19-10-2020, 02:57 PM
(18-10-2020, 06:56 PM)ppppenguin Wrote: 15750Hz was the original 525 line line rate. When they went colour it was dropped by 1000/1001 giving 15734Hz. The reason was to do with the relationship between sound carrier and colour subcarrier though I don't know why. One had to move and it was decided not to risk having to retune the sound IF on millions of sets. The resulting 59.94Hz field rate has been a PITA ever since timecode was invented a few years later.
The common 13.5MHz sample frequency for 525 and 625 "601" digital TV was a fortunate coincidence. It subsequently became a slight PITA because the pixels aren't square and are different shape on each standard. For HDTV they settled on square pixels with different sample rates. 74.25MHz and 74.25 *1000/1001.
Amazingly the 59.94Hz related standards options have persisted even up to the highest 4K standards.
This article gives a good account as to why the frame rate needed to be altered with the introduction of NTSC Color.
https://www.tvtechnology.com/opinions/wi...nd-of-5994
