What is Input Lag?
Input lag is described as the lag between the output from a graphics card and
the image which is displayed on the screen you are using. For LCD screens this
should not be confused with
pixel response time which describes the speed at
which a pixel can change from one orientation to another. Pixel response times
impact aspects such as motion blur and ghosting in moving images. On the other
hand input lag is a delay between what is sent to the monitor, and what you
actually see. This can have impacts particularly in gaming where if the screen
is lagging at all, it can have adverse affects on first person shooter games and
the likes where every millisecond counts.
The level of lag really
depends on the TFT display, and is controlled by many signal processing factors
including, but not limited to the internal electronics and scaling chips. Some
manufacturers even take measures to help reduce this, providing modes which
bypass scaler chips and options which reduce the input lag. These are often
reserved for gamer-orientated screens but the results can be quite
noticeable in some cases.
We are making some
improvements to the way in which we record input lag here due to reader feedback
and improvements that have been made in recent years to testing methods. We're
always keen to improve our reviews and testing methodology and so I hope this
comes as positive news to our readers. We have also spoken at length to Thomas
Thiemann who has carried out extensive studies around input lag and has written
studies including a well-known and regularly referenced article over at
Prad.de. He is also the man behind the SMTT tool which some readers may be
familiar with. We will discuss all of this throughout this article.
Input Lag Measurement
firstly wanted to give an overview of some of the different techniques used to
test input lag commonly by end users and review sites. These methods have
changed somewhat in recent years so here is a summary of them all.
The Stopwatch Program
example stopwatch program, produced by
Traditionally input lag
was widely measured by hooking up a CRT screen to the same graphics card and PC
as the TFT display. By cloning the graphics card output, the user could provide
a comparative test of the output of the CRT vs. the output of a TFT. It is
assumed in this test that a CRT would show no lag on top of the output from the
graphics card which is vital for those wanting to play fast games, where
reaction times are key. This is what many users are used to, having come from
older CRT displays. Many high end gamers still use CRT's as well for high
refresh rates and frame rates and so the move to a TFT can be worrying,
especially when you start throwing in a conversation about lag of the output
By running the screens
side by side in this way in clone mode, you can often see that the TFT lags
behind the CRT. This is sometimes noticeable in practice even if you clone a
game or move windows around your screen, but stopwatch programs have been used
for many years to give a way to display and synchronise the output so that the
difference could be recorded in some way and quantified to a figure in
milliseconds. High shutter speed photographs can then be taken to show just how
much the TFT lags compared with the CRT.
example stopwatch program, Xnote stopwatch
This stopwatch method has
been used for many years by many review websites and end users. It's easy to set
up, doesn't cost anything and allows a reasonable comparative view of a
CRT output vs. a TFT output. It can also be useful for providing a comparison
between different models over time.
The method is not 100%
accurate however. There are areas of inaccuracy inherent to this method. Some
stopwatch programs are based on flash which can introduce issues with frame rate
and update rate support, especially when viewed from an internet source and
browser. All basic stopwatch programs can introduce a degree of error if vsync is active and
due to 2D native refresh rate settings of 60Hz. There's never been a defined
standard for measuring input lag and so this has been used for a long time and
widely accepted as a decent enough representation of what a user may experience.
I will say that this
method has been used for many years by many sources and although there is likely
a varying degree of error introduced in this method, it can still allow you to
give a reasonable comparison between displays. Classification of the lag
into low, medium and high for instance is possible and the method can help give
you an idea of the relative output of a TFT compared with a CRT. It's an
indication though as opposed to a precise measurement. More advanced and
reliable methods are of course preferred where possible. We will talk about the
limitations of these kind of programs a little later on in this article as well
in the interview with Thomas
SMTT - An Improved Stopwatch Process
SMTT stands for 'Small
Monitor Test Tool' and is a program which has been produced by Thomas Thiemann.
