Dnia Tue, 2 Jan 2018 17:04:57 +0100, Michal Jankowski napisał(a):
> W dniu 2018-01-02 o 16:28, J.F. pisze:
>> Ale ... ten 1.001 z jakis powodow wprowadzili, czesto sie spotyka
>> takie przesuniecia, ponoc po to, aby sie harmoniczne nie nakladaly.
>>
> 1.001 wynika z tego, że przy tworzeniu podnośnej koloru wygodnie było z
> jakiegoś powodu dać ułamek (5*7*9)/(8*11) MHz, czyli 315/88 MHz. A potem
> to częstotliwość odchylania poziomego wyszła (315/88)*(2/455)=9/572 MHz,
> a pionowego (9/572)/525 MHz = 30000/1001 fps.

Wiki ma szersze wyjasnienia
https://en.wikipedia.org/wiki/NTSC

The 59.94 rate is derived from the following calculations. Designers
chose to make the chrominance subcarrier frequency an n+0.5 multiple
of the line frequency to minimize interference between the luminance
signal and the chrominance signal. They then chose to make the audio
subcarrier frequency an integer multiple of the line frequency to
minimize visible (intermodulation) interference between the audio
signal and the chrominance signal. The original black-and-white
standard, with its 15,750 Hz line frequency and 4.5 MHz audio
subcarrier, does not meet these requirements, so designers had either
to raise the audio subcarrier frequency or lower the line frequency.
Raising the audio subcarrier frequency would prevent existing (black
and white) receivers from properly tuning in the audio signal.
Lowering the line frequency is comparatively innocuous, because the
horizontal and vertical synchronization information in the NTSC signal
allows a receiver to tolerate a substantial amount of variation in the
line frequency. So the engineers chose the line frequency to be
changed for the color standard. In the black-and-white standard, the
ratio of audio subcarrier frequency to line frequency is
4.5 MHz/15,750 Hz = 285.71.
In the color standard, this becomes rounded to the integer 286, which
means the color standard's line rate is 4.5 MHz/286 ? 15,734 Hz.
Maintaining the same number of scan lines per field (and frame), the
lower line rate must yield a lower field rate. Dividing 4500000/286
lines per second by 262.5 lines per field gives approximately 59.94
fields per second.

Co prawda nie bardzo rozumiem czemu podnosna koloru musi byc
polowkowa, a podnosna audio nie musi ...

J.