Fast Sync vs Vsync Smooth

Discussion in 'Videocards - NVIDIA GeForce Drivers Section' started by Martigen, Jan 14, 2018.

  1. Martigen

    Martigen Master Guru

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    So, uh, what's the difference between them?

    When should one be used over the other, or indeed over standard Vsync for SLI?
     
  2. cryohellinc

    cryohellinc Maha Guru

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  3. RealNC

    RealNC Maha Guru

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    Fast sync is intended to be used for games where your FPS is a multiple of your refresh rate. It works best if your games run upwards of 240FPS if you're on a 60Hz monitor. It has much lower input lag compared to vsync.

    If you can't reach these high FPS, then fast sync will result in more visible stutter. What I noticed here is that if FPS is a higher multiple of the refresh, the less stutter there is:

    5x refresh: Virtually perfect. No stutter.
    4x refresh: Very low stutter, not noticeable most of the time.
    3x refresh: Visible stutter, but not TOO bad.
    2x refresh: Very annoying stutter.
    1x refresh: It kind of works without stutter for a while (like vsync) and then it stutters badly at random.

    But in the end, just try it for yourself. If you can't see any stutters, then obviously it's fine for you.

    Of course keep in mind that higher FPS means higher GPU/CPU use and thus higher power consumption and higher temperatures.
     
    Last edited: Jan 14, 2018
  4. Martigen

    Martigen Master Guru

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    Thanks Cryo will read that in a min.

    EDIT: This is largely focused on Gsync. But see below.

    Just quickly -- I don't have Gsync, and monitor is 3440x1440 @ 100Hz. Oh and SLI, hence Vsync (Smooth) as an option.


    Thanks RealNC. That's interesting -- but who realistically is going to be able to do that, unless they're playing Half Life 1 to hit those caps!

    In fact, the question is: what problem is Fast Sync designed to solve? Going by Cryo's link, Fast Sync seems to be just about reducing input latency -- though not as well as RTSS or other frame limiters.

    And Vsync Smooth, what was that designed to solve?

    I have experimented with both in the past but, to be honest, they seemed to make things worse hence the question. I feel like I'm missing something as to their purpose and intended usage.
     

  5. TimmyP

    TimmyP Master Guru

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    I can tell you that in some games like Overwatch, fast sync is a must. You get hitching if you aren't at least 10fps above your refresh rate, but if you can maintain that, input lag feels the same as vsync off.

    But most of the time its useless. I don't understand why it works so well with OW.
     
  6. -Tj-

    -Tj- Ancient Guru

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    Not that it stutters per say, but jitter..

    And it doesn't have to be multiple refresh rates.. It use to be at first, but now its HZ independent. You can use fastsync and cap fps with e.g. rtss @ 90fps and it will be smooth.. It all depends on game engine and fps cap.. uncapped never really was 100% jitter free..


    And the only diff is yes, less input lag vs normal vsync. But by normal vsync you can remove lag too, e.g. 60hz + 60fps limit + 1frame to render ahead = virtually no lag, unless you're very Very sensitive to it.
     
    AsiJu and BuildeR2 like this.
  7. Dragondale13

    Dragondale13 Maha Guru

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    With SLi, vsync smooth or adaptive + rtss frame limiter, pre-rendered frames 1, works best.The frame limiter being the one to focus on.You'll know when you find the sweet spot.
     
  8. RealNC

    RealNC Maha Guru

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    It was designed to get rid of tearing, like vsync, but unlike vsync, it's meant to not have a big impact on input lag. The cost you pay is some microstutter, and you need very high FPS too.

    It's targeted at esports-like games (csgo, overwatch, quake, etc) where people with with 300+FPS.

    Vsync solves tearing. For modern video games, it means input lag. You can reduce input lag with vsync though by using the "low-latency vsync" method, described here:

    https://forums.guru3d.com/threads/the-truth-about-pre-rendering-0.365860/page-12#post-5380262

    Well, that's why g-sync was invented. It combines the best of both worlds. No tearing, no input lag, no stutter, no need for very high FPS. But that required a redesign in display technology. Vsync and fast sync do not require any special display hardware and work with all monitors.
     
  9. Martigen

    Martigen Master Guru

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    Thanks for the replies all. Purpose of Fast Sync understood :)

    Yes I'm familiar with Vsync :) I should probably have been clearer -- when you have SLI enabled, a new option shows up in the NV conotrol panel called 'Vsync (Smooth)'. I haven't noticed any major difference with it, if anything performance seemed worse with the few games I tried.

