Why do [some] 240HZ monitors have more lag than 144HZ AHVA

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KKNDT
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Why do [some] 240HZ monitors have more lag than 144HZ AHVA

Post by KKNDT » 01 Jan 2018, 10:28

I have read reviews by Tftcentral and Prad.de. Both shows 240HZ e-sports monitors have more input lag than the popular all-round monitors equiped with AUO 144HZ AHVA panel, like PG279Q. Why???

Having read some articles and several replies here, I know 240HZ monitors clearly own the advantage of scanout lag. I just can't understand what make these 240HZ monitors defeated by 144HZ AHVA monitors in TFT and PRAD's lag measurement?

One more question: how does "framebuffer processing" display work during V-SYNC OFF?

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by RealNC » 01 Jan 2018, 10:38

KKNDT wrote:One more question: how does "framebuffer processing" display work during V-SYNC OFF?
There's no such thing as vsync on or off on the display side. That's purely a GPU-side function.
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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by Sparky » 01 Jan 2018, 14:17

Well, different monitors with the same refresh rate and panel technology can have vastly different lag. A lot of it depends on what kind of extra processing is done to the image before it's displayed, and how much priority was placed on latency in developing the hardware and firmware of the monitor.

"e-sports" is a purely marketing term. It doesn't actually mean anything. That's part of why reviewers need to test latency in the first place.

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by Chief Blur Buster » 02 Jan 2018, 02:33

The prad.de measurement for this specific monitor may have used a 60Hz lag-chain measurement or some other input lag measuring methodology that creates bigger numbers. I'm going to try to reach out to Andrea Roth and compare notes as it's important.

For example, in our Blur Busters G-SYNC 101 series, written by Jorim, of the button-to-pixels test in a real-world game, for the XB252Q, in CS:GO, measured 12ms for VSYNC OFF at 1000 frames per second (last few bars). That's much less than Prad's monitor-only measurement -- and that was via our high speed video camera.

It's a "first-anywhere-on-screen" reaction methodology for that specific game, as eSports players often play with peripheral vision too -- and this methodology can produce dramatically lower numbers than "first-single-point" measurements or "VBI-to-photons" measurements.

Image

These numbers are the full chain, from mouse button to pixels, taken via high speed camera, in GSYNC 101 Part #3.

Image

Numbers for the full whole chain would naturally be higher than the monitor-only lag (if that is what prad.de is trying to measure).

Not saying their numbers are incorrect, but they need to document their input lag measuring methodology. I suggest that prad.de to fully document their lag measurement method to properly documenting HOW they measure lag -- it will help compare notes better.

Lag methodology will output different values for:
-- Lag from GPU-side to monitor pixels
-- Lag from monitor input to monitor pixels (excludes cable transmission overheads, e.g. +1ms)
-- Lag from mouse to monitor pixels
-- Lag from keyboard to monitor pixels

And screen location:
-- Lag from VBI to monitor top (ala VSYNC ON input lag)
-- Lag from VBI to monitor center (ala VSYNC ON input lag)
-- Lag from VBI to monitor bottom (ala VSYNC ON input lag)
-- Lag of pixel transmitted from GPU to corresponding pixel shown on monitor (more representative of VSYNC OFF input lag)

And how the lag tester starts the lag stopwatch:
-- Button press
-- Dongle on cable (VBI detector)
-- Black box (Leo Bodnar, etc)
-- API call (e.g. Direct3D Present() or OpenGL glutSwapBuffers)
-- etc.

And how the lag tester stops the stopwatch:
-- Photodiode on a specific location on screen (e.g. oscilloscope, Leo Bodnar, etc)
-- Differentials between two screens
-- First reaction anywhere on screen (e.g. high speed camera)

And how soon to stop the stopwatch
-- First GtG photons detectable
-- GtG 10% (recommended -- very human visible now by then)
-- GtG 50% (recommended)
-- GtG 90%
-- GtG 100% (artificially long, not recommended)
-- Undocumented (e.g. Leo Bodnar, ugh).

