I've read that the best display vertical refresh rate for a DVD material watched on progressive scan is 72Hz, while the best refresh rate for watching TV (progressive or interlace) is 60Hz.

After installing Knoppmyth R5A12 on my XGA DLP front projector system, my XF86-Config-4 file was automagically set up with a default refesh rate of 76Hz.

So...

Does anyone have a recommendation here on whether I should change the refresh rate and/or what I should change it to? I suspect I'll be happiest changing it to 72Hz...until I get the HDTV setup...then I'm not so sure...

-brendan

Displaying interlaced content on a progressive display is always going to be problematic. If you want to avoid interlacing artefacts, you will need to de-interlace somehow, and after that, it is going to be best to have a refresh rate that is equal to or a multiple of the field rate of the interlaced content to prevent tearing. Interlaced content in NTSC land (never the same colour) has a field rate of 60 Hz and in PAL land (pefection at last) is 50 Hz.

Most or all deinterlacing algorithms are some sort of compromise. You should read up on it to have a bette understanding. http://www.100fps.com/

I've read the articles on that site earlier, which is what got the wheels turning...

I've been doing some more reading tonight, and it occurred to me it is even more complicated, primarily as I am using a digital output device. Currently I have two source->output chains:

1. Cable/OTA SDTV live/recorded -> mythtv -> X -> nvidia driver -> VGA -> DLP front projector.

2. DVD -> mplayer -> X -> nvidia driver -> VGA -> DLP front projector.

and may be adding a 3rd:

3. OTA HDTV live/recorded -> mythtv -> X -> nvidia driver -> VGA -> DLP front projector.

What I thought I wanted was one frame per refresh or equivalent (e.g. one frame per 3 refreshes). Now, the DLP can sync to various input frequencies, so I thought, perhaps, I'd want to have it sync at ~60Hz for SDTV/HDTV and 72Hz for DVDs (assuming I can tell mplayer to reverse the 3:2 pulldown), and perhaps I'd set up separate XF86Config-4 files for those.

However, I just stumbled upon a reminder that my DLP has a 2x60Hz colorwheel. I'm not entirely sure, however, if that means that I'm essentially locked at a 120Hz native refresh rate on that box, and it performs whatever magic inside to map the incoming VGA signals refresh rate to the physical rate? If so, I probably want to lock the X settings to 60Hz and deal with the jutter on the DVD output...

...on the other hand, maybe it doesn't necessarily stay on the same frame as it rotates through the 3-4 colors a half turn (R,G,B, and optional W) every 1/120th of a second and may allow pixels to change between color pulses in the mapping of the variable input rate to the fixed output rate?

Alternately, maybe it just samples the input signal every 1/60th or 1/120th of a second?

So far, google hasn't helped me sort this out yet...so, probably the best thing for me to do is experiment with some heavy panning DVDs...

-brendan

The ddpprobe command returned:



I bet the reason that the standard modes returned are based on computer industry timings instead of home theater timings is that the projector is aimed as business use and not home theater use. The DMD chip is 1024x768, and the autoconfig of XF86Config-4 found that the best non-interlaced vertical refresh setting returned was 75Hz. That seems to explain that.

Q: If I wanted to use 72Hz or 60Hz at 1024x768, would I need to find the values to feed the XF86Config-4 file using powerstrip on a windows box?

-brendan

[EDIT: If only the projector could do 120Hz vertical refresh (5x24 frames per second or 2x60 fields per second...)

The comments I got (and searched for) at avsforum.com led me to one conclusion for the PB6200: set up X to use a 60Hz vertical refresh at the native resolution of the projector and just leave it like that. Let the HTPC do any software magic it needs to do to meet the projector at its native refresh rate.

I downloaded, untarred, and compiled `videogen` in order to generate the correct Modeline for this.

Thanks for reading!

-brendan