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G-Sync And FreeSync - A Primer on Similarities And Differenc

Talk about NVIDIA G-SYNC, a variable refresh rate (VRR) technology. G-SYNC eliminates stutters, tearing, and reduces input lag. List of G-SYNC Monitors.

G-Sync And FreeSync - A Primer on Similarities And Differenc

Postby Haste » 19 Apr 2017, 12:33

There is currently a post on reddit r/hardware by redditor /u/jaykresge that gained a lot of traction (there are even replies from AMD and other industry representatives!) explaining the difference between the two implementations of variable refresh rate technologies.

It is surprisingly accurate. Yet it's not final and there are certainly a few potential corrections that could be made.

This has the potential to combat effectively common misconceptions and misinformation on the subject.

I invite everyone to read and check for possible corrections, improvements.
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Re: G-Sync And FreeSync - A Primer on Similarities And Diffe

Postby RealNC » 19 Apr 2017, 20:03

What's the point? Nobody will get to see this, unless they just happen to visit that subreddit within a 1-2 day window...

I don't understand why people post such things on Reddit. They get seen for a day, then they're gone forever.
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Re: G-Sync And FreeSync - A Primer on Similarities And Diffe

Postby Chief Blur Buster » 19 Apr 2017, 20:16

Reddit can be fascinating if you're into it. Double edged sword, sure.

Also, sometimes it's an incubating ground for reddit-vetting before crossposting elsewhere (other than reddit). They can be the original source of great brainstorm posts, which will get converted into a website article (with permission of that reddit author, for example). Popular reddit articles like these often gets promoted to some blog/review website.

And look at the reddit comments! It looks like a NIXEUS monitor rep is commenting on that reddit and he's trying to loan monitors to monitor reviewers such as TFTCentral willing to post monitor reviews; a great lead for me (as Blur Busters), as I've contacted monitor manufacturers through reddit before. As Blur Busters ramps up monitor reviews. In the past, Blur Busters reached out to them through many leads (e.g. through an email contact, Facebook contact, Twitter contact, reddit contact). While we've been slow from 2015-2016, we're clearly gradually ramping up this year (2017) with the brand new relaunch.

reddit also can be good for temporary surges of popularity. Sometimes a reddit gives a specific brand-new TestUFO test coverage (IIRC, once got upvoted 2,500 times in one of the reddit channels).

Historically (on average), reddit is _very_ useful to Blur Busters.

***UPDATE: jaykresge has given permission to me to repost***
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Re: G-Sync And FreeSync - A Primer on Similarities And Diffe

Postby Chief Blur Buster » 20 Apr 2017, 12:29

Here's the crosspost, preserved here for posterity, converted to forum format, permission was given from kaykresge given to Blur Busters to crosspost here.
jaykresge of reddit wrote:I wanted to make a singular concise post about this because I'm seeing a LOT of misinformation about how these two relate to each other. Fans of both brands lob false accusations about the other rather than trying to understand what actually makes them tick. And this spread of misinformation then propagates to unsuspecting users who may not be biased and are genuinely looking for the best product for their individual needs.

Because G-Sync came out first, it's easier for me to address this in the format of "G-Sync works like this, here's AMD's counter." So here goes.

