Input Lag and Response Times
We've heard frequent complaints about input lag on various LCDs, particularly after our last review of the Samsung 245T. We decided it was time to take a closer look at the subject and see if we could come up with a repeatable test. We ended up settling on a test similar to what we were using to show response times, with a few changes.
We run the Wings of Fury benchmark in 3DMark03, with the resolution set to the native LCDs resolution -- in this case 1920x1200. Our test system is an overclocked quad-core Q6600 (3.30 GHz) running two Radeon HD 3870 cards in CrossFire on a Gigabyte GA-X38-DQ6 motherboard. (This is the same system used in our initial testing of 3DMark vantage.) We connect the test LCD and a reference LCD to two outputs from the Radeon 3870 and set the monitors to run in clone mode.
The reference Monitor is an HP LP3065, which we have found to be one of the best LCDs we currently possess in terms of not having input lag. (The lack of a built-in scaler probably has something to do with this.) [Ed: Before you ask, no, I do not have any CRTs around that I can use as a reference monitor, and frankly I don't want any. They're huge, heavy, and require more power, and the best ones were made over five years ago. Sorry - LCDs are where everything is heading. R.I.P. CRT.]
While the benchmark is looping, we snap a bunch of pictures of the two LCDs sitting side-by-side. We set our camera to f/2.2, ISO-400, and a 1/400 sec exposure in order to get a clear snapshot of the on screen action. (Note that these settings have changed from previous articles.) 3DMark03 lists a runtime with a resolution of 10 ms at the bottom of the display, and we can use this to estimate whether a particular LCD has more or less input lag in our reference LCD. We then sort through the images and discard any where the times shown on the LCDs are not clearly legible, until we are left with 10 images for each test LCD. We record the difference in time relative to the HP LP3065 and average the 10 results to come up with an estimated input lag value.
It's important to note that this is merely an estimate -- whatever the reference Monitor happens to be, there are some inherent limitations. For one, LCDs only refresh their display 60 times per second, so any measurement less than approximately 17 ms is not 100% accurate. Second, the two LCDs can have mismatched vertical synchronization, so it's entirely possible to end up with a one frame difference on the time readout purely because of this. That's why we average the results of 10 images, and we are confident that our test procedure can at least show when there is a consistent input lag/internal processing delay.
Here is a summary of our results, followed by a sample image chosen to highlight the pixel response time of the LCDs. Despite what the manufacturers might advertise as their average response time, we found most of the LCDs were equal in this area -- they all show roughly a one frame "lag", which equates to a response time of around 16 ms.
| Display Input/Processing Lag vs. HP LP3065 | |||||||||||
| One | Two | Three | Four | Five | Six | Seven | Eight | Nine | Ten | Average (ms) | |
| ASUS MK241H | 10 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 |
| Dell 2407WFP | 10 | 20 | 30 | 20 | 10 | 10 | 30 | 30 | 10 | 20 | 19 |
| Dell 2408WFP | 30 | 40 | 40 | 40 | 30 | 30 | 40 | 30 | 50 | 50 | 38 |
| Gateway FHD2400 | -10 | -10 | 0 | 10 | 10 | 10 | 0 | 10 | 10 | 0 | 3 |
| Gateway FPD2485W | 30 | 10 | 20 | 20 | 20 | 10 | 0 | 30 | 20 | 20 | 18 |
| HP w2408 | 10 | 10 | 0 | 0 | 0 | 0 | 0 | 10 | 0 | 0 | 3 |
| LaCie 324 | 40 | 30 | 40 | 30 | 40 | 50 | 40 | 50 | 50 | 30 | 40 |
| Samsung 245T | 30 | 30 | 30 | 30 | 30 | 20 | 30 | 30 | 20 | 20 | 27 |
| Samsung 2493HM | 0 | 10 | 0 | 0 | 0 | 10 | 0 | -10 | 0 | 10 | 2 |
 ASUS MK241H |
 Dell 2407WFP |
 Dell 2408WFP |
 Gateway FHD2400 |
 Gateway FPD2485W |
 HP w2408 |
 LaCie 324 |
 Samsung 245T |
 Samsung 2493HM |
The table tells a clear story: all of the S-PVA panels as we mentioned clearly have more input lag/internal processing lag than all of the TN panels. This is a pretty shocking result, as it indicates that the problem may actually be inherent in S-PVA technology, although there are still panels that do better in this area. The Gateway FPD2485W and Dell 2407WFP both have an input lag just under 20 ms -- or a one frame delay on average. The Samsung 245T has a 27 ms delay on average, indicating it would be one or two frames behind what is actually happening. Worst of all are the Dell 2408WFP in the LaCie 324, which have a two or three frame lag. (This is discounting any other lag that is present between the user and what they are seeing on the display; there's also a slight amount of lag associated with reading input from your mouse/keyboard, processing that input, rendering the resulting image, and sending that to your display.) In contrast, the four 24" TN panel LCDs all more or less match the HP LP3065.
Thus, we have no choice but to conclude that if you are seriously concerned about input lag, you will have to sacrifice viewing angles, color accuracy, and/or overall display quality in order to avoid this on the current 24" offerings. On the other hand, we have played games on all of the test LCDs, and we honestly can't say that we noticed any difference in our overall performance. But we weren't hopped up on Bawls and we don't have a 1337 name like Fatal1ty. Competitive gamers will probably feel differently.
