Find and Fix Input Lag in Your HDTV or Monitor

HDTV and computer display manufacturers aren't shy about trumpeting their products' size, resolution, and contrast ratio, but they rarely report another spec: input lag--the time a monitor takes to catch up to your keyboard, mouse, or gamepad.

Input lag generally occurs in flat-screen LCD and plasma displays because the screen takes time to process the image in order to improve its quality. If you use your display or HDTV for doing general work, browsing the Web, or watching TV or movies, the lag is rarely significant; any delay is more likely to come from using a wireless keyboard and mouse and wireless Internet. On the other hand, if you use your display for anything that requires accurate timing (such as video, audio, or gaming), you may want to consider testing your setup for input lag.

Check Your Lag

There are several ways to measure input lag. One approach is to split the signal between a lagless CRT display and an LCD display (as demonstrated in this YouTube video). Alternatively, you can use a Web-based reaction test like this one at HumanBenchmark.com, which tests your response to changing colors. Try it a few times, and if you notice a significant difference (30ms or so) between the results on different configurations, one of them is probably lagging.

A laggy display can add as much as 68ms to this number.
A laggy display can add as much as 68ms to your results in a reaction time test.
Gamers might already have noticed input lag on their display; the longer-than-usual delay between pressing a button and its corresponding effect on-screen makes performing complex maneuvers or combinations more difficult. First-person shooters, fighting games, and rhythm games like Rock Band and Guitar Hero are all heavily affected by it.

Lowering Your Lag

Of course, some users are stuck with a laggy display and have no plans (or cash) to upgrade to a speedier model. Fear not--you can still take steps to reduce the lag. Since all flat-screen displays have some lag, your goal should be to lower it to the point where you cease to notice it.

First, check to see whether your TV has a Game mode--basically, a display mode that turns off postprocessing routines at the cost of a slight reduction in image quality. You might have to muck around in the manual to figure out exactly what it does--some manufacturers incorporate an Overdrive mode that may actually increase input lag.

Next, turn off as many other video-processing options as you can. Each manufacturer tends to identify its features with different acronyms such as DRE or 3DNR; try turning them off and seeing whether your lag improves.

If you use HDMI or component cables to connect your setup to your display, try using VGA instead. Display manufacturers sometimes restrict the postprocessing functions to HDMI or component video inputs, leaving the VGA input untouched. If your device doesn't have a proprietary VGA cable, you could try using an HDfury, though we haven't tested it in-house yet.

Finally, some apps and games have their own built-in latency calibration options. Both Rock Band and Guitar Hero, for example, include lag calibration functions as menu options to help you adjust the game's timing and to minimize lag. If these games are incorrectly calibrated, the faulty setting could be causing input lag, so be sure to test the settings before you try to play that fret-melting song.

Try Before You Buy

Ultimately, there's only so much you can do to reduce input lag on your display. If you plan to purchase a new HDTV or monitor, your best strategy is to research your purchase carefully.

Since input lag measurements aren't advertised, track down the model numbers and product names of the displays you're interested in and then search for "[model name] input lag" in Google to see whether it's among the more problematic displays. I tend to go with monitors that people recommend on the Tech Talk forum of the Street Fighter-centric Shoryuken.com Website because no one gets more nitpicky about input lag than fighting game fans.

Note: Though "response time" is measured in milliseconds, it isn't a measurement of input lag. Response time refers to how long a pixel on the display takes to change colors; higher response times can be an indication that images will "ghost" or leave artifacts on the screen. To minimize this phenomenon, many manufacturers have started using "overdrive" display modes; unfortunately, these modes can increase input lag. (Bit-Tech has a good explanation of Overdrive modes and input lag.) You'll still want a display that has low response times--but not for input lag-related reasons.

Consumer-oriented "twisted nematic" (TN) LCD panels tend to have the fewest problems with input lag, so photo-professional-grade LCD displays may not be a good match for your needs. Another source of low-lag displays is "digital signage"--displays marketed to hospitals, airports, and other entities. These screens often use the same panels as HDTVs but with the postprocessing stripped out. (You can search for digital signage models on Web sites such as PriceGrabber.)

The best and simplest way to conduct your research, however, is to bring your laptop or game console with you and ask the sales reps if you can see for yourself how the displays perform. If you intend to purchase your monitor online, look for a store that carries the model you want to buy and ask to test it there. (Even better, bring a copy of the online advertised price and see whether the brick-and-mortar establishment will match the online seller's price.) If you can't test the displays yourself, be sure to buy the one you settle on from a vendor that offers a generous return policy, so you don't get stuck with a laggy display.

For more tips on buying displays, check out our videos "How to Buy a Flat-Screen TV" and "How to Buy a Monitor" and our article "How to Buy a Monitor."

Patrick Miller is a staff editor for PC World. Find him off-duty @pattheflip.

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