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Actual refresh rate varying from time to time?

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Actual refresh rate varying from time to time?

Postby KuraiShidosha » 21 Feb 2018, 01:56

Using: https://www.vsynctester.com/

My ASUS PG279Q's real fresh rate varies from time to time and I have no idea what is causing the variation. Sometimes it's as low as 143.55Hz, other time it's spot on 144.00Hz. Right now it's 143.81Hz.

What's going on and is this indicative of a problem with my display? I do notice random 1 frame duration white lines that appear about 250 pixels long, 1 pixel tall at different spots on the monitor every 20-30 minutes. This I know is a defect and a sign of a problem with the display but since there's nothing else wrong with the screen (dead/stuck pixels etc) I don't want to RMA it and risk getting a beat up refurb with tons of problems over this.

I just want to know if the refresh rate changing constantly is normal or what.
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Re: Actual refresh rate varying from time to time?

Postby RealNC » 21 Feb 2018, 02:10

Refresh rate is always constant. It never changes, unless you're in gsync or freesync mode on such a display, which you are not.

This is a measurement issue, not a display issue.
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Re: Actual refresh rate varying from time to time?

Postby KuraiShidosha » 21 Feb 2018, 05:09

It turns out it's from g-sync being on. I turned it off and my refresh rate is always spot on 144.00hz again. As soon as I turn g-sync back on it starts to fluctuate in these web browser tests, typically 143.5-8hz.
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Re: Actual refresh rate varying from time to time?

Postby Chief Blur Buster » 21 Feb 2018, 13:52

This is normal.

VRR windowed mode causes microscopic variances in refresh rate with Windows Desktop Manager.

Sometimes it's 143.9Hz. Sometimes it's 144.1Hz. It varies.
It tries to stay fixed but GSYNC-enabled Microsoft Windows is actually continually varying in a microseconds timescale.

It typically doesn't affect anything, unless you're trying to do ultra-precision frame pacing.

RealNC wrote:This is a measurement issue, not a display issue.

Actually, few people know this, but it's actually a normal VRR behavior.

I have the same behaviour when I have GSYNC enabled in windowed mode, when just sitting at the Microsoft Windows Desktop.

The display is simply refreshing on demand by software-triggered refresh cycles via graphics drivers, instead of on its own volition.

One bonus of G-SYNC powered windowed mode is there seems to be slightly less compositing lag. In exchange for letting your refresh rate be floaty (at the microseconds timescales), you reduce your compositing input lag in WDM a little bit. This is not 100% confirmed, and tests are needed (I'll do some tests soon).

This stops if you turn off G-SYNC Windowed Mode if this microscopic-variability bothers you. That way, G-SYNC only enables itself in full screen mode. And the display is refreshing itself automatically at virtually nanosecond-exact intervals instead (but that means forcing software to sync to the display -- aka VSYNC ON -- which is harder to be lag-free and stutter-free)

KuraiShidosha wrote:Using: https://www.vsynctester.com/


Also, we have our quick refresh rate tester too, http://www.testufo.com/refreshrate
(Displays 3 digits by default, but can be configured to display up to 8 digits. It usually reaches maximal accuracy within 10-15 minutes)



Note: If it incorrectly says 60 Hz, please see HOWTO: Fix TestUFO Stuck At 60Hz.
Also, most Linux systems will not display this accurately.


Please note, there is a small amount of clock-slewing going on between system clocks, browser clocks, and other clocks based on current clock rate of chip (e.g. Intel SpeedStep can affect this on some chips) so there's some imprecision going on at the 6th or 7th digits. Also, graphics clock may run slightly faster or slower than real world time by a tolerance factor (less than 0.1%). So the slew between computer clock and graphics clock may produce minor inaccuracies, but the ratio should stay fixed pretty well to roughly the 6th digit (after a 10 minute run of this TestUFO Refresh Rate measurement) -- meaning the number eventually will stabilize all the way to approximately the 6th digit -- unless VRR is enabled.

TestUFO Refresh Rate Calculator is one of the Internet's most accurate refresh rate calculators (along with VSYNC Tester) and these two testers are both sensitive enough to pick up when WDM refresh rate is varying -- and it correctly does. Yes, your refresh rate is indeed correctly varying (by design) at Windows Desktop.

Right now, browser microsecond clocks are accurate to 5 microseconds, so this refresh rate calculator is extremely sensitive -- it successfully is capturing your VRR-induced floating refresh rate! Even though one refresh cycle measurement can jitter a lot, by simply timing many refresh cycles over several minutes (and automatically discarding failed/framedropped refresh cycle measurements), TestUFO successfully gains sub-microsecond-accuracy refresh cycle measurement accuracy (assuming the clock slew rate between graphics and computer is sub-microsecond -- this surprisingly is a bigger error factor!)

However, in my experience, this TestUFO refresh rate is ultra-accurate at least to the 3rd digit to realworld time, and to at least 6th digit to graphics clock time (however faster/slower it may be relative to real world time).

