Response time stutter is an artifact of motion that happens when a frame stays on the screen for too long. It can be bothersome while watching movies or other low frame rate content because the TV has to hold each frame on longer. Stutter has an inverse relationship with a TV's response time; the quicker the response time, the more stutter there is, while a slower response time results in less stutter.
Test results
Test Methodology Coverage
Our Stutter test was initially added as part of our 1.2 test methodology. No significant changes have been made to the test since then, but we slightly changed the way we calculate stutter in our TV 2.0 update after making changes to our response time test. Instead of using the 100% Response Time result we used in our old testing methods, we now use the First Response Time result to calculate stutter. We also updated the scoring weights and spline to focus more on 24 fps stutter, as 60 fps stutter is almost never an issue. Because of these changes, you can't directly compare the scores and results for stutter between TVs tested before 2.0 and TVs tested after. However, the results are still close enough across all test methodologies that you can still get a good idea of how much response time stutter a TV has by looking at the results.
The test was recently renamed to 'Response Time Stutter' as part of our TV 2.1 update. This was done to make the test more self-explanatory and to better separate stutter from judder, since the two terms are often used interchangeably when they're actually different aspects of motion. This change didn't impact our results or scoring for response time stutter. Learn how our test benches and scoring system work.
| Test | 1.10 | 1.11 | 1.12 | 2.0 | 2.1 |
|---|---|---|---|---|---|
| Frame Hold Time @ 24 fps | ❌ | ❌ | ❌ | ✅ | ✅ |
| Frame Hold Time @ 60 fps | ❌ | ❌ | ❌ | ✅ | ✅ |
When It Matters
Not everyone will notice response time stutter, but if you do, you'll notice that camera movement looks jarring and uneven during long panning shots. Stutter has an inverse relationship with response time, so it's often a trade-off between having little stutter or a quick response time. Since there are ways to help reduce stutter, having a TV with a quick response time is almost always a better choice.
Above, you can see an example of stutter. The TV on the left has a quick response time, so there's no motion blur behind fast-moving objects, but the shot looks more jarring as each frame is held longer. On the right, the response time is much slower, so there's blur trail behind the ball, but the overall movement in the shot is smoother. You should easily see the difference if you pay attention to the plant in the foreground. Although response time stutter is more pronounced on TVs with very fast response times, such as OLEDs, most modern TVs exhibit at least some stutter since response times have gotten pretty quick on TVs overall. You won't notice stutter during most scenes, but it's most noticeable during scenes with slow camera movements, like a slow panning shot across a landscape.
Our Tests
Unlike most of our tests, stutter isn't measured directly on the TV. Instead, it's calculated from the TV's response time. The response time is the amount of time it takes for pixels to change from one color to the next. However, if the colors transition too quickly, they stay on the screen before transitioning to the next frame.
For the stutter tests, we calculate it for 24 and 60 fps content, but you can also use basic math if you want to find out the stutter with 30 fps content.
Frame Hold Time @ 24 fps
For 24p content (like movies), the signal sends 24 frames every second. Since there are 1000 milliseconds in a second, each frame is held on for 41.67 ms. To calculate for stutter, we simply take that time and subtract the TV's first response time from it. Taking the Sony X90L as an example, it has a first response time of 6.1ms. Subtracting that from the frame time of 41.67 gives us a frame hold time of 35.6 ms. This means that when watching 24p content, the image is static for approximately 85% of the time, resulting in noticeable stutter in scenes with slow camera movements.
Frame Hold Time @ 60 fps
The frame hold time @ 60 fps is calculated the same way as the 24 fps test but with a frame time of 16.67 ms instead. 60 fps stutter is almost never an issue since, even with an instantaneous response time, the frame is being redrawn often enough that most people won't notice it.
Why Do Modern TVs Have Stutter?
We mentioned above that stutter is directly related to a TV's response time, but why is that? It's all about the panel technology. Modern TVs all use a technique known as sample-and-hold to display an image. This means that once the pixels that make up a TV's image have drawn a frame, they remain static until it's time to draw the next one. It takes some time for a pixel to change from one color to the next; that time is known as its response time. The faster the response time, the longer that pixel remains fixed until it's time to change to the next color. The human eye doesn't expect motion to jump this way from one frame to the next; it expects motion to be fluid, so the longer the frame is held static on the screen, the more it'll appear to stutter.
This differs from older TV technologies like plasma and cathode ray tubes, which used short light bursts to produce an image instead. These older technologies are completely stutter-free, as they don't use sample-and-hold at all. This means that if you're upgrading from a plasma TV, for example, you'll likely be even more sensitive to stutter, and TVs with fast response times like OLEDs may actually appear to have choppier motion when watching movies and shows than your much older plasma.
You can learn more about stutter and motion in general through our series of videos on our Home Theater YouTube channel, starting with the first entry linked below.
How To Get The Best Results
While you can't change the TV's response time, there are a few settings that can help reduce stutter if it bothers you.
Motion interpolation
Motion interpolation is probably the best way to reduce stutter. This feature increases the frame rate of the video signal to a higher one. If you have a 120Hz TV and you're watching 24 fps content, increasing the frame rate can help reduce stutter because each frame isn't held on for as long. It doesn't change the response time, but it reduces the total time each frame remains on the screen. However, using motion interpolation too aggressively leads to the dreaded soap opera effect and distracting artifacts in the image.
Click here to learn more about motion interpolation.
Backlight strobing
Some LED TVs have a feature called backlight strobing, which is also known as black frame insertion (BFI) on OLEDs. LED TVs can flicker their backlight to help reduce the amount of blur trail behind each object. Although this isn't a direct way to decrease the amount of stutter, it decreases the amount of time each frame is shown on the screen. Overall, the point of the BFI feature is to improve the appearance of motion.
Click here to learn more about black frame insertion.
Judder removal
Judder and stutter, although they sound similar, aren't the same thing. Stutter is about the amount of time each frame is held on for after the pixels transition, while judder is an inconsistent frame time. There's also micro-judder, which affects the appearance of motion, but is caused by dropped frames during scenes with complex motion
Click here to learn more about judder and micro-judder.
Conclusion
Response time stutter can be distracting while watching low frame rate content, such as movies. It happens when a TV has a quick response time, as the pixels transition colors quickly, but then the TV has to hold the frame for a few milliseconds before showing the next. We measure stutter using a simple calculation from the response time, as stutter and the response time have an inverse relationship. There are a few settings to help reduce the amount of stutter, like motion interpolation, but there's no perfect solution to eliminate response time stutter on modern displays.