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1280x720@120hz XG-750 Windows 7

 
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Satanier



Joined: 25 Aug 2008
Posts: 185



PostLink    Posted: Mon Oct 19, 2009 12:06 am    Post subject: 1280x720@120hz XG-750 Windows 7 Reply with quote


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When I change the refresh rate to 120 hz I see a scrambled image almost like thousands of horizontal zig zagging partterns moving about. Wondering how I might go about fixing this.
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MikeEby



Joined: 24 Jun 2007
Posts: 5236
Location: Osceola, Indiana


PostLink    Posted: Mon Oct 19, 2009 12:08 am    Post subject: Reply with quote

120 Hz is to high...I've never tried it....I would not leave it that way..It could screw the projector bad.

Mike

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Last edited by MikeEby on Tue Oct 20, 2009 1:40 am; edited 2 times in total
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Satanier



Joined: 25 Aug 2008
Posts: 185



PostLink    Posted: Mon Oct 19, 2009 12:12 am    Post subject: Reply with quote

Would it be possible to run any resolution at 120hz on this XG? My interest is for stereoscopic 3D viewing purposes.
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AnalogRocks
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Joined: 08 Mar 2006
Posts: 25555
Location: Toronto, Ontario, Canada

TV/Projector: Sony 1252Q, AMPRO 4000G


PostLink    Posted: Mon Oct 19, 2009 12:14 am    Post subject: Reply with quote

Look up the specs for the XG-75. Maybe you can do 640x480 @ 120??? Maybe not....
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Spanky Ham



Joined: 22 Mar 2006
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PostLink    Posted: Mon Oct 19, 2009 3:17 am    Post subject: Reply with quote

I seem to remember doing 120 at like 800x600 on PG9+. Try doing it with XP or Vista and see if you have any issues.
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Mark_A_W



Joined: 15 Mar 2006
Posts: 3068
Location: Sunny Melbourne Australia


PostLink    Posted: Tue Oct 20, 2009 1:25 am    Post subject: Reply with quote

What scanrate is it?

If it is higher than 75khz, and I wager it is, then it won't work on an XG-75.
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VideoGrabber



Joined: 09 Apr 2006
Posts: 933
Location: Michigan


PostLink    Posted: Sun Oct 25, 2009 11:27 pm    Post subject: Reply with quote

Mark is correct. 720p is way outside it's range. 600p is the max you might be able to coax out of this PJ at 120 Hz. You may have to back off a bit, though 540p should work with no problems, though it will be soft on the horizontal axis.
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ecrabb
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Joined: 13 Mar 2006
Posts: 15909
Location: Utah

TV/Projector: JVC RS40, Epson 5010


PostLink    Posted: Mon Oct 26, 2009 3:50 pm    Post subject: Reply with quote

What Mark and Tim said.

I'll just add that unless you're trying to do something really demanding with stereo, I wouldn't run 120hz, anyway. I used to help set up SGI Onyx RE's at 96hz to display on Barco 1209, 909 and 9500's in a commercial/industrial stereo caves. That gave you 48hz per eye and more spatial resolution to play with, which is typically more important to most sims than just refresh rate.

Use this bandwidth calculator to look at different res/refresh combinations to see bandwidth and scan rate:
http://myhometheater.homestead.com/bandwidthcalculator.html

720p/120 requires about 166mhz and almost 90khz refresh, so like Mark said, is way beyond the capabilities of the XG and won't work.

You're going to want to get down in the 100mhz range for bandwidth (the less bandwidth, the sharper the image), and into a scan rate that the XG will be happy with. I'd probably start with 1024x576 @ 96hz, and go from there. That'll yield roughly 85mhz bandwidth and 58khz scan, and is probably a nice tradeoff between sharpness, temporal and spatial resolution, and should display on the XG. You could probably even go up a hair from there if you wanted to. 1280x720@96 might even work, but it will be softer, so probably not worth it.

SC
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yonexsp



Joined: 25 Apr 2006
Posts: 311



PostLink    Posted: Mon Oct 26, 2009 8:07 pm    Post subject: Reply with quote

How does Interlaced affect 3D stereoscopic setups?
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ecrabb
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PostLink    Posted: Mon Oct 26, 2009 8:18 pm    Post subject: Reply with quote

You can do it, but it looks pretty jagged (you'd be watching alternating fields in each eye, with empty fields between), but the main problem is brightness. LCD shutter glasses cut a big chunk of light output, and of course interlacing cuts it in half. So, you end up somewhere down around 1/4 brightness running interlaced.

SC
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Spanky Ham



Joined: 22 Mar 2006
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PostLink    Posted: Tue Oct 27, 2009 3:06 am    Post subject: Reply with quote

ecrabb wrote:
What Mark and Tim said.

I'll just add that unless you're trying to do something really demanding with stereo, I wouldn't run 120hz, anyway. I used to help set up SGI Onyx RE's at 96hz to display on Barco 1209, 909 and 9500's in a commercial/industrial stereo caves. That gave you 48hz per eye and more spatial resolution to play with, which is typically more important to most sims than just refresh rate.

Use this bandwidth calculator to look at different res/refresh combinations to see bandwidth and scan rate:
http://myhometheater.homestead.com/bandwidthcalculator.html

720p/120 requires about 166mhz and almost 90khz refresh, so like Mark said, is way beyond the capabilities of the XG and won't work.