SMTT has been around for some time, but Thomas has just completed a full refresh
of the tool with many improvements in the new
SMTT v2.0 which we will talk
about in a moment.
Thomas has carried out a
lot of research into input lag testing methodology and readers may well have
read his excellent in depth article over at
Prad.de in which various methods were tested and compared including
stopwatch programs, SMTT 1 and more advanced oscilloscope + photosensor methods.
Above: a screen
shot of the timer test from SMTT v1.0
The SMTT tool re-defines
and improves the stopwatch method and helps to overcome some of the potential
issues explained before. It runs without vsync active and is capable of very
high refresh rates of more than 1000 fps. This program provides multiple
stopwatches on the screen at once and so refresh rates can also be recognised
and accounted for when used which helps reduce a large part of the error
associated with a single stopwatch.
There were some drawbacks of this SMTT tool
however including difficulty in reading some numbers, hard to read output in
some cases which can lead to interpretation errors, and compatibility issues with DirectX and Windows platforms. All of
these have been addressed in SMTT v2.0 which we will look at now.
SMTT v2.0 - Updates and Improvements
SMTT 2.0 has been
redeveloped from scratch. With the acquired knowledge from his own input lag
studies and the previous development of SMTT v1, including all its strengths and
weaknesses, Thomas Thiemann replaced the old DirectX 9 based code with a modular
and future-oriented DirectX 11 based approach that combines full DirectX 10.0
support with a solid basis for future updates.
Due to the implied
optimizations SMTT 2.0 is not just offering marketing relevant, insubstantial,
forward-looking features you can print on a paper box. In fact it highly
improves the display performance and accuracy at the same time providing some
real benefits to the user right now.
The primary key feature of
SMTT 2.0 is still the input lag measurement that you can find in the software as
“High Precision Counter” test. This test has not just been updated by the
already mentioned transition to DirectX 11 but also by a new display technique
called “I.R.O.N.”. I.R.O.N. stands for Improved Readability Of
Numbers. This new display technique adds regular column switches to the
output on screen to omit any overlapping of the displayed values which reduces
the time needed in the evaluation process and increases the accuracy of the
In addition to the input lag testing element
of the tool, SMTT also provides other display tests which are useful.
The “Deep Color Test”
pattern has been redesigned to assists the human eye in the percipience of the
very fine contrasts that are displayed on screen.
The Deep Color Map, a 10
bit per colour capable multi-colour transition, shows flawless transitions in
all possible directions while the earlier versions of SMTT suffered from a
diagonal restriction in some cases. As the Deep Color Test the output will be
automatically limited to 8 bit per colour as soon as your system is unable to
display 10 bit color depth.
ramps can be defined in the Gradients section of SMTT. Instead of offering
just some presets it is up to the user to select start and end colours of a
transition as well as the number of steps within this very special transition.
So if your monitor has a display issue with certain colour shades you can
focus the displayed colour ramp on the corresponding shades.
Scaling tests that focus
on typical HD resolutions are new to SMTT 2.0. The implied test patterns
should help to determine if Full HD (1080p) or 720p signals are displayed with
their 16:9 aspect ratio and without any cut offs even if zoomed in to fill the
whole area of a monitor that offers a higher resolution than the signal that
should be displayed.
Last but not least the
whole user interface has been redesigned to offer the best ease of use possible.
Intuitive user controls, non-blocking tool-tips and live previews supersede the
manual most of the time. SMTT 2.0 is designed to support Windows Vista, Windows
7, Windows Server 2008 and Windows Server 2008 r2. Caused by the use of shaders
that require DirectX 10.0, SMTT 2.0 does not support DirectX 9 only graphics
cards or Window XP. SMTT v2 is a user-oriented modern test software with lots of
technical improvements that alleviate the usage and enhance the accuracy.
