Micro stuttering

Micro stuttering is a quality defect that manifests as irregular delays between frames rendered by a graphics processing unit (GPU). It causes the instantaneous frame rate of the longest delay to be significantly lower than the frame rate reported by benchmarking applications such as 3DMark, which usually calculate the average frame rate over a longer time interval.

A depiction of 5 display refresh cycles with what may be shown during a micro stuttering case. Each colored section represents one of the GPU's frame buffer and each color change represents a frame buffer swap. Assuming a 60 Hz refresh rate, a benchmark tool may report this as 144 frames per second. However, the user will perceive less due to some frames existing for a tiny fraction of a display's refresh cycle.

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.^[1][2][3][4]

The effects of micro stuttering vary 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.^[5]

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. 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 video in output.^[6]

The software program RadeonPro can be used to significantly reduce or eliminate the effects of micro-stuttering when using AMD graphics cards in CrossFire.^[7][8]

See also

• AMD CrossFireX
• Graphics processing unit (GPU)
• Jitter
• Nvidia SLi
• Rendering
• Screen tearing
• Graphics card

Notes

1. Under which frame rate the effects of micro stuttering become 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.
2. The generally accepted average frame rate for a smooth experience varies from game to game and user to user but is generally 30-60 frame/second and higher