Large vertical totals for low input lag

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crossjeremiah
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Large vertical totals for low input lag

Post by crossjeremiah » 05 Jul 2019, 20:33

Chief Blur Buster wrote:Editor's Note:
Before reading this thread, you need to understand Quick Frame Transport
See FAQ: Understanding HDMI Quick Frame Transport (lower lag)
So I have aw2518h and I increased the vertical of the 60hz to a little above 144hz pixel clock. Everything seems fine theres faint cross talk on the bottom with ulmb. so this higher pixel clock will make the input lag of 60hz comparable to the input lag if it was at 144hz.

So saying I'm playing 60fps emulator with >144hz pixel clock would it feel like I'm playing on 144hz input lag wise or would it much more feel like 144hz gsync

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Re: Large vertical totals for low input lag

Post by RealNC » 07 Jul 2019, 16:07

Yes, a 144Hz scanout speed at 60Hz through a large VT and vsync OFF is equivalent to what G-Sync does at 60FPS@144Hz. However, if you don't use vsync OFF, then it's not the same anymore because with vsync you'll get at least one buffered frame. And at 60Hz, one buffered frame means an additional 16.7ms of latency. Unless the emulator has implemented a "beam racing" lagless sync method. If the emulator doesn't implement that, then RTSS scanline sync can help.
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crossjeremiah
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Re: Large vertical totals for low input lag

Post by crossjeremiah » 10 Jul 2019, 07:28

I see thank you for your response.
What would you recommend to produce the most console like feel? I have ulmb enabled no vsync + scanline sync with increased pixel clock. Or would vsync be more close to it because consoles have built in vsync.

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Re: Large vertical totals for low input lag

Post by Chief Blur Buster » 10 Jul 2019, 18:53

crossjeremiah wrote:I see thank you for your response.
What would you recommend to produce the most console like feel? I have ulmb enabled no vsync + scanline sync with increased pixel clock. Or would vsync be more close to it because consoles have built in vsync.
Since you are already using scanline sync, using a large VBI sometimes further reduces strobe lag via the defacto Quick Frame Transport effect.

One problem is ULMB does not reliably support Large VTs....however, there's a workaround to get lower ULMB lag. ULMB hacks also lower lag too, using the custom-Hz ULMB hacks. Basically using the ULMB hack to create a lower-lag 85Hz or 100Hz ULMB via commandeering the ULMB 120Hz timings to get the same dotclock but lower Hz + larger VBI. ULMB lag of low-Hz ULMB can reduce by a few milliseconds this way.

The 60Hz ULMB hack gets a major jump in lower lag with RTSS Scanline Sync thanks to the QFT effect - up to 9ms reduction of input lag, by relocating frame presentation (144-60)/144ths of 60Hz = 9.74ms later into the refresh cycle, inputdelaying the input read of next Hz by almost 10ms, reducing strobe lag by 10ms for 60Hz ULMB Hack. Very huge lag reduction for emulators!

This is because the VBI of 60Hz ULMB Hack @ 144Hz ULMB Timings has a VBI that is (144-60)/144 = 0.5833. So a video signal is 58% VBI and 42% visible scanlines. Low-latency scanline sync relocates the frame Present()-ation from start of VBI to end of VBI. And since 58.3333% of a 16.7ms refresh cycle is 9.74ms.... that's your strobe lag reduction from the Quick Frame Transport effect!

This is great when you need framerate=Hz, such as emulators or a low-lag version of VSYNC that makes strobing feel massively better.

Benq Zowie is easier to get reduced-lag strobing from via Large VT + RTSS Scanline Sync.
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Re: Large vertical totals for low input lag

Post by Chief Blur Buster » 10 Jul 2019, 19:11

For readers who want to understand why Large Vertical Totals can reduce input lag, one needs to undersrand what the numbers in a Custom Resolution Utility is...

....here is a diagram of the structure of a refresh cycle on a video cable -- transmitted one pixel row at a time, left to right, top to bottom, with sync/porches as effective delimiters between scanlines and between refresh cycles.

Image

Refresh cycles are like endless loops, transmitting as, [...]Sync-BackPorch-Active-FrontPorch-Sync-BackPorch-Active-FrontPorch-Sync[...]

