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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  • snarfbot - Friday, July 17, 2009 - link

    i have a crt and a plasma tv, both essentially lag free.

    my friends have tn monitors, also no perceivable lag.

    the worst offender is my friends samsung tv, its noticeably laggy.

    but no where near as bad as wireless mice. they gotta be in the 30+ms region.
    Reply
  • nevbie - Friday, July 17, 2009 - link

    My mouse wire is about the same length as my monitor cable. It's too bad the latter doesn't have same relative bandwidth.

    1. But 16ms? Is it still around 16ms if the resolution is halved, which would cut the amount of data per frame to 1/4, or is the 16ms some kind of worst case?

    2. Does the "input lag"(I'd prefer calling it response time) change if you use VGA (analog) connection instead of DVI (digital)? That would be a funny workaround.
    Reply
  • DerekWilson - Friday, July 17, 2009 - link

    1) scanout is always around 16ms regardless of resolution. blanking is always around 0.5ms regardless of resolution as long as the refresh rate is set to 60Hz. it's the VESA standards that determine this. Higher refresh rates mean faster transmission times. cable bandwidth limits maximum resolution+refresh. LCD makers are really the ones to blame for higher refresh rates not being available with lower resolutions ... I believe the traditional limit to this was LCD response time.

    2) i don't believe so.
    Reply
  • bob4432 - Friday, July 17, 2009 - link

    so how slow is my ps/2 trackman wheel connecting into a 4 port kvm? never thought about this area of gaming...interesting. Reply
  • DerekWilson - Friday, July 17, 2009 - link

    I'm not sure if the kvm adds significant delay or not ... that'd be an interesting question.

    I do believe that ps/2 is 100Hz (10ms) though ... so ... ya know, slower :-)
    Reply
  • anantec - Thursday, July 16, 2009 - link

    i would love to see some analysis of wireless input devices, and keyboards. Reply
  • anantec - Thursday, July 16, 2009 - link

    for example, the wireless controler for playstation 3
    and recently razer made a wireless gaming mouse
    http://www.razerzone.com/gaming-mice/razer-mamba/">http://www.razerzone.com/gaming-mice/razer-mamba/

    as the article mentioned, usb device is limited to 1000Hz, what about bluetooth devices?
    Reply
  • Stas - Thursday, July 16, 2009 - link

    Really appreciate the article. Even though I didn't learn much from it. It is VERY useful to point people to when the topic comes up. "Huh, Input lag? What's that? I'm on broadband, dude, and I have a QUAD-CORE!!!" <--- With ppl like that, I, now, have more than 2 options (murder them, or spend 30 min explaining input lag), I can send them to AnAndTech. You guys, own. Reply
  • marraco - Thursday, July 16, 2009 - link

    Thanks for such useful article.

    The tweaking on the mouse was one I never had seen before (and I search for tweaks regularly).

    One thing that I would add, is that some games (as FEAR 2) include controls for mouse smoothing, and/or some way to increase mouse responsivenes. They really affect my imput lag perception.
    Reply
  • jkostans - Thursday, July 16, 2009 - link

    I use a G5 mouse, and a CRT running at 100Hz. As long as my computer pushes 100+fps I don't notice any input lag at all.
    This is what I've found to contribute to input lag in order of significance:

    Framerate, refresh rate, mouse rate. Oh and I've never used an LCD I can't stand the ghosting.
    Reply

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