LFC kicking in earlier

Talk about AMD's FreeSync and VESA AdaptiveSync, which are variable refresh rate technologies. They also eliminate stutters, and eliminate tearing. List of FreeSync Monitors.
christizzz
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LFC kicking in earlier

Post by christizzz » 03 Oct 2020, 09:29

Hello,

I witched from my old TN native Gsync monitor to an IPS freesync monitor ( lg 27 GL850).
The new LG monitor can show the refresh rate in the OSD.
i am running an nvidia gtx 1070 card..
the monitor has a range of 48-144hz...
But the LFC seems to be kicking early at 60fps i am seeing a refresh rate of 120...
shouldnt the LFC first kick off when FPS <48 ?

am i missing something ?

thanks
Last edited by christizzz on 04 Oct 2020, 07:05, edited 1 time in total.

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RealNC
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Re: LFC kising in earlier

Post by RealNC » 04 Oct 2020, 05:09

The refresh rate range only specifies the refresh rates the panel itself supports. LFC can be activated prior to reaching the lowest supported refresh rate. That's normal. It's beneficial to trigger FLC at higher FPS because it reduces ghosting in monitors that don't have variable overdrive, and it can also avoid flickering.
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christizzz
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Re: LFC kicking in earlier

Post by christizzz » 04 Oct 2020, 07:06

thank you for your reply...i changed the title of the post because i made a typo....

christizzz
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Re: LFC kising in earlier

Post by christizzz » 06 Oct 2020, 15:13

RealNC wrote:
04 Oct 2020, 05:09
The refresh rate range only specifies the refresh rates the panel itself supports. LFC can be activated prior to reaching the lowest supported refresh rate. That's normal. It's beneficial to trigger FLC at higher FPS because it reduces ghosting in monitors that don't have variable overdrive, and it can also avoid flickering.
thanks... today i tried several games..i noticed that its actually not always kicksing in at 60... sometimes it kicks at 60 some times a bit early and someitmes a bit late... the Hz shown on the OSD is like you said in the 48-144... so yea it is kicking around 60 (+/-10 fps)... so if i understood correctly it is driver controlled and and there is no "fixed" frame rate that kicks the LFC ?

thanks

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Re: LFC kicking in earlier

Post by Chief Blur Buster » 06 Oct 2020, 15:26

Possibly framepacing jitter.

1. 60fps may have some frames closer to 1/40sec and some frames closer to 1/80sec, to average 60fps. Large frametime variances can cause a display to enter/exit LFC operation rapidly, and create LFC-mispredict stutter. To prevent the problem, try improving your framepacing precision. Use RTSS instead of an in-game 60fps framerate cap. Ajust detail settings to prevent framerates from falling into LFC territory.

2. You have an LFC penalty of 1/144sec. A higher max-Hz (e.g. 240Hz max Hz) can reduce the LFC penalty by minimizing the stutter error margin to one fastest refreshtime (for a 240Hz VRR display, the display is busy for only 1/240sec refreshing even at a lower VRR framerate.) LFC stutter is caused by a new frame being forced to wait for the monitor to finish repeat-refreshing an old frame. Higher Hz means any LFC-triggered refresh cycles are "busy" for a shorter time period. Thus, LFC stutter is much more invisible on a 240Hz panel than a 144Hz panel.
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christizzz
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Re: LFC kicking in earlier

Post by christizzz » 06 Oct 2020, 15:37

thank you ...
1) i dont notice a lot of stutter actually... its just i misunderstoof how LFC works and i thought it only triggers when the FPS falls below the refresh rate of monitor less than 48 ( refdresh rate of the lg 27gl850 48-144). and i got a bit confused when i saw 120hz at60 fps.... but sometime it shows 60hz at 60 fps.... so is this just the algorithm in the driver calculating the best refresh rate based on the FPS /frame tiem fluctuation ?


