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Discussion Starter · #1 ·
Hi,

I am trying to find a DLP projector (last generation color wheel) with no "tearing" problem when the video signal has a refresh rate of 72 or 75Hz. Has anyone tried these refresh rates on the Sharp Z10000, Marantz 12SP2 or Yamaha DPX-1000?

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Hi !


The HT300+ works fine at 48Hz ( at least Sim2 is changing boards on those that do not ! ) without any tearing. It also works at 50 and 60 Hz without any tearing. Why would you need 72 or 75Hz if 48 and 50 are working ?


midiboy
 

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There is no reason to goto 72 or 75 hz on these PJ's. Just use 60hz (if need be use powerstrip). midiboy is correct.
 

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@Paul_seng:


ONLY if it works correctly at 48 and 50Hz ... THEN it is not necessary to do 72 and 75Hz. 60Hz is just good for NTSC video. It certainly causes stuttering for PAL and NTSC film sources if the projector cannot work at 48/50Hz correctly ( without internally upconverting to 60Hz that is )


midiboy
 

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I was under the impression that all single chip DLP projectors converted everything to 60hz internally, and that actually displaying another rate would require a variable speed color wheel. Comments?
 

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Discussion Starter · #8 ·
Why 72 or 75Hz?

Because of less "rainbow" effects and because you get a less tiring picture.

Check a refresh rate of 50Hz and then 75Hz on your PC monitor, you will see a difference.

72 is for PAL, 75 for NTSC.
 

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Quote:
I was under the impression that all single chip DLP projectors converted everything to 60hz internally, and that actually displaying another rate would require a variable speed color wheel. Comments?
This is wrong. The DLP based products that are targeted for home use support 50 Hz and 60 Hz sources with no frame rate conversion (FRC). All of them use a variable wheel rate design.


Some have enough engineering margin in the design to allow 48 Hz sources to work without FRC. Some do not. This is dependent on the projector manufacturer's design trade-offs, not the underlying technology.
 

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Quote:
Why 72 or 75Hz?

Because of less "rainbow" effects and because you get a less tiring picture.

Check a refresh rate of 50Hz and then 75Hz on your PC monitor, you will see a difference.

72 is for PAL, 75 for NTSC.
I'm assuming you are talking about the flicker of a CRT based PC monitor? DLP based systems don't flicker the way CRT based systems flicker. They have rainbow effects; but, I've never seen ANYTHING that links rainbow effects to refresh rates.


For a DLP projection system, use 48 Hz for NTSC (film based), 50 Hz for PAL (film and video) and 60 Hz for NTSC (video based).


EDIT: It would certainly be interesting to know if the projectors you mentioned in the first post support 48 Hz.
 

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I think every projector has its own sweet spot when it comes to this. The JVC Dilas, at least the G series, loves something like 75.1, but from what I remember reading most projectors use 60. The best thing to do is experiment and see what happens
 

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People, for one thing, video is encoded closer to 60HZ (I'm talking ntsc and ATSC video,not PAL as I have no experience with PAL). All HD2 based PJ's are engineered with video, not computer signals, in mind (although you can still use 72 and 75 Hz refresh rates. But since the question was with HD2 based PJ's, not the business end one's (which like 72 and 75hz), 60hz is optimum for video (there is no tearing at all with 60hz).

The color wheel does not slow down or speed up when fed different signals, the PJ internally syncs the signal to match the PJ's internal refresh rate.
 

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Paul - I'm not trying to be combative but this is not correct:
Quote:
The color wheel does not slow down or speed up when fed different signals, the PJ internally syncs the signal to match the PJ's internal refresh rate.
When a pattern generator is attached via DVI to the InFocus 7200 sitting in front of me or the Samsung 61" RPTV in the corner, any change in the refresh (vertical sync) rate is compensated for in the color wheel by speeding and slowing to maintain sync. This is audibly noticeable but also measurable.


As for 60 Hz input vs anything else, it depends on the input device, doesn't it? If I have a DVD player that will do 3:2 removal, excellent scaling and output a perfect 48 Hz 720p stream, I would use it instead of the 60 Hz 480i/p DVD output for film based material.


I admit, I should have been MUCH more verbose or at least explained what I meant better in my previous posts. Sorry about that. :(
 

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Quote:
When a pattern generator is attached via DVI to the InFocus 7200 sitting in front of me or the Samsung 61" RPTV in the corner, any change in the refresh (vertical sync) rate is compensated for in the color wheel by speeding and slowing to maintain sync. This is audibly noticeable but also measurable.
This is true on the HT300Plus too. The color wheel is much more quiet (slower) at 48 and 50Hz compared to 60Hz and input frequency is NOT converted to 60Hz internally. At least not for frequencies between 47 and 60 Hz. Everything above that is being downconverted on the HT300+

Quote:
Why 72 or 75Hz?

Because of less "rainbow" effects and because you get a less tiring picture.

Check a refresh rate of 50Hz and then 75Hz on your PC monitor, you will see a difference.

72 is for PAL, 75 for NTSC.
As Huckster correctly stated this is only true for CRT based monitors/projectors. LCD/DLP devices do not need high refresh rates. On the contrary, my LCD TFT monitor gives a clearer and sharper picture at 60Hz compared to 75Hz.


midiboy
 
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