And other variables to keep in mind:
-- Lag of a specific Hz (varies from Hz to Hz)
-- Leo Bodnar Tester is lag of VSYNC ON 60Hz
-- SMTT 2.0 is lag-differential between two screens and runs 1000fps VSYNC OFF
-- Lag of VSYNC OFF is also very different from lag of VSYNC ON.

Also different behaviours:
-- VSYNC ON lag testers will have more lag at bottom edge than top edge for most screens
60Hz vs 240Hz have massive differences
-- VSYNC OFF lag testers (at high frame rates) will equalize lag throughout the screen, since VSYNC OFF is scanout-following
60Hz vs 240Hz have less differences, but due to frameslice lag gradients, MIN/AVG/MAX is tighter at 240Hz
-- VSYNC OFF adds a slight lag-randomization of (1/Hz)th of a second. Lag is lowest just right below a tearline. Lag is highest just right above a tearline. And because the lag jitter is a full refresh cycle due to the random tearline locations - this results in MIN/AVG/MAX becomes much tighter at higher Hz than lower Hz when using VSYNC OFF lag testers.
-- Etc.

240Hz displays currently have bad 60Hz lag numbers (worse at 60Hz lag than the best 60Hz monitors) but excellent 240Hz lag numbers. But that is different from 240Hz lag -- not everyone even bothers using 60Hz. Depending on methodology, naturally, some results will be better and some results will be worse.

And lag numbers are not comparable between different review websites.

That is normal and acceptable but insufficient disclosure of lag test methodology is a huge problem. During 2018 we will communicate with other websites to standardize this further.

Also, IMHO, prad.de has done a great job of most tests, and very stellar reputation, one of the best in monitor tests..... except I consider their lag numbers are likely from old-fashioned test methodology. Their lag tests needs an upgrade and needs clearer disclosure of lag stopwatching methodology. And they need to begin pursuit camera photography for WYSIWYG pics of motion blur (now a peer reviewed proven technique). The instructions are quite easy now for reviewers.
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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

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by Sparky » 02 Jan 2018, 09:39

Yep, there's a whole lot of variation both in the accuracy of latency measurements, and in exactly what events you're measuring the time between.

I generally mistrust methods that require manual data collection(for example, looking through video frame by frame), because they're so incredibly tedious that it's difficult to test all the variables that might impact latency. That goes double for measuring the behavior of games, where framerate and settings have an impact on latency.

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by Chief Blur Buster » 02 Jan 2018, 11:00

Electronic methods can also be problematic too, especially since Leo Bodnar is an unknown if it is measuring to GtG 10% or 50% or whatnot.

That can vary many milliseconds away from real world human reaction which begins very early in the GtG cycle, so I consider fully-GtG-included (GtG 100%) lag measurements not properly representative and dramatically different from real world human reactions.

That said, no matter what method, full disclosure and caveats/disclaimers are needed since true effective lag is the important benchmark.
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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

KKNDT
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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by KKNDT » 04 Jan 2018, 07:34

Chief Blur Buster wrote:The prad.de measurement for this specific monitor may have used a 60Hz lag-chain measurement or some other input lag measuring methodology that creates bigger numbers. I'm going to try to reach out to Andrea Roth and compare notes as it's important.

For example, in our Blur Busters G-SYNC 101 series, written by Jorim, of the button-to-pixels test in a real-world game, for the XB252Q, in CS:GO, measured 12ms for VSYNC OFF at 1000 frames per second (last few bars). That's much less than Prad's monitor-only measurement -- and that was via our high speed video camera.

It's a "first-anywhere-on-screen" reaction methodology for that specific game, as eSports players often play with peripheral vision too -- and this methodology can produce dramatically lower numbers than "first-single-point" measurements or "VBI-to-photons" measurements.

Image

These numbers are the full chain, from mouse button to pixels, taken via high speed camera, in GSYNC 101 Part #3.

Image

Numbers for the full whole chain would naturally be higher than the monitor-only lag (if that is what prad.de is trying to measure).

