Asked in HDTV
HDTV

Will 120hz on a LCD TV affect a video signal from your TivoHD or does 120Hz just affect 24 frames per second sources?

Answer

Wiki User
10/21/2008

A 120Hz television features a frame doubler. Normal television signals have 30 frames each second with each frame made of two fields so there are 60 fields each second. A 120Hz television is thought to eliminate some of the flicker from an image by generating intermediate fields between each of the broadcast fields. Whether or not it improves the image is a matter of opinion. Adding fields introduces small errors in the image and although more fields can be created, never can a frame doubler add information that wasn't in the original signal. The 120Hz feature refers directly to broadcast signals at 60Hz and not to 24 frame material. 24 frame material is derived from film and instead of being made up with two fields, the complete image is produced 24 times each second. A frame doubler will increase the rate to 48 frames per second if it takes the 24 frame material in it's native format. However, film is normally converted to a 60Hz signal using a technique known as 3:2 pulldown. This means that the first film frame will be sampled twice and will create two fields. The next film frame will be sampled 3 times and create three television fields. So, in 1/12 of a second, two film frames generate 5 television fields. If, at any time, the 24 Hz material is converted to 60Hz using 3:2 pulldown, the television will simply double the frame rate to 120 Hz. Indeed, the line doubler may use this technique anyway. The precise methods employed vary from one manufacturer to another so although it is safe to say that a 120Hz television will affect all incoming signals, the way they handle signals will vary. As a final note: European television runs at 50Hz, not 60Hz. Line doublers will convert to 100Hz. Also, 3:2 pulldown is not used in Europe. As the European frame rate is 25 FPS, film is run slightly faster than its normal 24FPS to comply with television standard frame rates. It means that films become 4% shorter on television than in a movie theater.