The Basics
  • G-Sync matches your monitor's refresh rate to your GPU's framerate, within a specified range.
  • Contrary to popular belief (misinformation), FreeSync (and the underlying VESA Adaptive Sync standard) does the exact same thing.
  • The goal of this is to give the tear-free experience of "V-Sync On" while getting close to the reduced input lag of "V-Sync Off." Both standards do this amazingly well and are, IMO, the best things to happen to PC gaming since the advent of the discrete video card.
Closed and Open Standards
  • G-Sync (desktop) is a closed standard that relies on Nvidia hardware on both ends, an Nvidia GPU, and a monitor with Nvidia's G-Sync module. This module replaces the scalar in a traditional monitor.
  • DisplayPort Adaptive Sync (AKA VESA Adaptive Sync) is an optional part of DisplayPort 1.2a and higher. It is an open-standard in that anyone is free to use it, but it is not open-sourced.
  • G-Sync Mobile and FreeSync are both proprietary implementations of the VESA Adaptive Sync standard. G-Sync mobile allows for a type of adaptive sync on laptops. FreeSync is a driver and hardware-based implementation that requires a monitor with compatible firmware, a GPU with compatible hardware, and a driver supplied by AMD. Anyone is free to use this at no cost after certification by AMD (and there is no certification fee).
  • The open nature of VESA Adaptive Sync (and FreeSync being based off this standard) means that it (they) is/are limited by what hardware (scalar) is presently available (more on this later).
  • Contrary to popular belief, FreeSync is not open-sourced, except for some bits in Linux. It's debatable if it's really an open-standard as well. AMD has full control of the standard (unlike the consortium behind VESA Adaptive Sync) and requires a paid certification fee confirmed no certification fee but the hardware does have to be sent to AMD for certification. It's open in the same sense that the Apple App Store is open for anyone to use, so long as you submit to Apple's singular rules. I'll let the reader decide if this is an "open-standard" or not.
Adaptive Sync Range
  • G-Sync officially works within a range of 30hz to max refresh, as allowed by the display technology that the G-Sync module is installed in.
  • FreeSync on paper supports a range of 9-240hz, but is limited by the currently available scalars. This is a situation that is QUICKLY improving and the discrepancy between G-Sync and FreeSync is quickly closing. Initially, G-Sync 144hz displays had 30-144hz ranges, whereas the first FreeSync implementation was 35-90hz. This quickly improved with multiple 30-144hz FreeSync displays hitting retail. The first 240hz displays so far have ranges of 30-240 (G-Sync) and 48-240 (FreeSync). While AMD is clearly narrowing the gap here, there's still a ways to go before a majority of their displays have the consistent range found in equivalent G-Sync displays.
  • The discrepancy in this is due to the use of hardware scalars that were not originally designed for variable refresh rate (VRR). There are three companies that manufacture and sell scalars, and they are rapidly advancing the technology to support VRR tech. Nvidia bypassed this to do their own thing and, so far anyway, it's worked out well for them.
  • When your frame dips below 30fps on G-Sync, the refresh rates becomes 2x the framerate. So, if you drop to 25fps, you're at 50hz. This allows you to drop to 15fps with a 30hz minimum. Per multiple sources, G-Sync will allow this to go down indefinitely, IE, 6fps will run at 30hz (multiple of 5).
  • The scalars available to monitor manufactures cannot do this in hardware. As a result, the VESA Adaptive Sync standard does not specify this feature.
  • As a result, AMD came up with LFC (Low-Framerate Compensation) as a software-based workaround that does the same thing. It is essentially identical to G-Sync implementation with no noticeable differences.
  • AMD implemented this in driver form and this allowed the feature to work on existing FreeSync displays. Officially, the maximum refresh must be at least 2.5x the minimum refresh for it to work, IE, 30-75, 48-120, 58-144, etc. In practice, 2x works just fine. Samsung has it working on displays with a 70-144hz range and many have documented success with CRU getting it to work on 2x multiples.
Adaptive Overdrive
  • The above isn't an official term that I'm aware of, just my way of explaining how this works. Bear with me here, as this gets a little involved.
  • We've all seen response times (falsely) advertised on displays. Without overdrive, an IPS has a true GtG response time of 12-18ms depending on model and manufacturer (AHVA seems to be a little faster than current LG IPS, for example). Full transitions are roughly double that.
  • At 60hz, it takes 16.7ms for a screen to refresh. If the pixel has not fully transitioned by then, ghosting is seen.
  • Due to this, overdrive is used to try to get every transition below 16.7ms on a 60hz display. This number becomes 6.94ms on a 144hz display.
  • When overdrive is too aggressive, inverse ghosting is seen. It's hard enough to strike this balance. Now, try doing it on an variable refresh display...
  • The G-Sync module will actually adjust the amount of overdrive based on the current framerate/refresh rate. This minimizes (does not eliminate, nor could it) ghosting and inverse ghosting across the spectrum.
  • Standard scalars cannot currently do this, and as a result, TFTCentral and other reviewers will often specify a preferred overdrive setting for your FreeSync monitor based on the refresh rate you'll be hovering around. EXAMPLE - TLDR, Normal setting recommended for 60-100hz, Fast setting for > 100hz, in this particular display.
  • To clarify, FreeSync does support adaptive overdrive. However, the first display to actually make use of it is the ipcoming Nixeus EDG 27 (slated for May 2017 release).
  • There was an issue with some initial-release FreeSync displays where overdrive was disabled when FreeSync was enabled. This is an unrelated issue that has since been fixed in all relevant displays. While the Acer 75hz IPS (not AHVA) panel still has this "issue," it's a non-issue at 75hz.
Full-Screen and Windowed
  • Initially, both G-Sync and FreeSync were limited to Exclusive Fullscreen only.
  • Both have since added Borderless Windowed mode support. Viewing the relevant subs and support forums, both seem to have equal issues with relation to bugs in this mode.
  • G-Sync was first to implement this change.
V-Sync On vs. V-Sync Off
  • G-Sync initially required V-Sync to be on when using G-Sync.
  • FreeSync supported both V-Sync On or Off from the start, as well as framerate target control for those who want to remain in their FS range with V-Sync off, or reduce input lag with V-Sync on.
  • G-Sync did eventually add support for V-Sync off, but requires a 3rd party tool in most cases to limit the framerate (and some games have this in their options settings). There is still no driver-based setting like there is with AMD.
Cost difference, both monetarily and non-monetarily
  • G-Sync requires the use of Nvidia hardware. This not only goes into the bill of materials, but also in budgeting for space inside the monitor. Essentially, the monitor must be designed to use G-Sync from the get-go.
  • FreeSync has no real hardware requirements other than a compatible scalar (most modern monitors have this already and could get FreeSync support with a firmware update, if manufacturers were so inclined). As a result, FreeSync is far cheaper and easier to implement.
  • As a result of this, G-Sync is only oriented in displays already marketed towards gamers. FreeSync is added to displays marketed towards gamers and non-gamers alike, which increases the types of displays available. One example is pre-calibrated true-IPS displays with low-glow panels. There aren't any that I'm aware of for G-Sync, but numerous with FreeSync.

The point of this post was not to say that one is better than the other. Each has inherent pros and cons and it's better to have real understanding of them going into a purchase decision than to base your decision on some of the myths slung out there.

There are certain sections above where it seems like there is one clear winner. In reality and taken in as a whole, it's a series of compromises and the individual user needs to determine what is best for their intended use case.

If you have any questions or believe that any part of this may be incorrect, please let me know and I'll address it ASAP.
Update 1 - Made some edits/corrections per the community. There are too many people to thank, so just please, keep it up!
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