game FPS counter, Nvidia Control Panel’s G-SYNC Indicator, and the display’s built-in refresh rate meter were active at all times.

Testing was performed with a Casio Exilim EX-ZR200 capable of 1000 FPS high speed video capture (accurate within 1ms), and a Razer Deathadder Chroma modified with an external LED (credit goes to Chief Blur Buster for the mod), which lights up on left click, and has a reactive variance of <1ms.

Blur Buster's G-SYNC 101: Input Lag & Optimal Settings

To compensate for the camera’s low 224×64 pixel video resolution, a bright image with stark contrast between foreground and background, and thin vertical elements that could easily betray horizontal movement across the screen, were needed for reliable discernment of first reactions after click.

For Overwatch, Genji was used due to his smaller viewmodel and ability to scale walls, and an optimal spot on the game’s Practice Range was found that met the aforementioned criteria. Left click was mapped to strafe left, in-game settings were at the lowest available, and “Reduced Buffering” was enabled to ensure the lowest input latency possible.

Blur Buster's G-SYNC 101: Input Lag & Optimal Settings

For CS:GO, a custom map provided by the Blur Busters Forum’s lexlazootin was used, which strips all unnecessary elements (time limits, objectives, assets, viewmodel, etc), and contains a lone white square suspended in a black void, that when positioned just right, allows the slightest reactions to be accurately spotted via the singular vertical black and white separation. Left click was mapped to look left, in-game settings were at the lowest available, and “Multicore Rendering” was disabled to ensure the lowest input latency possible.

For capture, the Acer Predator XB252Q (LED fixed to its left side) was recorded as the mouse was clicked a total of ten times. To average out differences between runs, this process was repeated four times per scenario, and each game was restarted after each run.

Once all scenarios were recorded, the .mov format videos, containing ten samples each, were inspected in QuickTime using its built-in frame counter and single frame stepping function via the arrows keys. The video was jogged through until the LED lit up, at which point the frame number was input into an Excel spreadsheet. Frames (thanks to 1000 FPS video capture, represent a literal 1ms each) were then stepped through until the first reaction was spotted on-screen, where, again, the frame number was input into the spreadsheet. This generated the total delay in milliseconds from left click to first on-screen reaction, and the process was repeated per video, ad nauseam.

All told, 508 videos weighing in at 17.5GB, with an aggregated (albeit slow-motion) 45 hour and 40 minute runtime, were recorded across 2 games and 6 refresh rates, containing a total of 42 scenarios, 508 runs, and 5080 individual samples. My original Excel spreadsheet is available for download here, and can also be viewed online here.

Blur Buster's G-SYNC 101: Input Latency & Optimal Settings

To preface, the following results and explanations assume that the native resolution w/default timings are in use on a single monitor in exclusive fullscreen mode, paired with a single-GPU desktop system that can sustain the framerate above the refresh rate at all times.

This article does not seek to measure the impact of input lag differences incurred by display, input device, CPU or GPU overclocks, RAM timings, disk drives, drivers, BIOS, OS, or in-game graphical settings. And the baseline numbers represented in the results are not indicative of, and should not be expected to be replicable on other systems, which will vary in configuration, specs, and the games being run.

This article seeks only to measuring the impact V-SYNC OFF, G-SYNC, V-SYNC, and Fast Sync, paired with various framerate limiters, have on frame delivery and input lag, and the differences between them; the results of which are replicable across setups.

+/- 1ms differences between identical scenarios in the following charts are usually within margin of error, while +/- 1ms differences between separate scenarios are usually measurable, and the error margin may not apply. And finally, all mentions of “V-SYNC (NVCP)” in the denoted scenarios signify that the Nvidia Control Panel’s “Vertical sync” entry was set to “On,” and “V-SYNC OFF” or “G-SYNC + V-SYNC ‘Off'” signify that “Use the 3D application setting” was applied w/V-SYNC disabled in-game.

So, without further ado, onto the results…

Input Lag: Not All Frames Are Created Equal

When it is said that there is “1 frame” or “2 frames” of delay, what does that actually mean? In this context, a “frame” signifies the total time a rendered frame takes to be displayed completely on-screen. The worth of a single frame is dependent on the display’s maximum native refresh rate. At 60Hz, a frame is worth 16.6ms, at 100Hz: 10ms, 120Hz: 8.3ms, 144Hz: 6.9ms, 200Hz: 5ms, and 240Hz: 4.2ms, continuing to decrease in worth as the refresh rate increases.

With double buffer V-SYNC, there is typically a 2 frame delay when the framerate exceeds the refresh rate, but this isn’t always the case. Overwatch, even with “Reduced Buffering” enabled, can have up to 4 frames of delay with double buffer V-SYNC engaged.

Blur Buster's G-SYNC 101: Input Lag & Optimal Settings

The chart above depicts anywhere from 3 to 3 1/2 frames of added delay. At 60Hz, this is significant, at up to 58.1ms of additional input lag. At 240Hz, where a single frame is worth far less (4.2ms), a 3 1/2 frame delay is comparatively insignificant, at up to 14.7ms.

