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Discussion Starter · #1 ·
Is it so importante? I see a lot of you guys talking about programas to adjust that and so on..... can anyone explain why and how?
 

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You have to match the vertical refresh rate output by your videocard with the refresh rate expected by your display device. If they don't match, you will get stutters and possibly tearing.


For example, if your videocard outputs 60.0 hz, but your display device wants 59.94 hz, you will see a stutter/dropped frame every 16 seconds.


When you select 60 hz in your videocard's display panel, it may actually be output something else - not 60.0 hz as you would expect, but maybe something like 60.1 hz, or 59.8 hz, or maybe even 59.94 hz. There reason why it isn't exactly what you would expect is due to a hardware limitation on the videocard itself - which is why you would need a program like Powerstrip to change the various output timings to get it close to the refresh rate you really want.


With the later drivers for ATI and NVIDIA cards, you may not need to use Powerstrip to change videocard timings - you should be able to do this in the display panel settings. Your results may vary.
 

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There is also the issue if you are watching live TV, that your video card and display should be "locked" to the broadcast video rate.


If you are watching a 59.94Hz broadcast, but your display refresh rate is 72Hz, you can suffer from judder, resulting from some source frames being repeated, but others not.


This doesn't mean you have to fix the video/display refresh rate as the same as the broadcast rate, but there are common multiples etc., and it can alter depending upon whether you are watching film or video sources, and whether they are in 50Hz or 60Hz regions.


Examples being, 50Hz TV carrying film with 25fps movement is often displayed at 75Hz (with each frame repeated 3 times) , but 60Hz TV carrying 24fps film uses 3:2 pulldown, and so if you de-interlace and remove the 3:2 you can display this material at 72Hz (again with each film frame displayed 3 times)


(*) 24 and 60 are the rounded numbers - for actual broadcast 23.9 and 59.94 are used because of a legacy in the NTSC colour system.
 

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Discussion Starter · #5 ·
And how do I know when I put on a DVD what refresh rate does it really need so that I can select on powerstrip?
 

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Quote:
Originally Posted by sneals2000
Examples being, 50Hz TV carrying film with 25fps movement is often displayed at 75Hz (with each frame repeated 3 times) , but 60Hz TV carrying 24fps film uses 3:2 pulldown, and so if you de-interlace and remove the 3:2 you can display this material at 72Hz (again with each film frame displayed 3 times)


(*) 24 and 60 are the rounded numbers - for actual broadcast 23.9 and 59.94 are used because of a legacy in the NTSC colour system.
Hi


What about resolution ? I mainly watch r2 dvd's and have my resolution at 1280x720 with 72Hz in refresh rate. I should maybe switch to 75 Hz in refresh rate and 1536x864 (16:9 PAL) for a more correct picture ? Is that correct or what ?


Regards


Mads
 

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Quote:
Originally Posted by timetodoit
And how do I know when I put on a DVD what refresh rate does it really need so that I can select on powerstrip?
"PAL" DVDs will be 50Hz based. "NTSC" DVDs will be 59.94Hz based (aka 60Hz)


Basically - Europe and Australia = 50Hz, North America and Japan = 59.94Hz.


Now if you are watching a film sourced DVD - like a movie - then it is likely to be a 24 or 25 fps transfer.


In 50Hz land this will mean that the 50i signal only contains 25p material (with 2:2 pulldown), so a refresh rate of 50Hz, 75Hz or 100Hz would be good.


If the source is video (i.e. TV soaps, sport, light entertainment etc.) then 50Hz or 100Hz would be better (assuming your DVD replay software converts 50i to 50p, not 25p)


In 60/59.94Hz land there is the extra issue of 24/23.9 material employing 3:2 pulldown. If you are watching a feature film shot on film, and your DVD player software can reproduce this without 3:2 issues, then you should chose a 48/72/96 Hz refresh rate. (Or the 59.94 equivalent)


If you are watching video (rather than film) sources then 59.94Hz is probably best.
 

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Quote:
Originally Posted by MGR
Hi


What about resolution ? I mainly watch r2 dvd's and have my resolution at 1280x720 with 72Hz in refresh rate. I should maybe switch to 75 Hz in refresh rate and 1536x864 (16:9 PAL) for a more correct picture ? Is that correct or what ?


