Chief Blur Buster here.
The old low-lag VSYNC ON technique is wonderful but it creates a sawtooth input-lag artifact caused by the slow-slewing between framerate and refreshrate, as it slowly beat-frequencies. At 144Hz, the lag variance amplitude is only 6.9ms.
Sometimes for some games, the low-lag VSYNC ON capping technique is a tough goldilocks compromise on stutter beat frequency between:
- Too large (e.g. 59fps at 60Hz) and you get one single microstutter stutter per second.
- Too tight (e.g. 59.99fps at 60Hz) and you get a 100 second cycle of 80 seconds perfect smooth followed by 20 seconds of stutters.
So you have to tweak until you've essentially getting only 1 near-invisible microstutter every many seconds. For example, 59.9fps cap at 60Hz (0.1 difference) would generate 1 microstutter every 10 seconds. You keep going until the tiny microstutter becomes a sustained annoying burst of stutters (because of rounding error margins as it jitters back and forth past the blanking intervals). It's a very fiddly tweak that sometimes is hard to find a Goldilocks setting.
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The new perfect-matching raster-scanline based capping method is theoretically more user friendly (but it has a few catches that makes it fiddly in different ways -- further improvements are ongoing to automate some common sense, based on some suggestions).
The perfect framerate sync method eliminates this, and if you have excess GPU headroom, then why the heck not. If your game can blast 200fps anyway, then capping to 120fps won't degrade performance if your GPU has tons of headroom for the raster-synchronized tearingless VSYNC OFF mode that looks just like VSYNC ON (but with less lag).
The catches:
-- It only works if you have excess GPU horsepower and your GPU almost always want to run framerates above the cap. So this works well with older games.
-- In exchange for eating into some GPU headroom, you get more perfect framepacing with low-lag at capped framerates, creating a "VSYNC ON looking mode" via tearingless VSYNC OFF.
-- Tearing will reappear once your GPU utilization becomes high again. Tearlines will disappear again once GPU utilization falls below a threshold. Its quite dynamic. (So even if this happens only a percentage of the time, it doesn't mean this is useless)
Use SyncFlush=2 if you want to have even fewer tearlines, at the cost of eating up more headroom. It works best when your GPU utilization is well below 100%, which occurs when you're capping older games anyway. That way, you avoid the performance loss. Please be noted, it is a beta-only feature, and can be fiddly, and not guaranteed to make it all the way to the release version of RTSS. However, I'd love to hear more comments to see if it helps you.
Incidentially, it improves ULMB a lot:
Then doing 100Hz "perfect stutter-free jitter-free tear-free low-lag ULMB/LightBoost" at 100fps perfect cap -- then who cares if you're using only 50% of your GPU to get perfect low-lag ULMB motion? Many of us have hated the amplified stutter/tearing of ULMB, and the only way to fix that is using VSYNC ON with ULMB, which adds horrible lag. This allows people who like strobing otherwise) to have cake and eat it too (to a certain extent). There's still slight strobe lag, but ~75% of the lag seems gone (give or take), which can make strobing much more enjoyable, depending on which games you play (100fps@100Hz or 120fps@120Hz or 144fps@144Hz -- choose one depending on how much GPU headroom you have).
Again, remember -- this is a feature only avaialble in RTSS betas.
It is more likely to make it into final release if people say they like the feature. Test some older games (e.g. CS:GO) with this new capping feature.
And for ULMB users, test this out too, and find out how much snappier the aiming may feel during strobed operation.