Not saying their numbers are incorrect, but they need to document their input lag measuring methodology. I suggest that prad.de to fully document their lag measurement method to properly documenting HOW they measure lag -- it will help compare notes better.

Lag methodology will output different values for:
-- Lag from GPU-side to monitor pixels
-- Lag from monitor input to monitor pixels (excludes cable transmission overheads, e.g. +1ms)
-- Lag from mouse to monitor pixels
-- Lag from keyboard to monitor pixels

And screen location:
-- Lag from VBI to monitor top (ala VSYNC ON input lag)
-- Lag from VBI to monitor center (ala VSYNC ON input lag)
-- Lag from VBI to monitor bottom (ala VSYNC ON input lag)
-- Lag of pixel transmitted from GPU to corresponding pixel shown on monitor (more representative of VSYNC OFF input lag)

And how the lag tester starts the lag stopwatch:
-- Button press
-- Dongle on cable (VBI detector)
-- Black box (Leo Bodnar, etc)
-- API call (e.g. Direct3D Present() or OpenGL glutSwapBuffers)
-- etc.

And how the lag tester stops the stopwatch:
-- Photodiode on a specific location on screen (e.g. oscilloscope, Leo Bodnar, etc)
-- Differentials between two screens
-- First reaction anywhere on screen (e.g. high speed camera)

And how soon to stop the stopwatch
-- First GtG photons detectable
-- GtG 10% (recommended -- very human visible now by then)
-- GtG 50% (recommended)
-- GtG 90%
-- GtG 100% (artificially long, not recommended)
-- Undocumented (e.g. Leo Bodnar, ugh).

And other variables to keep in mind:
-- Lag of a specific Hz (varies from Hz to Hz)
-- Leo Bodnar Tester is lag of VSYNC ON 60Hz
-- SMTT 2.0 is lag-differential between two screens and runs 1000fps VSYNC OFF
-- Lag of VSYNC OFF is also very different from lag of VSYNC ON.

Also different behaviours:
-- VSYNC ON lag testers will have more lag at bottom edge than top edge for most screens
60Hz vs 240Hz have massive differences
-- VSYNC OFF lag testers (at high frame rates) will equalize lag throughout the screen, since VSYNC OFF is scanout-following
60Hz vs 240Hz have less differences, but due to frameslice lag gradients, MIN/AVG/MAX is tighter at 240Hz
-- VSYNC OFF adds a slight lag-randomization of (1/Hz)th of a second. Lag is lowest just right below a tearline. Lag is highest just right above a tearline. And because the lag jitter is a full refresh cycle due to the random tearline locations - this results in MIN/AVG/MAX becomes much tighter at higher Hz than lower Hz when using VSYNC OFF lag testers.
-- Etc.

240Hz displays currently have bad 60Hz lag numbers (worse at 60Hz lag than the best 60Hz monitors) but excellent 240Hz lag numbers. But that is different from 240Hz lag -- not everyone even bothers using 60Hz. Depending on methodology, naturally, some results will be better and some results will be worse.

And lag numbers are not comparable between different review websites.

That is normal and acceptable but insufficient disclosure of lag test methodology is a huge problem. During 2018 we will communicate with other websites to standardize this further.

Also, IMHO, prad.de has done a great job of most tests, and very stellar reputation, one of the best in monitor tests..... except I consider their lag numbers are likely from old-fashioned test methodology. Their lag tests needs an upgrade and needs clearer disclosure of lag stopwatching methodology. And they need to begin pursuit camera photography for WYSIWYG pics of motion blur (now a peer reviewed proven technique). The instructions are quite easy now for reviewers.

Thank you chief, for such useful information.

But even if we only talk about Tftenctral's number, we can clearly see these AHVA displays have extremely low signal processing lag. They've tested at least 4x AHVA(XB270HU, MG279Q, PG279Q, FS2735) and 2x 240HZ TN (PG258Q, AG251FZ), both includes G-SYNC and Freesync models. So I think the data is of valuable reference.

Image

However I have no idea ??? HZ do TFTcentral test. If they were actully comparing the lag with 240HZ VS 144HZ, the result shows these AHVA beat 240HZ TN even if they lose in scanout speed and GtG?

