Old NTSC tricks: 240p?
tsw-cc at johana.com
Wed Mar 18 05:25:48 CDT 2015
A discussion about sync rates on a TV signal.
Christian Corti <cc at informatik.uni-stuttgart.de> Wrote:
> This has absolutely *nothing* to do with NTSC or PAL (or SECAM or
> whatever). NTSC etc. are colour encoding standards and don't describe in
> any way how a image signal is generated (fields, syncs, timing). They only
> describe how to put colour information into the signal.
Sorry, but this is UNTRUE. There have been several NTSC standards. The first one defined the signals for standard Black/White TV, it dates from the 1940s. It defined such things as horizontal sync, vertical sync, field definitions, and equalizing pulses (among other things). This version used a horizontal sync rate of 15750Hz, and a vertical sync of 60Hz (field rate). The later NTSC standard (from the 1950's) added the color definitions (color burst, re-definition of horizontal sync, color phase signals, color sub-carrier, etc.). This version reduced the sync rates by 0.1%, yielding a horizontal rate of 15734Hz, and a vertical rate of 59.94Hz. This was needed to make things proper multiples of the color burst rate. A later definition added stereo audio (related to horizontal sync).
If you know things about the signal, you know that there are 4 field types in NTSC color that differ with phase start of color burst, and odd/even field. I believe that PAL has 8, but I'm not exactly sure.
Yes, PAL and SECAM are color definitions. They are encoded over various underlying TV sync systems. One can make a SECAM receiver work a PAL signal.
Many of the broadcast standards have been dictated by governments. I believe that the 625/50 standard is "CCIR" What devices generate is anybodys guess. What TV sets accept is a crap shoot if it isn't "standard".
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