-----Original Message-----
From: James Nazarian [mailto:jhn3@uakron.edu]
> The recording format and encoding are different; NTSC is
> recorded at 29.94
> frames per second, PAL and SECAM (Asia) are recorded at 24,
SECAM is French in origin. The only reason it exists is so the
French wouldn't have to use a color standard that wasn't invented
in France. I guess any Asian countries that use it are former
colonies. The Soviet Union also used it. They didn't want to
use the imperialist TV standards of RCA or the BBC. :-)
> The 29.94 FPS
> that NTSC uses
> was based on the frequency of a readily available oscillator
> used for the
> first B&W TVs. When color was invented they didn't want to
> obsolete the
> B&Ws so they retained the same crystal. The odd rate is
> compensated for by
> dropping one frame every minute except every tenth except
> every hour except
> every tenth hour, (get the picture?).
Close --
The NTSC-1 (and RCA 441-line standard from 1939) chose 30 frames/60 fields
per second so that the 60-cycle US line current wouldn't cause ripples in
the picture as the line current rate "rolled" through the frame rate.
This allowed the use of simpler power supplies in the receivers. Same
rationale for 25 frames/50 fields in Europe. When color came along, a
sync pulse was necessary for the color signal, and the "color burst" was
inserted by slightly lengthening the time between frames. This stretched
the frame rate out to 29.94 fps as adopted by NTSC-2. Existing B&W sets
had enough latitude in their sweeep circuits to lock up the the NTSC-2
signal without modification. The dropped frames are an artifact of
SMPTE timecode and allow the <30 fps to be readily translatable to the
24 fps of motion pictures.
|