TV Specs Demystified – Frame Rates
AKA scan rates or update rates
1080 – 24P – 60P – 120Hz – 240Hz – 480Hz
So you’re shopping for a new 1080P flat panel TV to upgrade your home theater, and one of the many confusing terms you see on all of these TVs is 24P, 60P, 120Hz, and 240Hz. And that is not the end. 480Hz is on the immediate horizon and there are some plasma TVs that feature “600Hz subfield drive”.
Well, like almost everything in life, it’s not what you do, it’s how you do it. 600 is only better than 60 if you do it right.
A bit of history in case you’re not a videophile. 24P means 24 frames per second (fps). That’s the frame rate most Hollywood movies are shot in. So each second of a movie is actually made up of 24 individual images. Television is a bit different. Most television shows are shot at 30 frames per second. The people in charge will tell you that there are very good reasons for the difference, but they are full of shit. They did it to piss us off.
The difference between 24 and 30 frames per second used to be a big deal in the days of CRT “tube” TVs, because it sucked, but now with today’s TVs, there’s a little less to suck. Today’s TVs have no problem switching between 24 and 30fps, but even if you play 24fps as it’s supposed to, it looks a bit choppy. Well, the people who make the televisions are smarter than the people who make the movies we watch on them, right? Of course they are. So they decided to screw everything up and gave us 120Hz.
By the way, Hz is short for Hertz, which is a measure of frequency over the course of a second. It is named after the German physicist Heinrich Hertz. He was smart when girls thought it was cool to be smart. If you didn’t graduate from elementary school, frequency means how often something happens during a given period. The speed at which the Earth revolves around the sun is measured at a frequency called a year.
So now that you know the frequency, you know that Hertz and frames per second are the same, so 24 fps = 24 Hz, right? Wrong. The reason they call it Hz, and not fps, is because they don’t actually display 120 unique frames per second. They’re just taking the original 24 or 30 images every second, multiplying them, retouching them occasionally, inserting some completely black “dark squares” here and there and making that mess of garbage add up to 120. So there’s a shred of honesty. in the “120 Hz” moniker, though I have a feeling that wasn’t done on purpose.
So now that we’re friends, and you know I’m not cheating on you, I can let you in on a little secret. 1080/60P is really 1080/30P, and pretty much every time you see 1080P on a TV, they mean 60P… or rather 30P because they just take the 30-frame image and display it twice. Well, that little trick gave them an idea.
Since there is no good way to convert Hollywood’s 24fps to TV Land’s 30fps without doubling every 4 frames (aka 3:2 pulldown) and causing judder, the TV makers remembered a trick of their kind from fourth grade math called “lowest common multiple”. Guess which is the LCM of 24 and 30? Yes, it’s 120. Going to 120 Hz made all the image processing so much easier. For 24fps film sources you have 5 cycles to work on each frame and for 30fps video sources you have 4 cycles. To take advantage of this, they can display the same image 4 or 5 times, they can insert completely black frames into the mix, or if they have a lot of video processing power, they can interpolate frames in between to smooth out the motion. .
Most manufacturers are combining all of these options and coming up with their own recipe to create the 120Hz picture. Some do it better than others and some are downright bad. But in my opinion, none of them have perfected 120hz yet, so I’m mystified by the new 240hz sets that are already available and especially the 480hz that will be here any minute. Most LCD TVs are technically incapable of displaying 480 unique frames in a second, even good ones. It requires a response time of 2 milliseconds (2 ms) (1/480 = 0.002), which is not impossible, but certainly not common in the world of LCD TVs. Just a few years ago, an 8 ms response time was a big deal.
There are now some plasma TVs branded with various forms of 600Hz marketing slogans, but most aren’t as advanced in terms of video processing as the better 120 or 240Hz LCD TVs. I’m sure there’s some technicality out there. lets them legally call it a “600hz subdural hematoma” or whatever, but for the most part, it’s marketing.