Why in some monitors you can disable VRR?

Talk about AMD's FreeSync and VESA AdaptiveSync, which are variable refresh rate technologies. They also eliminate stutters, and eliminate tearing. List of FreeSync Monitors.
Post Reply
andrelip
Posts: 160
Joined: 21 Mar 2014, 17:50

Why in some monitors you can disable VRR?

Post by andrelip » 11 Feb 2022, 10:16

What is the reasoning behind allowing people to disable freesync directly in the monitor by supporting multiple EDID's?

In theory, you could leave this enabled and control this in the OS.

Is there any known downside or compatibility issue?

User avatar
Chief Blur Buster
Site Admin
Posts: 11647
Joined: 05 Dec 2013, 15:44
Location: Toronto / Hamilton, Ontario, Canada
Contact:

Re: Why in some monitors you can disable VRR?

Post by Chief Blur Buster » 14 Feb 2022, 03:21

andrelip wrote:
11 Feb 2022, 10:16
What is the reasoning behind allowing people to disable freesync directly in the monitor by supporting multiple EDID's?

In theory, you could leave this enabled and control this in the OS.

Is there any known downside or compatibility issue?
A common issue is that overdrive algorithms are different for FreeSync=ON versus FreeSync=OFF. So you may still have different looking overdrive even with driver/OS FreeSync OFF if the monitor FreeSync is ON. And you are often unable to use certain features (e.g. motion blur reduction) if the monitor's FreeSync mode is enabled.

There's often two different sets of firmware functions running in the monitor depending on whether monitor FreeSync is ON/OFF -- causing the picture to look slightly different with these situations:
FreeSync=ON in monitor, FreeSync=ON in control panel
FreeSync=ON in monitor, FreeSync=OFF in control panel
FreeSync=OFF in monitor, FreeSync=OFF in control panel

For example, www.testufo.com/ghosting may have more ghosting or less ghosting with certain modes. And you're unable to enable strobing on most monitors when FreeSync is enabled on the montor's OSD.

For NVIDIA native G-SYNC, it does 2-way communication directly to the monitor, to tell the monitor to turn on/off VRR specific features (and also disabling ULMB when G-SYNC is enabled). So the user does not have to fiddle with the monitor OSD, because the NVIDIA is controlling the monitor setting over a sideband (I2C / DDC signalling or special DisplayPort packets).

Theoretically this could have been done for FreeSync, but it was not done that way, in order to keep it as simple/generic as possible. FreeSync (and G-SYNC Compatible, and VESA Adaptive Sync, all identical at signal level) is completely 1-way communication (always only from PC to monitor). It is also why it can be successfully adaptored (HDMI->VGA adaptor + ToastyX EDID override to force-enable "blind" FreeSync output on Radeon cards) to do FreeSync on certain multisync CRT tubes. It actually works if they don't have too aggressive refresh-rate-change blackout circuitry!
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter

Image
Forum Rules wrote:  1. Rule #1: Be Nice. This is published forum rule #1. Even To Newbies & People You Disagree With!
  2. Please report rule violations If you see a post that violates forum rules, then report the post.
  3. ALWAYS respect indie testers here. See how indies are bootstrapping Blur Busters research!

Post Reply