[mythtv-users] How I got great quality TV-out on my nVidia MX4000

Cory Papenfuss papenfuss at juneau.me.vt.edu
Thu Mar 10 12:41:38 UTC 2005


>>     The AD724 supports PAL encoding as well as NTSC, so it should be 
>
> But there is something different that goes beyond the frequency, AFAIK. If I 
> connect a PAL TV to an NTSC S-vid, I would get a B/W picture. Or was that 
> with composite (cinch)? Or is that AD724 switchable between PAL nad NTSC?
>
 	Yes, there are more differences between NTSC and PAL than simply 
the frequencies.  The most obvious ones are that the color subcarrier is 
at a different frequency (3.58MHz/NTSC, 4.43MHz/PAL)... that's why you'll 
get B&W picture if you connect a PAL TV to an NTSC S-vid.  The horizontal 
scan frequencies are 15.734kHz vs 15.625kHz... most likely close enough to 
lock onto for the luma with sync.  The 50/60Hz is another matter, but from 
what I understand lots of PAL TV's are at least pseudo-capable of viewing 
NTSC video, so the vertical scanning might be able to lock onto a 60Hz 
refresh even if it was designed for 50/100.

 	Now, for the chroma on the s-vid, everything is *way* off.  3.58 
is much different from 4.43 no matter how you slice it.  So, it'll not get 
much color info from it.

 	To answer your question easier, though... YES the AD724 has a PAL 
mode.  Feed it a correct PAL color subcarrier frequency, change one pin, 
feed it PAL RGBHV frequencies, and it goes.  I haven't done it, mind you, 
but it should work fine.

> That's right. But not all TVs have RGB-capable scart connectors.
>
> On the other hand, if you would do VGA->SCART with RGB, you would have 
> basically this, right?
>
> http://www.sput.nl/hardware/tv-x.html
>
> Someone else here wrote, that RGB is *too* sharp for MPEG2 video, meaning 
> that you see the artifacts then.
>
 	Correct.  I haven't noticed artifacts with what I'm doing, but I 
suspect that the chip does some filtering.  I haven't looked at the 
datasheet in awhile.

-Cory

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
*************************************************************************



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