cowardly Posted October 19, 2004 Posted October 19, 2004 Hi guys, I have a Sony PFM42X1 plasma display, and overall I am very happy with it. Its native resolution is 1024x768, but I am more concerned about its refresh rate. I am using it as the display for a HTPC, via DVI. I can feed it a variety of resolutions and refresh rates and it accepts them quite happily. Of course it is going to re-scale any signal to 1024x768, but it appears that it is also converting the refresh rate to 60Hz. The on screen display shows the resolution and refresh rate of the signal in the top left hand corner of the screen, but it only ever shows 60Hz as the refresh rate, no matter what refresh rate I am driving the signal at. For example, I have set up the HTPC to output a 1024x768@50 signal, but the plasma reports it as 1024x768@60. I have confirmed that the computer is driving the signal at 50Hz, but the picture on the screen does not pan as smoothly as it could. This could be due to dodgey timing on the HTPC, but I don't think so. It is my understanding that LCDs have a native refresh rate that can not be changed, and that it is usually 60Hz. Is this also true of Plasmas? If so, then that would explain what is happening to me. The silly thing is that through the component connection, It will accept a 50i signal no problem, and that it will display on the OSD as a 50i signal too. I haven't done any A-B comparisons of the smoothness of panning of the two signals yet, so I can't be sure what is going on. Can anyone help me? Are plasma displays locked to a particular frame rate?
ijd Posted October 19, 2004 Posted October 19, 2004 Are plasma displays locked to a particular frame rate? The NEC 42" 42XM3W (also 1024x768 - possibly the same glass as your Sony but with NEC electronics) claims to sync to any vertical refresh from 50Hz to 120Hz - but the table of 57 supported computer input resolutions shows a lowest of 56.2Hz @ 1280x768 (which is about as low as I can get my LCD monitor to go as well) and a highest of 120.0 Hz (@ 800x600). NEC also claims horizontal scanning from 15.5kHz to 110kHz - but again the table of computer resolutions supported shows a minimum of 31.0kHz to a maximum of 108.5kHz. I assume that the 50Hz minimum is for STBs in 50Hz countries and the 120Hz maximum is for DTV frame doublers in 60Hz countries. (The NEC has many different options for STB, DVD and PC connection to each of the various inputs). There are many experts who will read this thread who will probably help us out with 'Why this is so'? (are you there, Mozmo?) Ian
jewfish Posted October 19, 2004 Posted October 19, 2004 Most PC monitors I have seen are limited to 60Hz whilst on the DVI port, I have setup LCD monitors with the PC driving 85Hz and the on-screen display on the monitor still reports 60Hz
mozmo Posted October 19, 2004 Posted October 19, 2004 I suspect it's your video card, I've run the panel at 720x576/50 and it displayed that on the screen. Sames goes with 1280x720/50. What type of video card are you using, the panel should work and sync at 50hz with a dvi signal, I take it you're using powerstrip to get the 50hz refresh rate since 50hz isn't a standard vesa resolution rate. That's how I got my 9700pro to output 50hz via the dvi. I suspect the panel will only accept HDTV resolutions at 50hz, any other resolution like 1024x768 will probably only work at 60hz since that's what the vesa spec has for that res. BTW how exactly are you sure the video card is actually ouputing 50hz at 1024x768? You might be telling the card to do it via an app but the drivers just might actually doing it via emulation, ie it's actually pumping out a vesa 1024x768/60 signal and just doing 50hz vsyncs in the driver.
Billy Two Hats Posted October 19, 2004 Posted October 19, 2004 This would be dependant on the response time, the lower this is the higher the refresh rate. Most PC monitors I have seen are limited to 60Hz whilst on the DVI port, I have setup LCD monitors with the PC driving 85Hz and the on-screen display on the monitor still reports 60Hz <{POST_SNAPBACK}>
J.D Posted October 19, 2004 Posted October 19, 2004 Just as another point of comparison, my Fujitsu will only accept a 60Hz signal with a DVI connection but is quiet happy with 50Hz with a component connection. This is the case for the whole Fujitsu range. Its because of this I abandoned DVI for component and the better flexiblity.
