Should I Turn On V-Sync With Freesync..?

Discussion in 'Computer Monitor Forum' started by zeebaluch, Oct 23, 2017.

  1. Meccs

    Meccs Active Member

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    Just got my first FreeSync monitor, It's a 70 Hz FreeSync (FS) monitor (Iiyama ProLite XUB2792QSU) since I barely game on PC anymore. Still, I was curious how BF1 would run and noticed that even with FS in Radeon settings and on the monitor enabled I got tearing. So I limited the FPS in RTSS to 68 and still got tearing. I tried setting the FPS in the BF1 console and again got tearing. Only when I enabled VSync in addition to FS and the frame limiter I got rid of the tearing.

    The thing I noticed is that even though you set a FPS limit and the on screen display shows that you never go over that limit, that is not what is happening. My OSD on the monitor shows the fluctuating Hz counter when FS is enabled and it pretty much always spiked up to 70 Hz. It actually fluctuated quite a bit (from 63 to 70) even though the FPS counter in game showed always the set 67. That is the same thing Battle(non)sense noticed in this video here (at around the 6 minute mark):

    The only time I could use FS without tearing and with Vsync off and frame limiter off was when I actually constantly stayed below 70 fps in game. I forced this with the resolution scale setting in BF1.

    I still think that even with frame limiter to below the FS and VSync on you will not get FS and have the VSync lag because the actual Hz counter on the monitor was also hitting 70 Hz.

    So to sum up:

    FreeSync off, VSync off, no fps limit: tearing
    FreeSync on, VSync off, no fps limit: tearing (when exceeding FreeSync limit)
    FreeSync on, VSync off, fps limited to below FreeSync limit: tearing
    FreeSync on, VSync on, fps limited to below FreeSync limit: no tearing but probably sill no FreeSync because actual Hz counter did hit 70 Hz even though fps was limited to below that
    FreeSync on, VSync off, no fps limit + game actually staying below the FreeSync limit (because of high settings): no tearing and actual FreeSync

    That renders the low refresh rate FreeSync monitors kinda useless for the most part since you have to make sure that you actually stay in between the small FreeSync window.

    I am still not sure about the FS+VS+frame limit on but since the actual refresh rate did exceed the set fps limit I would expect that instead of tearing you get the full VSync delay, but I could not test this. This is an assumption.
     
  2. yasamoka

    yasamoka Ancient Guru

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    Please read the thread fully first as well as the linked G-Sync articles in order to understand what is going on. This has been covered multiple times. So, to avoid repeating all what was said, please read carefully and focus on discussions pertaining to the behavior of V-Sync on with G-Sync / FreeSync (frametime compensation).
     
  3. Meccs

    Meccs Active Member

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    I did. There is nothing about the actual monitor refresh rate being higher than what the fps counter shows when you limit the frames in game or with RTSS. Limiting the fps to 2-3 fps below FreeSync max and enabling VSync (as you suggested) does not work because the ACTUAL refresh rate is different, higher to be exact (it fluctuates, Battle(non)sense had to lower the fps limiter to -13 fps to not hit 144 Hz for example, the ingame fps counter showed lower fps than what the monitor used as FreeSync refresh rate).
     
    Last edited: Jun 8, 2018
  4. yasamoka

    yasamoka Ancient Guru

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    Yes, there is. Frames that take slightly shorter time to render are slightly offset when V-Sync (i.e. frametime compensation in the case of G-Sync / FreeSync) is enabled. Your effective framerate is then equal to the refresh rate, and that very brief spike does not show up in the framerate counter. The numbers don't matter if you're getting smooth frame output, which you should easily be able to discern with your eyes. When I had FreeSync, 58FPS RTSS cap + V-Sync on @ 60Hz worked flawlessly. Now, with G-Sync, 162FPS RTSS cap + V-Sync on @ 165Hz also works flawlessly.
     

  5. yasamoka

    yasamoka Ancient Guru

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    All of these scenarios indicate frames that take slightly shorter to render and don't end up waiting as long as the framecap entails. These frames escape the FreeSync window and you get tearing. Enabling V-Sync turns on frametime compensation which aligns these spiking frames to the next scanout without letting them escape the FreeSync window or turning on V-Sync-like behavior. Instead, latency is lowered to the minimum possible value such that all frames are aligned to the scanout. It is possible to have even lower latency but you will need to tear in the frame for that to happen since with frametime compensation, the frame is ever so slightly delayed. However, the latency achieved is quite lower than V-Sync-like mode latency.

