Micro stuttering is a term used in computing to describe a quality defect that manifests as irregular delays between frames rendered by the GPU(s), causing the instantaneous frame rate of the longest delay to be significantly lower than the frame rate reported by benchmarking applications, such as 3DMark, as they usually calculate the average frame rate over a longer time interval. In lower frame rates[note 1] when this effect may be apparent the moving video appears to stutter, resulting in a degraded gameplay experience in the case of a video game, even though the frame rate seems high enough[note 2] to provide a smooth experience. Single-GPU configurations do not suffer from this defect in most cases and can in some cases output a subjectively smoother video compared to a multi-GPU setup using the same video card model. Micro stuttering is inherent to multi-GPU configurations using alternate frame rendering (AFR), such as nVidia SLi and AMD CrossFireX but can also exist in certain cases in single-gpu systems.
The effects of micro stuttering varies depending on the application and driver optimizations. Beyond dual-GPU setups, CrossFireX/SLI setups do not seem to be as affected by micro-stuttering; the frame rate variability in a three-way CrossFireX/SLI setup approaches the smoothness achieved by a single GPU.
As of May 2012, with the latest release of hardware and drivers from nVidia and AMD, AMD's Radeon HD 7000 series is severely more affected by micro stuttering than nVidia's GeForce 600 Series. In tests performed in Battlefield 3, a configuration with two GeForce GTX 680 in SLi-mode showed a 7% variation in frame delays, compared to 5% for a single GTX 680, indicating virtually no micro stuttering at all. A configuration with two Radeon HD 7970 in CrossFireX-mode, on the other hand, showed an 85% variation in frame delays, compared to 7% for a single card, indicating large amounts of micro stuttering. These results are reflected in the perceptual experience when looking at the outputted video.
- Under which frame rate the effects of micro stuttering becomes apparent varies depending on numerous variables and how sensitive the human test-subject is. The worst-case scenario would be that the frames from all GPUs finish rendering at the same time, in such a case the frame rate perceived by the viewer would be half of the reported average frame rate in the case of a dual-card configuration, and just a fourth in a quad-GPU configuration.
- The generally accepted average frame rate for a smooth experience varies from game to game but is generally 30-40 frame/s and higher.
- Raffael Vötter (2008-02-08). "Video proof: Micro stuttering may destroy the performance gains from current multi GPU technologies". PC Games Hardware Online. Retrieved 2009-11-03.
- Raffael Vötter (2008-07-28). "PCGH proves micro stuttering on the Radeon HD 4870 X2". PC Games Hardware Online. Retrieved 2009-11-03.
- Kyle Lunau (2009-05-06). "Micro Stutter: The dark secret of SLI and Crossfire". Overclockers.com. Retrieved 2009-11-03.
- MrWizard6600 (2008-06-20). "GPU Microstuttering FAQ". Hardforum.com. Retrieved 2010-05-08.
- Igor Wallossek (2011-08-22). "Micro-Stuttering And GPU Scaling In CrossFire and SLI". Tom's Hardware. Retrieved 2011-09-24.
- "Geforce GTX 690 – Världens snabbaste grafikkort, Renderingstider/microstuttering" (in Swedish). SweClockers.com. 2012-05-03. Retrieved 2012-05-25.
- Igor Wallossek (2012-11-08). "Micro-Stuttering: Dynamic V-Sync (AMD)". Tom's Hardware. Retrieved 2012-11-08.
- Micro-Stuttering And GPU Scaling In CrossFire And SLI – Tom's Hardware
- Inside the second: A new look at game benchmarking – Tech Report
- How To Fix CrossFire Micro-Stuttering – ShareNoesis