    I'll try Dragondale's suggestion combining with RTSS, still wondering what problem it was designed to solve and how (googlefu turned up some information, but want to tap into the learned minds here).
    (Edit: Uh, Dragondale if you enable adpative + RTSS you'll always be tearing...)
     
  10. Vibe

    Vibe Member Guru

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    I just use Vsync or whatever the game sets by default. I never noticed any issues.
     

  11. jiminycricket

    jiminycricket Member Guru

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    In SLI, regular VSync is triple buffered. Smooth VSync changes to double buffering, which reduces input lag at the cost of potentially more stuttering.
     
  12. yasamoka

    yasamoka Ancient Guru

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    Triple buffering is inherent to SLi / CF, not optional. You can't magically disable the third buffer and resort to double-buffered V-Sync - one front buffer and one back buffer means that only one GPU is rendering at any one time, while the other GPU remains idle, completely negating the parallel rendering advantage of SLi / CF.

    This is what Smooth V-Sync does:
    http://nvidia.custhelp.com/app/answers/detail/a_id/3283/~/what-is-smooth-vsync?

     
  13. jiminycricket

    jiminycricket Member Guru

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    You can check what happens to the frame rate when it drops below monitor refresh rate in Smooth VSync. It behaves like double buffering. Eliminating the third buffer is why Smooth reduces input lag (by 27ms/1.6 frames at 60Hz) compared to standard VSync: https://displaylag.com/reduce-input-lag-in-pc-games-the-definitive-guide/

    That Nvidia page is wrong, because standard VSync is inherently triple buffered in SLI, that 60-30 FPS oscillation does not occur.
     
    Last edited: Jan 15, 2018
  14. yasamoka

    yasamoka Ancient Guru

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    Did you read what I posted?

    You cannot eliminate that third buffer. It's impossible and would break SLi. What you're essentially suggesting is that one GPU renders a single back buffer, which completely negates the advantages of SLi.

    Smooth V-Sync limits your framerate to 30 when you cannot approach 60. It's still triple buffering which means there's 1 more frame of input latency.

    Double-buffered V-Sync definitely causes this behavior, but seeing this behavior is not proof of double-buffering being used.
     
  15. Dragondale13

    Dragondale13 Maha Guru

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    Depends on the game and or driver.If it's a demanding game then no you shouldn't.
     

  16. jiminycricket

    jiminycricket Member Guru

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    Then how do you explain Smooth having 1+ frame less input lag than standard VSync?
     
  17. janos666

    janos666 Master Guru

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    In my experience (after a somewhat premature switch from 2k to 4k display where rock stable 60fps just won't happen in modern games on current affordable hardware), FastSync proved to be the obvious best choice for me with fps numbers floating between roughly 30 and 60 and averaging around 45 or so. It barely causes any additional stutter in this 0.5<x<1x range, it simply generates the missing frames by doubling the last one like Vsync would while operating with a more consistent and lower overall lag.
     
  18. yasamoka

    yasamoka Ancient Guru

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    I can't explain something I don't have access to. So link me to the data and I will examine it.

    Hint: input latency is caused by several buffers, not just the 2-3 frame buffers required by V-Sync. For example, frame capping is known to reduce input latency without changing the nature of V-Sync - whether double- or triple-buffered.
     
  19. jiminycricket

    jiminycricket Member Guru

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    It's in the article I linked before, here it is again: https://displaylag.com/reduce-input-lag-in-pc-games-the-definitive-guide/

    Oh so you don't have SLI? Where are you getting your info from? Seem like untested claims to me.
     
  20. yasamoka

    yasamoka Ancient Guru

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    It's clear you simply want to argue for the sake of arguing.

    You spread misinformation regarding an impossible situation (double-buffering with multi-GPU) when Nvidia (and probably AMD) has already stated the inherent triple-buffered-ness of SLi.

    As for "explaining somewhat I don't have access to", what I meant to say was that I can't explain the results concluded by data you did not provide for me to examine ... it is irrelevant whether I have SLi or not ...

    As for the article you provided ...
    What a great testing methodology. /s The smallest unit for their input latency measurements is 8ms ... what an accurate study. They then use averages in order to minimize that flaw in the methodology.

    Going by your logic, can you please explain to me why there's a 1+ less frame of input latency when going from V-Sync ON to Windowed V-Sync? Windowed V-Sync is triple-buffered. So is V-Sync ON quad-buffered? Or are there extra factors that contribute to total input latency other than framebuffers?

    Do you have any other invalid criticism or conclusion to present? Or are you going to keep at this?
     

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