Stutter of TVs
Stutter on TVs influences how smooth motion appears on the screen. It is generally most visible in slow panning shots with low frame rate content such as movies and causes a regular pattern of jerkiness. This is different to judder, which is an irregular pattern of jerkiness caused by inconsistent frame cadence. For watching movies or even field sports, it is important to get a TV with low stutter.
To evaluate the stutter of TVs with 24fps and 60fps content, we use the response time to determine how long a static image is shown between frame transitions.
When it matters
Abrupt scene changes are not always noticeable. However, with low frame rate content such as movies and 30 fps video games, it can be distracting, causing jerky motion, which is especially visible on slow panning shots. In high frame rate content (such as sports or 60 fps games) it is less of an issue as each frame spends less time on the screen.
Too much stutter can ruin motion sequences as the image jerks across the screen with each frame transition. Some people are more sensitive to this and notice it more frequently with different content.
Frame Hold Time @ 24 fps
The response time for 24 fps transitions is measured as described in the response time test. The average of the 100% response time for each transition is used to determine the length of time that the image is transitioning between frames - where there will be some overlap between the previous frame, and the new frame to show. The amount of time that a static image is visible is the frame time (1000 ms / 24 frames = 41.67ms per frame) minus the transition time.
Frame Hold Time @ 60 fps
The same procedure is followed, as described in the Frame Hold Time @ 24 fps test. However, this time, the frame time is lower due to the higher frame rate of the content (60 frames per second). The amount of time that a static image is visible in this case is the frame time (1000ms / 60 frames = 16.67ms per frame) minus the transition time.
Causes of stutter
Stutter is caused by 3 main factors:
- The response time, which affects the amount of blur between frames. A longer response time will cause the frame transition period to be longer, and the length of the static frame to be shorter, which reduces stutter.
- The frame rate. A higher frame rate results in less time for each frame. This lower static frame time results in a smoother image with less stutter.
- Flicker. A flickering image causes the persistence of the static frame to be shorter, resulting in the appearance of less stutter.
How to get the best results
Unlike many monitors, the response time of TVs is generally fixed. For a TV or monitor, which does allow response time adjustments, a longer response time will result in a smoother image.
If possible, watching content at a higher frame rate will result in a smoother image. Many TVs also have settings which will directly or indirectly reduce stutter, as described below.
- Usually, the source content will have a fixed frame rate (24 fps for movies, 30 fps for TV shows and 60fps for sports). For many TVs, there is a motion interpolation option which creates intermediate frames, reducing the frame time. This does introduce artifacts though, as described here.
- Many TVs have the ability to introduce backlight flicker, either through PWM dimming of the backlight or with a specific black frame insertion feature. This reduces the time the static image is shown, reducing the appearance of stutter. See more about flicker here.
- Stutter shouldn't be confused with judder, which is a result of an inconsistent frame rate. Stutter is a result of low frame rate, but consistent frame timing.
- When compared to LCD TVs, OLED TVs are much more likely to suffer from noticeable stutter due to their almost instantaneous response time.
Stutter produces an image which appears to jump between frames and is much more noticeable for low frame rate content such as movies and 30 fps video games. To evaluate the stutter of a TV, we measure the response time which shows the transition time between frames and use this to determine the time that a static frame is shown, which depends on the frame rate of the content.
If you want the smoothest image possible, look for a TV which has a longer response time to extend the transition between frames. You can also help to reduce the amount of stutter by watching higher frame rate content, enabling motion interpolation, or by flickering the backlight. These workarounds do have other side-effects though.