Analog output has Higher latency on modern Graphics cards?

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A Solid lad
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Analog output has Higher latency on modern Graphics cards?

Post by A Solid lad » 29 May 2018, 06:50

The last line of gaming graphics cards which can output an analog signal are the 900 series from nVidia... so If I want to game on my IBM p275 (sony trinitron tube) I better grab a 980 Ti for performance's sake.

That's all fine and dandy, HOWEVER I remember seeing some test results, in which they compare input lag between a CRT and a modern 144hz 1080p TN display and the LCD actually came out on top...

In the comments section (or mabye it was a reddit/ocn post...can't recall) of the test were a couple of guys speculating that this happened because on the modern card they tested with (980 Ti) digital signal output optimization was prioritised and analog signal output was just added as a second thought for compatibility with projectors, and old monitors...

Meaning that while they tried to reduce input lag to a bare minimum when outputting a digital signal, they didn't really care about the same with analog... leading to it having more latency.

Older cards like the HD 5870 I originally used with my CRT are supposedly not affected by this, but I don't want to use anything less powerful than a regular gtx 980.

What are your thoughts guys?
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Re: Analog output has Higher latency on modern Graphics card

Post by Sparky » 29 May 2018, 09:52

Could just as easily be a problem with the test methodology. Was this an absolute latency measurement or a relative latency measurement?

IIRC, flood measured absolute CRT latency at about 1.3ms with a gtx 970.

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Re: Analog output has Higher latency on modern Graphics card

Post by A Solid lad » 29 May 2018, 14:56

Sparky wrote:Could just as easily be a problem with the test methodology. Was this an absolute latency measurement or a relative latency measurement?

IIRC, flood measured absolute CRT latency at about 1.3ms with a gtx 970.
Relative... versus a 144hz LCD.
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Re: Analog output has Higher latency on modern Graphics card

Post by Sparky » 29 May 2018, 17:48

A Solid lad wrote:
Sparky wrote:Could just as easily be a problem with the test methodology. Was this an absolute latency measurement or a relative latency measurement?

IIRC, flood measured absolute CRT latency at about 1.3ms with a gtx 970.
Relative... versus a 144hz LCD.
I'd say it needs further investigation then, to determine exactly where that extra lag is coming from. Could be related to mirrored displays or scaling from the LCD's native resolution to something supported by the CRT. Did they try setting the CRT as the primary display and setting the LCD up as the mirrored display? Were the refresh rates the same? Were they comparing a single point of the monitor, or the time difference anywhere on screen?

How big was the difference, and what video card were they testing with?

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Re: Analog output has Higher latency on modern Graphics card

Post by A Solid lad » 30 May 2018, 00:48

I reckon they ruled out all of the possibilities mentioned...
The difference was around 4ms, but honestly I can't recall.

I'm not even interested in finding out whether or not this particular test was flawed, but rather other peoples' experiences regarding the same thing...
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Re: Analog output has Higher latency on modern Graphics card

Post by A Solid lad » 30 May 2018, 01:32

Tbh, I was hoping for Chief to stumble upon this post and tell us how likely it is for certain graphics cards to be actually having a less instantaneous analog output than digital...
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Re: Analog output has Higher latency on modern Graphics card

Post by Sparky » 30 May 2018, 10:56

I reckon they ruled out all of the possibilities mentioned...
That requires absolute latency measurements, otherwise you can't check whether the mirroring is causing the latency.
The difference was around 4ms, but honestly I can't recall.

I'm not even interested in finding out whether or not this particular test was flawed, but rather other peoples' experiences regarding the same thing...
4ms is more than double the existing absolute latency measurements(mouse click to light exiting monitor), and is too small to be reliably distinguished from a human perception based A B test.

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Re: Analog output has Higher latency on modern Graphics card

Post by Chief Blur Buster » 30 May 2018, 13:00

Sparky wrote:That requires absolute latency measurements, otherwise you can't check whether the mirroring is causing the latency.
This can theoretically be the cause. Mirroring delay deltas can reach 4ms.

But this may not be the cause. Needs to be verified.
A Solid lad wrote:Tbh, I was hoping for Chief to stumble upon this post and tell us how likely it is for certain graphics cards to be actually having a less instantaneous analog output than digital...
It can theoretically happen.

This occurs when the path is optimized for digital, and there's some additional buffering in an unoptimized digital-to-analog conversion that's bigger than a DisplayPort/HDMI micropacketization.

I've never seen this happen for real, and I have not verified the testing methodology, but it is technologically possible.

That said, it's important to do an apples-vs-apples test with same timings. Same Hz, same rez, same VT. Use same Vertical Totals (don't use different formulas, e.g. VESA CVT versus VESA CVT-Reduced) because the Vertical Total has a slight effect on input lag benchmarks.

Basically "adaptor lag". Instead of doing a clean RAMDAC path that's virtually lagless, it might actually be a jerryrigged adaptor on the graphics card of some kind. Some adaptors are virtually lagless and some adaptors are laggy. Whereas the GPU has a built in "laggy analog adaptor" for the digital signal. As if you've attached a laggy buffered adaptor, but that adaptor being built onto the GPU circuit board itself instead...

This may not be the cause, and this may be a wild goose chase. But It's technically possible for design decisions to lead to higher analog lag. Theoretically.

Could be mirroring lag, too.
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Re: Analog output has Higher latency on modern Graphics card

Post by A Solid lad » 31 May 2018, 01:27

Thanks for all the answers guys!
I'm so glad I finally have a place where I can ask questions like these and not get replies like "just learn to play" or "x amount of lag is insignificant, you shouldn't be worried about it" or "why are you aking this? you shouldn't even be using a CRT these days..."
(Well...not getting them for the most part. lol)
Those answers are not only useless, but infuriating at the same time...and make me feel like there's no poeple like me left on earth, who are just curious about stuff, and want to learn new things...and improve on things they use.

Thankfully, that's not the case here!

One more thing...now that we know it's possible, can we know how likely do you think that this was the case, given the circumstances... I mean, the gtx 980 ti was a top-end card...
What's your experience? Have you came across similar corner cutting on other high-end gfx cards in the past?
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Re: Analog output has Higher latency on modern Graphics card

Post by RealNC » 31 May 2018, 02:14

A Solid lad wrote:One more thing...now that we know it's possible, can we know how likely do you think that this was the case (inherently more delay for analog signals on the gfx card) given the circumstances... I mean, the gtx 980 ti was a top-end card, and on your experience? (maybe you came across similarly cut corners on other high-end gfx cards in the past)
I'd say this depends on the board manufacturer. The "important" parts, like voltage regulators and such are usually better on high-end products, but this stuff is usually the same across all boards, regardless of whether it's a high-end or low-end product.

But it does differ between manufacturers. An EVGA card might use a different analog output than a Gigabyte board, for example. So it's not about whether it's a mighty 980 Ti or a lowly 960. It's about what the PCB manufacturer decided to put on their range of 900-series boards.
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