In other words, a “frame” of delay is relative to the refresh rate, and dictates how much or how little of a delay is incurred per, a constant which should be kept in mind going forward.



303 Comments For “G-SYNC 101”

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orr-man
Member
orr-man

This is a really interesting read and I’ve followed this and tested this myself in Sea of Thieves tonight, by manipulating the graphics settings to be more or less demanding and then tweaking NVCP VSync vs. in game VSync; GSync on vs. off; and GSync with NVCP VSync on vs. off.

I took me too long to realise you have to close the game before changes made in NVCP take effect…

Anyhow, there is one thing I don’t really understand:-

My monitor is 240Hz and as far as I understand it, the GSync range is up to 240Hz. With GSync on and NVCP VSync off (and on the lowest graphics settings) my FPS exceeded 240, was above my refresh rate, and I could get tearing (although to my eyes, this was actually quite hard to notice – I had to really look for it).

But the article talks about having VSync on in the NVCP alongside GSync and it mentions that VSync behaviour will occur if the GSync range is exceeded. Am I correct in thinking that this only applies if the GSync range is not the same as the monitor’s maximum refresh rate, as VSync stops FPS from exceeding the maximum refresh rate?

E.g. My monitor is 240Hz and my GSync range is up to 240Hz. With GSync on and NVCP VSync on I benefit from frame time compensation when the frame rate is below 240. However, the frame rate can’t go above 240 and so the VSync behaviour can’t happen.

But if my monitor is 240Hz and my GSync range is limited to 144hz then when VSync is enabled I may get FPS above 144 (upto 240) at which point GSync no longer applies but VSync behaviour kicks in?

Or am I misunderstanding something?

With good settings and resolution I naturally sit below 240fps in pretty much every game, but I’d like to make sure I understand and am following this correctly.

Thanks.

DrGoku4star
Member
DrGoku4star

Hey, this has been driving me crazy for a while now, but i’m using a freesync monitor (MPG27CQ) With driver level ‘Gsync’ paired with a GTX 1080ti, latest driver.

Regardless of NVCP Vsync on or off with Gsync on, i can’t see any screen tearing. But, with Vsync on, my mouse feels heavier on my wrist, but with it off, it feels alot lighter and more responsive. It’s eaiser to flick shot with with NVCP Vsync on (not sure if that’s because i’m used to it) then it is with it off.

I use Riva 141 fps cap with it on my 144 hertz monitor. I also have a 1080p 60 hertz monitor oc to 72 (not sure if that could cause a problem)

I can’t help but feel this has something to do with using a Gsync module guide on a Freesync/Gsync set up. Will you be doing any testing on this?

Thanks in advance

Spazmore
Member
Spazmore

Hello. I have a AW2518HF 240hz G-sync compatible on a 8700k/1080ti/16GB 4133RAM PC and game I’m playing is BFV. I have G-sync enabled and V-sync ON, low latency mode ON in the NVCP and the game capped at 237fps through the CFG file. Also playing on lowest settings and not GPU bound.

What is the best way to get the lowest the lowest input lag and the best overall experience ? Should I cap my frames at say 200fps because the game sometimes dips to 90-100 fps in certain scenarios like on the map Metro or I should leave it uncapped seeing as it only ever reaches 240fps in 10% of the time. Thank you in advance.

Shadeless
Member
Shadeless

So when using GSync on a 165Hz monitor with FPS capped at 160 FPS (ingame limiter) and GSync + Vsync ON (in Nvidia driver, off in game), is using low latency mode “on” or “ultra” better to decrease input lag?

I’d guess using ultra would result in less input lag but the battlenonsense video made me question if that would actually be the case considering my GPU usage is lower than 95% almost all the time and based on his testing “on” resulted in lower lag than “ultra”…

Just wondering if it’s similar with Gsync or if ultra is better for the lowest latency there like at > 95% GPU usage when you use no sync.

I feel like low latency “ultra” gives me a slightly snappier response when using GSync but that could just be placebo…

tanzimfh
Member
tanzimfh

Hi, this was undoubtedly answered either in the article (which is exceptionally written btw) or the FAQ, but I can’t seem to understand the point of an FPS limiter fully.

I know that going over the frame rate of the monitor turns G-Sync off, but since V-Sync kicks in, shouldn’t we still get tear-free frames at the monitor’s frame rate? I can’t think of why there would be stuttering either since there is always a frame ready by each scan out.

I’m on a 144hz display with FreeSync, and for Rainbow Six Siege specifically, my 2060 can pump out around 250 fps, and I’m wondering if using G-Sync with an FPS limiter will give me any benefit over simply using V-Sync. I actually just got the monitor and my Displayport cable is yet to arrive, and I’m not sure if I should try to use G-Sync or stick to V-Sync and graphics settings that allow for >144 FPS at all times. Is there any real input lag when doing this (except the latest partway rendered “tear” frame that V-Sync avoids), and if so, why? I feel like I see an input lag much higher than just one frame, which makes me want to try adaptive sync, but I’m not sure. Thanks in advance!

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