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 Post subject: MAME emulator and 240Hz monitor
PostPosted: Thu Apr 29, 2021 9:32 am 



Joined: 14 Jul 2009
Posts: 4
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.
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 Post subject: Re: MAME emulator and 240Hz monitor
PostPosted: Thu Apr 29, 2021 4:55 pm 


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Joined: 16 Jan 2014
Posts: 1285
Interesting observation.


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 Post subject: Re: MAME emulator and 240Hz monitor
PostPosted: Mon May 03, 2021 10:27 am 



Joined: 14 Jul 2009
Posts: 4
I asked about that on Blur Busters forum and I got this answer:

Quote:
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 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).


Source: https://forums.blurbusters.com/viewtopi ... 838#p66807
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