Input lag is used to describe the delay between an electrical input from the point of stimulation to action—for example, pressing a button and seeing the event after as little as 1/24 of a second. In video games, input lag is either the delay between the television or monitor receiving a signal and its being displayed on the screen, or the delay between pressing a button and seeing the game react. In electronic hardware development, input lag is the delay between an electronic input signal being generated and processed. In this field, the phenomena detailed below are referred to as output lag. More formally, the terms input latency and output latency are also used. Due to gamers being largely unaware of the phenomenon of input lag at this low level, the terms input lag and output lag became confused over time, and the above description, where input and output lag are combined into a singular phenomenon known as input lag, has become popular. Overall, the correct terminology is clear: a delay between a physical input occurring and it being processed electronically is input lag, and a delay between an electronic output being sent and it being processed into a physically observable phenomenon, is output lag. In short, input lag occurs on input devices while output lag occurs on output devices. The following are descriptions based on the colloquial use of the term, as used by gamers.
Potential causes of delay from pressing a button to the game reacting
The potential causes for "input lag"- according to the second definition- are described below. Each step in the process increases "input lag", however the net result may be unnoticeable if the overall "input lag" is low enough.
Controller sends signal to console
For wired controllers, this lag is 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.
A videogame console or PC will send out a new frame once it has finished performing the necessary calculations to create it. The rate at which this is achieved is measured with the frame rate. Using common 60 Hz monitor as an example, the maximum theoretical frame rate is 60 FPS, which means the minimum theoretical input lag for the overall system is approximately. Theoretical maximum FPS is usually limited by the video monitor, since the game cannot display more frames per second than the monitor's refresh rate. In situations where the CPU and/or GPU load is high, FPS can drop below the monitors 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 pipelining architectures to process multiple frames concurrently, allowing for more efficient use of the underlying hardware. This has the consequence of exacerbating input lag, especially so at low frame rates.
Display lag
This is the lag caused by the television or monitor. Image processing takes time and therefore adds some degree of input lag. It is generally considered that input lag of a television below is not noticeable. Once the frame has been processed, the final step is the pixel response time for the pixel to display the correct colour for the new frame.
Typical overall response times
Testing has found that overall "input lag" times of approximately are distracting to the user. It also appears that is an average response time and the most sensitive games achieve response times of .
