Question about LCD monitors

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Mark Fable
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Joined: 29 Jul 2021, 16:01

Question about LCD monitors

Post by Mark Fable » 29 Jul 2021, 16:11

Hello, I'm new to this forum and I have a question. Are all LCD monitors "sample-and-hold" by default design, or are there LCD monitors behaving differently? I'm asking this because I want to ensure that my laptop's LCD display is not, by any chance, acting against the norm.

I am also asking this because my laptop sports a 120Hz display and I plan to run some (more demanding) games at 60 fps (VSynced) while maintaining the same cadence and smoothness I would get if the display were 60Hz instead.

Looking forward to your help!

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Chief Blur Buster
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Re: Question about LCD monitors

Post by Chief Blur Buster » 29 Jul 2021, 23:48

Mark Fable wrote:
29 Jul 2021, 16:11
Hello, I'm new to this forum and I have a question. Are all LCD monitors "sample-and-hold" by default design
Most of them are, though Blur Busters has also been classically been about strobe backlights as a form of display motion blur reduction.

Such systems turn sample-and-hold LCDs into impulsed LCDs. But the panel itself is always permanently sample-and-hold, with the impulse driving provided by stack-on measures such as backlight and/or blank refresh cycles (black frame insertion)

There are no strobed laptops (at the moment), so these are predominantly sample-and-hold by design.

60fps at 120Hz looks like 60fps at 60Hz. But because of those fine-granularity VSYNC events, 60fps can stutter a bit more unless you intentionally adjust settings (e.g. use graphics driver 1/2 VSYNC, or switch refresh rate downwards to 60 Hz via control panel).

Now, if you have a FreeSync compatible laptop panel, framerates look identical to perfectly VSYNC’d refresh rates, e.g. 53fps looks like perfect 53 Hz VSYNC ON, and 72.5fps looks like perfect 72.5Hz VSYNC ON, if you’ve got FreeSync or G-SYNC enabled. (It’s a good single-framedrop stutter eraser technology, demonstration at www.testufo.com/vrr …) … So for a FreeSync laptop panel, just run at 60fps and it’s already automatically smooth 60Hz, and any framerate error will usually be a lot more stutter-free.

Either way, as a nutshell, you get 60fps 60Hz experience with the following:

1. Play your game at 60fps (well-framepaced without 1/120sec framepacing error);
2. Or Play your game at 60fps via 1/2 VSYNC via driver setting;
3. Or Play your game with your 120Hz laptop LCD temporarily switched to 60Hz;
4. Or Play your game with FreeSync enabled at a 60fps cap

All the above should produce identical motion quality to 60fps 60Hz, but item (1) will be more likely to have stutters if the framepacing has enough error (1/120sec errors) so that a 60fps frame may show for 3 refresh cycle and the next 60fps frame may show for 1 refresh cycle (instead of 2 each). In that case, visible stutter will appear.

Item 4 may occasionally show visible stutter if frame pacing error is significant enough, but 1ms framepacing errors will generally be invisible as it will just show specific refresh cycles “1ms late” rather than stuttering 8.3ms (!/120sec) to the next refresh cycle.

The most reliable moves will be item #2 but may be slightly higher latency than the other options (equalling to 60fps 60Hz VSYNC lag, rather than the other moves that is more likely to get the 60fps frame refreshed in a mere 1/120sec)

The driver-and-display cooperation is playing a role here, as well as the velocity of the display refresh (1/60sec or 1/120sec) for the various different routes/options.

If you play casually rather than professionally you probably won’t notice any lag; even the worst lag option with typical 120Hz laptop LCDs here will typically be less laggy than, say, a typical 60 Hz plasma or 60 Hz OLED television display.
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