We will look at the improvements made in v2.0
along with more detail about why it is superior to traditional stopwatch
programs later on
in this article as well in
the interview with Thomas
Other Methods - Oscilloscopes
Some websites take this
whole area one step further and even use an oscilloscope and photosensor to
measure the input lag of a display. This is of course an even more precise
measurement and can help you show the true image lag along with the typical
response times of a pixel transition. This is then used to give you both the
overall experienced 'lag' of the image and the lag specifically between the
electronics and the pixel change instruction (the pure signal processing time).
It is the total of the signal processing lag and the pixel response time which
gives you a measurement of the perceived and experienced delay of a TFT compared
with a CRT.
We do not have access to such a method and the costs are extremely high for such
devices. If you are particularly bothered about input lag then I would encourage
you to compare results between sources and refer to other review sites as well
where methods like this are used.
Tektronix DSA71254 oscilloscope used in Thomas'
input lag studies
Keep in mind that even
with high-end measurement equipment there is no standardised measurement method
that exactly describes what has to be measured to be called 'input lag' or 'display
lag'. There is no rule that forces testers
to imply or to separate the response time from the raw processing time. Don't
fool yourself by taking measurements that show the raw processing time without
response time and believing that this would be the time you see a new picture in
Be careful when taking
these measurements that the definition of the 'input lag' figure quoted is
clear. Results using these methods may also differ depending on the measurement
equipment used, especially the optical sensors.
In Summary -
A New Input Lag Testing Method
The SMTT stopwatch method
will give a more accurate indication of a screens input lag compared with older
stopwatch methods. It offers many advantages to overcome the errors associated
with older methods and v2.0 has made some great improvements compared with older
versions. The results from our tests will measure the value of a delay between
the image content displayed visibly on each screen and should give you a good
indication of the perceived and experienced lag between a TFT and a CRT display.
Above: input lag
testing methods compared by Thomas Thiemann
As part of Thomas Thiemann's studies he has tested
the input lag measurements across various different techniques and the results
are shown above as an example from the NEC LCD2690WUXi monitor. This provides
the results recorded using an oscilloscope method, SMTT v2, SMTT v1 and then
traditional stopwatch methods both with V-sync disabled and enabled. As you can
see, SMTT 2.0 provides a very good level of accuracy and has made some
noticeable improvements over v1.0 as well. We don't want to over-praise
SMTT though as a well done oscilloscope measurement with high end equipment is
superior to SMTT and any other photo-based test. However, SMTT 2.0 is very
close to the results from an oscilloscope if you add the response time
measurement to the signal processing time. It is much better than any plain
stopwatch test or a "time code" (which is nothing else than a pre-recorded
single stopwatch) as these comparisons show and for the reasons discussed in
For our reviews we have also introduced a
broader classification system for these results to help account for any
remaining error in the method and classify each screen as one of the following
16ms / 1 frame lag - should be fine for gamers, even at high levels
2) A lag of
16 - 32ms / One to two frames - moderate lag but should be fine for many
A lag of more than 32ms / more than 2 frames - Some noticeable lag in daily
usage, not suitable for high end gaming
with the Author of SMTT
What is SMTT designed to do?
SMTT is a multipurpose monitor test tool. The combination of implied test
screens and interactive tests should help end users and editorial writers to
rate the display quality of a monitor. Including input lag measurements,
scaling, colour differentiation and colour resolution for 8 bit and 10 bit
The HPC (High Precision
Counter) test to determine the input lag, also known as display lag, outperforms
any other plain stopwatch application available and produces almost oscilloscope-grade results while keeping the costs at a reasonable level. Therefore it does
not only help reviewers to rate a monitor, gamers can use it as well to rate
their monitor. All that is needed is a CRT and a camera with adjustable fast shutter
The Gradients help to rate
the basic colour reproduction and differentiation in all colour shades. If your
monitor is prone to clipping colours at the upper or lower end of a gradient or
if banding within linear colour ramps is an issue you will find it with ease.
You may also set the part of the ramp to be displayed by selecting the starting
and end colour of the gradient on screen to magnify the area of interest.
