[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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