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With most displays such as laptops, TVs etc having refresh rates divisible by 60, the same as the AC rate, why do so many camcorders have odd rates such as 23.976 ( for 24), 29.97 (for 30) and 59.94 (for 60) frames per second? I understand there were technical limitations in the past with actual film, but with modern digital circuits I doubt this is still the case. It just results in dropped frames when producing the rendered product.
In the case of the frame rates, the 23.97 and 29.97 frame rates are the actual frame rates. But most people just round the number up so that they don’t need to remember the point-whatever. But also, with NTSC, back when it was just a b&w signal, it was actually transmitted at 30 frames per second. But when color was added the transmission needed to be slowed down by point-zero-three frames in order for the color to work.
As for why camcorders have these multiple speeds is that some producers want the film look (especially if their target is a movie screen) or in TV production some producers might want to shoot at 24p and then create bot NTSC & PAL masters from the 24p master, just like they used to do with finishing on film (I.e. SeaQuest DSV). Also, even if the production is going straight to DVD, 24p is one of the video standards. If you have a DVD with a film in anamorphic widescreen from both PAL & NTSC regions, you probably have the same transfers as the studio probably put the movie on in 24p and then left it up to your machine to convert it to either 25i/p (PAL regions) or 30i/p (NTSC regions).
59.94 is rather recent, as it was found that with 30p recordings, the action didn’t look as smooth as 30i recordings, so the frame rate is doubled so that the action is smooth.
It’s simply a maths based fudge, design to stop two elements of the picture interfering which each other. Back in the mid 50s, technology was limited and adding a subcarrier, to ‘invisibly’ piggy back on the colour information meant that the two signals produced a series of inter-modulation products and the picture was a bit sparkly to look at with lots of high frequencies being created by the sum and difference products of the luminance and chrominance paths. It’s not really right to say it was slowed down, but it kind of works. They simply lowered the horizontal line rate from from 15,750 to 15,734 lines per second – and if you do the maths behind it – this creates the weird frame rate. So simply a fudge that worked. We’ve lived with the results ever since.