Input lag or input latency is the amount of

time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, to ...

that passes between sending an

electrical signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The ''IEEE Transactions on Signal Processing'' ...

and the occurrence of a corresponding action. In

video games Video games, also known as computer games, are electronic games that involves interaction with a user interface or input device such as a joystick, game controller, controller, computer keyboard, keyboard, or motion sensing device to gener ...

the term is often used to describe any latency between an input and either the game or the display reacting to that input, despite the fact that this may emerge from a combination of input and output lag.

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 (steps which have negligible contributions to the input lag have been omitted). 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.

Console/PC processes next frame

videogame console A video game console is an electronic device that outputs a video signal or image to display a video game that can be played with a game controller. These may be home consoles, which are generally placed in a permanent location connected to a t ...

or PC will send out a new

frame A frame is often a structural system that supports other components of a physical construction and/or steel frame that limits the construction's extent. Frame and FRAME may also refer to: Physical objects In building construction *Framing (con ...

once it has finished performing the necessary calculations to create it. The amount of frames rendered per

second The second (symbol: s) is the unit of time in the International System of Units (SI), historically defined as of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds ...

(on

average In ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of the numbers divided by how many numbers are in the list (the arithmetic mean). For example, the average of the numbers 2, 3, 4, 7, ...

) is called the

frame rate Frame rate (expressed in or FPS) is the frequency (rate) at which consecutive images (frames) are captured or displayed. The term applies equally to film and video cameras, computer graphics, and motion capture systems. Frame rate may also be ca ...

. Using common 60 Hz monitor as an example, the maximum theoretical frame rate is 60

FPS FPS may refer to: Arts and entertainment * "F.P.S." (''Law & Order: Criminal Intent''), an episode of the TV show ''Law & Order: Criminal Intent'' * '' fps magazine'', a defunct magazine about animation * ''The Fabulous Picture Show'', a televi ...

(frames per second), which means the minimum theoretical input lag for the overall system is approximately . The

monitor Monitor or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, West ...

is usually the

bottleneck Bottleneck literally refers to the narrowed portion (neck) of a bottle near its opening, which limit the rate of outflow, and may describe any object of a similar shape. The literal neck of a bottle was originally used to play what is now known as ...

for the theoretical maximum FPS, since there is no point in rendering more frames than the monitor can display per second (unless trying to gain advantage on some pc titles). In situations where the CPU and/or

GPU A graphics processing unit (GPU) is a specialized electronic circuit designed to manipulate and alter memory to accelerate the creation of images in a frame buffer intended for output to a display device. GPUs are used in embedded systems, mobi ...

load is high, 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 engine A game engine is a software framework primarily designed for the development of video games and generally includes relevant libraries and support programs. The "engine" terminology is similar to the term "software engine" used in the software i ...

s often make use of pipelining 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 (which is also called "input lag" by the first definition above, but "output lag' by the second definition). Image processing (such as upscaling, motion smoothing, or edge smoothing) takes time and therefore adds some degree of input lag. An input lag below 30 ms is generally considered unnoticeable in a

television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...

. Once the frame has been processed, the final step is the updating the

pixel In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device. In most digital display devices, pixels are the smal ...

s to display the correct color for the new frame. The time this takes is called the

pixel response time In technology, response time is the time a system or functional unit takes to react to a given input. Computing Response time is the total amount of time it takes to respond to a request for service. That service can be anything from a memory ...

Typical overall response times

Testing has found that overall "input lag" (from controller input to display response) times of approximately are distracting to the user. It also appears that (excluding the monitor/television display lag) is an average response time and the most sensitive games (

fighting games A fighting game, also known as a versus fighting game, is a genre of video game that involves combat between two or more players. Fighting game combat often features mechanics such as blocking, grappling, counter-attacking, and chaining attac ...

first person shooters First-person shooter (FPS) is a video game genre, sub-genre of shooter video games centered on gun and other weapon-based combat in a First person (video games), first-person perspective, with the player experiencing the action through the eye ...

and

rhythm games Rhythm game or rhythm action is a genre of music-themed action video game that challenges a player's sense of rhythm. Games in the genre typically focus on dance or the simulated performance of musical instruments, and require players to press ...

) achieve response times of (excluding display lag).

References