High refresh rate monitors at 60hz?

[2mg]

As much as I like how deep this thread went, I still don't technically understand why 60Hz locked on specifically high refresh rate panels has extra lag - did the developer simply not tune 60Hz or something?

And how come when VRR falls to 60 it doesn't add that locked 60hz extra lag?

Because in all cases the scanout is at the speed of the max refresh rate of such a monitor.

[Chief Blur Buster]

As much as I like how deep this thread went, I still don't technically understand why 60Hz locked on specifically high refresh rate panels has extra lag - did the developer simply not tune 60Hz or something?

Hardware-based 60Hz means it takes 1/60sec from first through last pixel, because it's a 60Hz signal.

Just because a cable is transmitting 60Hz to a 480Hz monitor, does not necessarily mean the frame transport over HDMI/DisplayPort is any faster, even if the display is fast. This is operating system responsibility, not game responsibility.

VRR unlocks this limitation.

And how come when VRR falls to 60 it doesn't add that locked 60hz extra lag?

Hardware-based 60fps VRR at 480Hz means it takes 1/480sec from first through last pixel, because it's 60fps inside 480Hz signal.

Because in all cases the scanout is at the speed of the max refresh rate of such a monitor.

No, only if it's VRR (very common, easy) or a custom "Large Vertical Total" non-VESA tweak (rare).

Switch to VRR whenever you're doing 60fps locked content. This allows you to get "60Hz" with the low-lag benefits of 480Hz. (VRR = automatic fast frame transport).

[RealNC]

As much as I like how deep this thread went, I still don't technically understand why 60Hz locked on specifically high refresh rate panels has extra lag - did the developer simply not tune 60Hz or something?

Hardware-based 60Hz means it takes 1/60sec from first through last pixel, because it's a 60Hz signal.

Just because a cable is transmitting 60Hz to a 480Hz monitor, does not necessarily mean the frame transport over HDMI/DisplayPort is any faster, even if the display is fast. This is operating system responsibility, not game responsibility.

VRR unlocks this limitation.

I think this question is more about the 60Hz mode of some monitors having more lag than necessary. For example, an rtings display latency test (middle of the screen) at 240Hz gives 2.6ms. Which means processing lag is about 0.5ms. At 120Hz, it's 6.3ms so processing lag is 2.1ms. At 60Hz, the result is 14.6ms, which means processing lag is 6.3ms.

In other words, the latency increases more than it should when lowering the refresh rate, because the processing latency gets worse. And it doesn't look like a linear increase, it's more like exponential (or geometric,) while ideally, processing latency should be constant.

[Chief Blur Buster]

I think this question is more about the 60Hz mode of some monitors having more lag than necessary. For example, an rtings display latency test (middle of the screen) at 240Hz gives 2.6ms. Which means processing lag is about 0.5ms. At 120Hz, it's 6.3ms so processing lag is 2.1ms. At 60Hz, the result is 14.6ms, which means processing lag is 6.3ms.

In other words, the latency increases more than it should when lowering the refresh rate, because the processing latency gets worse. And it doesn't look like a linear increase, it's more like exponential (or geometric,) while ideally, processing latency should be constant.

That's correct --

Yes, that's definitely a factor too.

If it's the monitor, then yes, the "monitor developer did not tune 60 Hz".

So there's multiple bottlenecks on 60 Hz:

1. The slowness of frame transport; and
2. The suboptimal monitor scaler/TCON underperforming on a 60 Hz signal. (Slower than an optimal 60Hz display)

Both stack on each other, to extra-penalized latency. You can't get around item (1) for an ordinary non-custom 60Hz signal, but the monitor vendor can optimize (2).

The easiest band-aid to bypass all the above is simply use VRR. It concurrently solves (1) and (2) at the same time. 60fps frames get transmitted over the video cable at the manufacturer's optimized MaxHz velocity (e.g. 1/480sec for a 480Hz monitor).

[Chief Blur Buster]

As much as I like how deep this thread went, I still don't technically understand why 60Hz locked on specifically high refresh rate panels has extra lag - did the developer simply not tune 60Hz or something?

