[MPlayer-users] Re: which deinterlace filter

[D Richard Felker III]

On Tue, Oct 21, 2003 at 03:01:19PM +0200, Reimar Döffinger wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> Hi,
> > But you have the numbers upside-down. :)) I don't see how having a
> > 60Hz clock source helps you get a clock source for horizontal refresh
> > (much higher). You're dividing time, not multiplying it, when you
> > multiply clock by a "nice integer"...
> 
> First of all I want to say that I don't know anymore where I read that 
> the framerates have to do with the frequency of the power supply, so I'm 
> not absolutely sure if it's true, but it seems to make sense to me.
> First of all you must think of the fact that at the time the first TV 
> sets appeared, you didn't have a quartz to create frequencies, but you 
> had to use a capacitor and a coil (hope that's the right word...).
> For high frequency you need only very small and simple components, so 
> it's easy to get a (more or less) exact frequency.
> For low frequencies (like 60Hz) you would need such a high capacity, 
> that you would probably have to use for example electrolytic 
> capactitors, which have a tolerance of more than 10%, which means your 
> resulting frequency will be at least +- 10% and temperature dependant 
> (and those old TVs got really hot because of the tubes in them), and 
> also aren't supposed to be used with alternating currents.
> Now suppose you use that already not too stable frequency generator in 
> an environment where there is everywhere a frequency only 20% apart.
> I think you would be lucky if it would continue working at all, but then 
> probably at something like 52Hz instead of 60Hz...
> And last but not least, I think you can use a low, exact frequency very 
> easily to improve the accuracy of a high-frequency resonant circuit (if 
> it's accurate enough to begin with) by simply plugging them together.
> The other way round you will have to either use a counter or frequncy 
> divider, with I think both couldn't support that high frequencies at 
> that time (at least today they work digitally, a technology that was int 
> its beginnings at that time).
> 
> Hope I could explain why I think I am right.. ;-)

I just don't understand how a 60Hz clock source is useful to begin
with in a television. It seems to me that all you should need is the
tuner clock, and then the actual sync pulses in the signal can drive
the refresh. Perhaps old B&W TV's somehow aligned the electron beam
vertically using the phase of the A/C current to control the magnets?

...BUT this shouldn't be possible, because if they did, the picture
wouldn't have stabilized when watching new 59.94 Hz color signals on a
B&W TV... So I'm still at a loss regarding how the 60 Hz from the
power supply is useful.

Rich