couple questions about freesync

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.
fowteen
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couple questions about freesync

Post by fowteen » 18 Mar 2020, 16:36

hey i am new to all of this adaptive sync stuff so i am trying to understand things a little at a time by asking some questions. I read in g sync 101 that when freesync is active, no other sync method is active so I was wondering when does vsync activate when both freesync and vsync are enabled. Also was wondering what situations/games would you use no freesync + no vsync, freesync on + vsync off, both on.

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jorimt
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Re: couple questions about freesync

Post by jorimt » 18 Mar 2020, 17:37

fowteen wrote:
18 Mar 2020, 16:36
hey i am new to all of this adaptive sync stuff so i am trying to understand things a little at a time by asking some questions. I read in g sync 101 that when freesync is active, no other sync method is active so I was wondering when does vsync activate when both freesync and vsync are enabled. Also was wondering what situations/games would you use no freesync + no vsync, freesync on + vsync off, both on.
As stated in the second entry of my Closing FAQ:
https://blurbusters.com/gsync/gsync101- ... ttings/15/
Wait, why should I enable V-SYNC with G-SYNC again? And why am I still seeing tearing with G-SYNC enabled and V-SYNC disabled? Isn’t G-SYNC suppose to fix that?

The answer is frametime variances.

“Frametime” denotes how long a single frame takes to render. “Framerate” is the totaled average of each frame’s render time within a one second period.

At 144Hz, a single frame takes 6.9ms to display (the number of which depends on the max refresh rate of the display, see here), so if the framerate is 144 per second, then the average frametime of 144 FPS is 6.9ms per frame.

In reality, however, frametime from frame to frame varies, so just because an average framerate of 144 per second has an average frametime of 6.9ms per frame, doesn’t mean all 144 of those frames in each second amount to an exact 6.9ms per; one frame could render in 10ms, the next could render in 6ms, but at the end of each second, enough will hit the 6.9ms render target to average 144 FPS per.

So what happens when just one of those 144 frames renders in, say, 6.8ms (146 FPS average) instead of 6.9ms (144 FPS average) at 144Hz? The affected frame becomes ready too early, and begins to scan itself into the current “scanout” cycle (the process that physically draws each frame, pixel by pixel, left to right, top to bottom on-screen) before the previous frame has a chance to fully display (a.k.a. tearing).

G-SYNC + V-SYNC “Off” allows these instances to occur, even within the G-SYNC range, whereas G-SYNC + V-SYNC “On” (what I call “frametime compensation” in this article) allows the module (with average framerates within the G-SYNC range) to time delivery of the affected frames to the start of the next scanout cycle, which lets the previous frame finish in the existing cycle, and thus prevents tearing in all instances.

And since G-SYNC + V-SYNC “On” only holds onto the affected frames for whatever time it takes the previous frame to complete its display, virtually no input lag is added; the only input lag advantage G-SYNC + V-SYNC “Off” has over G-SYNC + V-SYNC “On” is literally the tearing seen, nothing more.

For further explanations on this subject see part 1 “Control Panel,” part 4 “Range,” and part 6 “G-SYNC vs. V-SYNC OFF w/FPS Limit”
As for when "V-SYNC" activates when using FreeSync + V-SYNC, refer to this chart:
Image
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

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fowteen
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Re: couple questions about freesync

Post by fowteen » 18 Mar 2020, 17:57

sorry I don't understand what it means when it says ' so what happens when just one of those 144 frames render in 146 fps average instead of 144' so is that referring to when the fps sometimes goes 1 or 2 fps above the max refresh rate fps limit?

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Re: couple questions about freesync

Post by Chief Blur Buster » 18 Mar 2020, 18:22

fowteen wrote:
18 Mar 2020, 17:57
sorry I don't understand what it means when it says ' so what happens when just one of those 144 frames render in 146 fps average instead of 144' so is that referring to when the fps sometimes goes 1 or 2 fps above the max refresh rate fps limit?
Frame rates aren't always perfectly consistent.

Each frame has a unique frame rate.

144fps means sometimes two frames might be 1/143sec apart and other two frames are 1/145sec apart.

In the real world, the time interval between frames often varies slightly.

Most frame rates you read are always averages (like a 1-second average or such).

But there can be 144 different instantaneous framerates with 144fps (average).

The time interval between two frames, is often called "frametime".

Likewise, at Blur Busters, the time interval between two refresh cycles, I call "refreshtime"

So in short, unique frametimes faster than refreshtimes, means the frame has to actually WAIT for the monitor to finish refreshing the previous frame. So that WAIT = LAG.

That's the Plain English(tm) version.

Also, it's not as simple as 1/143sec vs 1/145sec apart. It's more like random fractions such as 0.99346723 * (1/144) versus 1.01345347788 * (1/144), so frametimes are often like snowflakes -- no two frametimes are perfectly identical if you measure super accurately enough (to microsecond or nanosecond precision).

So that's why we cap below Hz when we play games on a VRR display. This ensures fluctuations to frametimes doesn't enroach into faster-than-refreshtime. That's why we use approximately 3fps-below on VRR displays (though can be tight as 0.5fps below to more than 5fps below, depending on situation)> And if you hate capping, you can also get a higher Hz VRR monitor, so that your frame rate fluctuation range is always within VRR range. (e.g. 50fps-200fps works better on a 240Hz VRR monitor than a 144Hz VRR monitor).
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       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
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fowteen
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Re: couple questions about freesync

Post by fowteen » 18 Mar 2020, 18:41

ah okay thanks, can you also explain to me as simply as possible when screen tearing can occur with just freesync on, no vsync, with the -3 fps cap. also not sure if you can help with this but I was messing around with vsync in my control panel (amd radeon software) and noticed that when I put vsync to always on for a game in its profile in the control panel, the game isn't capped at my refresh rate which probably means it is not being activated through my control panel.

