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25th August 2011, 22:41 | #2 | Link |
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It relates back to analogue TV days and the refresh rate used.
NTSC Lines and refresh rate (second paragraph). Last edited by hello_hello; 25th August 2011 at 22:44. |
1st September 2011, 20:30 | #3 | Link | |
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thank you.
Quote:
But with analogue TV days now long gone by, why do we still complicate our lives by encoded digital video in odd frame rates? |
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1st September 2011, 20:45 | #4 | Link |
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Because analog tv is NOT gone. Yes all high power television stations in the US broadcast in digital, and all sets sold must receive digital. But there is a huge installed base of analog receivers that will take time to be replaced. We can't just stop supporting them overnight and force everyone to buy new receivers. And there are still analog broadcasters (low power stations do not have to convert to digital yet).
Also there is a huge library of material recorded in NTSC, digitizing it works better at its native refresh rate. |
2nd September 2011, 04:34 | #5 | Link | |
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that makes sense. very interesting read, you
so odd frame rates won't disappear in the foreseeable future, right? Quote:
That would have eliminated the beating/intermodulation and still have provided a "round" framerate of 59 fps (so that each second of film always has an equal amount of frames). Last edited by lovelove; 2nd September 2011 at 04:40. |
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2nd September 2011, 21:32 | #6 | Link |
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For easy technical implementation. The 59.94 are locked to (i.e. derived from) the 60Hz power frequency: 59.94006 = 60x1000/1001.
1000 and 1001 are integer numbers which are more easy for technical (hardware) realization. Last edited by Sharc; 2nd September 2011 at 21:58. |
2nd September 2011, 22:09 | #7 | Link |
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I know that 60 x 1000 / 1001 ~ 59.94006 (see OP!)
so what? how is *1000/1001 easier than *59/60 ? And even if it were easier (which is still unclear) then it's not a good argument to do it because it's easier, when it was easily foreseeable that odd framerates bring along all sort of problems. |
3rd September 2011, 04:05 | #8 | Link |
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It is a little more complicated than 1000/1001, which is an approximation. For a good explanation of how the horizontal rate was lowered, resulting in a lower frame rate, see http://en.wikipedia.org/wiki/NTSC
The biggest considerations were to eliminate the existing audio interference with the video, add color, and maintain compatibility with monochrome sets. One thing not explained in that article is why the particular ratio of chrominance subcarrier to horizontal line rate. It is 455/2 - 455 is the product of three prime numbers (5*7*13), virtually eliminating the chance of harmonic interference. |
4th September 2011, 10:32 | #9 | Link | |
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Quote:
Reading that article, I see the line frequency was changed from 15750 Hz to 4.5MHz/286, which is a factor of 4500/(15.75 x 286), or exactly 1000/1001. |
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