Regards


Mads
16:9 PAL in square pixels is 1024x576 at 50Hz. The 702x576 16:9 anamorphic material on a DVD is remapped to this format (NB: 720x576 material is remapped to 1050x576 - 720x576 is a little bit wider than 16:9 to allow for timing errors in D/A and A/D conversion)


If you are watching film material on R2 "PAL" (not R2 Japan "NTSC") discs then the material will have a 25fps frame rate (The two 50i fields will be from the same frame, so a simple weave de-interlace will create a clean 25p sequence if all is well)


To display this clearly, a 50Hz (one source frame repeated twice), or 75Hz (on source frame repeated three times) will avoid needless judder.


If you are watching video sourced material - and your PC creates a 50p sequence from 50i (i.e. a frame per field) for fluid motion - then 50Hz or 100Hz refresh rates are better. A 75Hz refresh rate will favour some fields/frames more than others.


1024x576 @ 50Hz progressive is effectively square pixel 576p.


However it depends on your display device what resolution you run on it. If you are using a 1280x720 display (like a DLP or LCD device) then it makes sense to keep your PC running at this resolution - unless the display device has a better scaler than your PC software.
 

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First your refresh rate needs to match your display. Then you want to adjust the refresh rate (if you can) to eliminate flicker, especially on CRTs. Also some hardcore gamers claim to have better scores on faster refresh rates since they can see changing scenes sooner. For any video related display you would want to keep refresh rate at something standard like 50Hz,60Hz,75HZ or 120 Hz and here Powerstrip is not needed. Most people use powerstrip to adjust resolution and other discrete video timings, like pixel timing, to match their computer video card to TV display which uses totally different settings. Since it's something rather new to use let's say HD LCD TV as computer monitor and settings and resolutions available on video card wouldn't match anything close to what your TV would like, powerstrip sometimes was the only way to get things work properly (Thank you, author of powerstrip). Lately, most newest video drivers have more settings compatible with HD TV needs and the whole thing becomes another chapter in history. You could experiment with different refresh rates and see what works best for you and your equipment. As far as myself, anything CRT I ran at over 75 Hz, otherwise I see flicker which bothers me, anything LCD I'll run at 60 Hz.
 

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Discussion Starter · #10 ·
Humm ok thanks guys but....... HOW ABOUT the 1:1PIXEL how can i check if it's ok? Is there a program that can tell me like "Your pc matchs the projector on 1:1 pixel"?
 

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Quote:
Originally Posted by timetodoit
Humm ok thanks guys but....... HOW ABOUT the 1:1PIXEL how can i check if it's ok? Is there a program that can tell me like "Your pc matchs the projector on 1:1 pixel"?
No but there are test patterns you can search for - also a seach will probably tell you if your projector can do 1:1 pixel mapping.


Brian
 

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Quote:
Originally Posted by maxleung
You have to match the vertical refresh rate output by your videocard with the refresh rate expected by your display device. If they don't match, you will get stutters and possibly tearing..
I would say you want to match the refresh rate of your display to the frames per second of the source. If you don't it's going to judder. (You also need to run reclock.)


Therefore

PAL = 25 fps = 50hz or 75hz

NTSC film =- 23.976fps = 47.952 or 71.928hz

NTSC video = 29.9xxfps = 59.94hz


Of course you need a true multisync display device.
 

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Quote:
Originally Posted by Mark_A_W
Therefore

PAL = 25 fps = 50hz or 75hz
Whilst this is true for "PAL" sources carrying 25fps film, "PAL" video has a 50fps interlaced frame rate - so 75Hz may cause noticable judder on video sourced material where each field is de-interlaced to create a display frame (i.e. 50i converted to 50p) - which the better de-interlacing software solutions provide for. (i.e. the two fields in a 50Hz interlaced frame are from two DIFFERENT points in time, separated by 1/50th of a second - hence the more fluid motion of 50i vs 25p)


The poorer implementations de-interlace 50i video to 25p - thus removing the fluid motion. (Though 25p is less computationally intensive, so better suited to lower power PCs)


What this means is that whilst 25p sources - like "PAL" "film" material, or PAL video that has been shot at 25p (now possible) or post-produced to 25p for the film-look (common on UK drama like the new Dr Who and other mid-range drama) - will look good at 75Hz, video production at 50i - like sport, entertainment shows, soaps etc. may appear to have motion judder - as 75Hz display of 50Hz video will repeat some fields more than others.


