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Input lag, or specifically display lag, is considered by many gamers to be the dirty little secret of the digital display age. Go shopping for a new HDTV and ask the sales assistant about input lag and be prepared to be met by puzzled glances or to be quoted the displays response time, which is something totally different. When gamers talk about input lag, they are referring to the delay between the picture changing at the source and being displayed on the tv/monitor. While input lag was virtually non existent in the days of CRT televisions, it is now very common for TV manufacturers to include all sorts of image processing in their sets. Systems like these might buffer one or more frames, perform image processing on them and then display them, meaning the image you see on your TV could be as much as 60 milliseconds or more behind the image output from your games console.
Input lag can affect video material by causing the audio to become desynchronised from the video, but it is a bigger problem still for game players. While there is undoubtedly a point where input lag can be noticed, its effects on gameplay when it’s not noticeable are less well understood. Studies into alcohol and driving have, for instance, linked even a small amount of alcohol to a reduction in reaction times and overall driving ability. Next time you miss that platform or fail to dodge that fireball by a fraction of a second, maybe it wasn’t your fault after all.
Logging the Lag
Until recently, the most common way of measuring input lag was to use a video signal splitter, a second display (usually a CRT) and a highspeed camera. By feeding in video footage of a clock display, then taking a photograph while the two displays were running side by side, it was possible to visually see the difference between each display and use this to calculate input lag. Needless to say, this method was rather cumbersome. Few electrical stores would tolerate their customers lugging a CRT around the shop floor. Furthermore, some experts have questioned the accuracy of this method of testing (see for instance this German article on Prad.de). Fortunately now, thanks to Leo Bodnar, there’s an alternative.
Leo Bodnar’s hand held input lag tester comes in an unassuming red plastic case. Powered by two double A batteries (included) it connects to the TV or monitor via a HDMI cable (not included). On top of the unit, there’s a push button that activates the device. After connecting the unit to the TV, it’s just a matter of pressing and holding the button to make an image appear. You will then see a display with a counter and three flashing white bars. To take a reading, you simply move the lag tester over the flashing white bars, it then uses a light sensor recording to work out how long it takes for the signal to reach the TV from the lag tester. The tester itself is fixed at either 1080p or 720p output at 60hz. You must choose which resolution when you first buy it and it can only be reprogrammed by sending it back to the manufacturer. Ideally we’d have liked user selectable resolutions and refresh rates. For maximum flexibility, we’d recommend the 720p version. There doesn’t seem to be any lag at all introduced on most sets when upscaling from 720p to 1080p and the 720p version is compatible with more sets.
Tips for testing lag
Basic use of the lag tester is of course pretty straightforward. On some displays you will notice that the different flashing bars give different readings. This can occur because it actually takes the display some milliseconds to draw the entire image. Other displays (typically those that have a frame buffer) will register a more consistent reading across the three flashing bars. While most sets tested without a hitch, a couple of Sony sets gave us some inaccurate readings first try. If you get a reading that is inconsistent or unexpectedly low, try the following:-
- Reduce the amount of ambient light in the room (e.g by waiting until after dark or closing the curtains).
- Turn down the TV’s backlight and try increasing the brightness.
- Make sure there’s no glare directly on the screen.
Generally, any reading under 16ms on the middle or bottom bars you should double check.
Expanding the lag tester
Apart from testing HDMI displays, the lag tester actually has quite a few other applications too. By adding a simple HDMI to DVI adaptor, you can test the input lag on DVI displays too. By running the tester through a video processor, you can see exactly how much extra lag these devices are adding. Interestingly, in our tests we also found that the HD-Fury line of HDMI to VGA adaptors were completely lag-free, meaning you can add one to the lag tester and test VGA sources too, you may need an external power supply for the HD-Fury when you do this however.
Example lag test readings
Here are some of the more interesting readings the lag tester turned up:-
- 31ms – Sony KDL-40Z4500 – Game mode on ( A TV reported as having 0 to 10ms on other sites).
- 6ms – DVDO Edge in Gamemode
- 18ms – XRGB Mini (lower than others have logged but still disappointing)
- 0 to 1ms – HD Fury HDMI to VGA adaptor
- 0ms – Extron RGB interfaces
- 0ms – Cambridge audio Azur 551r in passthrough mode (other users report some home theatre systems add lag even in passthrough mode).
116.2ms – DVDO Edge with game mode off and Sony KDL-40Z4500 with game mode off.
When experimenting with the tester, remember that you must output a 60hz image for the tester to work properly. Don’t be tempted to use a video processor to convert the signal to 24hz for instance, as the tester simply won’t work then.
The Leo Bodnar input lag tester is a useful device for any videophile to have in his or her toolbox. Apart from an obvious alley to have with you when shopping for a new HDTV, the device can also be used to more accurately calibrate audio delay, though keep in mind if your setup supports HDMI1.4 ARC it may already have done this calibration for you. Although it’s likely to spend a lot of time on your shelf, the lag tester will be an invaluable tool from time to time and is especially recommended for anyone who is shopping for a new display.
The input lag tester is available now, exclusively at LeoBodnar.com.