cowardly Posted October 19, 2004 Author Posted October 19, 2004 Thanks for the reply Mozmo. I remember you claiming you had it working before. I have a Nvidia Fx5200 as my card, and I am driving it using Linux with a custom Modeline (comparable to using PowerStrip). I can't be certain that the driver isn't fudging the refresh rate, but it certainly thinks I am working at 50Hz according to xvidtune, which shows the timing information being used. Interestingly enough, the Monitor reports (via EDID, the code that the monitor sends back to the card identifying itself) that the refresh rates it is capable of handling are between 55Hz and 65Hz, clearly indicating that it wants a 60Hz signal. I had to instruct the driver to ignore the EDID information in order to get it to work with the 50Hz modeline at all. The manual claims that it supports resolutions up to 85Hz, so all I can say is that I am getting very confused . I will try 720x576/50 and see if that works. The only way to really know is to write a program that scrolls a graphic across the screen at the frame rate, and see if it jumps or not. Can I ask, when you feed it a 720x576/50 signal, is that what it displays on the OSD? Can I get you to send me the Powerstrip settings? They can be converted into X.org modelines fairly easily.
cowardly Posted October 19, 2004 Author Posted October 19, 2004 It looks like you are right Mozmo, I tried the 720x576/50 resolution tonight, and it displayed, although the OSD reported 1024x768/60 even though I was clearly driving the signal with 720x576/50, as evidenced by big fonts and blurry pixels. So, instead I tried the same set up with a VGA connection. Hey presto, 1024x768/75 worked fine and displayed fine, although I couldn't get it to lock onto 720x576/50. What this means is that my graphics driver must be automatically converting any signals that I feed it into a standard format (1024x768/60) before passing it along via DVI. This is really frustrating. In the end, I suppose I can live with a VGA connection if I have to, even though I can easily see the noise...... Bugger, why is it so hard to get devices to talk to each other?
mozmo Posted October 20, 2004 Posted October 20, 2004 Don't bother using the 85hz setting, the panel will accept it but the screen only operates in 50/60hz refresh rates, so you'll see some jerking/stuttering because the panel is frame converting from 85hz to 60hz. It's best to keep your refresh rates at 50/60hz so that you computer pumps out frames that can be displayed in sync with the panels native display rate. Cowardly do you have access to a friends lcd monitor? You could experiment on that and find out more what's going on. I think it's your card drivers that are screwed up, one option would be to use windows xp and the nvidia detonators for xp which properly work correctly with the dvi.
cowardly Posted October 22, 2004 Author Posted October 22, 2004 Just as a follow up, I installed Windows XP on a spare Hard Drive, along with the latest NVIDIA drivers and PowerStrip. After a bit of experimentation, I did convice it to do 1024x768/50 via DVI, although the setting probably need a bit more tweaking before they will be fully stable. I copied the settings down, changed back to Linux, converted the settings across to X.org modelines, and gave it a whirl.... No luck. The drivers still decided to emulate another mode. I also tried the modes via standard VGA, and they didn't work at all. oh well, back to the drawing board.
ero Posted October 22, 2004 Posted October 22, 2004 I've been playing around for a long time now with PowerStrip and software in general. Haven't done it for a while but when using PowerStrip I could get the OSD of the Sony Plasma to show 1024x768/50Hz....would sometimes show 49Hz too.....so, it can be done at 1024x768 but to my eyes i couldn't notice any difference between 50HZ and 60HZ so i've just left it at the 60HZ and infact not even using PowerStrip anymore.
cowardly Posted October 23, 2004 Author Posted October 23, 2004 Hey ero, The reason that I want to get 50Hz is for showing TV, which displays at 25 fps. If you try to view 25 fps material that contains pans or other large amounts of motion (e.g. CNNNN tickertape down the bottom) on a 60Hz display then it is fairly easy to see the motion shudder, as some frames will be displayed 50% longer than others. It is really only noticable when there is a large amount of smooth motion on the screen, like for pans or tickertape displays, but it still annoys me. To be able to display movies correctly, You really also need a 48Hz or 72Hz mode as well, as movies are displayed at 24Hz.... Like you, I have been able to convince the PFM42X1 to display at 50Hz using Powerstrip on Windows, but I would prefer to run my HTPC under Linux if at all possible. At this stage, the linux graphics drivers, which are supposed to share 95% of the codebase with the windows drivers, are refusing to allow these modes to work, instead emulating them on the graphics card. I haven't worked out why.