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by Sparky » 04 Jan 2018, 10:34

How do they select refresh rate? Do they use 60hz for everything, do they use the highest supported refresh rate at any resolution, or do they use the highest refresh rate for the maximum supported resolution? Something else?

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by Chief Blur Buster » 09 Jan 2018, 01:06

AFAIK, TFTCentral uses the highest Hz for lag tests. I'd have to doublecheck.

Nontheless, GtG lag is sometimes high subjective (human sensitivity varies), but the best industry standard for lag stopwatching is either GtG10% or GtG50%.

GtG10% because the photons are visible by then. 10% of the way from black to white is a dark gray. That's still visible. And manufacturer GtG response measurements are typically from 10% through the 90% point. So the GtG 10% point lines up very well with that.

GtG50% because it is a midpoint of numeric fairness (even if not human fairness) and is usually extremely close to GtG10% on many monitors (within 1ms) so reasonably close to human subjectivity.

RTings now currently standardizes their stopwatching end-of-lag on GtG1% (I asked).

I have talked to some reviewers and am trying to converge on a standardization, including full disclosure of the lag stopwatching process (the start signal & the stop signal). Including where in the GtG cycle is used as the stop signal for input lag measurements. (Unfortunately GtG percentage info is not always available: Leo Bodnar is quite the veritable black box).

Different sites may stopwatch to a different point of GtG or even show an approximate band (TFTCentral style), but publishing only GtG100% lag results (and not also other GtG<100% lag results) is useless from a human reaction time perspective. This is because those ultra-conservative lag numbers often only the last dim-ghost far beyond the strong image (sometimes 2 refresh cycles later!) that the human already reacted-timed to (duh) so sites that only publishes GtG100% numbers are publishing conservative numbers often far bigger than human reaction real-world numbers. An OLED with a GtG100% would be closer to real world reaction time, since OLEDs are very fast (and usually complete) to GtG100% but an LCD may only stairstep to GtG90% on next refresh cycle then GtG99% two refresh cycles later, and finally GtG100% three refresh cycles later.

Rheoretically, why is certain particular (unnamed) sites measuring the input lag of the last remaining laggy faint ghost after-after-image, instead of the strong image that the human reacts to?. Going all the way to 100% GtG doesn't make sense from a human-reaction-time perspective. The lag of the refresh cycle containing the majority of the GtG cycle is the most important for human-reaction-time perspective.

Lower lag plus slower GtG can still feel more responsive to an extent -- depending on the curve shape. But you still want clearer (less blurry) images, so fast GtG is still quite preferred.
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter

       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
       • List of FreeSync Monitors
       • List of Ultrawide Monitors

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Re: Why do 240HZ monitors have more lag than 144HZ AHVA

Post by StrobeMaster » 09 Jan 2018, 10:16

Chief Blur Buster wrote: Nontheless, GtG lag is sometimes high subjective (human sensitivity varies), but the best industry standard for lag stopwatching is either GtG10% or GtG50%.

GtG10% because the photons are visible by then. 10% of the way from black to white is a dark gray. That's still visible. And manufacturer GtG response measurements are typically from 10% through the 90% point. So the GtG 10% point lines up very well with that.

GtG50% because it is a midpoint of fairness and is usually extremely close to GtG10% on many monitors (within 1ms) so reasonably close to human subjectivity.
Yet, one should keep in mind that GtG10% or GtG50% usually refer to momentary luminance levels. It is not that, at the time the luminance curve crosses the 10% mark, we actually can perceive a 10%-gray already; the over-all luminance profile has to be taken into account as well. This becomes especially problematic when using the numbers for comparing screens with very different luminance profiles (CRT vs. LCD/continuous backlight vs. LCD/strobed). Moreover, detecting some white digits on a black background is rather different from any real-life situation. All in all, it is very difficult to come up with a perceptually meaningful measure, which doesn't mean we shouldn't try (see also https://display-corner.epfl.ch/index.ph ... #Input_lag).

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