You're going to want to get down in the 100mhz range for bandwidth (the less bandwidth, the sharper the image), and into a scan rate that the XG will be happy with. I'd probably start with 1024x576 @ 96hz, and go from there. That'll yield roughly 85mhz bandwidth and 58khz scan, and is probably a nice tradeoff between sharpness, temporal and spatial resolution, and should display on the XG. You could probably even go up a hair from there if you wanted to. 1280x720@96 might even work, but it will be softer, so probably not worth it.

SC


Sigh

Man I was hoping that would die. This was discussed on AVS a couple of years ago. Extron promoted that -3 BS, so that everyone thinks they need uber bandwidth to do high resolution. If you use that calculator, then divide by 3 and that gives you the bandwidth figure. I think Scott actually gave the pixel clock formula in a thread over at AVS if anyone wants to figure that out.
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ecrabb
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PostLink    Posted: Tue Oct 27, 2009 4:25 pm    Post subject: Reply with quote

But, you do need über-bandwidth to do high-resolution - if you want to do it well, that is. At least, that's what I understand.

My G70 is a 120mhz machine on paper. Now, take a 1080p signal... Using only the pixel clock formula you referenced (plus some for blanking and retrace), you get about 85mhz worth of necessary bandwidth to display it. Unfortunately, my 120mhz G70 isn't even CLOSE to being able to reproduce a 1-pixel-on/1-pixel-off pattern. Not even close. Why? Because you need a hell of a LOT more than 85mhz worth of bandwidth to reproduce that signal.

I'm not an engineer, but this is how I understand it: If we just wanted to do sine waves at a given pixel clock rate, then the pixel-clock based bandwidth would be perfectly adequate. But, we don't want a sine wave. A sine wave won't reproduce pixels! For that, we need a square wave - or at least something approaching it. To get something some close to a square wave (at high-resolution), we need a video chain that can handle the extremely short rise/fall time of the harmonics of the square wave... To do THAT, you need an extremely fast video chain - i.e. bandwidth to burn. At least, that's what I've gotten from reading Mike Parker's posts over the years. But, maybe I'm wrong.

If you disagree, I'd like to hear why. I'd also like to see that thread on AVS you're talking about. I couldn't find it from a casual search. Can you?

SC
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Spanky Ham



Joined: 22 Mar 2006
Posts: 5643
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PostLink    Posted: Wed Oct 28, 2009 4:27 am    Post subject: Reply with quote

The 120mhz was just a marketing number. It has long been understood that the number was fudged by all of the manufacturers.

I find it interesting that you can't even achieve a minimal level of 1 off/on pixel, while other G70 owners are. Scott demonstrated this when he started the 8" 1080p thing. It may have a low MTF, but it should still resolve the pixel.


Regarding bandwidth, have we ever heard any numbers from anyone? Maybe Scott can come over and answer this, but I don't believe I have ever heard him talk about bandwidth numbers. From my visits with him (and it has been almost two years), he is usually talking about a MTF at specific resolution.

As for the threads over at AVS, maybe Nash has them on speed dial.Smile A couple were started by Scott like three years ago. Chiem also did a nice thread about this around the same time. Remember him, as he was the physicist from Princeton. I think his screen name was CWM9.
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ecrabb
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PostLink    Posted: Wed Oct 28, 2009 5:37 am    Post subject: Reply with quote

I know the G70 was only 120mhz on paper, and that in reality it was much lower, but you're sort of making my point!

I have achieved a 1-on/1-off vertical pattern, and "minimal" is a good way to describe it. I can clearly see the vertical 1-on/1-off pattern, but it sucks. It's clearly a low MTF... I'd guess down in the 20% (.2) ballpark.

Now, my machine is pretty pristine, the focus is excellent... I can't quite see 1080p scan lines, but horizontal on/off are very sharp and well-resolved. My corners are almost as good as the center, it looks almost as good with all three CRTs turned on as it does with red and blue muted. So, not to toot my horn, but I'd guess I've probably gotten my setup to within 80-90% of where a guy like Ken Whitcomb could get it. Yet, it's still a low MTF. Why? Pure and simple: Bandwidth. The G70 video chain doesn't have nearly enough of it. If you take the lenses out of the equation, MTF is practically synonymous with bandwidth. Put simply, MTF = bandwidth. Lower bandwidth = lower MTF. Higher bandwidth = higher MTF.

I'd like to hear where both Scott and Mike P come down on this.

I'll see if I can go find the thread over on AVS. If Scott started the threads, that narrows it down a lot. I'll see what I can find.

Hell yeah, I remember Chiem... That was about the last time I was remotely interested in anything in the CRT section at AVS... I loved it when he was playing around with the idea of an anamorphic squeeze with first-surface mirrors and running the optical simulations... The new guy is a crazy man! Didn't he move to Hawaii or something?

SC
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Spanky Ham



Joined: 22 Mar 2006
Posts: 5643
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PostLink    Posted: Mon Nov 02, 2009 9:48 pm    Post subject: Reply with quote

I am not so sure it is all about the bandwidth. I think there may be other factors at play especially regarding ANSI cr. Your MTF is probably lower than you think. It is probably in the single digits. Even a 9" is pretty low.

I will start a new thread over in the main forum.
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