Input lag at different set refresh rate with VRR

[flagbender]

Some monitors have higher processing lag at non-native refresh rates. I've seen here that VRR reduces this processing lag to minimum.

What about a case where I manually set a non-native refresh rate, but the monitor is working in Gsync or Freesync mode?

To give an example with made up figures, XG27AQMR is a 300Hz display with a Freesync compatible traditional scaler. Let's say that it has 5ms total input lag at 300Hz+300fps and 12ms input lag at fixed 240Hz+240fps due to scaling behaviour. With VRR, the total lag at 300Hz+240fps cap might be 8ms instead.

1. a) What if I set Windows to 240Hz but with Freesync enabled - would 240Hz+240fps have closer to 8ms input lag or 12ms?

b) And a sub-question, if the monitor is in Freesync mode, is that engaged at all times, or does the content displayed have to actively be engaging the VRR to get the QFT-like behaviour?

2. My example assumes this particular monitor has fixed scan rate. Does anyone know if it has scan rate multisync instead?

[jorimt]

Some monitors have higher processing lag at non-native refresh rates. I've seen here that VRR reduces this processing lag to minimum.

VRR doesn't necessarily reduce processing lag, but allows you to effectively simulate lower refresh rate operation while still retaining a higher physical refresh rate.

1. 120 FPS non-VRR at a 120Hz physical refresh rate = monitor refreshes 120 times per second, with each refresh completing in 8.3ms.
2. 120 FPS VRR at 240Hz physical refresh rate = monitor refreshes 120 times per second, with each refresh completing in 4.2ms.

In other words, VRR allows you to "bypass" the extra processing latency (and any other issues) of the lower physical refresh rates on the given monitor model by still using the highest available physical refresh rate.

What about a case where I manually set a non-native refresh rate, but the monitor is working in Gsync or Freesync mode?

Ideally, you should never lower your physical refresh rate when VRR is enabled, and instead use an FPS limiter to reduce effective refresh "rate."

Lowering physical refresh rate with VRR will simply reduce maximum scanout time (delivery speed of each refresh), increasing overall frame delivery latency, regardless of framerate.

1. a) What if I set Windows to 240Hz but with Freesync enabled - would 240Hz+240fps have closer to 8ms input lag or 12ms?

VRR has no control over the scanout time of the current physical refresh rate (only how many time the scanout process repeats per second), so the above scenario will retain whatever processing latency (and any other issues) the 240Hz physical refresh rate has on that monitor.

b) And a sub-question, if the monitor is in Freesync mode, is that engaged at all times, or does the content displayed have to actively be engaging the VRR to get the QFT-like behaviour?

The former.

2. My example assumes this particular monitor has fixed scan rate. Does anyone know if it has scan rate multisync instead?

The closest thing to that is VRR + max physical refresh rate + lower framerate = lower effective refresh rate while retaining scanout time of max physical refresh rate.

[flagbender]

Not the answer I was hoping for but thank you for the detailed response nonetheless.

I wanted 240Hz on that 300Hz monitor because:

1. You can manually toggle DSC off, limiting the fresh rate to 240Hz. Figured I may as well disable it since I'm not going to be hitting 300fps anyway.

2. More video content would display without judder on 240Hz (~24fps content), so no need to fiddle around with refresh rates specifically for video.

I would have been happy with the PG279QM, but those aren't sold any more. The PG27AQN is also an option, but it requires DSC (not a huge deal, but 240Hz would have been fine for me...) and has always-on active cooling . Not to mention bonkers price. So I thought the XG27AQMR would be good, since it has variable overdrive despite being Freesync. But if there's potential input lag due to scan out conversion or whatever it's called, eh.

[jorimt]

1. You can manually toggle DSC off, limiting the fresh rate to 240Hz. Figured I may as well disable it since I'm not going to be hitting 300fps anyway.

Yeah, DSC is an issue for things like DSR and custom resolutions.

I would have been happy with the PG279QM, but those aren't sold any more.

They're still available in the US, so I assume you're in another region?

The PG27AQN is also an option, but it requires DSC (not a huge deal, but 240Hz would have been fine for me...) and has always-on active cooling .

I'm receiving a PG27AQN this week (will use my PG279QM as a secondary), so it will be interesting to see how much a hindrance DSC and the fan is in my particular use case (probably not at all).

Not to mention bonkers price.

Again, you must be in a non-US region then; the price is on the higher-end here, but not quite "bonkers" considering what the PG27AQN is offering.

[flagbender]

Yeah, not US. Availability of this class of monitors has been spotty across Europe. And the value statement was more in absolute terms - it's not terrible for what it is, but it's lot of money to pay for a luxury item.