    Theoretically speaking, for every game you try, depending on frametime variance, you would need different framecaps sufficiently below the refresh rate in order to lower / avoid spikes that go over 70FPS (i.e. below 14.29ms). Whenever a spike is large enough, you will get tearing if you leave V-Sync off. Pretty much no point to leaving it off.

    No, again, not what happens. G-Sync / FreeSync do not switch over to V-Sync when FPS = refresh rate, either. They switch to V-Sync-like behavior with added latency over the highest framerates achievable in the G-Sync / FreeSync window but with lower latency than V-Sync on @ FPS = refresh rate (G-Sync / FreeSync off).

    With a framerate cap below the refresh rate @ -2 / -3 FPS and V-Sync on, frametime compensation is enabled. G-Sync / FreeSync does not switch to V-Sync-like behavior.

    No FreeSync.

    Framerate exceeds refresh rate and escapes FreeSync window.

    Some frames take slightly shorter and escape FreeSync window.

    No, explained earlier.

    Yes, but this is not exclusively the region where FreeSync works.

    Wrong conclusion from hasty assumptions.

    Just use the combination and enjoy your games .. and read the G-Sync BlurBusters articles very thoroughly. They explain exactly what happens in each and every mode. The same mechanisms apply to FreeSync.
     
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  6. Meccs

    Meccs Active Member

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    Well I replied mostly because I thought your whole point was that you NEED VSync to have FreeSync working. This is not true and anyone can test this easily when you take a game that is stressing on your Gfx card so that you never reach the monitor refresh rate limit. FreeSync will work 100% even without limiter or VSync as long as you stay between the max an min FreeSync limits. I believe you said a few pages earlier that in order to FreeSync to work, VSync has to be enabled. If it wasn't you then sorry.

    Fact is: you never need VSync (nor any limiter) if your game is stressing enough so that you never exceed (or go below) your FreeSync limits (easier with 144 Hz monitors than 70/75 Hz ones of course)

    Also another observation: when you stay below your max FreeSync refresh rate (lets say 75 is the max and actual in game fps are 70 because of a demanding game) and have VSync and Limiter disabled, you get smooth playback (FreeSync is working) but as soon as you use an in-game our 3rd party limiter and limit the fps to whatever number (doesn't matter which one), you get tearing hence FreeSync is no longer working. I tested this with two monitors today. There is no way around it. As soon as you limit your fps (without VSync) FreeSync is not working anymore.

    That still leaves the point that you suggest, meaning VSync on and fps limited to -2/-3 fps blow the max FreeSync range. I still assume that FreeSync isn't working in that case because of the aforementioned interference of the limiter. I feel like the game doesn't behave as responsive with that setup as with the "real FreeSync" setting (no nothing and inside range because of demanding game). I do believe however that you should not use the G-Sync specs to explain the FreeSync mechanism. This would be an assumption as well.

    However I will still use VSync + -2 fps Limit because of the chance that you are right and mostly because that is the only way to get tearing free gameplay for games where I can get more fps than the FreeSync limit. So there is that. Starting to think I should have bought a 144 Hz FreeSync monitor but I don't game as much anymore...
     
    Last edited: Jun 8, 2018
  7. yasamoka

    yasamoka Ancient Guru

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    This is weird behavior that is not supposed to happen. It is possible that certain frame limiters break FreeSync when AMD mess something up between drivers. However, it's more than likely that there's something you're setting up incorrectly. An in-game frame limiter is invisible to AMD drivers and cannot possibly *break* FreeSync. To test this, load up a game that has a 60FPS hard cap and you should find FreeSync working. No difference to a game where the framerate is capped in-game.

    No, it is not an assumption because I tested both and they are identical down to the mechanisms. If FreeSync is getting disabled when you use the framerate cap, then V-Sync on should put you back in V-Sync territory. This means that if you cap your FPS to -2 below the refresh rate, 2 frames will be repeated each second. Each skipped frame should be clearly visible. -3 means 3 skipped frames and so on.

    It doesn't depend on whether my advice is correct or not. You can try out all the configurations you suggested and see what feels best and stick to that. The wrong configurations should be blatantly obvious particularly at lower refresh rates. Trying, for example, a framerate cap of 30FPS @ a mismatched refresh rate such as 70Hz should clearly indicate whether FreeSync is working or not. If you can't tell a difference at all then it probably doesn't matter.
     
  8. Meccs

    Meccs Active Member

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    I actually did this with BF1, it can limit the fps to 60, monitor refresh (which is 70 and 75 with my two monitors), 120, 144, 200 etc. It breaks FreeSync when I set it to 60 and you get tearing. I need to correct this a bit though. It breaks FreeSync not for any number but for any that is lower than the max FreeSync limit. If I set it to 200 again then FreeSync starts working.
     
