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This topic contains 60 replies, has 12 voices, and was last updated by Kryyss Kryyss 11 Jul 2018 @ 5:08am.

Viewing 15 posts - 16 through 30 (of 61 total)
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  • #17853
    TwoCables
    TwoCables
    Kickstarter Backer
    Topics: 118
    Replies: 1474

    Moon: all G-SYNC and FreeSync does is, it synchronizes the monitor’s refresh rate to the framerate. This is very different from V-SYNC which tries to keep the framerate synchronized to the refresh rate.

    So, the only real benefit of G-SYNC and FreeSync is, you can enjoy far less screen tearing (or none). In addition to that though, all motion at high refresh rates (like say maybe 100 Hz and higher) is noticeably smoother. So let’s say you have a G-SYNC or FreeSync monitor that can have a high refresh rate of 144 Hz or 165 Hz or higher, and let’s say that you can easily have sustained framerates well into the 100s, like around 120, or 130 or 140. That would mean your refresh rate while gaming will be nice and high (matching the framerate), which will make all motion look smoother.

    There’s also much less input lag with G-SYNC and FreeSync compared to V-SYNC.

    There are no other benefits. Even so, it still makes quite a big difference.

    Prepare for Overload…

    #17881

    hypersonic
    Kickstarter Backer
    Topics: 18
    Replies: 220

    Ya fast CPU/GPU and vsync w/triple-buffering seems best. AFAIK with triple-buffering the GPU will simply output from the most recent completed buffer, and the GPU will write new frames to the oldest buffer. If the GPU writes to the buffers faster than the monitor can render then some frames are simply skipped as it always outputs the most recent frame.

    #17886
    TwoCables
    TwoCables
    Kickstarter Backer
    Topics: 118
    Replies: 1474

    Seriously, G-SYNC and FreeSync is noticeably much better than that. V-SYNC has much more input lag, and you are forced to have your framerate locked to your refresh rate. With G-SYNC and FreeSync, there’s very little input lag and the refresh rate gets locked to whatever the framerate is. It just follows the framerate around very smoothly.

    Prepare for Overload…

    #17887

    hypersonic
    Kickstarter Backer
    Topics: 18
    Replies: 220

    I could only see G-sync Free-sync being useful for displays that are capable of very low frametimes (<10ms) So the display would always be ready for the next frame just as soon as the GPU can produce them. A chain is only as strong as it’s weakest link, best start with the display and work your way down the chain.

    Beware of 4K displays claiming very high framerates (low frametimes.) They might degrade the image using chroma sub sampling to achieve this
    https://www.reddit.com/r/hardware/comments/8rlf2z/psa_4k_144_hz_monitors_use_chroma_subsampling_for/

    For 4k 120hz HDMI 2.1 or DisplayPort 1.3 interfaces are needed if you want to avoid chroma sub sampling. (if bits per color isn’t high)

    #17888

    bwabbit
    Participant
    Topics: 2
    Replies: 18

    I thought it was the other way around really. You wouldn’t care about synchronisation if the refresh rate was really high because you wouldn’t gain much latency from having to wait for the next refresh anyway. For a hypothetical 1000Hz monitor if it takes you 10.1ms to generate a frame and then have to wait 0.9ms it’s not really a big deal.

    I think the actual input-lag is in the worst case:
    > For 3-Buffer-Swap-Chain (old Direct3D-style triple-buffering): 3n->6n going from full-fps to half-fps
    > For every other sync method (including none at all): Same as above but 2n->4n
    (where n is the (minimum) refresh interval of the monitor – its highest refresh rate)

    With adaptive (or no) sync you can have 2.1n or whatever (one full-speed frame and one slightly-slower one) so average is better ofc.

    #17889

    hypersonic
    Kickstarter Backer
    Topics: 18
    Replies: 220

    I was thinking that if the GPU is much faster than the display, you’re going to throw away frames no matter what (no tearing) system is in place.

    I could be wrong, but I think that with triple buffering, neither the GPU nor the display has to wait for the other to sync.
    -whenever the display is ready to show another frame the newest completely drawn frame is there waiting. If the display has already shown the newest completely drawn frame then just continue showing it until the instant a newer one becomes available.
    -whenever the GPU is ready to draw another frame it draws to the oldest frame buffer that the display isn’t currently reading/showing.

    https://en.wikipedia.org/wiki/Multiple_buffering#Triple_buffering

    #17891

    bwabbit
    Participant
    Topics: 2
    Replies: 18

    I was thinking that if the GPU is much faster than the display, you’re going to throw away frames no matter what (no tearing) system is in place.

    The software can generate frames at whatever rate it likes up to maximum CPU/GPU usage.
    Triple-buffering (the flavour where you can overwrite the oldest frame) does work as you describe though apart from maybe one point:

    If the display has already shown the newest completely drawn frame then just continue showing it until the instant a newer one becomes available.

    Did you mean to say ‘instant’ there? That would happen with adaptive-sync but not v-sync regardless of buffering.

    If we’re talking about latency and adaptive-sync…on a normal monitor you have to wait for however-many refreshes to display the frame (with vsync), even though triple-buffering allows you to write new frames as fast as you like. If you had a slow monitor without adaptive-sync that’s a big deal. A frame could be ready just a little too late and you have to wait an extra refresh. On a fast monitor you wouldn’t be waiting very long either way. The main reason for adaptive-sync is just to do away with the extra wait-before-vsync delay which is going to be higher on a slower monitor and leads to rapid frame-rate jitter and increased latency.