VBI = "FrontPorch+Sync+BackPorch" totalled.

Now, we can compare a normal signal and a large-VBI signal. This is known as a Quick Frame Transport, delivering a refresh cycle faster than the time period of a refresh cycle. It is in a HDMI spec but it can be done DIY with a Custom Resolution Utility on any cable, to any supported display, and RTSS forces the benefits into Windows (against undesired VSYNC ON default behavior of Present() at beginning of VBI).
People who may have heard of a new method of delivering refresh cycles faster. We're very familiar with this, but few people are.

See HDMI Version 2.1 on HDMIFORUM.org which says:
HDMI Forum wrote:HDMI Quick Frame Transport (QFT) reduces latency for smoother no-lag gaming, and real-time interactive virtual reality.
Image

But what the hell is Quick Frame Transport? Well, it's simply a large blanking interval.

Around here, we sometimes call this the Large Vertical Total trick, which also has other benefits such as reducing strobe crosstalk.

Normally, refresh cycles are transmitted one after the other, in tight fashion with a tiny blanking interval:
Image
However, it's possible to scanout quicker, such as delivering 100Hz refresh cycles in 1/144sec:
Image
It's possible to go even further, such as delivering 60Hz refresh cycles in 1/240sec! Basically, a frame-delivery acceleration of 4x factor, for supported platforms.

HDMI Quick Frame Transport, while specified by HDMI, the fundamental technique also works on DisplayPort and DVI connections, since it's simply a large blanking interval. A refresh cycle is transmitted faster, with a longer pause between refresh cycles.
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crossjeremiah
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Re: Large vertical totals for low input lag

Post by crossjeremiah » 11 Jul 2019, 06:17

Wow that's very interesting. Thank you for your response. I know that you want your framerate=refresh rate = strobe rate.
So 60hz @144hz pixel clock @60fps would be slower but that would be 1ms MPRT than
120hz @ 240hz pixel clock @60fps.( I increased the verticals of a 240hz to get 120hz also works with 180hz too all stable if that's the correct way to get those certain rates)
So that would be 8ms MPRT.
Or is their some frame pacing issues I dont see.

I've tried 180hz bfi software but it's just way too dark and theres alot of color defects at higher contrasts at higher overdrive. So if I want to use superfast I will have to lower the contrast alot. I dont know if this has to do with with software bfi its self or just the monitor.

Best picture for me is 60hz with tweaks and such at ULMB. Yes ulmb does get kind of weird with the strobe crosstalk at t the mid bottom of the screen. But it's not noticable when playing in a emulator like dolphin with scanlinesync for me.
But you recommend low lag vsync with strobing over scanline sync with ulmb. Why is that?
Also I've read that scanlinesync+regular vsync dont mix well.

I hope we can get ulmb chart comparison soon like you guys did with lightboost.

Which I appreciate all the hard work and information you guys have been putting out. Some of my questions are so obscure that I only get one result in Google and there you guys are .

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Re: Large vertical totals for low input lag

Post by Chief Blur Buster » 11 Jul 2019, 20:22

I didn't say that in this specific thread -- I refer to RTSS scanline sync as one of the many low-lag "VYNC ON" lookalikes.

In this thread, I have only recommended RTSS scanline sync (which is the newer low-lag VSYNC method even though you use VSYNC OFF).

I will have to review my terminology to be careful about the two techniques of low-latency alternatives to plain VSYNC ON -- scanline sync being one of them, since it brings a "VSYNC ON" lookalike to "VSYNC OFF". Sorry about the confusion.
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Re: Large vertical totals for low input lag

Post by RealNC » 11 Jul 2019, 20:31

crossjeremiah wrote:What would you recommend to produce the most console like feel?
Limit your fps to 30 (you can use scanline sync x/2 at 60Hz,) enable motion blur if the game has it, and always use a gamepad. :mrgreen:
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crossjeremiah
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Re: Large vertical totals for low input lag

Post by crossjeremiah » 12 Jul 2019, 06:11

You're good. Ya I saw in one of your posts chief. You said "QFT does not help with VSYNC off because frame slices is like realtime streaming to scanout.
That QFT is hugely beneficial to VSYNC ON in dramatically lowering full frame delivery latency. And that VSYNC ON helps with the frame pacing with ULMB.
(frame rate = refresh rate = strobe rate (60hz=60fps=60hz) in this scenario)
So I have to do a limiter plus scanline sync w/ vsync on with ULMB.
or will scanline sync w/ vsync off with ulmb look identical
or will the QFT not do anything because of frame slices.