  9. yasamoka

    yasamoka Ancient Guru

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    So now try the framerate cap again and enable V-Sync. Do you get a perfectly 60Hz-like experience with no stutter? If so, then FreeSync is working.
     
  10. RealNC

    RealNC Ancient Guru

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    That's not exactly true.

    Neither FS nor gsync can prevent tearing when they need to refresh the monitor prematurely and you have disabled frame time variance compensation.

    What you need to keep in mind is that "FPS" is a very misleading term. You need to look at frame times, not frames per second. As an extreme example, If you get 100FPS for half a second, and then 0FPS for another half a second, that's 50FPS, but freesync will not work.

    More realistically, frames can very often arrive too late. At which point, freesync needs to go ahead and refresh the monitor again to avoid visual glitches on the pixels and even damage. It is very likely that during that forced refresh the new frame will arrive, and that results in a tear line. And you will see random tearing "flashes" (for just one frame or two) quite often if you disable frame time variance compensation (which is controlled by the vsync setting.)

    Some games will suffer from this more than others, but you can never guarantee perfectly evenly spaced frame times. Sometimes, some frames are just going to miss their mark. Windows is not a real-time operating system.
     
    Last edited: Jun 8, 2018

  11. Meccs

    Meccs Active Member

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    And in this specific case enabling Vsync would prevent this tearing because of premature refreshing?
     
  12. yasamoka

    yasamoka Ancient Guru

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    Come on.
     
  13. Meccs

    Meccs Active Member

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    No, not really. There is no apparent tearing but quite a bit of stuttering.
    In fact, VSync and limit to 73 fps has also a bit of stuttering compared to VSync with no limiter. Looks like duplicate frames in the slo-mo footage I took. I don't believe for a second that in this case with BF1 and VSync + limit to 73 that FreeSync is working!
     
    Last edited: Jun 8, 2018
  14. yasamoka

    yasamoka Ancient Guru

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    Can you describe your configuration down to the very details? Specs, drivers, games, third-party apps used, etc...
     
  15. Meccs

    Meccs Active Member

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    iiyama ProLite XUB2792QSU and Samsung C27H711

    Radeon 18.5.2, latest Win 10 Update, Afterburner with RTSS nothing else in background except Origin.
     

  16. yasamoka

    yasamoka Ancient Guru

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    Disable Origin overlay and test.
     
  17. Meccs

    Meccs Active Member

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    First thing I turned off after installing it ;)
    The stuttering might be a problem with the Samsung Monitor. The Iiyama behaves differently. I have to test this a bit more. Interestingly enough, even with VSync and limited to 60 the Hz counter on the monitor OSD spikes up to the max range of 70 Hz sometimes. It does fluctuate around 60 Hz most of the time though which would indicate that FreeSync is working (because it isn't working at a fixed refresh rate).

    When I turn off FreeSync in Radeon and have VSync + limiter on, the Iiyama shows the same behavior as the Samsung which indicates that Samsung hasn't FreeSync enabled with that configuration. Sadly only the Iiyama shows the Hz counter on the OSD.

    So having tested this, VSync on + limiter to lower than max FreeSync AND the TV showing a variable Hz counter makes me believe that, at least on the Iiyama, FreeSync is working as you said. I don't think the monitor would have a variable refresh rate when Vsync has taken over. In fact, turning FreeSync off and having VSync + 60 fps limiter shows the Hz counter fixed at 70 Hz which pretty much confirms that.

    There might be a problem with the Samsung.
     
    Last edited: Jun 8, 2018
  18. RealNC

    RealNC Ancient Guru

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    Yes. Because then the frame can be held back a bit until the refresh finishes. With vsync off, the frame will not be held back, and thus a tear line will appear.

    Edit: The behavior might be different across different displays though. With such a low FS ceiling (70Hz), it stands to reason that frame time variance compensation cannot work that well, and low frame rate compensation might not work at all, which could explain why your display sticks to 70Hz for long periods of time. A wide free sync range (something like 40Hz-144Hz) should work much better.
     
    Last edited: Jun 8, 2018
  19. Rich_Guy

    Rich_Guy Ancient Guru

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    Ive got a BenQ XL2730Z 144Hz FreeSync monitor, and i have FreeSync on, V-Sync disabled in game, and disabled in the Radeon Settings too (Wait For Vertical Refresh = Always Off), and i use RTSS to set a frame limit (which i have to 80fps, as thats fine for me) , and i get no tearing etc... at all. :)
     
  20. yasamoka

    yasamoka Ancient Guru

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    What is the point of owning a 144Hz FreeSync monitor if you cap your framerate to 80 dude ...
     

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