Keeping Pace with TV Refresh Rates - The New Numbers

View slideshow for list and details on 9 LCD and plasma models which contain 72 or 120 Hertz technology.

Frames per second and 120 Hertz? What you now need to know when shopping for a TV.

It used to be a lot easier to buy a TV. You didn’t have to weigh the technical merits of plasma versus LCD or versus DLP or versus D-ILA for that matter. You just looked at tube TVs and chose on the basis of picture quality, price and a feature or two.

These days you face a dizzying array of specs that read more like a scientific experiment than a feature list for an entertainment device. To make it worse, in an effort to one up the other guy, manufacturers give splashy (or not) names to features when a generic label would do.

120 Hz is one of the hot new features. It refers to the refresh rate, or the speed at which a display is redrawn every second, measured in Hertz. Refresh rate has become an issue for LCD TVs, which by nature lag behind plasma and DLP in their ability to reproduce fast motion without blurring.

We discussed the issue with Scott Ramirez, TV marketing VP at Toshiba, who explains it this way. “The refresh rate for a normal LCD TV is 60 Hz, which means 60 frames per second,” he says. “Every 1/60th of a second the panel puts a pixel there and holds it. If an object was moving across the screen it might not be in the same spot during the next refresh, and that’s when your eye might notice movement.”

The way to eliminate the blur (which only occurs on fast action and scrolling text) is to double the number of frames, Ramirez says. “If you have 120 frames, nothing is held for more than 1/120th of a second. In that amount of time, your brain doesn’t register the blur.” Of course, even with a 120-Hz refresh rate, you’re not watching linear motion at all. It’s all illusion, whether you’re viewing video or film. “You have pixels coming at 1/60 or 1/120 of a second,” Ramirez says, “and we only perceive motion.”

Refresh rate is especially important today with the advent of HD DVD and Blu-ray discs which are transferred to video in their native 24 frame-per-second frame rate. “When a movie is made into Blu-ray or HD DVD, it’s done at 1080p and 24 fps,” says Chris Walker, senior manager of product planning and marketing at Pioneer. “Trouble is, our TV system for the last 50 years has operated at 30 frames per second. So the player has to add additional frames that weren’t there for every second of video.”

That’s how 3:2 pulldown came about years ago and it affects all types of TVs, not just LCD. With 3:2 pulldown, engineers compensate for the difference between film recorded at 24 frames per second and the TV standard’s 30-frame-per-second frame rate. They did so by breaking the frame into fields and reorganizing those fields to end up with 30 frames per second. The trouble with 3:2 pulldown is it leaves stuttering artifacts called “judder.”

“If you have a TV that can actually reproduce the original 24-frame-per-second signal and triple it or quadruple it to 72 Hz or 120 Hz, then panning will look much smoother,” says Walker of Pioneer. Pioneer’s high-end plasma TVs use a 72-Hz refresh rate.

Other manufacturers are taking on response time and motion artifacts with a variety of solutions, each with its own catchy tag. Samsung developed a technology called Auto Motion Plus 120Hz in which the motion artifacts on an LCD are minimized by interpolation rather than frame repetition. Hitachi’s Reel60 uses its own method of interpolation to eliminate the jitters.

Bottom line: Look at the pictures rather than studying the specs. Says Bill Whalen, director of product development for Hitachi: “Consumers should stay away from the marketing numbers as much as possible because they’re not a reliable way to compare products. They should trust their own eyes when viewing products at the retail store.”