Madpacket wrote:Wait so to be 100% clear here. The XL2450 acts like older BenQ monitors WRT strobing?
Therefore what Chief is saying about only a 2ms penalty is the about the best we can expect?
If so that's awesome.
This will be the case
assuming if we're successfully able to use strobing with a double-sized Vertical Total (e.g. VT2160 for a 1080p signal) AND strobe phase adjusted to be 50% earlier (to keep up with the accelerated refresh cycle). The double-sized Vertical Total makes the graphics card transmit a 120Hz refresh cycle twice as fast over the video cable (1/240sec) to the screen.
Double VT (VT2160p+) combined with strobing, combined with early strobe phase (brought 50% earlier), will halve the strobing input lag penalty to approximately ~2ms. (OK, well, ~3ms if you add the 1ms GtG on top of it, but pixels become visible enough for the beginning of the 100-to-200ms human reaction time window, after around 25%-50% of the GtG, so 2.25ms would effectively round off to 2ms
).
I think the ideal ultra-low-latency-strobing-VSYNC-ON setup is the following:
- One of the 240Hz monitors that supports double-size vertical totals (VT2160p+) via Custom Resolution Utilities
- Run at 120Hz (in order to enable strobing blur-reduction at 120Hz)
- Adjust strobe phase to flash 1/240sec earlier. In theory, ghosting is not affected much because the frame delivery has already finished in 1/2 the time.
In theory, the monitor should already automatically set optimal strobe phase, while reducing lag, during ULMB + Large Vertical Totals.
You might have a *tiny* amount of strobe crosstalk along the bottom edge of the refresh cycle, but that's OK.
- Use one of the low-latency framerate limiters, such as in-game Source Engine fps_max and set it slightly lower than Hz.
Set the frame cap fractionally lower than refresh rate (e.g. fps_max 119.9 combined with 120.0Hz VSYNC ON) for the lowest lag. Please note, actual refresh rate of monitor may not be exactly 120.0Hz, so make sure to verify the fractional refresh rate in the Custom resolution Utility, and then set the fps_max accordingly.
= In theory, only ~2ms more lag than VSYNC OFF.
Real world might be bigger than that because of other ineffiencies (drivers, game engine, frame rate capping inefficiencies, etc). But if the rendering chain is pulled off perfectly enough, the latency penalty is shrunk to an amount small enough that it is very useful to competitive players that like the blur reduction features. It can eliminate most (even if not all) of the VSYNC ON latency penalty. Some experimentation will be needed, but this would be the closest we've achieved to a dream "VSYNC ON" setup.
Caveat on Monitor Overriding Behaviours on Large Vertical Totals
LightBoots and ULMB
already does internal scan-acceleration logic to artificially create large blanking interval pauses between refresh cycles (to let LCD GtG transitions settle before flashing the backlight). Whatever logic the monitor uses in ULMB, must be designed to adapt correctly with Large Vertical Totals, in order to get latency-reducing benefits of Large Vertical Totals. Even if scan-acceleration is already being done with ULMB, the fact that large Vertical Totals cause quicker delivery of refresh cycles to the monitor, should allow ULMB to begin the scanout sooner (or even in real-time, if it calculates predicted LCD scanout is going to be equal or sloewr than the large-VT-accelerated frame delivery speed over video cable). There's a BIG caveat; the monitor LCD panel scanout must be accelerated to keep up with the larger Vertical Total. (The top-to-bottom refresh scanning effect you see in high speed video at
http://www.blurbusters.com/lightboost/video ...) i.e. the screen should "wipe" top-to-bottom in 1/240sec during a 120Hz refresh cycle. Otherwise, this lag-reducing trick won't work. Not all monitors will adapt to a faster panel top-to-bottom refresh during the Large Vertical Total trick (the BENQ XL2420Z and XL2720Z have lower lag during VT1350 than default VT).
NOTE: Remember not to increase Vertical Back Porch too much because that will increase lag in increments of 1/(Vertical Total)th of 1/(refresh rate)th of a second, for every count added to Vertical Back Porch. The transmission of a refresh cycle from computer to display over the cable, begins with the Verticdal Back Porch (since Vertical Back Porch is equivalent to the first week of the "date calendar" metaphor of Custom Resolution signal timings, of the sequential delivery of pixels over a video cable between a graphics card and a computer monitor.
Note: If you have a DisplayPort connection, it's possible for a graphics card to deliver the frame to the monitor at full DisplayPort bandwidth, regardless of the actually used refresh rate. GSYNC apparently does this; each frame is delivered at the same speed as the maximum refresh rate the monitor supports, regardless of the current refresh rate running.