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Vertical Refresh Rates for plasmas and LCDs - does your screen Frame Rate Convert?

StooMonster

Well-known Member
Simple definition
Vertical Refresh Rate (VRR) is how many times a second the screen is redrawn with a new image -- e.g. 60Hz is 60 complete frames per second.

Some displays say they can accept huge ranges of Vertical Refresh Rates -- e.g. Panasonic plasmas can accept and display video signals with VRR of 48Hz through 120Hz.

But are they really displaying these rates?
Modern analogue displays (CRT, RPTV, CRT-projectors) can display almost any available VRR with no problems and no Frame Rate Conversion.

However, many digital displays (plasmas, LCDs, LCD-projectors) have an internal frame buffer which performs a Frame Rate Conversion. How this works is the display will sample the image at the frame buffer's own rate and do a Frame Rate Conversion on the source material. What this means is that it will introduce "motion judder" and/or "tearing artefacts". :(

For example, if a screen has a fixed Internal Frame Buffer of 60Hz and it's fed a 50Hz signal (e.g. PAL) it will add additional frames to increase 50fps to 60fps, or if it's fed a 75Hz signal (e.g. PC or PAL with 3:3 pull down) it will drop frames to decrease 75fps to 60fps.

How can I tell?
Visible judder to tearing is a give away, especially visible on scrolling titles on television programmes. For example, if you are watching 50Hz PAL signal (e.g. Sky digital or DVD) and "credits" stutter and judder then it's quite likely your screen is Frame Rate Converting to 60Hz.

Even better way to test: “judder tester”.

A "judder tester" is a moving bar test pattern, intended to identify the frame rates at which a digital display will operate.

There is a useful PC program called "judder test" that you can use (if you can plug PC into your display) which is available here, there is also a Microsoft MWP9 test pattern (hard to get hold of), and the DVDO iScan HD.

These "judder testers" all consist of a vertical bar which moves slowly either back and forth or simply across the screen. The bar's motion is updated once in each VRR period (e.g. 50Hz), and it moves a fixed number of pixels horizontally in each VRR period.

If the digital display is not performing any frame rate conversion -- i.e. it is actually displaying the output frame rate of the judder test -- the motion will be very smooth. However, if the digital display is performing any type of frame rate conversion there will be very noticeable stutter introduced in the smooth motion. Not just limited to "judder" either; there may also be other objectionable artefacts introduced depending on how the display actually performs the Frame Rate Conversion. These include tearing (top and bottom portion of the bar are horizontally misaligned) and image distortion.

How did my tests go?

Panasonic plasma has three level internal frame buffer: 48Hz, 50Hz, 60Hz. No Frame Rate Conversion on common sources (NTSC, PAL, DVI, NTSC 2:2 pulldown), but 3:3 pulldown is out (for NTSC 72Hz and PAL 75Hz).

* American Panasonic screens may only support 60Hz.

Pioneer MXE plasma has one internal frame buffer: 70Hz. PAL (50Hz) and NTSC (60Hz) and DVI input (60Hz) and 3:3 pulldown are internally converted to 70Hz and introduce judder at best, and tearing at worst.

* New Pioneer screens claim 100Hz buffer, I'm interested to know what that means ... is it like Panasonic one where 50Hz signal is displayed twice, or have they changed Internal Frame Buffer to 100Hz up from 70Hz?

Grundig 17” Widescreen LCD has one internal frame buffer: 60Hz. Explains why Sky digital has jerky picture in my bedroom.

* I understand that most LCDs have 60Hz internal buffer, is this right?

Dell 17" LCD monitor has two internal frame buffers: 60Hz and 75Hz. NTSC and PAL 3:3 or DVI @ 75Hz look great!

What can you do if your screen has rubbish Frame Rate Conversion that judders or even worse tears?
Check out DVDO iScan HD, it's got excellent Frame Rate Conversion feature that minimises the effects; and probably does it much better than internals of display. Even mad 60Hz DVI look almost acceptable with PAL for me.

* Yes Gordon, sure the Lumagen scalers have the same feature. ;)

So, what does your screen support?
Post below and let us know, expand the knowledge base!