RodN Posted October 24, 2004 Posted October 24, 2004 Cowardly - if your Plasma can do what Ian suggests then you could be going for 75Hz anyway this is 3 times the 25fps and produces a very nice smooth movie like pan. Worth trying but it sounds like your video card might need an upgrade - do you have the latest catalyst drivers for it?
hifi007 Posted October 25, 2004 Posted October 25, 2004 You will find although a plasma will take various input rates, it internally operates at only one rate. The reading (frame rate, resolution) that the menus on plasma give is only of the input rate.
MichaelCPE Posted October 25, 2004 Posted October 25, 2004 I think many people above are rather confused. As I own a Pioneer, I did the research for that brand. If displaying interlaced PAL the refresh rate is 50Hz, but a full frame is displayed. For NTSC the refresh rate is 60Hz. Note that if there is movement between the fields, the full frame will look funny. When the Pioneer detects film source, the refresh rate is increased to 72Hz for NTSC, and the effects of 3:2 pull down are removed. So, as you would expect, the refresh rate for PAL and NTSC input is different (and I would be surprised if any plasma did not treat PAL and NTSC appropriately). Regards, Michael
cowardly Posted October 25, 2004 Author Posted October 25, 2004 Cowardly - if your Plasma can do what Ian suggests then you could be going for 75Hz anyway this is 3 times the 25fps and produces a very nice smooth movie like pan. Worth trying but it sounds like your video card might need an upgrade - do you have the latest catalyst drivers for it? <{POST_SNAPBACK}> Nobby, Yes I did try the latest drivers with Windows XP, and I did manage to get a somewhat unstable picture at the correct frame rate, and I'm sure with a bit of tinkering that I could get it to stabalise. I want to run Linux though, so I have to try and make the linux drivers, which are supposed to share 95% of the codebase with the windows codebase, work correctly. 75Hz would be fine, but no better than 50Hz in my opinion. If I can get 75Hz working, I will be fairly happy.
cowardly Posted October 25, 2004 Author Posted October 25, 2004 You will find although a plasma will take various input rates, it internally operates at only one rate. The reading (frame rate, resolution) that the menus on plasma give is only of the input rate. <{POST_SNAPBACK}> It is my understanding that plasmas (and LCDs) do not have refresh rates at all, at least not in the traditional CRT sense. Because all pixels are driven at the same time, there is no need to refresh the phosphor on the screen like a CRT. What this means is that for most purposes, driving a LCD or Plasma at 60Hz is fine because you won't see any flicker. Data still needs to be streamed to the panel from the graphics card, and that is the refresh rate that panels use and display on their OSD. Because it doesn't make a whole lot of difference for flicker, some panels will ONLY accept a certain refresh rate, as hifi007 says. Unfortunately, it does make a difference for video, as some frames end up getting displayed for longer than others, causing judder. Now as far as I know, the Sony PFM42X1 does accept at least 50 and 60 hz, and it looks like a lot of other refresh rates as well. and as MichaelCPE says, some plasmas are even smart enough to switch to 72Hz mode when NTSC film is displayed. The problem I have is getting the linux drivers to drive the DVI connection in the correct way.
hifi007 Posted October 26, 2004 Posted October 26, 2004 It is my understanding that plasmas (and LCDs) do not have refresh rates at all, at least not in the traditional CRT sense. Because all pixels are driven at the same time, there is no need to refresh the phosphor on the screen like a CRT. You are correct. I am still quite amazed that most people can't work out that increasing the input frame rate (in even multples) on what is a (mostly) digital device doesn't work on the image like it does on an analog crt. What anomolies (or how much better) the image "looks" when changing the input frame rate is only related to how well that input rate converts to the devices internal native display rate / resolution. If the electronics can take a 24/25fps input it will not display on the screen any quicker than if you input 48/50fps. They are not a crt.
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