(The reason I put "PAL" in quotes - is that PAL isn't really used for much 50Hz material any more. PAL is the composite sub-carrier system used for analogue broadcasting - digital component techniques, and MPEG2, are used for DVDs and Digital TV - and have nothing to do with "PAL"... My mainstream viewing of TV and DVD hasn't involved much PAL since 1998...)
 

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Quote:
Originally Posted by sneals2000
16:9 PAL in square pixels is 1024x576 at 50Hz. The 702x576 16:9 anamorphic material on a DVD is remapped to this format (NB: 720x576 material is remapped to 1050x576 - 720x576 is a little bit wider than 16:9 to allow for timing errors in D/A and A/D conversion)


If you are watching film material on R2 "PAL" (not R2 Japan "NTSC") discs then the material will have a 25fps frame rate (The two 50i fields will be from the same frame, so a simple weave de-interlace will create a clean 25p sequence if all is well)


To display this clearly, a 50Hz (one source frame repeated twice), or 75Hz (on source frame repeated three times) will avoid needless judder.


If you are watching video sourced material - and your PC creates a 50p sequence from 50i (i.e. a frame per field) for fluid motion - then 50Hz or 100Hz refresh rates are better. A 75Hz refresh rate will favour some fields/frames more than others.


1024x576 @ 50Hz progressive is effectively square pixel 576p.


However it depends on your display device what resolution you run on it. If you are using a 1280x720 display (like a DLP or LCD device) then it makes sense to keep your PC running at this resolution - unless the display device has a better scaler than your PC software.
My projector is a CRT Barco Data 808 so I can display many resolutions. 95 % of my dvd's are region 2 (europe) so would you recommend 1536x864 with 75 Hz refresh rate or is that totally misunderstood ?


Mads
 

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Hi sneals2000 and Mark_A_W,

Thank you for the great posts and clearing up a lot of confusion around here. Living in PAl land, i would also like to add that 50Hz refresh rate is critical for viewing of PAL 720p HDTV material. These 1280x720 @ 50FPS stuff would look awful on a 60 or 75Hz display.

Have been serching for a multisync digital display device (projector and lcd panel). Any info would be much appreciated.
 

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Mariner - I have found that PAL 50i material works fine at 75hz, but for 50p PAL, it obviously doesn't. But as PAL movies are 25p I'm not loosing any sleep over it.


I don't think there really is a true multisync digital display device - not the way a CRT is multisync.


Sneals2000, a PAL mpeg 2 DVD is still "PAL", in that it represents a PAL analogue signal in the same way that a "NTSC" mpeg 2 DVD is still NTSC. Even the new HD stuff is still "PAL" or "NTSC".....sort of...


MGR, I'd use 1440x768 at 75hz for an 808 with PAL (I have a PG Xtra....actually 4 PG Xtras....)
 

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Quote:
Originally Posted by Mark_A_W
MGR, I'd use 1440x768 at 75hz for an 808 with PAL (I have a PG Xtra....actually 4 PG Xtras....)
Hi Mark,


Why 1440x768 at 75 Hz and not 1536x864 ? I thought PLA was 576 lines and with widescreen 16x9 you just calculated with that. Can you enlighten me :) ?


Regards

Mads
 

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Quote:
Originally Posted by Mark_A_W
Sneals2000, a PAL mpeg 2 DVD is still "PAL", in that it represents a PAL analogue signal in the same way that a "NTSC" mpeg 2 DVD is still NTSC.
Except :

1. 576/50i YCrCb data encoded in MPEG2 4:2:0 is NOT a representation of a PAL analogue signal, it is a digital representation of a 576/50i analogue component signal. No PAL involved - the 576/50i analogue component could equally be describing a MAC or SECAM signal...

2. There is no PAL analogue signal involved in the production chain these days


Sure the source for the DVD could be PAL composite (say in the case of a video production made before the 90s) - but it doesn't HAVE to be PAL composite... It could be PAL-less analogue or digital component (or SECAM for that matter) sourced.