So that means if the 2nd decimal digit keeps changing -- then you almost definitely have a floating refresh rate (i.e. software-triggered refresh cycles from WDM -- that's exactly what happens if your monitor OSD says "G-SYNC" while you are at Windows Desktop).

In my experience with TestUFO Refresh Rate after 10 minutes of letting digits settle:
2nd or 3rd digit still keeps changing -- You've got windowed G-SYNC enabled
4th digit still keeps changing -- Clockrate ratio changing (e.g. Intel SpeedStep keeps changing, background web surfing, etc)
5th digit still keeps changing -- Typical slow-performing system.
6th digit still keep changing -- Typical system, idling.
7th digit still keeps changing -- Very fast/accurate/precise system. Congrats if you've locked 6 decmial digits
Varies system-to-system.
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Re: Actual refresh rate varying from time to time?

Postby KuraiShidosha » 21 Feb 2018, 15:56

Thanks for confirming my suspicions. One thing to note is the behavior is visible even with just fullscreen mode g-sync engaged. Perhaps it's a flaw that requires a restart to fully change, but it was showing the same lower than expected refresh rate just toggling on fullscreen only mode on and off.
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Re: Actual refresh rate varying from time to time?

Postby Chief Blur Buster » 22 Feb 2018, 09:54

The easy way to check is display OSD. If it says GSYNC enabled, your refresh rate is always floaty - at least at the microscopic timescales.

Doesn't matter, full screen or windowed, but as long as it says GSYNC at desktop, then your refresh cycles is software triggered, and thus slightly floaty (at an invisible level) even at desktop. If you turned off GSYNC windowed but monitor still says GSYNC, you may need to reboot for it to fully disengage and revert to classic hardware-driven refresh rate.
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Re: Actual refresh rate varying from time to time?

Postby RealNC » 22 Feb 2018, 10:38

Even with windowed g-sync disabled and only fullscreen g-sync enabled, the monitor always shows "G-SYNC" in the OSD. The only way to get "Normal" or "Fixed refresh" in the OSD is to *completely* disable g-sync.

With that being said, I do not observe such behavior here. OSD says "G-SYNC", windowed g-sync is disabled, and there's no Hz fluctuation.
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Re: Actual refresh rate varying from time to time?

Postby Chief Blur Buster » 22 Feb 2018, 12:22

RealNC wrote:Even with windowed g-sync disabled and only fullscreen g-sync enabled, the monitor always shows "G-SYNC" in the OSD. The only way to get "Normal" or "Fixed refresh" in the OSD is to *completely* disable g-sync.

With that being said, I do not observe such behavior here. OSD says "G-SYNC", windowed g-sync is disabled, and there's no Hz fluctuation.

It's only in the millihertz! 2nd or 3rd decimal digits and sometimes the fluctuation is slow -- different times of the day rather than in real time.

1. Boot Windows
2. Enable GSYNC
3. Wait for vsynctester/testufo to stabilize (a few minutes).
4. Record Hz

Repeat the run at different times of the day. The previous day. The next day. The Hz will be different. You may have fairly stable Hz but it can fluctuate in the millihertz leagues.

Now fully disable GSYNC, and try the same for fixed Hz. Measure at different times of the day, you'll get far more similar results, than if GSYNC is enabled.

I've seen fluctuating going in more realtime (especially when more graphics processing is going on, e.g. background windows) and it's easy to dismiss different Hz in TestUFO as actual browser error -- but it isn't. The errors disappear when you repeat tests in GSYNC-disabled, so it's definitely not browser error.
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Re: Actual refresh rate varying from time to time?

Postby Chief Blur Buster » 24 Feb 2018, 00:08

1. http://www.testufo.com/refreshrate#digits=5

2. wait a few minutes for all 5 digits to fully settle.

3. Do this at 3 different parts of the day (especially with different computer loads, etc).

Three runs at three different times a day, GSYNC turned off -- 144.00035 144.00035 144.00035
Three runs at three different times a day, GSYNC turned on -- 139.99416 139.99372 139.99518

Typical behaviour. It's normal.

The varying isn't always noticeable in realtime, you have to repeat TestUFO averaging runs. Some computers will vary more, some computers will vary but slowly, etc.

It's subtle. But it's there. It's simply a quirk of software-triggered refresh cycles.
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Re: Actual refresh rate varying from time to time?

Postby RealNC » 24 Feb 2018, 03:42

Well, what you are saying might be happening, but this is definitely not:

My ASUS PG279Q's real fresh rate varies from time to time and I have no idea what is causing the variation. Sometimes it's as low as 143.55Hz, other time it's spot on 144.00Hz. Right now it's 143.81Hz.


This doesn't sound normal. Could be a driver bug. I'm not still not on the latest W10 version (I constantly postpone the update because I boot into Windows very rarely right now and don't have time for the update.) This might be a factor.
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