2) another question... i followed the gsync settings on ur guide ( caped FPS in nvidia control panel to 141 fps and turned vsync to on ( it is off in the games) )..i noticed when in a game i am at 141 fps, the monitor is showing 144hz... shouldnt be 141Hz ? ( constant 141fps)

PS: i am coming from a native gsync monitor i couldnt show the refresh rate .... so i dont know if it had the same beahviour...
i switched to this LG monitor because i wanted an IPS panel and i was annoyed by the flickering that occured on my previous gsync monitor... it always flickered when frame time was changing quickly... i dont see any flicker in the games whe the flicker used to happen ... i also notice really faint flicker in the pendulum test...whereas my old native gsync showed really horrible flicker...

thanks

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Re: LFC kicking in earlier

Post by Chief Blur Buster » 06 Oct 2020, 18:08

christizzz wrote:
06 Oct 2020, 15:37
1) i dont notice a lot of stutter actually... its just i misunderstoof how LFC works and i thought it only triggers when the FPS falls below the refresh rate of monitor less than 48 ( refdresh rate of the lg 27gl850 48-144). and i got a bit confused when i saw 120hz at60 fps.... but sometime it shows 60hz at 60 fps.... so is this just the algorithm in the driver calculating the best refresh rate based on the FPS /frame tiem fluctuation ?
Normally, LFC should not activate by itself for 60fps at 120Hz, but it can if frameraters were lower prior to it.

Such as 40fps suddenly becoming 60fps, since LFC deactivation can be intentionally delayed for a good reason: Preventing flicker.

Also, there should be no stutter from LFC if framerates are consistent or smoothly ramping. It takes erratic framerates to generate amplified LFC-caused stutter, because LFC tries to predictively time a repeat-refresh between frames. It takes a finite amount of time to repeat-refresh. As long as the time duration of a repeat-refresh scanout isn't colliding with the delivery of a new game frame, there is never any LFC stutter.

<Advanced>
LFC algorithms occasionaly has a "sticky effect" to prevent problems of the transitions in/out of LFC. If framerate briefly falls below 48fps, LFC may stay activated temporarily when you exit LFC range. For example 40fps rising to 60fps may still stay in LFC longer to "make sure" framerates are sustained above minimum. This is a lesser-of-evil than the rapid transitions in-and-out of LFC (creates slight flicker caused by different LCD behavior at different refresh rates), like the complaints about faint VRR / G-SYNC / FreeSync flicker from 240fps suddenly falling to 30fps then back to 240fps, when a menu appears/disappears -- rapid framerate changes can create a minor flicker (e.g. <1% brightness change) because as hard as they try to engineer screens from looking different, sometimes low Hz and high Hz have very slightly different colors = a very slight flicker effect for extremely huge framerate changes. Since sudden LFC on/off is a sudden change to the refresh rate, it's in the monitor's interest to use a "sticky LFC" algorithm to make sure framerates jittering rapidly across the LFC thresholds aren't creating a rapid LFC enable/disable effect.
</Advanced>
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christizzz
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Re: LFC kicking in earlier

Post by christizzz » 07 Oct 2020, 01:21

Thank you!

1) speaking of flicker... i really dont see any a lot of flicker in game with the LG 27GL850... i usedto see a ton of flicker in the menus with my old Acer XB271hu ( TN panel) which was native gsync.
the only flicker ( and i needed to squint my eyes to notice them) was in the Pendulum test. Forcing the FPS to 60 in the pendulum test from nvidia... still showed a slight flicker... is it maybe the software ? ploting framte time and frame rates showed constant behavior... still a small flicker occured when the pendulum was at its maximum height ( left or right)...
but as i said again..i dont see anyflicker in games whereas before i had flickers with the acer



2) i plugged the old acer again (Native gsync)...and tried the same thing with forcing the pendulum to 60fps..same flickers but way more noticeable... so i would guess its the software ?

3) i forced the fps to drop to 20fps in the pendulum using the acer... i noticed that the VRR is 20Hz... so Gsync doenst have LFC ? does it follow the frame rate exactly and pass it to the refresh rate ?

thanks

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Re: LFC kicking in earlier

Post by Chief Blur Buster » 07 Oct 2020, 02:20

Older VRR monitors didn't have the sticky LFC behaviors that newer VRR does, to prevent the LFC-rapid-cycling effect.

So it's a beneficial effect of "LFC kicking in earlier" -- whereas it's simply "LFC exiting late" (when framerates goes back up after LFC has already triggered).
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       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
       • List of FreeSync Monitors
       • List of Ultrawide Monitors

christizzz
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Re: LFC kicking in earlier

Post by christizzz » 07 Oct 2020, 02:37

thanks so this is normal that the older GSYNC acer doesnt have LFC ?
I tsill dont undestand why also some flickers occurs in the pendulumn test when forcing the FPS tp 60...
Frame rate is constant , frame time is also constant.

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