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Nvidia G-Sync / Freesync range

Talk about NVIDIA G-SYNC, a variable refresh rate (VRR) technology. G-SYNC eliminates stutters, tearing, and reduces input lag. List of G-SYNC Monitors.

Nvidia G-Sync / Freesync range

Postby TechnoRush » 17 Jan 2019, 22:17

I have a 29UM69G and I'm trying to extend the Freesync range of the monitor to take advantage of LFC, the stock range is 40 - 75.

I used Nvidia custom resolution to verify everything from 39 - 30 should display and it did just that, then used CRU 1.4.1 and edited the range and added a Freesync Data block for 30 - 75, restarted the system instead of the included .exe and enabled G-Sync in NVCP.

I then used Nvidia Pendulum to confirm my changes and... I'm getting flickering or what I call blackouts, specifically at 37 - 38 fps / hz and everything above and below that works as expected. G-Sync indicator is present and I can see G-Sync is working on the test pattern.

My monitor does not have Refresh rate monitoring on OSD.

Am I doing something wrong here or is it something else?
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Re: Nvidia G-Sync / Freesync range

Postby Chief Blur Buster » 17 Jan 2019, 22:21

TechnoRush wrote:I have a 29UM69G and I'm trying to extend the Freesync range of the monitor to take advantage of LFC, the stock range is 40 - 75.

I used Nvidia custom resolution to verify everything from 39 - 30 should display and it did just that, then used CRU 1.4.1 and edited the range and added a Freesync Data block for 30 - 75, restarted the system instead of the included .exe and enabled G-Sync in NVCP.

I then used Nvidia Pendulum to confirm my changes and... I'm getting flickering or what I call blackouts, specifically at 37 - 38 fps / hz and everything above and below that works as expected. G-Sync indicator is present and I can see G-Sync is working on the test pattern.

My monitor does not have Refresh rate monitoring on OSD.

Am I doing something wrong here or is it something else?

It might be a VRR range underclocking artifact.

You're underclocking your monitor severely at 37-38Hz, and sometimes underclocking causes blankout effects you see. When the LFC kicks in the problem solves itself, e.g. 28Hz means 28Hzx2 = 56Hz which is no longer underclocking. But once the frames stop doubling, e.g. 38Hz, you're trying to run native 38Hz, and that's the tiny underclock region you're hitting (38-39Hz).

You might find you need to do underclock/overclock both ends of the VRR range, e.g. 39Hz-78Hz -- to get the 2.0x you need for LFC. Normally you really need 2.4x for much more reliable LFC, as even 2.0x is still very tight.

Extending VRR range to 2x is necessary for LFC, but sometimes the act of extending this requires underclocking the low-end of VRR range or overclocking the high-end of VRR range.

Can you try overclocking to 76Hz-78Hz, and raise the lower end to 38.5-39Hz? See if that solves the problem....you're getting the underclock artifact at the bottom end of your VRR range, maybe you won't have an overclock artifact at the top end.

You're in a rather interesting situation where your VRR range is 1.87x (40Hz-75Hz) and only need the remainder 0.23x+ either via underclocking/overclocking the ends of your VRR range.

Fixed-Hz 39Hz aren't a reliable test of VRR 39Hz at 75Hz, because VRR 39Hz is like a Large Vertical Total on 39Hz, at a ratio of approximately 75:39 in blanking interval size (plus minimum VBI size at max Hz). Also, refresh rate slewing is sometimes the cause of the blackouts, not the Hz. (e.g. frametime change suddenly changing from 1/75sec to 1/30sec and vice versa) -- sometimes rapid refresh rate slew patterns causes the flicker artifact. Testing reliability of fixed Hz using VRR timings is done via ToastyX, locking the dotclock or horizontal scanrate then increasing Back Porch until the refresh rate lowers to the desired Hz. Then now you're got a VRR-simulating low-Hz fixed-Hz signal (it's not a standard VESA CVT, VESA CVT-Reduced, or other standard timings formula)

To avoid that, you want to try to narrow your VRR range and try avoiding problematic Hz that causes blackouts, by shifting around your VRR range a little bit until you hit a 2.0x VRR range that doesn't have artifacts.

