Re: Benq XL2411 - Can't get rid of ghosting
Posted: 16 Feb 2017, 13:25
Yes that looks right. If you set the strobe duty to 003 or lower, there will be no crosstalk at the top but the image will be very dim.
Duty and phase are VERY easy to understand.
Duty is simply persistence.
A strobe lasts for a refresh cycle. So at 120hz that's 1/120th of a second. I know you can understand that.
A strobe is an ON+OFF backlight cycle.
So that's 0.083 ms per "point" of strobe duty" at 120hz. (8.3 divided by 100, because 120hz is 8.3 MILLISECONDS). But remember a strobe is an ON +OFF CYCLE. The ON time is much much shorter than the off time. The TOTAL Time is 8.3 milliseconds for both on and off. So if you were using a "1.0 millisecond" persistence, the on time would be 1.0 milliseconds and the OFF time would be 7.3 milliseconds. Because 7.3 + 1.0 = 8.3. Simple math.
The problem is, the 0.083ms per POINT of strobe duty is assuming NO VT tweaks are in use. So on a fresh config without a VT Tweak. strobe duty=012 would be 1.0ms of persistence because 12 x 0.083= 0.996=1 ms (close enough).
VT tweaks however cause the strobe timings to "Revert" to 60hz timings. which means the timing is based on 16.7ms, or 0.167ms per point of strobe duty. Why? I don't know. But if you check the monitor OSD, you will see it reports "60hz" at 120hz. That's why it reports 60hz. I assume this is a failsafe by the firmware when a Vertical Total is used that doesn't belong to an established refresh rate. So therefore, Strobe Duty 006 is equal to 1.0ms with a VT tweak, because 0.167 x 6=1 ms.
Again unless you're just bad at math, you should be able to understand this.
Strobe PHASE is simply at what "POINT" in a frame (the 8.3ms frame) the strobe begins at. Changing strobe phase moves the start of the strobe from the "beginning" of the current refresh cycle (strobe phase=100) to the "END" of the current refresh cycle, in effect adding 1 frame of input lag (Strobe Phase=000). When using a VT Tweak, the strobe phase is COMPRESSED into a LOWER effective range. Remember everything is based on a 60hz baseline and other refresh rates are "interpolated" by the firmware so that strobe phase 0-100 still works. HOWEVER when using a VT weak, this interpolation gets reverted back to the base 60hz values, so that 0-100 doesn't work anymore at 120hz with a VT tweak. Since 120hz is double 60hz..........where do you think the "backlight shuts off" at?
(remember strobe phase starts at 000, NOT 001).
You got it.
50.
That's why the strobe phase range at 120hz with a VT Tweak is 0-49.
(Without a VT tweak it would be 0-100).
Duty and phase are VERY easy to understand.
Duty is simply persistence.
A strobe lasts for a refresh cycle. So at 120hz that's 1/120th of a second. I know you can understand that.
A strobe is an ON+OFF backlight cycle.
So that's 0.083 ms per "point" of strobe duty" at 120hz. (8.3 divided by 100, because 120hz is 8.3 MILLISECONDS). But remember a strobe is an ON +OFF CYCLE. The ON time is much much shorter than the off time. The TOTAL Time is 8.3 milliseconds for both on and off. So if you were using a "1.0 millisecond" persistence, the on time would be 1.0 milliseconds and the OFF time would be 7.3 milliseconds. Because 7.3 + 1.0 = 8.3. Simple math.
The problem is, the 0.083ms per POINT of strobe duty is assuming NO VT tweaks are in use. So on a fresh config without a VT Tweak. strobe duty=012 would be 1.0ms of persistence because 12 x 0.083= 0.996=1 ms (close enough).
VT tweaks however cause the strobe timings to "Revert" to 60hz timings. which means the timing is based on 16.7ms, or 0.167ms per point of strobe duty. Why? I don't know. But if you check the monitor OSD, you will see it reports "60hz" at 120hz. That's why it reports 60hz. I assume this is a failsafe by the firmware when a Vertical Total is used that doesn't belong to an established refresh rate. So therefore, Strobe Duty 006 is equal to 1.0ms with a VT tweak, because 0.167 x 6=1 ms.
Again unless you're just bad at math, you should be able to understand this.
Strobe PHASE is simply at what "POINT" in a frame (the 8.3ms frame) the strobe begins at. Changing strobe phase moves the start of the strobe from the "beginning" of the current refresh cycle (strobe phase=100) to the "END" of the current refresh cycle, in effect adding 1 frame of input lag (Strobe Phase=000). When using a VT Tweak, the strobe phase is COMPRESSED into a LOWER effective range. Remember everything is based on a 60hz baseline and other refresh rates are "interpolated" by the firmware so that strobe phase 0-100 still works. HOWEVER when using a VT weak, this interpolation gets reverted back to the base 60hz values, so that 0-100 doesn't work anymore at 120hz with a VT tweak. Since 120hz is double 60hz..........where do you think the "backlight shuts off" at?
(remember strobe phase starts at 000, NOT 001).
You got it.
50.
That's why the strobe phase range at 120hz with a VT Tweak is 0-49.
(Without a VT tweak it would be 0-100).