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does benq blur reduction has input lag

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does benq blur reduction has input lag

Postby Bluffergod » 02 Dec 2015, 13:50

does it reduce response time or add input lag? if so how much?
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Re: does benq blur reduction has input lag

Postby Sparky » 02 Dec 2015, 14:33

Less than 1/refresh rate. Basically it's just turning the backlight off while the pixel transitions happen, so we're just talking about the delay between the pixels starting to change and the backlight pulsing.
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Re: does benq blur reduction has input lag

Postby Bluffergod » 02 Dec 2015, 14:51

Sparky wrote:Less than 1/refresh rate. Basically it's just turning the backlight off while the pixel transitions happen, so we're just talking about the delay between the pixels starting to change and the backlight pulsing.


I see, i dont know much about this but I guess its nothing in terms of responsiveness, delay, lag lol
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Re: does benq blur reduction has input lag

Postby Falkentyne » 02 Dec 2015, 15:00

(Without vertical total tweaks):
The basic rule of how strobe phase and persistence and pulse widths work with the refresh rate is this formula:


Strobe width persistence = Refresh rate persistence / maximum strobe phase value (100)
The refresh rate persistence is the "ms" of the refresh rate, which is always equal to 1000 divided by refresh rate (1000 / hz)=milliseconds. So you get 144hz=6.9ms, 120hz=8.3, 100hz=10.0 ms, 60hz=16.7ms.

So the strobe width persistence is equal to the refresh persistence divided by 100 since 100 is the maximum strobe phase WITHOUT a VT tweak.

Strobe phase 100 has NO added input lag.
Strobe phase 000 has exactly ONE FRAME of input lag which is equal to the 1000 divided refresh rate in milliseconds.

there may be a few milliseconds of framebuffer lag however, far less than a refresh. This is because technically with a strobe phase of 100, the strobe duty should be exactly 001 (the persistence value for the refresh rate), e.g. Strobe phase 100 at 144 hz refresh rate should be equal to 0.069 ms persistence and the strobe duty should not be able to go higher than 001. However the duty is able to rise higher than 001 even with strobe phase of 100, so there is probably some sort of buffering done. It's not anything anyone can measure.

Strobe phase 000 is a phase that is strobed *ONE FRAME BEHIND* the current frame, so the exact input lag is equal to the refresh rate's frame time lag. E.g. at 120hz its 8.3ms of input lag, at 144hz its 6.9ms of input lag, at 100hz its 10.0ms, and so on (plus probably a few ms of buffering).


WITH a vertical total tweak, things change because the buffer is removed and the strobe width persistence is changed to a fixed value of 0.167ms. These are the 60hz persistence values and this is why the OSD reports "60hz" when a VT tweak is active.

This also means that the strobe duty is locked directly to the strobe phase (in reverse), so the max strobe phase limits the max strobe duty. So you wind up with this formula.

Strobe width persistence = Refresh rate persistence / maximum strobe phase value.
Which is now:

0.167 (ms) = (1000 / hz) / MaxStrobePhase
Instead of 100, maximum strobe phase value is changed and depends on the current refresh rate. Then you can calculate the max strobe phase easily, depending on the refresh rate persistence (1000 / hz).

So at 120hz, you can see the max strobe phase is 049.
proof:
0.167 = (1000 / 120) / (max strobe phase)
0.167 = 8.3 / Max_strobe_phase
0.167 * MaxStrobePhase = 8.3
MaxStrobePhase=8.3 / 0.167
Maxstrobephase=49.7

Strobe phase 050 will shut off the backlight.
At 100hz refresh rate, you can do the math and find out that this happens at strobe phase 060.


Because the buffer is completely removed, the max strobe DUTY at phase 049 is duty 001. increasing strobe duty has no effect.
At strobe phase 048, the max duty is 002. increasing duty past 002 has no effect.
This is because the buffering is completely removed.

going past the MAX STROBE PHASE will shut off the backlight (Because you're attempting to begin the strobe before the current frame, which drops the persistence to 0 milliseconds. thus the backlight remains off the entire frame).

This also means that if you use the max strobe phase possible (remember to go a few points lower so you can get enough strobe DUTY), the input lag is IDENTICAL with blur reduction on and blur reduction off--there is NO added input lag at all.

If you use strobe phase 000, it's exactly 1 frame HIGHER input lag, just like before (1000 divided by hz).

The windows blur busters utilty is wrong about the strobe phase. it says "000" <----is EARLIER strobe phase and 047 (max slider) is later strobe phase. this is incorrect. LATER strobe phase means the strobe occurs LATER in the frame and at strobe phase 000, the strobe occurs in the NEXT frame, not the current frame. So strobe phase 000 should read "LATER strobe phase" on the windows utility for the left slider, and EARLIER strobe phase (current frame) to the right. The windows utility is capped at 047 maximum strobe phase. You can use the Service Menu to go up to 100 strobe phase (remember with a VT tweak, going too high will shut the backlight off).
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