In gaming, input lag is defined as the delay between the when a user does something with an input device and when that action is reflected on the monitor.

The definition is straightforward, but the reality of input lag is much more subtle than may readily be apparent. There are many smaller latencies that contribute to the overall whole of input lag and understanding the full situation may prove beneficial to gamers everywhere.

The first subtlety is that there will always be input lag. Input lag is an unavoidable reality that can only be minimized and never eliminated. It will always take some amount of time for input data to get to the software and it will always take some amount of time for the software to use that data to display a frame of animation on the monitor. Keeping this total time as low as possible is a key mission of hardcore twitch gamers out there.

This article will step through all the different contributors to input lag, and we'll give some general estimates on the impact of each different contributor. Exact numbers will vary widely with different hardware and software combinations. But knowing where to focus when optimizing for input latency should help those who are interested.

After drilling down into the causes of input latency, we will provide a few examples of different hardware and settings in our lab. The extra twist is that we will be evaluating actual input latency using a high speed camera to count frames between input activation and monitor response. We'll be looking at three different games with multiple settings on both CRT and LCD monitors.

Reflexes and Input Generation
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  • mathew7 - Thursday, September 08, 2011 - link

    What I realized (i)racing in the past year is that a consistent lag can still offer playable experience when everything is under control (like no tire grip losing in racing). I think this is why consoles seem to get away with laggy TVs. What I mean is that the brain will train itself to anticipate any movement. For instance, there was a comment about turning in earlier. But if the lag is inconsistent (let's say +/- 1 frame, that would mean 32ms between lowest and highest lag), the brain cannot adapt to it, as this is unnatural. FPS stutter is such an inconstistency, as is loading something during play (and game controls freezing for much less than 1s).

    But even consistent lag will not offer the best performance (I'm talking about lap times, not FPS), because anticipation is just 1 part, reflex is another, and your reflexes are what input lag affects most. During my racing, I found that I can actually recover from most slides with my LCD TV as opposed to my (much newer) LCD monitor. Some tests with a low-res high-speed camcorder (192x108x240fps), cloned displays and fast steering wheel movement showed 2-4 frames lag between TV and monitor. That is 32-64ms. The TV itself had around 1-2 frame lag compared to the wheel, but this included the complete chain of wheel sampling->USB->game CPU->GPU->TV.
    Reply
  • junior262133 - Monday, March 04, 2013 - link

    Oh sweet baby Jesus thank you for this article. It saddens me knowing that Counter strike Global offensive has horrendous input lag in comparison to counter strike source. This issue has been plaguing me since it was in beta. I would mostly rank first in css when playing, but going over to global offensive was a living nightmare. What baffles me is almost no one seems to notice, considering most of us come from a background of CS:s or 1.6 on a Crt.

    On top of that nvidia has completely removed the option to set pre-rendered frames to zero.

    i have tried submitting tickets in to patch cs:go but they seem to not be getting any attention. Maybe i'm talking to the wrong people. If you could please do so, visit these 2 pages in which i try to address the issues at hand. It wouldn't hurt if you could explain in one comment that the reason there is input lag in Cs:go is because of the game code and not some random pc glitch of mine. Most people seem to be oblivious to the problem.

    http://64bitvps.com/csgo/ticket/mouse-laginput-mis...

    http://64bitvps.com/csgo/ticket/let-us-have-the-op...

    THANK YOU SO F*****G MUCH!!!!!
    Reply
  • jigglywiggly - Saturday, October 05, 2013 - link

    does afr in sli add one frame of input lag? Reply
  • ibaldo - Sunday, October 06, 2013 - link

    I am looking for information about possible difference in lag between monitor connections.
    I mean, comparing VGA vs DVI.
    Thanks for this excellent article!
    Reply

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