I don't know why I'm Bumping.
(but I am!)
Y'know I'm starting to suspect this was Sizzyl's master plan
Ah yes speedrun.com the place to bump threads and check
I have nothing interesting to say today
@jackzfiml So asks the person who never has anything interesting to post.
@jackzfimI I bother posting because this thread has fallen worryingly low on the thread list!!
That post requires a long and somewhat technical answer, but bear with me and all will be - well, perhaps not exactly clear, but hopefully at least a little less puzzling.
The original U.S. TV standard was based on exactly a 60.000 Hz field rate and so a 30.000 Hz frame rate. Audio was FM, living on a carrier 4.5 MHz up from the bottom of a 6 MHz channel (or nearly the bottom; the audio subcarrier is actually referenced to the video carrier frequency, and the choice of a 4.5 MHz spacing wasn’t entirely arbitrary, either - but I’m trying to keep this shorter than a novel, so I’ll leave it at that), and all was well with the world. The components of the video signal didn’t interfere with the audio or vice-versa.
Then along comes “compatible color,” originally an invention of NBC and their parent company, RCA. In this system, which eventually became known around the world as the 1953 NTSC color television system, two new signals had to be added to the existing video + audio combination, without going outside the limits of the 6 MHz TV channel allocation. The way color is encoded in the system is to add a pair of “chrominance” or “chroma” signals, which along with the original video (now luminance, or “Y”) could be mathematically combined to generate the RGB signals needed to drive a color CRT. But getting these additional signals to coexist with the Y and audio required some ingenious shoehorning. The color information would be modulated on a new “color subcarrier,” that would be parked somewhere between the original video carrier frequency and the existing audio subcarrier. Because of the way AM works (and both the original video signal and the modulation of the color subcarrier are versions of amplitude modulation), the components of the resulting signal show up clustered around multiples of the line rate (for the U.S. system, originally 15,750 Hz). So if you picked the right color subcarrier frequency, you could get the original luminance signal’s components and the new chroma components to nicely interleave with one another, and in the receiver be separable using a circuit called a “comb filter.” So it was easy - just pick a color subcarrier frequency that was an odd multiple of half the line rate (don’t worry about it, just know that the math works out), and this trick would work out. A color carrier offset around 3.583 MHz was chosen, as 3.583 MHz = 455 x (15.750/2) kHz. Problem solved!
Except that it wasn’t. There was some concern that, because of the relationship between the color and audio subcarriers (remember, I said the choice of 4.5 MHz for the audio wasn’t completely arbitrary either; it’s also tied to the line rate), the two signals would interfere with one another. The solution was to either move the audio subcarrier a little bit, or move the color subcarrier a similar amount. There was some concern that moving the audio would cause problems in existing receivers, so the color subcarrier frequency had to change. But remember, THAT frequency HAS to be related to the line rate, or the luminance and chroma components would interfere.
So to make a long story short (I know, too late), the line rate - and with it, the frame and field rates - was dropped by a factor of 1000/1001 (and there’s no need to make this even longer by analyzing why THAT was a good choice). The 15,570 Hz line rate became 15,750 x (1000/1001), or 15,734,26+ Hz. The color subcarrier wind up at the now-familiar 3.579545) MHz, and the field rate at 59.94005994… (exactly 60 x 1000/1001). And since the frame rate is half the field rate, we wind up with the 29.97+ Hz frame rate. The audio subcarrier, though, was left right where it was.
The kicker is that a while after the system was adopted, they went back and tested some of the black-and-white sets that had been on the market at the time, and found that they could easily have handled the shift in the audio subcarrier, had that been the route chosen! But by then, of course, it was too late to change, and we’ve had to put up with the weird-looking numbers in the NTSC color TV standard ever since.
