G-SYNC 101: Range


Blur Buster's G-SYNC 101: Range Chart

Exceeds G-SYNC Range

G-SYNC + V-SYNC “Off”:
G-SYNC disengages, tearing begins display wide, no frame delay is added.

G-SYNC + V-SYNC “On”:
G-SYNC reverts to V-SYNC behavior when it can no longer adjust the refresh rate to the framerate, 2-6 frames (typically 2 frames; approximately an additional 33.2ms @60 Hz, 20ms @100 Hz, 13.8ms @144 Hz, etc) of delay is added as rendered frames begin to over-queue in both buffers, ultimately delaying their appearance on-screen.

G-SYNC + Fast Sync*:
G-SYNC disengages, Fast Sync engages, 0-1 frame of delay is added**.
*Fast Sync is best used with framerates in excess of 2x to 3x that of the display’s maximum refresh rate, as its third buffer selects from the “best” frame to display as the final render; the higher the sample rate, the better it functions. Do note, even at its most optimal, Fast Sync introduces uneven frame pacing, which can manifest as recurring microstutter.
**Refresh rate/framerate ratio dependent (see G-SYNC 101: G-SYNC vs. Fast Sync).

Within G-SYNC Range

Refer to “Upper & Lower Frametime Variances” section below…

Upper & Lower Frametime Variances

G-SYNC + V-SYNC “Off”:
The tearing inside the G-SYNC range with V-SYNC “Off” is caused by sudden frametime variances output by the system, which will vary in severity and frequency depending on both the efficiency of the given game engine, and the system’s ability (or inability) to deliver consistent frametimes.

G-SYNC + V-SYNC “Off” disables the G-SYNC module’s ability to compensate for sudden frametime variances, meaning, instead of aligning the next frame scan to the next scanout (the process that physically draws each frame, pixel by pixel, left to right, top to bottom on-screen), G-SYNC + V-SYNC “Off” will opt to start the next frame scan in the current scanout instead. This results in simultaneous delivery of more than one frame in a single scanout (tearing).

In the Upper FPS range, tearing will be limited to the bottom of the display. In the Lower FPS range (<36) where frametime spikes can occur (see What are Frametime Spikes?), full tearing will begin.

Without frametime compensation, G-SYNC functionality with V-SYNC “Off” is effectively “Adaptive G-SYNC,” and should be avoided for a tear-free experience (see G-SYNC 101: Optimal Settings & Conclusion).

G-SYNC + V-SYNC “On”:
This is how G-SYNC was originally intended to function. Unlike G-SYNC + V-SYNC “Off,” G-SYNC + V-SYNC “On” allows the G-SYNC module to compensate for sudden frametime variances by adhering to the scanout, which ensures the affected frame scan will complete in the current scanout before the next frame scan and scanout begin. This eliminates tearing within the G-SYNC range, in spite of the frametime variances encountered.

Frametime compensation with V-SYNC “On” is performed during the vertical blanking interval (the span between the previous and next frame scan), and, as such, does not delay single frame delivery within the G-SYNC range and is recommended for a tear-free experience (see G-SYNC 101: Optimal Settings & Conclusion).

G-SYNC + Fast Sync:
Upper FPS range: Fast Sync may engage, 1/2 to 1 frame of delay is added.
Lower FPS range: see “V-SYNC ‘On'” above.

What are Frametime Spikes?

Frametime spikes are an abrupt interruption of frames output by the system, and on a capable setup running an efficient game engine, typically occur due to loading screens, shader compilation, background asset streaming, auto saves, network activity, and/or the triggering of a script or physics system, but can also be exacerbated by an incapable setup, inefficient game engine, poor netcode, low RAM/VRAM and page file over usage, misconfigured (or limited game support for) SLI setups, faulty drivers, specific or excess background processes, in-game overlay or input device conflicts, or a combination of them all.

Not to be confused with other performance issues, like framerate slowdown or V-SYNC-induced stutter, frametime spikes manifest as the occasional hitch or pause, and usually last for mere micro to milliseconds at a time (seconds, in the worst of cases), plummeting the framerate to as low as the single digits, and concurrently raising the frametime to upwards of 1000ms before re-normalizing.

