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Discussion Starter · #1 ·
I thought that I would get a debate going as to why this is. It maybe that this is only true when connected to a PC. Anyway it is very annoying that us digital projector owners cant make use of the 72 and 75Hz refresh rates that allow CRT owners to decrease pan judder. The only explanation that I have read to date is that the electronics aren't fast enough to cope with higher rates and that this results in tearing. However I don't buy this because I see tearing at 50Hz as well. There appears to be a reason why 60 Hz is the magic number. A theory of mine is that they are fixed 60Hz devices but have the means to accept other rates and translate them back to 60 Hz. Anyway we have a few experts out there who maybe able to get to the bottom of this so its worth a try.


Jeff
 

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Not sure what you are trying to say. I run my DILA at 75hz and have tried 60hz, 72hz and others. A digital projector unlike a CTR has a fixed panel refresh rate. No mater what refresh rate you send, the refresh rate must be converted to the projector's native refresh rate. I my case the DILA's panel refresh rate is 75 hz. The projector you have must have a native 60hz refresh rate.
 

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Discussion Starter · #3 ·
William,


If it is true that all digital projectors work to a native refresh rate (and I believe it is) then people who use 72Hz to reduce judder are waisting there time. Yet there are people that insist that 72Hz works well. Also I'm yet to be convinced that the native refresh rate applies to conponent inputs and the like. What about PAL which is 50Hz, with my PC I get tearing at 50Hz, would I also get tearing from a PAL progressive scan DVD player?


Jeff
 

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it lies in the processing.


Some projectors are synchronous and some are Asynchronous.


What this means is that some can "deal" with other rates, some can't.


This is just the way it is.
 

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Dizzmann


Which ones can deal properly with changing refresh rates?


I've been trying to get to the bottom of this for ages.


Willem


DiLA should be async but it seems that JVC have made a fixed rate of 75.1Hz for some reason.


Jeff


As to why? I would guess price, the electronics to convert all incoming VGA to 60hz must be cheap and is probably brought off the shelf. The cost of putting a decent front end and testing it would probably put the projectors out of reach. I'm surprised that people don't notice tearing on projectors when used for the normal powerpoint stuff. There is normally lots of motion that would look bad in most presentations or does evryone run at 60Hz.


John
 

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1. Frame Rate conversion is expensive and difficult to do right.


2. It is impossible to tell from a spec sheet as most manufacturers do not bother with this as it is unimportant. 99% of all displays are getting 60 Hz. THe only other rates that matter are 75 and 85. THis is the reality of the entire world of display devices.


As far as finding out... I have been racking my brain trying to come up with a way of telling from a simple test either with a laptop or a video signal and a scaler.


Anybody have any thoughts?
 

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That could certainly explain why no matter what I try, 60Hz is best for smoothest playback on my LCD projector. Though if it's converting internally, I don't understand why if I give it something other than 60Hz, it indicates that refresh rate on the display, when pressing the projector remote Input button. I would think this would indicate the true refresh of the display, not what the input is "trying" to give it. So maybe it is asynchronous, but it so happens that 60 is still best :rolleyes:.


I have a Dell 1701FP flat panel which is optimized for 72Hz. Says right in the manual. Though it will take up to 75Hz. If I run it at 72Hz I get tearing on some scenes and some studder. If I run it at 60Hz, it's fine.


Guess you just have to go with whatever works, as it can get far too confusing than it's worth.


Carey
 

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My PJ (PLUs U2-1080) has a maximum color wheel speed of 7200 RPM (2 X 60 Hz). If you increase the refresh rate to 72 Hz the color wheel is unable to match this increase. There are two options in dealing with this problem:


1. Reduce the color wheel speed to 4320 RPM (1 X 72 Hz). This creates a severe rainbow effect.


2. Leave the spin rate at its maximum (7200 RPM)

which is not sync'd to the refresh rate. This causes tearing on my projector.


PLUS chose the second option for my PJ. Other manufacturers may chose the first option.
 

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Discussion Starter · #9 ·
This is not just a DLP problem, most if not all LCD projectors also have this. It is also worth noteing that these projectors are also used in PAL land which is 50 Hz. So is this just an issue with the VGA input? What happens with component?


Jeff
 

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LP 350 can handle everything between 45-85 Hz, but looks the best between 55-60 Hz.
 

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On a DLP you can tell if the projector is changing its update rate if you can hear the tone of the projector changing as you change refresh rates. Some are static but most are dynamic.


However, As Richard pointed out, some do double data rate at 60Hz to make the projector work at 2X.


I am not sure if the LT150 does that or not. One forum member commented that the rainbows were reduced the most at 60Hz. This could imply that the LT150 (which has a PLUS mechanical design) has the same 2X speed at 60Hz that Richard is refering to.


The d-ila likes 75Hz the best and that makes the frame cadence 3,3,3,4,3,3,... etc. instead of 3,2,3,2. Not perfect but an improvement.


I don't know what other LCD's do. Rember however the LCD pixels don't have much better than a 20ms response time, which means 60Hz is already too fast for them to completely react. I would bet most LCD's run at a 60Hz rate.


But most importantly, give the different refresh rates all a shot and find the one you like.


-Mr. Wigggles
 

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JohnAd, its interesting that you mention 75.1 as after reading the same discussion on a UK forum I checked my projector's signal from the HTPC and its vertical refresh rate was 75.1, and I get no screen tearing whatsoever at this rate on my Sony VPL-CX1.


James
 

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Quote:
Originally posted by Dizzman
As far as finding out... I have been racking my brain trying to come up with a way of telling from a simple test either with a laptop or a video signal and a scaler.


Anybody have any thoughts?
Video2000 contains a tearing test that can be run. Try different refresh rates, and the one that produces the least tearing is probably the one closest to the internal rate of the projector. The LT150 I believe is locked at 60Hz as that produces the least tearing, plus I can't hear a pitch change indicating a color wheel speed change when I switch refresh rates.
 

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Quote:
Originally posted by William
... I my case the DILA's panel refresh rate is 75 hz. The projector you have must have a native 60hz refresh rate.
William,

According to JVC's white paper, the crystals in the LCOS chips used in all G10/15/20 projectors can't update faster than 16mS (60Hz), regardless of the incoming refresh rate.


-Tom
 
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