And how come when VRR falls to 60 it doesn't add that locked 60hz extra lag?

Because in all cases the scanout is at the speed of the max refresh rate of such a monitor.

The Internet Upload Metaphor, Except It's DisplayPort/HDMI

Imagine DisplayPort/HDMI as a fast Internet connection between PC and display. Pretend that the display is on the other end of a (really fast) Internet connection.

- Refresh cycles are simply uncompressed images (like an uncompressed screenshot)
- Metaphorically, the GPU has to "upload" each refresh cycle as an uncompressed image from computer to monitor.
- Lag from frame transport = the upload time from GPU to display.
- If the refresh cycle upload is slower (more milliseconds), you have more lag.
- It behaves like a slow dial up modem at 60Hz and a fast cable modem at VRR+MaxHz.
- Refresh cycles at 1920x1080 (24bit = 3 bytes per pixel) = 6 megabytes per refresh cycle!
- Refresh cycles at 3840x2160 (24bit = 3 bytes per pixel) = 24 megabytes per refresh cycle!
- Cables cannot transmit a whole image instantly. It's transmitting like a super fast modem connection.

Thusly, even at a mere 1080p 60Hz, your GPU is uploading (over HDMI/DP) a new 6 megabyte image (refresh cycle) to the monitor's framebuffer every 1/60sec during 60Hz, and every 1/240sec during 240Hz.

When the GPU and cable is at 240Hz (normal VESA timings), it's 4x faster than when configured to 60Hz (normal VESA timings). Higher MaxHz = like a faster Internet connection between GPU and display = less lag!

You can also use non-VRR at max Hz, e.g. 60fps at 480Hz too. That works too. But a lot of 60fps capped games switch to 60Hz, so you have to override that behavior by forcing it to use Max Hz, and often the easiest way to do that is simply enable VRR.

Running 60fps over high Hz (such as VRR) includes what we call "quick frame transport", which is like that fast cable modem connection, instead of slow dial up. All low frame rates transmits faster, at the MaxHz speed, even if it looks like ordinary 60fps 60Hz.

Optimization metaphor: There's a metaphorical "Internet router" inside your display called a scaler/TCON. Just like cheap modems and cheap poor-performing Internet routers, the same modem speed can be more optimized or less optmized. So some displays have really slow routing for 60Hz signals but fast routing for 240Hz signals (more than 4x difference because the poorly optimized 60Hz is slower than 1/4th of the well optimized 240Hz). Only a few displays have fast routing for 60Hz signals and fast routing for 240Hz signals, where 60Hz is no slower than 1/4th the frame transport velocity of 240Hz (at regular default VESA timing).

Or if you prefer mobile phones:
- Each new refresh cycle is a brand new picture. A brand new photo. Sometimes it's unchanged (Microsoft Word) and sometimes it's always changed (high frame rate game).
- How's that for the computer metaphorically "texting" 60 or 240 or 480 pictures per second to the monitor?
- The 60Hz non-VRR is like 3G connection, while enabling VRR turns on a metaphorical 5G. Even if it's only 60 pictures texted per second.
- It's like separate upictures texted very fast in milliseconds, instead of video, because the monitor has to display each picture in real time as quickly as possible, without the lag of compression.

Yep. Exactly. That's what is metaphorically happening behind the scenes (in a binary language instead of English).

It's very single-minded and single-brained style of "Hello monitor. I'm computer. I texted you this new picture. Its 1920x1080. Display now. New picture coming in 1/240 second. Goodbye for a millisecond.".

Except it's all binary data that is crammed into a packet protocol, with literal data instructions (EDID plug and play data, header data, footer data, sync, porches, resolution, timings, etc) that tells the display how to display or scale the picture.

TL;DR: Turning on VRR makes that "Internet Upload" faster (of refresh cycle frames) from your computer to the monitor. It still looks like 60Hz, but VRR gives permission to the GPU to upload faster those individual "60fps 60Hz" frames (1/480sec instead of 1/60sec from first to last pixel) from computer to monitor.