The Deep Color Test is, as
far as I know, still unique. I am one of the happy people that have access to
NVIDIA Quadro graphics cards that are able to reproduce 10 bit per colour if you
have a proper display connected. But there is no test pattern available. Neither
in the driver nor in the software deployed with the monitor. Displaying a plain
image is always risky as the software may be limited to 8 bit colour processing
or the colour management of the software or operating system may cause strange
colour shifts and other effects like colour clipping and banding which may
reduce the number of colours that are finally displayed on screen. All of these
mentioned problems are circumvented accessing the output directly. The deep
colour test pattern is easy to evaluate. You won’t need more than five to ten
seconds to find out if your display shows an 8 bit output or a 10 bit output.
And there are the new
scaling test screens that offer some nifty little details that assist the
reviewer for multimedia monitors and TV sets to rate the scaling performance.
When I had to test the scaling performance myself I wished to have a clear
display for the cut off pixels. Usual test screens offered e.g. white arrows
without a clear mark at their tip. Displayed at the outer pixels of the screen
it was often hard to say if the first pixel at the arrowhead was still displayed
or already cut off. The new scaling test patterns do not suffer from this
Why is SMTT 2.0 better than other stopwatch programs?
There are several reasons. At first all other approaches to measure input lag
with one stopwatch or time code on screen assume that two displays that are
connected to the same graphics card and setup to run in clone mode are totally
synchronized. That means that they assume that the vertical sync signal which
introduces every new frame is being sent at the same time to both monitors and
that both monitors run at the very same frequency.
During my studies I tested
this assumption as one of the first and realized that it is absolutely wrong.
Connecting a TFT with the digital DVI-D and a CRT using analogue D-Sub cabling
to a graphics card caused the monitors to have unsynchronized vertical sync
pulses and slightly different frequencies depending on the used graphics card.
Using a high end
oscilloscope, like the Tektronix DSA71254 that I used, offers the ability to
trigger on the unique bit stream inside the digital TMDS (transition minimized
differential signal) 8b/10b coded signal that represents the v-sync pulse. When
you assume that both signals are totally synchronized both v-sync pulses should
be transferred synchronized or with negligible delay. But that’s not the case.
If you use the very same hardware and just unplug the CRT and reconnect it to
the computer the vertical sync pulse is set to a new random point of time. This
may fit to the v-sync within the digital signal or it may differ by any amount
within a range of zero to 16.6 ms.
Figure Analogue v-sync 5.2 ms ahead of digital v-sync.2 (right):
Analogue v-sync 3.1 ms delayed after reconnection. Click for larger versions.
As long as the frequencies
are identical you can randomize the v-sync lag by reconnecting the monitor.
Depending on the drivers it may be even enough to disable the secondary display
and enable it again. If this is taken into account for display lag measurements
you have the first reason why measurements with single stopwatches may differ by
up to 16.6 ms. It just depends on the time the monitor is activated.
But the frequencies may be
slightly off as well. You setup both monitors to run at 60 Hz as usual but the
frequencies are just close to 60 Hz. In these cases the relative positions from
analogue v-sync to digital v-sync differ slightly from frame to frame. Depending
on the actual difference it may take several seconds or even minutes until the
v-sync signals pass each other for the next time. In the example the difference
is 0.02 Hz. With every frame the temporal difference between the v-sync pulses
grows as the faster signal advances by 1/3001 of a single frame. It takes about
50s until the higher frequency signal is that far ahead that it reaches the next
frame. Of course the signal is not travelling to the future – it has to display
the same frame two times causing the advance to be reduced by 16.6 ms.
Frame rate within the digital signal: 60.02 Hz. Figure 4 (right):
Frame rate within the analogue signal: 60.04 Hz. Click for larger versions.
