Touch Latency Vs Screen Latency. Which is more important?

Each new smartphone these days is marketing either a 120Hz refresh rate or 240HZ touch sensing. While this is impressive and all. But what do these terms mean for an average consumer or even power users?

Do these terms benefit you at all in your daily usage or is it just a new way to sell smartphones at an expensive price tag.

More specifically, if you had to choose between a better touch response or a better refresh rate, which one should you choose?

Touch Latency

Touch response rate, touch sensing, touch response, and touch latency represents more or less the same thing in the real world. They are not exactly the same but their impact in the real-world is similar.

The sampling rate means the frequency at which the touchscreen tracks the movement of your fingers. Higher the sampling rate, lower the latency.

You can measure the difference in the sampling rate and how it relates to latency and responsiveness but it requires more than just running your finger on the screen and slowing it down to view the difference.

When you tap or touch your smartphone, you are expecting it to respond to your touches instantly. But it is not the case, there is a delay between when you touch your smartphone and when it executes the specified command. This is called touch latency.

Touch latency is the time between when you tap on the screen and when your touch is registered on the device. You can’t actually view the touch latency because when you tap on the screen, the display renders the frame accordingly and show it to you. You only get the results when the render is complete and not the process.

There are a lot of processes in between which adds additional delay. These processes may be touch sensing hardware, application or operating system, display driver and graphics output.

For simplicity, you can assume the kernel is the operating system (Android or iOS), the touch is the touch sensing hardware.

The touch sensing hardware commands go to the kernel. The Kernel then executes the commands on the hardware or SOC. The hardware components then display the results on the output display.

How fast the output display can show those results depends on the refresh rate.

The touch sample rate of a typical smartphone these days is 60HZ. If the touch sample is not written, it will probably be 60Hz. Hertz (Hz) is the unit of frequency and the reciprocal of frequency is time.

So, 1/60=16.67ms is the time a smartphone should take to register a touch. But the lowest touch latency we have ever seen is in the Asus ROG Phone 2 which is 49ms. In an ideal scenario, it should be 16.67ms but due to the delay in the execution of commands from hardware to software and back to the output device which is also hardware, it is not possible.

It is important to point that this is the first time any device has beaten the iPhone in touch latency after a long time.

Gamebench did a detailed touch latency comparison between iPhone XS Max and Samsung Note 10. They ran different games on both smartphones and tested the touch latency during gameplay. Gamebench is trying to set a standard for touch latency and this is what they came up with.

The average touch latency of an iPhone XS Max during gaming is 88ms and the average touch latency of Samsung Note 10 during gaming is 86.2ms. I just took the average of the touch latencies for both smartphones in all the games to get these numbers.

It is important to point out here that the iPhone XS Max has 120Hz sensing and Samsung Note 10 has 60Hz touch sensing. Still, the Samsung Note 10 was able to beat iPhone XS Max in touch latency. We are testing a gaming load and the Samsung Note 10 hardware is better at this load which is one reason why it has lower latency to execute the whole process.

Gaming performance varies from smartphone to smartphone. I have explained it here all the factors that might affect a smartphone gaming performance.

This further proves that just adding a better touch sensing hardware is not the only way to improve touch latency.

A lower Touch latency represents a better-optimized software for hardware on a specific application or task. In this case, Samsung Note 10 is better optimized for gaming than iPhone XS Max. This also does not mean that the touch latency of the Samsung Note 10 would be better than the touch latency of the iPhone XS in every application and task.

To be fair, Samsung Note 10 was released in 2019 and iPhone XS Max was released in 2018.

Refresh Rate

Screen Latency also is known as Refresh Rate.

Displays are not static. The refresh rate is actually the blinking rate of our smartphone displays. A smartphone blinks so fast that it appears stationary to us.

Normally the refresh rate is 60Hz which means that the display updates the content on the screen 60 times every second.

The content that we see on a smartphone display are still pictures. When a lot of pictures are shown in one second, the picture appears to be a video. Normally, our smartphone displays show us 60 pictures or Frames per second (FPS) to give us the illusion of a smooth video.

The refresh rate and the frames per second (FPS) are two different terms. the FPS means how many images the display can output per second while the refresh rate means how many times a display can refresh the image. A 60Hz display can output frames higher than 60 easily. For more information on the FPS VS Refresh rate, click here.

The only drawback is if the FPS is a lot higher than the refresh rate of the screen, there will be screen tearing.

The refresh of almost all the display until 2018 was only 60Hz. In 2019, the Google Pixel 4 and 4Xl and OnePlus 7 Pro had 90Hz. In 2020, more and more smartphone manufacturers are putting higher refresh rates on their display.

Check out the list of smartphones with higher refresh rates.

Now that basic stuff is out of the way, let’s go into numbers.

Suppose a 60Hz screen has to display 60 FPS, it would refresh a frame every 1/60=16.67ms and therefore 60 FPS every second. If the hardware of the smartphone is not capable enough to produce 60 FPS, and let’s assume it outputs 30 FPS, the display would refresh half a frame every 16.67ms or one frame every 33.34ms.

The display would have no problem refreshing a frame a little slower than 16.67ms but the display can not refresh a frame faster than 16.67ms. Therefore, if the hardware is producing 90 FPS on a 60Hz refresh rate display. The display would have to display 1.5 frames every 16.67ms which is not possible. In this scenario, the display would show parts of 1.5 frames in one frame and display it in 16.67ms, this is the cause of screen tearing.

