Input lag

Input lag or input latency is the amount of time that passes between sending an electrical signal and the occurrence of a corresponding action.

In video games the term is often used to describe any latency between input and the game engine, monitor, or any other part of the signal chain reacting to that input, though all contributions of input lag are cumulative.

Potential causes of delay from pressing a button to the game reacting
The potential causes for input lag are described below. Each step in the process, however small, increases total input lag, however the combined result may not be noticeable if all input lag is low enough.

Controller sends signal to console
For wired controllers, this lag is normally negligible. For wireless controllers, opinions vary as to the significance of this lag. Some people claim to notice extra lag when using a wireless controller, while other people claim that the 4–8 milliseconds of lag is negligible.

Console/PC processes next frame
A videogame console or PC will send out a new frame once it has finished performing the necessary calculations to create it. The amount of frames rendered per second (on average) is called the frame rate. Using common a 60 Hz monitor as an example, the maximum theoretical frame rate is 60 FPS (frames per second), which means the minimum theoretical input lag for the overall system is approximately 16.67 ms (1 frame/60 FPS). The monitor is usually the bottleneck for the theoretical maximum FPS, since there is little point in rendering more frames than the monitor can show. In situations where the CPU, GPU, memory, bus, etc. load is bottlenecked, FPS can drop below the monitor's refresh rate.

Individual frames need not be finished within the interval of a screen refresh to output at an equivalent rate. Game engines often make use of pipelined architectures to process multiple frames concurrently, allowing for a more efficient use of the underlying hardware. This exacerbates input lag, especially at low frame rates.

Display lag
This is the lag caused by the television or monitor (also called output lag). In addition to the latency imposed by the screen's pixel response time, any image processing (such as upscaling, motion smoothing, or edge smoothing) takes time and therefore adds more input lag. An input lag below 30 ms is generally considered unnoticeable in a television. Once the frame has been processed, the final step is the updating the pixels to display the correct color for the new frame. The time this takes is called the pixel response time.

Typical overall response times
Testing has found that overall input lag (from human input to visible response) times of approximately 200 ms are distracting to the user. It also appears that (excluding the monitor/television display lag) 133 ms is an average response time and the most sensitive games (fighting games, first person shooters and rhythm games) achieve response times of 67 ms (excluding display lag).