The point of this is that
the delay shifts over time. If you take your photos at the beginning there will
be almost no delay, if you wait 20s there will be a mediocre delay and if you
take your photo at the end of such a period you will encounter the maximum
delay. But this has nothing to do with the display lag. It’s caused by the
graphics card but not by the internal signal processing of the monitor. The
signals that were presented before are taken both from the input side of the
So the most important
assumption for a plain single stopwatch based measurement has been disproved. It
does not matter where you place the stopwatch on screen: On top, in the middle
or at the end of the screen. It does not matter what time source you use: A
stopwatch application, a time code from a video or whatever. When the first
monitor starts updating its content the other monitor will most likely update
some other part of the screen. As screen updates are done pixel by pixel, line
by line from the upper left hand to the lower right one of the attached monitors
may update the first few lines of the screen while the other is updating some
lines at the lower half.
This fact opposes up to
three different update areas on one screen to the same number of areas on the
second screen. Depending on the position of the single stopwatch and the exact
point of time the photo is taken you will measure one of the possible three
measurement results. Almost totally random but affected by the speed of your
camera and used graphics card.
Opposing update areas with activated v-sync.
This example is taken with
the old version of SMTT just for display purposes. Consider each line to
represent the possible position of a single stopwatch on screen.
In the area marked with a
green “A” you compare the updated area of the CRT with the updated area of the
TFT. The values are identical as vertical sync forces one screen buffer to be
kept as long as needed until the screens are completely updated. In this case it
does not mean that the TFT has no input lag it just means that the input lag is
not “several frames” long.
In the area marked with
the red “B” you compare the old screen content of the CRT with the already
updated new content of the TFT. In this case the TFT seems to be ahead of the
CRT! I can assure you that the CRT has been tested for input lag and that it
does not have any remarkable input lag that could cause this delay. It is just
caused by the temporal difference of the screen refresh caused by asynchronous
Area “C” is almost like
Area “A”, just that it opposes two old frames. The added thick yellow
bars represent the actual position of the screen update. These positions change
over time, they are of course not fixed. The figure is just an example for a
specific point of time.
Now consider to place your
plain stopwatch application at the top of the monitor: It will show no lag at
the given point of time the example deals with. But what if your stopwatch is in
the middle of the screen, in Area “B”? You will see 16 ms of “negative lag”.
That is of course impossible. If this TFT would have 16 ms true input lag it
would show 0 ms in the middle of the screen. This would make the tester to feel
much more comfortable but would still be wrong.
In fact it does not matter
where you place your stopwatch. The results will not represent the input lag of
the monitor but signal delay + input lag + response time + x. That’s one of the reasons
why SMTT displays many counters on screen (without v-sync): No matter at which
position the monitor is updating its content it will always present the most
up-to-date value that was available at that position of the update process. So
the missing synchronization is a non-issue using SMTT.
Usual stopwatches are
running as plain applications on the desktop or even in the browser using flash
for their output. Flash has a very harsh limitation in terms of the speed the
code is processed: It is run once per frame of the output. The problem is that
the maximum frame rate of flash is limited. The highest frame rate that I could
reproduce with flash was at 120 frames per second. Usual Flash based programs
run at much lower frequencies, some browsers limit Flash to 60 Hz that is
reasonable for usual flash based applications and 60 Hz as typical screen
refresh rate. So the maximum theoretical precision of a flash based stopwatch is
limited to 1/120 s. Displaying three digits after full seconds means 1/1000 s or
single milliseconds. Offering an accuracy that is 8 times worse is somehow
strange but no one seems to care.
Even if you do not use
flash most stopwatches are bound to the 2D refresh rate of the Desktop. Well, to
be more precise: All are bound to the 60 Hz of your monitor for their output but
many of them may be bound to their precision to the same update rate. It does
not matter how great your programming skills are: One value on screen will be
updated only once during every screen update that takes place every 16.67 ms if
you are running a monitor at 60 Hz. You are already lucky if this very special
value is up to date. During my tests I realized that the Windows desktop seems
to use some sort of v-sync that can’t be disabled. Remember that the V-Sync
setting in the driver of your graphics card is meant for 3D only.