There IS/WAS a digital PAL composite system (known as 4fsc because the sampling rate is locked to 4 times the subcarrier). However 4fsc was only in widespread use for broadcast VTRs like D2 and D3. It is no longer in widespread use (though the BBC used it for their PAL composite 4:3 production throughout the 90s) - and wouldn't be used for domestic applications as it wasn't as easy to compress as component video - it was a true analogue representation of the PAL composite signal, subcarrier and all.

Quote:
Even the new HD stuff is still "PAL" or "NTSC".....sort of...
I've never heard a broadcast engineer describe HD as "PAL" or "NTSC". I've only ever heard them use the line standard - especially as in PAL regions you have :


1080/25p

1080/50i

720/50p

720/25p

576/50p

576/25p

576/50i 4:3

576/50i 16:9


at least as 50Hz formats in potential SD and HD production and/or broadcast use.


Sure you may get people using it to differentiate between 50Hz and 60Hz signals - but it is poor slang.


PAL = Phase Alternate Lines.


It is the subcarrier modulation technique used to modulate a 4.43MHz (for most 625/50) or a 3.58MHz (for 525/60 in Brazil and some 625/50 in other bits of South America) subcarrier used in analogue composite video. It defines nothing else.


Modern production techniques haven't used PAL composite since the 90s - when component analogue and component digital production techniques arrived. Now that digital delivery systems (with component or RGB outputs) - DVD, DVB, ATSC etc. - are available for standard definition delivery - there are no composite elements in most production chains - from camera to screen - so there is no PAL subcarrier, hence no PAL.


Sloppy short-hand has developed, whereby 625/50 digital component is described as "PAL", and 525/60 digital component as "NTSC" - even DVDs (very annoyingly) use it on their packaging. Doesn't mean it is correct.


Whilst NTSC also defines the line standard (525/60) - and could arguably be more accurately used, PAL doesn't even define a line standard as it is deployed in both 525/60 and 625/50 regions, unlike NTSC.
 

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Quote:
Originally Posted by Mark_A_W
Mariner - I have found that PAL 50i material works fine at 75hz, but for 50p PAL, it obviously doesn't. But as PAL movies are 25p I'm not loosing any sleep over it.
But in motion terms there should be no difference between 50p material and 50i material converted to 50p for display. (Sure some of the detail might be a bit softer in the 50i sourced material, but the number of source frames each second will be the same. After all 50i video is derived from CCD cameras these days, and these are 50p devices internally, creating a 50i video output by line averaging each 50p frame using a line-offset to improve the resolution between fields.)


As there is little-to-no 576/50p production gear in the market place, 576/50p material is usually derived by downconverting 1080/50i, 1080/25p, or up converting 576/25p or 576/50i. Don't think there are many people shooting 720/50p for 576/50p yet - though this may change if Europe embraces 720/50p.


This implies to me that 50p is identical in motion issue terms to 50i upconverted to 50p - which any PC based display system should do (rather than downconvert 50i to 25p, unless the source material is 25p - i.e. film or 25fps video)

Quote:
I don't think there really is a true multisync digital display device - not the way a CRT is multisync.
I think that it depends on the display technology and how it is implemented. I think some plasmas, DLPs and LCDs will run at 50 and 60Hz natively - but I believe you may well be correct about the other frequencies.


This may well mean for non-CRT applications the refresh rate the PC runs is irrelevant to a degree, as it is re-sampled in the projector anyway? Others may well be able to post accurately on this.


I know some early plasmas sold in 50Hz regions actually did a naff 50/60 conversion and looked dreadful...
 

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Quote:
Originally Posted by MGR
Hi Mark,


Why 1440x768 at 75 Hz and not 1536x864 ? I thought PLA was 576 lines and with widescreen 16x9 you just calculated with that. Can you enlighten me :) ?


Regards

Mads
864 is beyond the spotsize and bandwidth capabilities of the projector - it will soften. So this is why I suggest 786p. You'll probably get objectionable scanlines at 720p. I use 1920x1080i at 75hz BTW - beyond the spotsize limit, but not beyond the bandwidth due to interlacing.


Then you have to pick either a 16:9 square pixel res, or cleaner (2xDVD) horizontal scaling. It depends what you watch on the pj.


Sneals - 50hz flickers, 100hz is beyond the bandwidth capabilities of almost any pj. 75 is the compromise. We have no 720 50p material here (one OTA channel is 576 50p, but it sucks), so it doesn't matter.
 
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