    Kinda like this:
    Slow/VSync: [xxx][xxx][yyy][zzz] – frame ‘x’ displayed for two monitor refreshes, ‘y’ and ‘z’ are delayed
    Slow/Adapt: [xxxx][yyy][zzzz]
    Fast/VSync: [x][x][x][x][y][y][y][z][z][z][z] – refresh is fast enough that there’s (little) waiting for display
    Fast/Adapt: Almost same as above if refreshes are fast enough

    I may well be missing something though. 🙂

    #17892

    hypersonic
    Kickstarter Backer
    Topics: 18
    Replies: 220

    With CRTs to hold a image it has to has to keep scanning with the electron gun onto to the screen. However with newer displays I’d assume that an image can be held without scanning the screen. So I’d assume that literally instant while waiting, meaning it doesn’t have to wait for a scan to the screen to complete to start showing a new image (while avoiding tearing.)

    #17893
    Nightmare
    Nightmare
    Participant
    Topics: 1
    Replies: 5

    I installed and just headed into the game without checking any settings. I have a decent computer, but slightly older video card.

    i7-4790K CPU @ 4 GHz
    16 GB Ram
    Nvidia GTX 760

    I admit that I spray and pray… :/

    #17894

    bwabbit
    Participant
    Topics: 2
    Replies: 18

    (think I broke the forum!)

    #17895

    bwabbit
    Participant
    Topics: 2
    Replies: 18

    With CRTs to hold a image it has to has to keep scanning with the electron gun onto to the screen. However with newer displays I’d assume that an image can be held without scanning the screen. So I’d assume that literally instant while waiting, meaning it doesn’t have to wait for a scan to the screen to complete to start showing a new image (while avoiding tearing.)

    That’s essentially what FreeSync does (not sure about G-Sync). LCDs still ‘scan’ but the pixels hold their state for a lot longer than CRT phosphor. FreeSync dynamically adjusts the delay between frames (vertical blanking period) to keep monitor refreshes and framerate in sync. As I understand it, it’s not especially complicated – it’s just that standard monitors, LCD or not, work just like the old CRTs in terms of how timing is determined.

    #17896

    hypersonic
    Kickstarter Backer
    Topics: 18
    Replies: 220

    (You did seem to mess up the formatting!)

    Unlike with electro guns of CRTs, the ‘scanning’ process I’d imagine would be very quick, maybe like 1 ms. (can’t scan that fast with CRT because a certain amount of dwell time is needed to adequately excite the phosphorus.)

    I’d imagine that with LCD (especially OLED) scanning would simply involve quickly flipping a bunch of light switches (or dimmers.) Once flipped you don’t have to do anything and the image stays indefinitely (power is constantly applied.)

    You’d think that with the new interfaces (HDMI/DisplayPort) stuff like G-Sync/FreeSync would be built in. Actually I think it is built in to DisplayPort (adaptive sync), and that Freesync uses it, but if it is built in why G-sync / Freesync?

    Just found this link (haven’t read through it just yet though)
    https://www.reddit.com/r/buildapc/comments/4p0q7a/lets_talk_about_vsync_freesync_gsync_adaptivesync/

    Interesting quotes:
    “Adaptive sync is a VESA standard and is the foundation of Free-Sync.”
    “Currently Nvidia does not support Adpative-Sync but Tom Peterson said that if enough people wanted it, Nvidia is willing to reconsider. It is rumored that Nvidia’s mobile G-Sync solution is a derivative of Adpaptive-Sync since they do not use an FPGA in their laptops that are G-Sync certified.”

    #17897

    bwabbit
    Participant
    Topics: 2
    Replies: 18

    Not sure about LCD speeds but found this ( https://superuser.com/questions/286755/does-the-refresh-rate-affect-lcd-screens ):

    “LCDs are “scanned” via an X-Y matrix of wires, with a pixel at each point where two wires cross. Only one pixel can be manipulated at a time. The voltage on a pixel must be maintained long enough to “charge” the pixel, so that it will hold the charge until refreshed, and all pixels must be visited on each refresh cycle.”

    Yup, Adaptive-Sync is the core protocol used by FreeSync over DisplayPort, although it’s been implemented over HMDI as well now. Due to it being a VESA standard (at least the DisplayPort version) an increasing number of monitors are supporting it and they’re not especially expensive.
    G-Sync on the other hand requires a special module in the monitor itself. I’m pretty sure NVidia just came out with their own standard for marketing reasons. Make money by selling the modules for the monitors and try to get people to stick with their NVidia GPUs. Having said that I don’t know which one came out first.

    #17898

    hypersonic
    Kickstarter Backer
    Topics: 18
    Replies: 220

    Fast sync appears to be what I’ve described earlier (though I think they could explain it better)

    He states that triple buffering simply fills up the buffers, then basically stops until they are empty.

    In Nvidia settings I just noticed you can enable Fastsync or adaptive sync globally or per program. With Fast Sync enabled I’m not sure how Gysnc or Freesync helps when enabled concurrently.

    EDIT: ugh, apparently game support is limited
    http://nvidia.custhelp.com/app/answers/detail/a_id/4160/~/does-fast-sync-work-for-all-games%3F

    I thought that once an LCD/OLED scanned, it can stop scanning and pixels will maintain color indefinitely (each pixel with a constant charge to maintain light emittance.) This image implies that a display doesn’t have to constantly scan
    https://images.anandtech.com/doci/8008/Gsync_slide.png

    #17899
    TwoCables
    TwoCables
    Kickstarter Backer
    Topics: 118
    Replies: 1474

    In my experience and in the experience I have seen from many others, G-SYNC and FreeSync are both far superior to V-SYNC because it synchronizes the refresh rate to the framerate and there’s much less input lag.

    To answer whether it’s necessary: no, but I absolutely recommend it.

    Prepare for Overload…

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