This is an email I wrote to a group at the office explaining 120Hz with respect to HD TV sets. (Keep in mind this is written for an American audience, so I used the NTSC standard 30fps (60 fields/second). European countries have a different electrical system which operates at 50Hz thus there television standards (SECAM, PAL) were defined as 25fps (50 fields/second)
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There is a lot of incorrect information out there about 120Hz. There are two separate technologies and problems being solved, however, most sales people cannot separate them.
So first let us define the problems
1. Judder - This is when the image appears to stutter on sweeping camera moves or similar. Judder occurs because of a difference between the refresh rate of the display device and the frame rate of the source.
2. Motion Blur - This is an artifact of the fact that all video/film is moving pictures (e.g. sampled). The blur occurs because our eyes bridge the gap between frames.
Below we will define the two technologies which are unfortunately both referred to as 120Hz by most people
1. 120Hz - this is the refresh rate of the monitor, so how many full frames/fields per second which can be displayed. (Most devices have historically had 60Hz refresh)
2. Auto-Motion Plus (Samsung's TM, Sony named theirs MotionFlow) - This is an interpolation technique which attempts to create intermediate frames to increase the clarity and decrease the bridging your eyes need to do.
Now we know the two technologies and problems we are trying to solve.
The 120Hz (refresh rate alone) is designed to solve judder. To explain why this is we need to learn a little about video/film. As you may know film is recorded at 24 fps (frames per second), TV programing is filmed in 30 fps (60 Hz interlaced). So with a 60 Hz display we get a none equal pattern to display film (24 fps) with 60 Hz we get a 3:2 pattern so the first frame is displayed 3 times, then the second twice and that continues to fill out 24 fps into 60 fields/second, this is where the judder comes in as there is a caddence mismatch between the original film and the display. To correct this we look to 120Hz and the display rate becomes 5:5 each frame is displayed 5 times thus creating a standard cadence (however, the 3:2 cadence is hard coded into standard DVD video so you need to rely on a good de-interlacer to restore the original 24fps and then pass them at that rate to the TV so that we get 5:5 output.
The Auto-Motion (interpolation) changes the original quality of the video because it is adding frames that didn't originally exist. Some people like the extreme crispness of the image it produces. I prefer to see the directors intent and very much dislike the video which is produced by this interpolation.
So for me 120Hz would be a big buying point today, however, I would need to be able to ensure that the interpolation is off. For a normal consumer I would say it isn't a make or break feature.
Whew that was a lot of typing to let you know that I doubt it would matter to you or your family, however, hopefully it has educated and my assist others in deciding.
