sabre9917 wrote: ↑02 Apr 2026, 15:52
How on Earth are the graphs for the higher refreshes so bad?! If both the up and down transitions can be essentially fully complete within 0.9ms, and we assume that's the fastest it can do these transitions, then sure, 360Hz may be bottlenecked. But the 120Hz graphs (and even 240Hz) should look
way better than that, no?
Like, the 120Hz PW 10 has the rising and falling "edges" taking a full 2ms each, the voltage not even reaching -6V (much less -12V), with really jagged internal peaks and valleys... What is going on? This has to be a bug, right? I, like many of you, were shocked to see how good the 60Hz mode looked compared to the other modes, and with this data it definitely seems much more likely the backlight performance IMO than it is any sort of limitation on pixel transition times.
Good question! I'm still solving the rolling edge-lights puzzle, but so far these are some of my theories:
Light dispersion/diffusion:
The minimum pulse width is restricted by the light dispersion. I look at it as a kind of backlight GtG response. Similar to how CRTs used to have phosphors. If you try to flash each dispersed zone for the same amount of time, you're essentially getting multiple pulses with different intensities across the screen. That's where the
staircase/stepped look of the pulse comes from - the zones abruptly switch from one to the other.
Pulse width method #1 (the classic method):
Now if u try to strobe the same zone for a very short period, the aforementioned stepping turns into multi-strobe-stepping. This happens whenever zone is flashed for less than
"refresh time / number of vertical zones = X" amount of time. This basically shortens multiple small pulses within one larger pulse. This is nicely demonstrated on "PW 10
oscillographs" and some of the
pursuit shots. On the opposite, when pulse time is greater than "X", the lengthening of the larger pulse happens. This is also visible in PW 100 oscillographs.
...examples
Pulse shortening method #2 (the superior, dispersion-optimized method):
The above is describing standard-timing resolutions. Beyond that, a clever workaround for dispersion can be achieved by using a form of QFT which scans the pulse faster down the screen. This trick perceptually squashes/shortens the same pulse (pixels are illuminated for a shorter period) which helps with the dispersion. When the scan speed is doubled, the pulse duration is halved, and the brightness decreases proportionally. This implies that the pulse needs to be taller/wider to compensate for the brightness loss. The squashing is evident on these high-speed camera
frames of DyAc 2, and examples of pulses going taller/wider can be found in this Discord server
discussion. The same effect also appears in 60 Hz ULMB
oscillographs.
"Backlight QFT" vs QFT as we know it
If QFT is the real reason for 60 Hz looking better, than that means PW setting is adjusting the scan-out speed factor. And this is where I start to doubt my theories because this normally doesn't happen without screen blackouts (just like when changing resolutions/refresh rates). However, maybe they've separated the backlight layer control from the pixel layer to avoid that. This way scaler limitations are avoided and pulse speeds can be manipulated more effectively. The only remaining limitation would be the pixel GtG response and its scan speed (actual QFT). They'd only have to make sure the pulse doesn't enter/touch the GtG zone during the process.
The general rule for strobing still applies here. For least amount of crosstalk pulse needs to happen when GtG transitions are most complete - at the back of the frame as Nvidia stated, or for large headroom situations, somewhere sooner between GtG zones for better latency.
The thing with QFT is that it normally can't be used at max refresh rate, because what QFT essentially does is utilizing
maximum scan-down speed (of max Hz) at reduced refresh rates. So as refresh rate goes up, QFT benefits reduce. Once it reaches max Hz there is none. Find out more
here.
Looking at the graphs, I realized the backlight scan boost (or even QFT) factor can likely be derived if zones were counted. Holding onto my theories, anything above 10 zones would indicate that QFT is in use - At 360 and 240 Hz, there are ~10 zones (no QFT), while at 120 Hz there are ~13 (a rather insignificant ~1.3× or ~150 Hz scan boost). At 60 Hz, the situation is a bit different but it aligns with my theories. For PW 100 I counted about 25 "zones" (~2.5x, ~150 Hz); for PW 50 around 50 (5x, ~300 Hz); and for PW 10 the exact number is unclear, but it’s likely in the triple digits. PW 10 far exceeding a 360 Hz boost is what initially led me to the idea of "backlight control separation", because I don’t see another way this could be achieved. There is a possibility for an overclock of sort, but then the question is why wasn't it used for higher rates.
Professor Chief, can you help with homework! Does any of this make sense?
brownvim wrote: ↑30 Mar 2026, 05:30
Would it be worth asking NVIDIA to give the 120/240/360 Hz ULMB2 modes the same full adjustable pulse width range as the 60 Hz mode? Even if brightness drops at very low PW settings, many of us would like the option for maximum clarity at high frame rates.
I'm not entirely sure why they didn't do it in first place. If my theories here are going right direction, what all this would translates to is: I believe 360-120 Hz is doing method #1 (for the most part), and 60 Hz is doing #2+1. So 120 Hz can probably be improved a bit, 240 Hz significantly less so, and 360 Hz by none.
What also crossed my mind is what if consoles can't do very large QFT ratios like PCs can, so they were unable to maximize the boost and limited it to ~150 Hz, leaving 120-240 Hz on the PC in the dust. I'm not familiar with that kinda stuff, so I won't go into it.
brownvim wrote: ↑30 Mar 2026, 05:30
Finally, I wasn’t even aware there was now a user-customizable overdrive slider (0–400 gain). What benefits does this actually give in practice? I’m curious how much it helps with overdrive tuning across different frame rates.
When overdrive is implemented this well, gain doesn't offers many benefits beyond temperature compensation and allowing users to adjust to their liking. They nailed it so well this time that they could've just made it on/off toggle or even leave it on permanently. But generally it's good to have it just in case manufacturer tuned something wrong.