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feraltoad - Friday, May 2, 2008 - link
Do you think a subsequent Dell Revision will fix this or as you suggest are we seeing possible limitations in that panel technology?Currently some users are reporting a "red tint" on the left side of their monitors. Has anyone experienced this?
Owners of the Dell 2408 I would appreciate some opinions about this monitor, because I want to upgrade to a 24inch LCD (& get rid of a CRT on a second PC), but as I currently have a 21inch LCD (HP f2105) that I am mostly happy with I want to get something thing that will be a definite improvement. As Jarred states the Dell, sans any lemons, looks to be perfect except for the slight input lag, and that's the concensus I've seen among opinions on various sites. I don't think I could even notice but I would like to hear some people with experience with the 2408. I would value Anandtech readers' opinions more than reviews off Dell's site since we are probably more on the same page.
Gast - Friday, May 2, 2008 - link
http://forums.anandtech.com/messageview.aspx?catid...">http://forums.anandtech.com/messageview.aspx?catid...From this should come your dork binding monitor, which looks to be the DoubleSight DS-263N with the chance of a polarizer. I'm sad that the article neglected to even mention this great resource.
rcraig - Friday, May 2, 2008 - link
I, too, am waiting for a review of the DoubleSight DS-263N. I have read a lot about this monitor in another forum and it seems to be the one monitor to rule them all. Great colors for phtotgraphs, low lag for games, IPS for great viewing angles, and 26 inches for only $680! It only lacks the many input features some offer, but it does offer dual DVI, VGA, and 4 USB's.JarredWalton - Friday, May 2, 2008 - link
I've sent a couple email messages to DoubleSight, so far with no response. Same goes for a variety of other manufacturers. I'd love to go out and buy the LCDs I want to review, but that's not financially practical. :-(XtAzY - Friday, May 2, 2008 - link
I'm just skimming through the article, but does it mention anything about GHOSTING?JarredWalton - Friday, May 2, 2008 - link
You're talking about pixel response times. See page 12 and look at the images.musicman1352000 - Friday, May 2, 2008 - link
I have been waiting - desperately hoping and praying - that anandtech would review the dell 2408. It seems to be a stand out performer to me but I've been really put off buying it by the number of complaints of pink/red "tint", uneven brightness, colourful font halos, and bad input lag posted in forums. Reviews contradict each other and many people are waiting for a revision to solve the perceived problems like input lag (coming from an engineer, I am fully aware this particular problem can't be solved by a revision!). What I'd like to know is whether you noticed any of the problems I mentioned (not including the input lag which you obviously picked up on), and what revision of monitor you received (A00 or A01)? Also, Dell don't seem keen on telling users what versions of HDMI and displayport are used - do you know anything about this?JarredWalton - Friday, May 2, 2008 - link
I noticed no problems with the quality of the panel on the 2408WFP I received, with is revision A00. However, that doesn't mean some panels don't have problems. If overall quality is that important, LaCie seems to do a better job judging by their reputation (and price).I imagine part of the problem users have is that the default brightness on many monitors is way too high, and sometimes color settings need to be turned down as well. You can see that at 80-80-80 RGB with 50 on brightness and contrast, the Dell achieved exceptional color accuracy even without calibration. Is this just a cherry-picked sample? I certainly hope not!
I have no idea what version of DisplayPort the 2408 uses - and lacking any video cards with the feature I couldn't even test it right now. For HDMI, I would assume it's not 1.3, but I could be wrong. Probably v1.1 or maybe 1.2 - is there any easy way to tell? If someone can point me to a utility that will report the HDMI version, I'll be happy to test.
musicman1352000 - Friday, May 2, 2008 - link
Mmm okay - thank you for replying.One of the worst things about living in New Zealand is the increased cost of buying computer parts, and the reduced ranges available (see http://www.pricespy.co.nz/cat_5.html#g147)">http://www.pricespy.co.nz/cat_5.html#g147). The Dell costs $1199.00 NZD here (and the Lacie is unavailable). That's approximately $930 when translated to USD. As I understand it the cost is ~$700 in the US?
With regards to the HDMI/displayport versions: unfortunately I don't know of any way in which you could test the display to find out. Tektronix offers software for 1.3b compliance testing (trial: http://www2.tek.com/cmswpt/swdetails.lotr?ct=SW&am...">http://www2.tek.com/cmswpt/swdetails.lo...CDSA7160...
but I think this is more engineering oriented. Maybe someone else has a suggestion?
Thanks once again for your opinions :)
feelingshorter - Friday, May 2, 2008 - link
I hope anandtech reviews some of the cheaper monitors in the future also. The cheapest monitors reviewed, being the gateway/samsung at 450 is a steep price for some of us.Just to name the cheaper ones on newegg, SCEPTRE X24WG is at 300 (AR) and seems to be the poor man's 24, or the KDS K-24MDWB at 350 is also at a reasonable price. Plus wouldn't comparing the low end be a good idea to see if you can justify paying for a $1000 lacie (or 500+) gets you more?