Now if we increase the refresh rate to 90Hz, the display can refresh a frame every 11.1 ms. At 120Hz, the display can refresh frames every 8.3ms. Just watch the video below to understand how the fluidity or smoothness changes as we increase the refresh rates of a display.

If you have no idea about your smartphone or computer display refresh rate and want to calculate the refresh rate. You can do so by going to this website testufo. I can not guarantee the website is 100% accurate but it worked correctly for my computer and different smartphone displays.

Touch Latency vs Refresh Rate

We know that touch latency and refresh rate are two completely different terms. Apple iPhones have 120Hz touch-sensing but 60Hz display, Google Pixel and OnePlus 7 Pro have 90Hz display but 60Hz touch sensing.

Which one of these combinations should provide a more fluid experience.

Smartphones	Touch Sample Rate (frequency)	Touch Sample Time (milliseconds)	Display Refresh Rate (frequency)	Display Refresh Time (milliseconds)
Samsung S20	60 Hz	16.67 ms	120 Hz	8.33 ms
ASUS ROG Phone 2	240 Hz	4.167 ms	120 Hz	8.33 ms
One Plus 7T	60 Hz	16.67 ms	90 Hz	11.11 ms
Realme X2 Pro	60 Hz	16.67 ms	90 Hz	11.11 ms
Xiaomi Poco X2	60 Hz	16.67 ms	120 Hz	8.33 ms
Xiaomi Mi 10 Pro 5G	180 Hz	5.55 ms	90 Hz	11.11 ms
Nubia Red Magic 3s	60 Hz	16.67 ms	90 Hz	11.11 ms
Oppo Reno 3 Pro	60 Hz	16.67 ms	90 Hz	11.11 ms
Google Pixel 4 and 4XL	60 Hz	16.67 ms	90 Hz	11.11 ms
Sharp Aquos R3	60 Hz	16.67 ms	120 Hz	8.33 ms
Razer Phone 2	60 Hz	16.67 ms	120 Hz	8.33 ms

When we press or tap on the screen, after the touch is registered, the hardware starts rendering the frames and then display the frames as output. If we reduce the touch latency, the frames would start rendering faster. But the time to display the frames is always fixed.

A 60Hz display refreshes 60 times in one second, a 90Hz display refreshes 90 times in one second, a 120 Hz display refreshes 120 times in one second. The more refresh rate a display has, the smoother it will feel. A higher display refresh rate means more refreshes at the same time. But it does not reduce the rendering time of a frame.

If we had to display 60 FPS on different refresh rates (60Hz,90Hz,120Hz), there would be no difference in fluidity or time required to display those frames.

But if we reduce touch latency, the touch would be registered faster by the OS and the hardware would start rendering the frame a little bit faster. For 60 FPS only, reducing the touch latency would improve the smoothness of the device and increasing the refresh rate would not provide any benefits.

This is exactly the case with iPhone XS Max Pro. A guy on Youtube tested OnePlus 7 Pro (90Hz) vs iPhone XS Max(60Hz) display latency and the iPhone won. This is surprising because the iPhone XS Max has a 60Hz display vs OnePlus 7 Pro 90 Hz display.

Please do not think, this would always be the case. The thing is OnePlus 7 Pro touch latency is really bad and touch latency on iPhone XS Max is phenomenal. But I wanted to show that the huge difference in touch latency causes the OnePlus 7 Pro to lose in actual screen latency because of all the factors I explained earlier.

Also, measuring smartphone latency by just looking at the touch latency and screen latency is not the right way. There are of other things in a smartphone that causes delay. The major ones are the Operating System, how much is the software or application is optimized for specific hardware, hardware specifications and compatibility with the Kernel and how efficiently the Operating system executes all these commands.

Summary:

Suffice it to say, a smartphone is a complex item. Therefore, the performance and latency depend on various factors.

I have given two examples in this article:

1. Samsung Note 10 has 60Hz touch-sensing and it has beaten the iPhone XS Max which has 120 Hz touch-sensing in touch latency. TLDR: The touch latency of iPhone XS Max in gaming is 88ms and Samsung Note 10 has 86.2 ms touch latency in gaming.
2. The second example is the comparison between iPhone XS Max(60Hz) vs OnePlus 7 Pro(90Hz) screen latency. The OnePlus 7 Pro lost to iPhone XS Max in screen latency despite having a higher refresh rate.

For average consumers, if you had to pick one between touch latency(touch sensing) and screen latency (refresh rate), you should choose touch latency or touch sensing. The thing is, most smartphones may not even be able to produce 60 FPS and you need to be able to cross 60FPS to notice the difference between 60 Hz and 90 Hz. But having a more touch responsive smartphone is better in every scenario.

For Power users, I would say the touch sensing should be double the refresh rate to get the best results. Take the ASUS ROG Phone 2, touch sensing is 240 Hz and the screen refresh rate is 120Hz. But if we had to choose just one from the touch latency and screen latency, I would still pick touch latency because there is no point in having a better screen refresh rate if your touches are not registered fast enough to make the difference.

For all the people saying, 90Hz is not worth it. It is due to the other lag factors on a smartphone. Just putting a 90Hz display on a smartphone does not make it faster (looking at OnePlus). This is why I have concluded that lower touch latency should be given priority over higher refresh rates for now.