TL;DR: If VRR range-bottom underclocking fails, try VRR range-top overclocking. Or a combination.

Future: Driver enhancements can theoretically add partial LFC to 1.8x and 1.9x VRR ranges by avoiding the problematic underclock range (= slight extra stutter at certain framerates), and I think the native AMD Radeon FreeSync drivers already do it, but NVIDIA drivers does not (yet). There's a continuum of increasing LFC reliability for wider VRR ranges.
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Re: Nvidia G-Sync / Freesync range

Postby TechnoRush » 17 Jan 2019, 23:06

You lost me when you started talking about Fixed 39Hz.

How would I properly overclock my VRR range? Do I just edit the range and data block to the appropriate value or would I also have to setup a custom resolution in NVCP for 78Hz?

EDIT: I tried setting up a custom resolution with 80Hz without G-Sync in NVCP and it's blurry, no idea why.
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Re: Nvidia G-Sync / Freesync range

Postby MonarchX » 28 Jan 2019, 04:21

Is there some way to force G-Sync to operate fully at at least 30fps/hz? 36 is just too high for many games, regardless of the rig specs. MINIMUM framerate is extremely important. It takes a single micro-stutter to mess up a nice synchronization scene in Assassin's Creed game. In games like GTA V and The Witcher 3, FX (especially modded ones), such as explosions or magic, bring FPS down from 90's to low 30's for just 1-3 seconds and that's enough to ruin motion.

The FreeSync 2 / VRR that's upcoming is supposed to go down to 2fps/hz and that's without any extra hardware module. G-Sync's extra $100-200 should allow for at least 30fps @ 30hz without doubling, etc.
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Re: Nvidia G-Sync / Freesync range

Postby RealNC » 28 Jan 2019, 09:39

MonarchX wrote:Is there some way to force G-Sync to operate fully at at least 30fps/hz?

It goes down to 1FPS. The LFC is completely transparent, meaning going from 30FPS/30Hz to 29FPS/58Hz produces no stutter at all. It is completely seamless and looks like you're going from 30Hz to 29Hz. (Or whatever the lowest Hz of the panel is.)

I've tested this a lot when I first got a g-sync monitor in many games. Cranked up the graphics in games so that I'm in the 20-40FPS range depending on where I'm looking in the game, and I panned the camera smoothly using an XBox controller so that FPS gradually goes from ~40 to 20-ish, and it is completely seamless, no stutters. However, this is on an IPS panel. It could be that some TN panels might produce momentary brightness flicker as LFC kicks in.
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Re: Nvidia G-Sync / Freesync range

Postby jorimt » 28 Jan 2019, 13:57

MonarchX wrote:Is there some way to force G-Sync to operate fully at at least 30fps/hz? 36 is just too high for many games, regardless of the rig specs.

If you're specifically referencing part 2 of my G-SYNC 101 article, That's effectively an arbitrary minimum number (for G-SYNC monitors w/module), and I do say (highlighted in bold):

Once the framerate reaches the approximate 36 and below mark

36-37 FPS was found to be the LFC start point for a 2015 G-SYNC monitor (w/module) in PC perspective's original LFC functionality tests via an oscilloscope:
https://www.pcper.com/reviews/Graphics- ... ies-Differ

I'm sure the LFC start point varies here and there on specific panel types and/or models containing a G-SYNC module.
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Re: Nvidia G-Sync / Freesync range

Postby Chief Blur Buster » 28 Jan 2019, 17:45

I hope that LFC thresholds can be made configurable later.
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       To support Blur Busters:
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       • List of G-SYNC Monitors
       • List of FreeSync Monitors
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