I've been playing Quake 4 since it's release day, and I've noticed there's either a v-syncing or caching issue where the framerate seems to jump for a split second every second or so, I've been calling it a heart-beat all these years.

I first noticed it on my ATI X800 Pro many years ago, assumed it was some weird gpu thing and didn't think much of it. Later I got a GTX 460, while it was much smoother, this weird ticking still occurred. Now I'm using one of the fastest GTX 580s ever made, and seemingly no matter what I do to the settings, I can smooth it out a little, but that micro-stutter is still there every second or so.

Did anyone ever figure out what this was? I've seen this on Intel Cpus, AMDs...Laptops...Desktops...Xeons...Opterons...With SMP, without SMP....I'm not sure what could be causing it outside of just plain bad code that never got addressed.

  • Are you possibly using multiple GPUs? – Nolonar Dec 10 '15 at 19:05
  • Across the board, no, I never have. Though it'd be an interesting test... – Volumetricsteve Dec 10 '15 at 19:06

This is called microstutter and it is related to the interaction between the simulation ticrate and the renderer framerate, possibly with some vsync added in.

I do not recall the specific explanation, but it may be a result of cumulative errors (i.e. successive integer rounding and then a large step correction)

For Doom3-based games, the cvar for this is com_fixedtic.

As an aside, some people have noticed that games like Fallout 3, skyrim etc, higher framerates result in a faster simulation (and slower framerates reduce the simulation speed). This is the same issue that com_fixedtic is meant to address, and one of the settings will result in the doom3/Q4 simulation running faster/slower along with the framerate (the benchmarking tool being the extreme example).


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