I was told to use a
stopwatch once that used a font which looked like an old fashioned seven segment
display. Even such little things like a bad font may causes problems. At that
time I tested some monitors that had a relaxed response time so that two
subsequent frames overlapped. I recognized that the values I wrote down
accumulated the numbers 8 or 9 as last digit.
Accumulation of values using improper fonts.
The given example shows
overlapping of the digit “4” with all other possible values. As you can see there is
just one overlapping (underscore) that does not look like a valid digit. This is
an optical effect. The CRT won’t show the overlapping but the TFT will. Using such
digits on a single stopwatch with a fixed position will add some randomness in
the lag by wrong readings.
And there are more traps
to fall in. Did you know that the timer inside of every operating system which
counts the passed milliseconds is not updated every millisecond? Using
Microsofts Sysinternals ClockRes you can check the timer resolution of your
system. Usually the resolution of this timer is somewhere between 10 ms and 16
System clock resolution displayed by Sysinternals ClockRes
So using the so called
“system ticks” as time reference for a stopwatch is OK as long as you do not
want to get a temporal resolution of milliseconds. SMTT uses high precision
timers that offer much higher precision than needed and are updated often enough
to resolve milliseconds.
So with a plain stopwatch
you get a single counter somewhere on screen whose output is updated every 16
milliseconds during the screen refresh showing the content that has been stored
in the screen buffer for up to 16 milliseconds and that may be calculated with a
temporal precision of another 16 milliseconds, depending on the used code. Maybe
based on system ticks with a resolution of about 16 ms. Lots of potential errors
that can sum up to a total error you can’t get rid off by taking the average of
your measurements. SMTT updates its high
precision counters with every frame while running at several thousand frames per
second. It is of course impossible to display more than 60 frames per second on
a screen that runs at 60 Hz per second but each displayed picture on your
monitor that is the results of the SMTT output is a patchwork that consists of
approximately 32 pieces from different frames, assuming SMTT to run at 2000 fps.
Such high frame rates are quite usual for SMTT 2.0.
SMTT does not need to take
control of the picture processing time inside the graphics card. All that is
needed is a regular and high-speed update of the output buffer that is accessed
by both monitors. While the content of the buffer is transferred to the monitors
it is still updated. What would cause so called tearing in a game is used to
display many values line by line during one update process. All you have to do
is disable v-sync for 3D output. High precision counters,
optimized high speed code and several thousand updates per second try to
guarantee true millisecond precision on screen.
On the other hand you have
to consider that Microsoft Windows is no “real time operating system”. There is
no guarantee that a given task will be performed during a fixed period of time.
So SMTT may suffer from slight fluctuations if there are other tasks that
interrupt the processing. But if you take a look at
a picture that has been taken from the SMTT HPC test you will recognize that the
values are updated every single millisecond almost every time. So all you have to do is
to find and compare the most up-to-date values on both screens. These are most
likely not at the same position on the screen, but that is intentional. You
compare last-displayed values that represent the lag difference between the
monitors instead of additional lags that are caused by asynchronous graphic
outputs, inaccurate programming or vertical sync offsets.
What’s been improved in v2
Thiemann: Well, I had to start from scratch as the old DirectX 9 based
code could not be updated to DirectX 10 or DirectX 11. The last versions of SMTT
v1 featured a HPC test that was strictly DirectX 9.0 based which used sprites
for text rendering while the old Deep Colour tests used DirectX 10 as colour
depths of 10 bit per component are not supported by DirectX 9. That was hard to
maintain and prone to cause errors on the long run. A simple switch to DirectX
10 was impossible because sprites are not supported in DirectX 10. I was stuck
between two features that could not be run from the same code basis. Now the
code is written for DirectX 11 but uses DirectX 10.0 features only. The sprites
have been removed with my own bitmap font that improves the display performance.
