Blur Busters Forums

Why does overdrive 'update' twice as fast at 60Hz if display refreshes normally internally? Why some monitors usually start doubling below 85Hz specifically? How does it work?

In this example VG27AQ is an exception.

https://www.aperturegrille.com/reviews/ ... p-Full.png

These charts nicely demonstrate how same Overdrive level can look completely different at different refresh rates and how response times stay consistent. When OD is fully disabled response curve is same throughout refresh range for same transition.

Discorz wrote: ↑

28 Dec 2021, 07:57

Why does overdrive 'update' twice as fast at 60Hz if display refreshes normally internally? Why some monitors usually start doubling below 85Hz specifically? How does it work?

On all LCD panels ever invented, overdrive tuning needs to be stronger for higher Hz than lower Hz. This is true regardless of how the panel is tuned.

- Some uses the same OD tuning for all Hz. This means lower Hz creating worse artifacts than higher Hz. OD is too strong at lower Hz, OD is too weak at higher Hz.

- Some models use different OD tuning profiles for different Hz at various presets (usually the EDID modes). This is more balanced, but can still produce OD differences (stronger/weaker) at different Hz, especially if custom Hz is created between the EDID Hz settings.

That's another reason why I'm a big fan of the Overdrive slider adjustment (100 level Overdrive).

Chief Blur Buster wrote: ↑

02 Jan 2022, 14:42

On all LCD panels ever invented, overdrive tuning needs to be stronger for higher Hz than lower Hz. This is true regardless of how the panel is tuned.

- Some uses the same OD tuning for all Hz. This means lower Hz creating worse artifacts than higher Hz. OD is too strong at lower Hz, OD is too weak at higher Hz.

- Some models use different OD tuning profiles for different Hz at various presets (usually the EDID modes). This is more balanced, but can still produce OD differences (stronger/weaker) at different Hz, especially if custom Hz is created between the EDID Hz settings.

That's another reason why I'm a big fan of the Overdrive slider adjustment (100 level Overdrive).

I can see that. But this is in VRR mode. If we enable OSD fps/Hz counter for quick check we will see display is still refreshing at normal 60Hz (e.g. VG279QM). By default LFC starts kicking in at 48Hz. So I don't know what is really doubling there, something else halves the overshoot. Also why is 85 Hz so common? Wouldn't it be better if started doubling at half the max refresh, e.g. 120Hz on 240Hz display instead of 85.

Oh yes and Happy New Year!

Discorz wrote: ↑

03 Jan 2022, 02:16

I can see that. But this is in VRR mode. If we enable OSD fps/Hz counter for quick check we will see display is still refreshing at normal 60Hz (e.g. VG279QM). By default LFC starts kicking in at 48Hz. So I don't know what is really doubling there, something else halves the overshoot. Also why is 85 Hz so common? Wouldn't it be better if started doubling at half the max refresh, e.g. 120Hz on 240Hz display instead of 85.

LFC inherently has to be "sticky" because of differences between LFC and non-LFC.

Otherwise, framerate fluctuations from 47.5fps to 48.5fps may cause LFC to cycle rapidly, which can lead to really strange effects such as erratic flicker (ghosting-edge flickers as it rapidly cycles between strong-overdrive and weak-overdrive, or because of inversion artifacts appearing/disappearing, or the <1% brightness difference caused by GtG fade of slower/faster refresh cycles).

Staying in LFC also usually creates better quality than immediately exiting and reentering LFC repeatedly.

So LFC has to be "sticky" to prevent rapid LFC cycling effects.

Once LFC is activated, framerates need to increase lots to exit LFC.

Depending on the panel, Blur Buster's generally prefers a 55Hz LFC for 144Hz panels, and a 65Hz LFC for 240Hz panels. Artificially editing LFC to higher often improves display motion quality, if the overdrive is better-tuned at lower frame rates. Raising the LFC minimum often also reduces accidental below-VRR-range occurences, where display drivers "forget" to activate LFC at 47 Hz, and the display goes black (those annoying random 2-second blackouts are from driver issue).

Ideally the panel should be designed to refresh as low as 30Hz while LFC does 48Hz, to give some breathing room below VRR min range for software-controlled refresh cycles, but sometimes manufacturers like to cut it close...