RealNC
So I should limit my in game limiter to 30 fps and use scanline x/2? That's very interesting , but it might affect netplay . What's the benefit of using scanline x/2 is there input lag benefits that I'm not aware of. This is mainly use with dolphin , and I'm using it with melee. Does the game run at 30 fps on the gamecube? Correct? I might try offline but netplay is a no go.

UPDATE:
30limiter is a no go. RTSS Scanline Sync was much more smoother with vsync off than vsync on. It was probably the noticable input lag difference. But using Scanline Sync 2x felt smoother than 1x. But might be a placebo though.

UPDATE2:
Is scanline sync x2 + vsync on comparable vsync on with triple buffering in open gl mode. Is it like 3 sync stacked? Because I tried X2+ vsync on and it feels really really good. (vsync on (w/ RTSS Frame limiter (0.01 method) )

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Re: Large vertical totals for low input lag

Post by RealNC » 12 Jul 2019, 23:10

crossjeremiah wrote:RealNC
So I should limit my in game limiter to 30 fps and use scanline x/2? That's very interesting , but it might affect netplay . What's the benefit of using scanline x/2 is there input lag benefits that I'm not aware of. This is mainly use with dolphin , and I'm using it with melee. Does the game run at 30 fps on the gamecube? Correct? I might try offline but netplay is a no go.
I was half-joking and only referring to modern consoles, where almost everything is capped to 30FPS. This doesn't apply to emulators.

With Dolphin, you can try using it in RetroArch (there's now a Dolphin core). Then use RA's low latency features (in the "Latency" section):
  • Enable "Hard GPU sync".
  • Set "Hard GPU frames to 0". If your CPU can't keep up, set it to 1.
  • Set "Poll Type" to "Late".
  • Increase "Frame Delay". This depends on your system. The faster your system, the higher you can set this. The value is in milliseconds. Every millisecond you add is a millisecond of reduced latency. At 60Hz, the frame time is 16.7ms. If you had an extremely fast system, you'd set this to something like 15, meaning you'd only get 1.7ms of latency (16.7 - 15). No system is that fast for Dolphin though (this works well with NES emulators and such, but CB/Wii emulation is much more demanding.) But you can try lower values like 3, 4, 5 or so. At some point though if you keep increasing it, you'll get severe FPS drops because there's no more time left for Dolphin to emulate the next frame.
With that being said, when it comes to latency, you're not gonna beat running your display in VRR mode (g-sync/freesync). RA supports a special VRR mode that gives the emulator full control over the refresh rate. This is enabled in the "Frame Throttle" section. It's the "Sync to Exact Content Framerate (G-Sync, Freesync)" setting. This allows the emulator to run the game at the exact same speed/FPS as the original console and with no added lag. See:

https://www.libretro.com/index.php/upco ... ync-users/

Use the highest refresh rate of your display in this case, to reduce latency further. 240Hz in your case, which means a frame scanout delay of just 4.2ms (regardless of the FPS the emulator runs at.)

You'd have to give up on ULMB of course. So you need to decide what your trade-off is gonna be. If you want the lowest input lag and accurate original console frame timing, game speed and accurate graphical tricks/effects*, use g-sync with the correct RetroArch settings. If you want the lowest motion blur, use ULMB.

Not everything is lost though when it comes to motion blur if you choose g-sync. RetroArch has motion blur reduction feature called "black frame insertion." It is a software-based "ULMB", where it blacks out the screen every other frame. This doesn't work as well as true ULMB of course, but at 240Hz, where the scanout speed if 4.2ms, it might actually look OK. I don't know for sure (I don't have a 240Hz monitor.) Might be worth trying. This feature introduces NO input lag whatsoever.

* If you wonder what "accurate tricks/effects" means, see this video demonstration of how g-sync allows for accurate effects emulation:

https://www.youtube.com/watch?v=2CeZ0xbtfDo

Of special note are the character shadows, which can't be displayed properly if you want to run games at their original speed.
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