jorimt wrote:Finally, his tests showed there was virtually no input latency difference between G-SYNC + v-sync off and G-SYNC + v-sync on with the same framerate limit on the laptops, so I'm also not sure why he ultimately recommended G-SYNC + v-sync off + framerate limit.
Probably doesn't matter due to the frame cap preventing it from mattering -- but most people trust VSYNC OFF not to have input lag.
BTW, for a completely stationary tearline (not a single pixel above/below), you need an accuracy of 1/(horizontal scanrate)th of a second. At 1920x1080 120Hz, that would be 1/135,000th of a second accuracy! Even if the tearline vibrates up and down in an amplitude of 5 pixels, that's still 5/135,000th of a second accuracy. Damn impressive.
RealNC wrote:Good video. But he got the vsync off/on case wrong. The best default when using g-sync is vsync on. It doesn't cost you latency, and it makes sure there's no tearing when there's frame time spikes, and it should allow you to cap more near the refresh rate (73 or 72) without starting to tear.
Unless microseconds matter. (Which it does not...even Olympics races aren't that close!)
The position of tearline moves downwards by 1 pixel during every 1/(horizontal scanrate)th of a second. The closer the tearline to the bottom edge of the screen, the less lag penalty will occur if you had waited before the tearline went off (that you had VSYNC ON ).
So from this, here's an example: Say, a tearline occurs 27 pixels up from the bottom edge of the screen. The lag difference between a bottom-edge tearline 27 pixels from the bottom of 1920x1080@120Hz (135KHz scanrate) would mean using VSYNC ON instead would add an input lag delay of 27/135,000th of a second if you chose to use GSYNC+VSYNC-ON instead of GSYNC+VSYNC-OFF.
Maybe a little bit more, given the blanking interval consists of front/back porches and sync
, but with a common Vertical Total of 1125 (1080 visible, 45 blanking interval), that's only another 45/135,000th of a second extra at the most (on top of 27/135,000th). Still tiny. But even VRR also has a mandatory minimum pause between refresh cycles, so all things considered, let's exclude this for simplicity's sake. Even if it was included, it's a tiny fraction of one millisecond.
Yes, nitpicking. But of interest for those Advanced Users who know more details behind the scenes of "what-if-VSYNC-was-ON-instead" during tearline-occurence situations. Mathematically, it's possible to determine how much input lag you saved in this "WHAT-IF" exercise, simply by knowing where the position of the tearline was.
TL;DR: If tearline occurs near the bottom edge of the screen, the lag difference of going VSYNC ON is less than a millisecond in this particular situation.