In deference to saylor and others who do not "enjoy" this exchange on the dynamics of what's happening with the 120hz refresh rates, I'll make this final post and then quit.
First, for an excellent discussion of interlaced/progressive conversions and why it's needed, take a look at this article: Film-to-Video Conversion
Scroll down the page to where the background changes color. That's where the good stuff starts.
Also, I keep a database of interesting stuff I come across on the web. Here are parts of three posts, I believe by "walk," that I saved concerning the display of 24hz-based material at 120hz. 5:5 pulldown and a lot of other stuff is covered. In my opinion, the information is correct. But be aware, it is a combination of fact and speculation in regard to how the displays actually work. Here are the three original posts (by walk?):
You guys are actually doing the math backward. It is mostly a matter of semantics, but here is how it actually works....
The 120Hz frequency is actually 5 times faster than the 24Hz frequency. You're not displaying a 24Hz frame 5 times to reach 120Hz, you're actually displaying a 120Hz frame 5 times to reach a 24Hz refresh. When you think about it backward, you can end up confusing yourself.
A 60Hz refresh must display one frame 3 times and the next frame 2 times in the same time it takes to display 2 frames of 24Hz. That is where the term 3:2 cadence comes from. If you have 24Hz frames that are called A, B, C, and D, the native 24Hz would be displayed like this A B C D. The 60Hz display (being 2.5 times faster) will display A A A B B C C C D D (3:2 cadence). With the 60Hz refresh, frames A and C would get equal display time whereas B and D would only get 2/3 of the time displayed. This causes judder. A 120Hz frame rate would look like this... A A A A A B B B B B C C C C C D D D D D. This is where the term 5:5 cadence comes from. In the time it takes to display 2 of the 24Hz frames, each of those frames would have been displayed 5 times at 120Hz. Each frame would get equal time. In 120Hz, each frame would get equally displayed, thus smoother motion.
Now, if you have black frame insertion, you might have something like this with 120Hz.... A A A _ _ B B B _ _ C C C _ _ D D D _ _. The blanks would represent a black screen and are placed there to create a more natural motion, like old film projectors. Motion enhancing might look like this A A A AB AB B B B BC BC C C C CD CD D D D DE DE... and so on where the double letters would represent an artificially generated frame. You can see where you might get some blur with the motion enhancing mode.
I know that most of you know this stuff, just trying the help new people understand it better. When we speak of converting a 24Hz signal to 120Hz, we know what we are talking about, we actually say it backward because it is easier to use those terms. What is actually done is what is described above, ie. convert a 120Hz refresh to make it look like a 24Hz refresh. Keep that in mind when you read these threads.
A few other things. A previous poster asked about inverse telecine and what the TV would do when it got back to 24p....
What happens when a video processor (VP) does inverse telecine is that it must recognize a 3:2 cadence (A A A B B C C C D D at 60Hz) and convert it back to its natural 1:1 cadence (A B C D at 24Hz).
This set is a 120Hz set and it can only function at 120Hz. If it is able to recognize the 3:2 cadence and convert back to 24Hz, the set would display a 5:5 cadence. If it does not recognize the telecine (3:2 cadence), it would just display the 60Hz signal twice and you'd have (A A A A A A B B B B C C C C C C D D D D) a 6:4 cadence. This would look much like the 3:2 cadence I guess.
This set doesn't have a 24Hz refresh, but it is compatible with a 24Hz refresh (24p). Sets that just double the 60Hz signal are not compatible with 24Hz refresh in the way the Sony is and still have judder due to 6:4 cadence. It remains to be seen if the Sonys will perform the inverse telecine.
Broadcast TV is sent out at 60Hz. For a movie with a 24Hz refresh, that means they have to perform telecine (3:2) on the signal to be compatible with the 60Hz signal before it is sent out. The TV (if it is 120Hz) can either double the 60Hz frame (giving a 6:4 cadence), or perform inverse telecine and give you a 5:5 cadence. You can see why the latter is preferred. Some VP's will perform the inverse telecine (mostly high end units costing thousands, but perhaps the Onkyo 905 or the new Denons AVR's can).
While I'm at it, I thought I'd throw out a few more things. Not everything out there is filmed at 24Hz (24p from now on). Some things are filmed at 60Hz (60p). Movies and some TV series (eg. 24) are filmed at 24p as this is supposed to give you a very natural feeling of movement. Here is where I get a bit fuzzy... I believe sports are filmed at 30 or 60p. This is where the math starts to change a little. Most of the previous sets were 60Hz refresh sets and could display a 30p or 60p picture natively without giving you judder. The good thing about a 120Hz display is that, not only can it display a 24p without judder, it can also display the 30 and 60p images without judder as 24, 30, and 60 are all multiples of 120. ie. each frame can be displayed an equal amount of time on a 120Hz set. The 30p would give a 4:4 cadence and the 60p would give a 2:2 cadence.
If for instance, you had a 72Hz display, that would display the 24p picture better than the 60Hz would, but it would reek havoc with the 30p and 60p cadences. As long as they don't start throwing 50p or some other weird refresh at us, we'll be alright with the 120Hz displays.