When I see shows from America being on air on a British TV channel (I watch on the BBC), I noticed that the sound of the films, music or in general, they go up by one. Why does that happen?
In: 7006
American TV is 59.94 fields per second, while British TV is 50 fields per second.
Movies are shot at 24 frames per second.
So in order to broadcast a movie:
1. If it’s for British TV, 24 and 25 are so close to each other that you can just get away with speeding up the movie by ~4%. While this gets unnoticed for video, you can hear the change in audio pitch, especially if a song you know is playing in the film. After the 24fps to 25fps speed change, you just double each frame so it’s 50 fields per second.
2. If it’s for American TV you can’t get away with speeding it by 25%. So a process called 3:2 pulldown is used. First you slow it down by 0.1% so you get 23.976 frames per second and then you split every frame into two fields and every second frame into two fields with one duplicated, so you get a 2-3-2-3-2-3.. pattern and with that 59.94 fields per second with only 0.1% speed change.
So why aren’t British TV shows faster when broadcast on domestic TV? Because they are shot at 25 frames per second and then you just have to duplicate each frame to fit into 50 fields per second. While American TV shows are shot at 24 fps.
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