Does LFC make a wide VRR range irrelevant?

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.
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ArrowLynx
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Joined: 16 Feb 2023, 11:42

Does LFC make a wide VRR range irrelevant?

Post by ArrowLynx » 16 Feb 2023, 11:50

Hello! Me and a friend were discussing this, the question is, does LFC make a wide VRR range irrelevant?

Example:

Same panel performance, same settings, same everything (for the sake of argument)

Monitor 1: Game runs at 35 FPS, monitor refreshes at 70Hz (VRR range 60-144)

Monitor 2: Game runs at 35 FPS, monitor refreshes at 35Hz (VRR range 30-144)

Would the experience be the same? Down to input lag?

If they offer the same result, would that only be at a locked framerate? Or would the effect still be the same at a variable frame rate? (varying between 35 FPS and 50 FPS for example).

Thank you!

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Chief Blur Buster
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Re: Does LFC make a wide VRR range irrelevant?

Post by Chief Blur Buster » 18 Feb 2023, 18:28

ArrowLynx wrote:
16 Feb 2023, 11:50
Hello! Me and a friend were discussing this, the question is, does LFC make a wide VRR range irrelevant?

Example:

Same panel performance, same settings, same everything (for the sake of argument)

Monitor 1: Game runs at 35 FPS, monitor refreshes at 70Hz (VRR range 60-144)

Monitor 2: Game runs at 35 FPS, monitor refreshes at 35Hz (VRR range 30-144)

Would the experience be the same? Down to input lag?

If they offer the same result, would that only be at a locked framerate? Or would the effect still be the same at a variable frame rate? (varying between 35 FPS and 50 FPS for example).
The real answer is "it depends"

1. LCD GtG decay
2. Flicker
3. Scrolling chessboard artifacts (inversion artifact)
3. LFC Stutter or lack thereof.

A higher min Hz actually can be better quality because LCD GtG differences between 60Hz and 240Hz is smaller than 30Hz vs 240Hz. The problem with LFC is frame collision-related stutter, where a new frame is stalled due to monitor being busy repeat-refreshing. However, if your VRR(max) is very high, e.g. 360Hz, then the monitor-busy is only 1/360sec. So LFC penalty is almost negligible for monitors 240Hz and up, and completely invisible at 360Hz and up, in theory at least. A native non-LFC-assisted VRR range of 65Hz-360Hz can be better quality than 48Hz-360Hz, as an example, if it minimizes flicker and other artifacts such as scrolling chessboard-pixel artifacts (especially on TN panels, which are prone to that artifact).

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Ultra-low-Hz has a nasty tendancy to make this artifact visible on TN panels, so minimizing this with a higher VRR(min) and using LFC instead, can eliminate this from being blatantly visible.

OLED is immune to this, but OLED has a gamma flicker issue which can be more visible with low min-Hz. On the other hand, the rapid cycling of LFC=on / LFC=off from wildly gyrating frame rates, can amplify gamma-related flicker, but that may not happen if the graphics driver has a LFC-stiction behavior that forces LFC until the frame rate is much higher (e.g. back into triple digits).

It's a game of pick-poison. Personally, as long as VRR(min) and VRR(max) is still minimum 4x-5x apart, I prefer LFC over native VRR(min). 2.77ms of LFC stutter (1/360sec) is much more invisible than 21ms of MPRT (1/48sec of motion blur). As long as erratic-stutter is much smaller than the motion blur amplitude, the LFC stutter is rendered essentially invisible. On the other hand, LFC is a software-driven algorithm on all VRR panels (other than G-SYNC native chipped with the FPGA/ASICs) which is subject to computer-performance-jitter error margins...
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