SMTT 2.0 does no longer
have any known memory leaks. So you may try to start the tests as often as you
like without any crashes. The graphical user interface has been redesigned to
offer the highest possible ease of use and needed precision for adjustments
without being too complex or looking overcrowded. There is a setup process that
checks for software requirements and tries to resolve them if needed. The High
Precision Counters are optimized to run at even higher frame rates than they
used to and the accuracy has been improved with I.R.O.N.. And there are the
complete new scaling tests and the easier to use deep colour tests. Even a
display issue with the deep colour map has been resolved.
Well, almost everything
has been improved without sacrificing the key features. The software is still
easy to handle, small, does not “call home”, it does not collect your data. It
is still a small monitor test tool.
Tell us more about I.R.O.N.?
I.R.O.N. stands for improved readability of numbers. This new display technique
adds column switches every 16 ms to the output of the counters on the screen to
omit any overlapping of the displayed values which reduces the time needed in
the evaluation process and increases the accuracy of the readings. SMTT v1
displayed two columns displaying identical values on both sides of the screen.
It was meant to be symmetrical so that the reviewer could place his CRT on the
left or the right side of the TFT. You could zoom in to the area where the
monitor frames touched one another and still had all counters visible. Well,
that’s the theory. The problem was the latency of the TFT displays. Several
values overlapped causing complicated readings that were prone to errors,
reviewers to “guess” values or to waste a lot a time finding an up to date
I.R.O.N. avoids these
overlapping values. Depending on the intensity of the text you can easily
determine which values are new or old and it is easy to find the most actual
value on screen – the value that is needed to determine the input lag of the
monitor. Improved speed for each evaluation and higher accuracy by improved
What is coming up next?
There is a 32 bit version planned for Vista and Windows 7. The most time
consuming work for a 32 bit version will be the setup process. SMTT code is licensed by
an American start-up with great experience in game development that may
incorporate SMTT core functionality and know-how to future game development
platforms for reducing the overall lag you experience in computer games. SMTT is programmed on a
modular basis and it is designed to be extended in the future. Therefore
additional features are possible in upcoming versions of SMTT.
Hopefully this article has given you a good
insight in to how input lag can be measured and the various pros and cons of
each method which can be used. I'd like to thank Thomas Thiemann for his input
and thoughts on the matter and would recommend you also read his other studies
which have already been linked to in this review over at Prad.de. As the studies
have shown, there are a lot of possible issues with traditional simple stopwatch
methods which can result in a varying degree of error. This is more apparent if
you then try to compare the results between different sources and different
methods. SMTT v1.0 made some good improvements to the stopwatch method although
had some initial limitations with its use, mainly around readability and some
possible interpretation errors. SMTT v2.0 is a great improvement offering a host
of updates to make measurement of input lag easier and more accurate, and also
providing some new useful tools for testing your display. An oscilloscope can
offer a higher level of accuracy if it is well defined and the equipment is of a
high standard. Be wary of input lag figures though which crop up without
explanation as to how they were obtained as there is no defined standard for
what input lag is when using these kind of tools. Overall as long as the signal
processing time and pixel response time are accounted for then an oscilloscope
should provide a very high level of accuracy and a good measurement of the lag
experienced by the end user of the display.
Through Thomas' tests and in his production of
SMTT 2.0 he has managed to create a very useful tool for measuring input lag
without the need for very expensive equipment like this, and also providing a
high level of accuracy even when compared with such a method.
It is acknowledged that
this tool provides the ideal photo method for measuring input lag and so we will
be using this method in our tests to help improve accuracy from now on and in
the absence at the moment of very expensive oscilloscope methods.
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SMTT - Thomas Thiemann,
Input Lag Tests and Studies -
Prad.de (Thomas Thiemann, translated version)
Input Lag Tests and Studies -
Prad.de (Thomas Thiemann,
original language version)