G-SYNC eliminates traditional V-SYNC stutter caused below the maximum refresh rate by repeated frames from delayed frame delivery, but frametime spikes still affect G-SYNC, since it can only mirror what the system is outputting. As such, when G-SYNC has nothing new to sync to for a frame or frames at a time, it must repeat the previous frame(s) until the system resumes new frame(s) output, which results in the visible interruption observed as stutter.

The more efficient the game engine, and the more capable the system running it, the less frametime spikes there are (and the shorter they last), but no setup can fully avoid their occurrence.

Minimum Refresh Range

Once the framerate reaches the approximate 36 and below mark, the G-SYNC module begins inserting duplicate refreshes per frame to maintain the panel’s minimum physical refresh rate, keep the display active, and smooth motion perception. If the framerate is at 36, the refresh rate will double to 72 Hz, at 18 frames, it will triple to 54 Hz, and so on. This behavior will continue down to 1 frame per second.

Regardless of the reported framerate and variable refresh rate of the display, the scanout speed will always be a match to the display’s current maximum refresh rate; 16.6ms @60Hz, 10ms @100 Hz, 6.9ms @144 Hz, and so on. G-SYNC’s ability to detach framerate and refresh rate from the scanout speed can have benefits such as faster frame delivery and reduced input lag on high refresh rate displays at lower fixed framerates (see G-SYNC 101: Hidden Benefits of High Refresh Rate G-SYNC).



3028 Comments For “G-SYNC 101”

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b1l3yiwnl
Member
b1l3yiwnl

I just want to say that I really appreciate the effort and knowledge that you’ve put into this! This really is some amazing work and should be appreciated. Although, I’ve got a question. Do you think that with higher fps/refresh rates (>360hz) pairing g-sync with v-sync and a capped fps is beneficial to a competitive gamer? I’m a tier 3 CS2 player that has the XL2566K, on some maps I drop below 360fps and was wondering whether or not it would help me to feel the game better. Thank you so much for your work!

cwwafc3gfv
Member
cwwafc3gfv

And whats with the pre-censorship now? Since when a website like this need pre-censorship of comments?!
In fear of people posting something that the owner does not agree with? .
Stop that 1984-orwellian crap. C’mon.

cwwafc3gfv
Member
cwwafc3gfv

@author jorimt or whoever

Rewrite your “Reflex* Settings” and “Low Latency Mode* Settings” section a bit, or add this for clarifiation that it also works in different ways now.
For example in the 2023’s game “The Finals”, my settings with a g-sync compatible Samsung S95C TV are:

TV: Game mode on (so G-sync compatible/VRR mode is the active signal mode)
Ingame: V-sync etc. is OFF, fps limit to 140 (or whatever I set it to), and reflex to either ON or ON + BOOST.
NVCP: G-sync compatibility, g-sync enabled “for this display”, Low Latency Mode: Ultra, V-Sync to OFF.

So here the difference is NVCP: V-Sync to OFF.
The difference now is: Despite ingame reflex to ON/ON+Boost and NVCP’s LLM set to “Ultra”, the framerate is not hard capped at 138, but whatever I chose.
If I however set NVCP’s V-Sync to “ON”, then the frame rate will be hard capped at 138.

So I get the benefits of Reflex and LLM, but without the hard frame rate cap.

mike-lesnik
Member

Hello jorimt, thank for your ansers!!
What do you think about theory from this video? https://youtu.be/1OQjqWOm1uA?t=170
In it, the author claims:
“on an Nvidia GPU I found that if you combine Gsync+Vsync you actually only need to add 0.3ms of latency for VRR to work correctly:
240Hz = 223fps
144Hz = 138fps
120Hz = 115fps”

His formula for calculating:
1000ms\240hz=4.166ms
4.166ms+0.3ms=4.446ms
1000ms\4.446ms=224.9fps

It turns out he recommends limiting fps to the same values as LLM Ultra, but without having to turn it on.

spiewalk
Member
spiewalk

Great write up. Are there any additional settings or changes one can make regarding VRR flicker on OLED panels? Specifically LG C series TV’s with G-Sync technology?

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