MAME emulator and 240Hz monitor

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CorvusCorax
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MAME emulator and 240Hz monitor

Post by CorvusCorax » 28 Apr 2021, 03:41

Hi all,

I recently discovered strange thing in MAME emulator.

When I set my monitor to 144Hz + G-sync emulated games works in native refresh rate, for example Raiden II in ~57Hz

but

When I set my monitor to 240Hz + G-sync the same game works in ~114Hz (double the native game refresh rate)

It's not big deal, because it's still smooth and works great. I'm just curious why it is working that way.

PedroPortnoy
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Re: MAME emulator and 240Hz monitor

Post by PedroPortnoy » 01 May 2021, 07:39

What Monitor do you have?

My guess is it works that way because your monitor has different overdrive voltages for 144Hz and 240Hz. Usually, as far as I know, fast monitors have better responde times and less overshoot close to their maximum refresh rate.

That said, I suppose the GPU driver sets the LFC to start doubling your frames at higher framerates when you set your monitor to 240 Hz to avoid any ghosting/reverse ghosting. Just make sure your framerate isn't too close from the bottom of the VRR range: going in and out of LFC tends to cause noticeable flickering.

For example, my monitor is a Samasung Odyssey G7 27" (1440p 240Hz) and my LFC kicks in at around 90 FPS: anything below that is doubled. If my framerate fluctuates around this value: lots of flickering. What I do if I get performance around that framerate is either cap my framerate a little below that or change the VRR range with CRU to something like 60-240 (so it stays above) or 120-240 (so it stays below).

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Chief Blur Buster
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Re: MAME emulator and 240Hz monitor

Post by Chief Blur Buster » 01 May 2021, 14:10

Unless you're using strobed modes, LFC (repeat refresh cycle logic) can be superior to non-LFC when the framerate is steady.

On many 240 Hz LCD panels, 114 Hz can have superior picture quality to 57Hz by speeding up the inversion logic to avoid inversion artifacts from becoming visible (i.e. avoiding scrolling chess board textures). Also, flicker goes down too, since faster LCDs are more likely to decay quicker to rest state (white screen or black screen, depending on panel tech) when a lot of time has passed between refresh cycles. Even if the unrefreshed-too-long LCD fade is only a 1% or 2% brightness change at 57Hz, it can still produce visible flickering during low frame rates. Also, you can get fewer mode blackouts (more common on FreeSync or "G-SYNC Compatible") when frametimes briefly dip below VRR range without LFC kicking in at a high enough Hz.

So there you go, three big reasons a higher LFC trigger is superior for 240Hz+ monitors:
(A) Reduce inversion artifacts
(B) Reduce slight flicker of low frame rates (from pixel fade on panels that have been unrefreshed too long)
(C) Reduce occurence of 1-second blackouts (LFC failing to activate at a high enough framerate below framerates fall below VRR range)

LFC is 100% harmless (and actually beneficial) for steady-framerate material like emulators. Don't worry about it.

Blur Busters always recommends a higher minimum Hz for 240Hz+ G-SYNC monitors, i.e. 55Hz-240Hz or 65Hz-240Hz ranges instead of 30Hz-240Hz ranges. A higher LFC threshold has fewer poisons and bigger benefits on wide-VRR-ranges (240Hz+)

So LFC actually produces better image quality whenever the VRR range is wide enough, because native low-Hz LCDs have more artifacts than LFC-assisted low Hz.

On a related note -- for 240Hz-and-up monitors, where you prioritize image quality, I now universally recommend editing FreeSync ranges (via ToastyX CRU) from 48-240Hz into 55-240 or 65-240, even if you don't have the (C) problem (reduce occurrence of 1-second blackouts). You notice I include a safety margin away from common framerate numbers (e.g. 60fps) which is why I don't recommend a FreeSync range of "60-240" because you might rapidly modulate into/out of LFC mode when 60fps material subtly varies from 59fps-61fps -- it's the LFC transitions that are the most problematic. Transitions into and out of LFC (the enabling/disabling of frame doubling) can be seamless (invisible) but sometimes those repeat-refresh cycles can collide with new frames, lagging the new frames by between 0/240 and 1/240sec depending on when the new frame was presented while the monitor is busy repeat-refreshing the previous frame -- more common during erratic frame rates, since LFC logic tries to precisely time repeat-refreshes between two frames, in order to stay seamless. LFC has a smaller penalty on higher Hz, as a 240Hz FreeSync monitor refreshes in only 1/240sec (4 milliseconds) while a 75Hz FreeSync monitor refreshes in 1/75sec (13 milliseconds).
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CorvusCorax
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Re: MAME emulator and 240Hz monitor

Post by CorvusCorax » 03 May 2021, 05:24

Chief Blur Buster wrote:
01 May 2021, 14:10
Unless you're using strobed modes, LFC (repeat refresh cycle logic) can be superior to non-LFC when the framerate is steady.

On many 240 Hz LCD panels, 114 Hz can have superior picture quality to 57Hz by speeding up the inversion logic to avoid inversion artifacts from becoming visible (i.e. avoiding scrolling chess board textures). Also, flicker goes down too, since faster LCDs are more likely to decay quicker to rest state (white screen or black screen, depending on panel tech) when a lot of time has passed between refresh cycles. Even if the unrefreshed-too-long LCD fade is only a 1% or 2% brightness change at 57Hz, it can still produce visible flickering during low frame rates. Also, you can get fewer mode blackouts (more common on FreeSync or "G-SYNC Compatible") when frametimes briefly dip below VRR range without LFC kicking in at a high enough Hz.

So there you go, three big reasons a higher LFC trigger is superior for 240Hz+ monitors:
(A) Reduce inversion artifacts
(B) Reduce slight flicker of low frame rates (from pixel fade on panels that have been unrefreshed too long)
(C) Reduce occurence of 1-second blackouts (LFC failing to activate at a high enough framerate below framerates fall below VRR range)

LFC is 100% harmless (and actually beneficial) for steady-framerate material like emulators. Don't worry about it.

Blur Busters always recommends a higher minimum Hz for 240Hz+ G-SYNC monitors, i.e. 55Hz-240Hz or 65Hz-240Hz ranges instead of 30Hz-240Hz ranges. LFC has fewer poisons and bigger benefits on wide-VRR-ranges.

So LFC actually produces better image quality whenever the VRR range is wide enough, because native low-Hz LCDs have more artifacts than LFC-assisted low Hz.

On a related note -- for 240Hz-and-up monitors, where you prioritize image quality, I now universally recommend editing FreeSync ranges (via ToastyX CRU) from 48-240Hz into 55-240 or 65-240, even if you don't have the (C) problem (reduce occurrence of 1-second blackouts). You notice I include a safety margin away from common framerate numbers (e.g. 60fps) which is why I don't recommend a FreeSync range of "60-240" because you might rapidly modulate into/out of LFC mode when 60fps material subtly varies from 59fps-61fps -- it's the LFC transitions that are the most problematic. Transitions into and out of LFC (the enabling/disabling of frame doubling) can be seamless (invisible) but sometimes those repeat-refresh cycles can collide with new frames, lagging the new frames by between 0/240 and 1/240sec depending on when the new frame was presented while the monitor is busy repeat-refreshing the previous frame -- more common during erratic frame rates, since LFC logic tries to precisely time repeat-refreshes between two frames, in order to stay seamless. LFC has a smaller penalty on higher Hz, as a 240Hz FreeSync monitor refreshes in only 1/240sec (4 milliseconds) while a 75Hz FreeSync monitor refreshes in 1/75sec (13 milliseconds).
Thanks for answer. That was super informative :)

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