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Re: couple questions about freesync

Post by jorimt » 18 Mar 2020, 22:30

fowteen wrote:
18 Mar 2020, 18:41
can you also explain to me as simply as possible when screen tearing can occur with just freesync on, no vsync, with the -3 fps cap.
While this info is fully available in my article, along with the material I quoted/linked in my previous post here, I will reiterate once more...

The "V-SYNC" option is actually part of FreeSync within the refresh rate, and if you take it away (by disabling it), it removes the element of FreeSync operation that otherwise allows 100% tearing prevention within its working range.

Further, the V-SYNC option only acts like traditional V-SYNC with FreeSync when the framerate is outside the working FreeSync range (aka typically above the the max refresh rate of the monitor).

As for when tearing can occur with FreeSync + V-SYNC "Off"...

1. When the average framerate is sustained outside the working FreeSync range (e.g. above the refresh rate).
2. When the average framerate abruptly rises, drops, or oscillates rapidly inside the FreeSync range (aka frametime variances).
3. When the average framerate rapidly oscillates inside/outside the FreeSync range near the max refresh rate.

FreeSync + V-SYNC "On" will prevent tearing caused by the three occurrences above.

FreeSync + V-SYNC "On" + (a minimum) -3 FPS limit, will prevent tearing caused by the three occurrences above AND prevent traditional V-SYNC input lag, by keeping FreeSync in its working range at all times.
fowteen wrote:
18 Mar 2020, 18:41
also not sure if you can help with this but I was messing around with vsync in my control panel (amd radeon software) and noticed that when I put vsync to always on for a game in its profile in the control panel, the game isn't capped at my refresh rate which probably means it is not being activated through my control panel.
I'm not an AMD user, so maybe someone else can chime in on this, but I hear the global V-SYNC option in the AMD control panel isn't always as reliable as the Nvidia control panel equivalent, and may not always work in every game it is enabled for, which in these cases, would mean you would still effectively be running FreeSync + V-SYNC "Off."

Have you tried the in-game V-SYNC option in these instances instead? Because 99% of the time, for the purpose of pairing with FreeSync, it will be identical to enabling control panel V-SYNC.
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

Displays: Acer Predator XB271HU / LG 48CX OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA RTX 3080 FTW3 UG RAM: 32GB G.SKILL TridentZ @3200MHz

fowteen
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Re: couple questions about freesync

Post by fowteen » 19 Mar 2020, 06:47

thanks for replying, I know this might be annoying as you are repeating yourself most of the time but thanks for trying to help I just have not read the entire GSYNC 101 article and this is my first time learning about this type of stuff so thanks for helping but when I have tried to use freesync and in game vsync I got really bad freezing and input lag even with the -3 fps cap

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Re: couple questions about freesync

Post by jorimt » 19 Mar 2020, 07:21

fowteen wrote:
19 Mar 2020, 06:47
when I have tried to use freesync and in game vsync I got really bad freezing and input lag even with the -3 fps cap
Unlike G-SYNC monitors containing hardware modules, not all FreeSync monitors (which are instead driven entirely by driver-side software) are created equal; you haven't shared your FreeSync monitor model, its max refresh rate, or its VRR (variable refresh rate) range.

The information I shared primarily applies to FreeSync "2" variant models featuring wide working VRR ranges and full LFC (low framerate compensation) support, so depending on your monitor specs, that could be a factor here.
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

Displays: Acer Predator XB271HU / LG 48CX OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA RTX 3080 FTW3 UG RAM: 32GB G.SKILL TridentZ @3200MHz

fowteen
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Re: couple questions about freesync

Post by fowteen » 19 Mar 2020, 08:54

so freesync 2 monitors have larger vrr ranges? and after reading a little bit about lfc, does its effects get rid of screen tearing and stuttering from 0 fps to 48 for example if the monitor only has freesync vrr from 48 to 144?

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jorimt
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Re: couple questions about freesync

Post by jorimt » 19 Mar 2020, 09:39

fowteen wrote:
19 Mar 2020, 08:54
so freesync 2 monitors have larger vrr ranges? and after reading a little bit about lfc, does its effects get rid of screen tearing and stuttering from 0 fps to 48 for example if the monitor only has freesync vrr from 48 to 144?
Typically, yes. FreeSync 2 w/LFC effectively means a 0-144Hz FreeSync range (on a 144Hz monitor, etc).

This still doesn't eliminate the need for FreeSync + V-SYNC "On" in scenario #1-#3 for the 100% tear-free FreeSync operation I listed out in my previous post, but it does mean with FreeSync + LFC, you can no longer "drop out" of FreeSync in the lower framerate/refresh rate range like you can with a FreeSync monitor that features a smaller VRR range without LFC support.

As for stutter specifically, FreeSync (along w/LFC) can only eliminate sync-induced stutter, it does nothing to reduce or even alleviate system-side stutter (for instance, engine-side frametime spikes due to asset loads, background asset streaming, etc).
(jorimt: /jor-uhm-tee/)
Author: Blur Busters "G-SYNC 101" Series

Displays: Acer Predator XB271HU / LG 48CX OS: Windows 10 MB: ASUS ROG Maximus X Hero CPU: i7-8700k GPU: EVGA RTX 3080 FTW3 UG RAM: 32GB G.SKILL TridentZ @3200MHz

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