Old NTSC tricks: 240p?

On Tue, Mar 17, 2015 at 1:06 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote: No, the 1000/1001 change doesn't in any way prevent that. Instead televisions use filters to remove the color carrier from the luminance. Originally this was done with low-pass filters, which significantly reduced the available luminance bandwidth, and thus horizontal luminance resolution. Starting in the 1980s (or maybe late 1970s?) comb filters were used that could better separate the luma and chroma with less degradation of the horizontal luma resolution, though it is imperfect so there still are some artifacts such as dot crawl. What the 1000/1001 sync rate change did was reduce the interference between the color information and the 4.5 MHz sound subcarrier used on broadcast. The problem actually was not an issue for the transmitting and receiving equipment of the day, but became an issue years later with comb filters. The NTSC committee requested that the FCC change the audio subcarrier frequency by 1001/1000, which would not have caused any problem whatsoever, but for whatever inscrutable bureacratic reason the FCC didn't want to do that, to they changed EVERYTHING ELSE by 1000/1001 instead, causing all manner of annoying issues, such as a frame rate error when converting film by telecine, and the abomination of drop-frame time code.