Explaining "Refresh Rates" From 120 Hz to 240 Hz and Beyond
By Adrienne Maxwell
Many new LCD HDTVs offer a refresh rate of 120Hz or higher. The 120Hz technology is designed to accomplish two goals: to reduce motion blur in faster-moving scenes and to reduce judder in film-based sources. (See our article "Explaining a TV's refresh rate" for more information.) In most cases, the TV's setup menu includes the ability to turn the 120Hz features on and off. This begs the question, when should you use this technology? Logic would dictate that you'd always use it, since you've probably paid extra money to have it in the TV. The truth is, depending on how the 120Hz technology is implemented in your particular display--and how well it works--you may not always want to enable it.
Early 120Hz LCDs addressed the problem of motion blur by inserting black frames or repeating frames. In these TVs, it made sense to keep the feature enabled at all times, as the function did not affect the quality of motion. It just reduced the blur. That changed when manufacturers began to experiment with motion interpolation, where the video processor pulls information from existing frames to create the new frames. With film-based sources (like a movie on DVD or Blu-ray), motion interpolation changes the inherent look of the movie, eliminating the judder by producing a super-smooth effect that makes film look more like video. Whether or not you like this effect will dictate how you configure the TV's 120Hz settings.
Some LCD manufacturers divide the 120Hz function into two menu items. The first item is a basic on/off setting designed specifically to reduce motion blur. Toshiba's mode, for example, is called ClearFrame (or ClearScan in the company's 240Hz TVs). This setting can be left on at all times, as it doesn't change the quality of motion. If you're sensitive to motion blur in faster-moving action scenes and sports programming, you definitely want to enable this function, especially on a larger-screen TV. The second menu item is a de-judder mode that employs some type of motion interpolation. This function is intended for use with film sources. Toshiba calls this mode Film Stabilization. The menu may just include on/off settings, or it might offer different levels of smoothness, with low, medium, and/or high options. If you don't like the smoothing effects of motion interpolation, then you can just leave this mode off and still get the benefits of the anti-blur function. If you prefer (or at least don't mind) the look of motion-interpolated content, then it makes sense to activate the function when you're watching a film-based source. We should point out that some plasma TVs now incorporate a de-judder or smooth mode, even though they are not technically 120Hz displays.
Other LCD companies choose to offer a single 120Hz function that addresses both motion blur and film judder. You can't get the blur reduction without the de-judder control, so you had better like the smoothing effect. The menu usually contains multiple settings to dictate the level of smoothness; you can choose a low setting to minimize the effect, but it will still be present. Samsung, for instance, uses a combined 120Hz technology called Auto Motion Plus, with low, medium, high, and off settings. (Samsung's higher-end LED-based TVs include separate functions to address motion blur and film judder.)
Even if you like the effects of de-judder modes, the technology isn't necessarily suited to every source you watch. In general, de-judder functions perform their best with 1080p/24 Blu-ray signals. This is the purest film signal you can get, so it's the easiest for the TV's processor to handle. With 60Hz DVD and Blu-ray content, results can be mixed. In my experience, the most difficult content for a de-judder mode is a TV source. TV signals jump back and forth between film and video, and the inconsistent cadences seem to trip up many a de-judder mode. The function winds up adding more motion artifacts than it corrects, producing obvious smearing or choppiness in the signal. So, depending on how well your particular TV's de-judder modes perform, you might want to disable the function when you're watching TV signals. Some TVs allow you to set different 120Hz settings for each input, so you could turn off the de-judder mode for the TV source and turn it on for DVD/Blu-ray source. Or, if you're using an advanced control system, you can program it to automatically enable the de-judder mode for movie playback and disable it for TV playback.
Our recommendation is to experiment with a TV's 120Hz features before you buy it, using TV, DVD, and 24p Blu-ray sources. Make sure that you like the effects of the de-judder mode and that it performs well with the different sources you plan to watch. If you aren't satisfied with a certain TV's 120Hz implementation, there's no point in spending the extra money for a feature you won't use.