Final note: sometimes US sourced screens only support 60Hz internal frame buffers whereas non US models of same screen support multiple refresh rates.

StooMonster (see Acknowledgement in DVDO iScan HD manual)
 
E

Eagerbeaver

Guest
I thought the 434/504 HDE Pioneers supported both 60Hz and 72Hz user selectable by the pure cinema function.
 

SimonO

Novice Member
Pioneer literature states that on both the new 434/504HDE models the pure cinema feature runs PAL film based material at 75Hz...
 

StooMonster

Well-known Member
Good job I didn't mention Pioneer HDE in my piece then wasn't it? ;)

Now, have you tested this or just going by the literature, which is often not completely true. :)

So, what does your screen support?
Data and tests results obviously preferred to marketing collateral. :)

StooMonster
 
E

Eagerbeaver

Guest
Mine is currently packed away whilst decorating so I'll have to wait and see, unless someone else gets to test theirs.
 

MattB

Standard Member
My 433MXE tears/jerks horribly through the VGA and DVI inputs but looks smooth through the others (for PAL and NTSC). Has anyone found a 'magic rate' which is accepted and gives smooth motion with a PC source?

I use a nvidia G4 Ti 4600 graphics card and wonder how much of the problem is at that end?
 

SimonO

Novice Member
StooMonster, where are Pioneer claiming 100Hz frame buffer on new models..?
 

Jasonjo

Well-known Member
Stu,

Nice post, I was wondering the other day if had found all of the internal rates supported on my Panny...

Panasonic plasma has three level internal frame buffer: 48Hz, 50Hz, 60Hz. No Frame Rate Conversion on common sources (NTSC, PAL, DVI, NTSC 2:2 pulldown), but 3:3 pulldown is out (for NTSC 72Hz and PAL 75Hz).
Exactly what I found with my Panny PWD6 when using the 'judder test pattern' on my iScan HD.

JJ
 

StooMonster

Well-known Member
Originally posted by MattB
My 433MXE tears/jerks horribly through the VGA and DVI inputs but looks smooth through the others (for PAL and NTSC). Has anyone found a 'magic rate' which is accepted and gives smooth motion with a PC source?

I use a nvidia G4 Ti 4600 graphics card and wonder how much of the problem is at that end?
See above in first post, 70Hz is the internal frame buffer of MXE plasma. At least it was on the 50" one I tried. :)

StooMonster
 

StooMonster

Well-known Member
Originally posted by SimonO
StooMonster, where are Pioneer claiming 100Hz frame buffer on new models..?
Note sure if it is Internal Frame Buffer, which is why I said "* New Pioneer screens claim 100Hz buffer, I'm interested to know what that means ... is it like Panasonic one where 50Hz signal is displayed twice, or have they changed Internal Frame Buffer to 100Hz up from 70Hz?"

It was on some printed collateral I got from my local hi-fi retailer, will look up later; it says "100Hz progressive scan" whatever that means!

Try GOOGLE "+pioneer +plasma +100Hz" (all three words required in any order) http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=+pioneer++plasma++100Hz&btnG=Search generates 19,600 results. So it must be mentioned quite frequently!

StooMonster
 

kaspj

Standard Member
Thanks Stoo. Very useful follow-up to your previous comments on Panny refresh rates.

*DVI card question removed - answered on Panny Series 7 thread

JP.
 

Jackass

Well-known Member
Stoo,

Is there any chance of you making a sticky with a definative list of all panels that accept native rez via DVI, VGA and whether or not they are HDCP compliant (DVI port only) and wether they frame rate convert the incoming signals on DVI and VGA?

You seem to be the man for the task with all the knowledge and this would be a god send for making future purchases :)

Steve.
 

rscott4563

Standard Member
I'd definitely second that, a sticky list would be great and very much appreciated..

Ryan :smashin:
 

StooMonster

Well-known Member
Originally posted by Jasonjo
Yes IIRC. PAL @ 60Hz is actually pretty good....
Originally posted by Urotsukidoji
I agree pal at 60hz is perfectly watchable. You get used to it very quickly.
Depends what's doing your frame rate conversion, some good some bad.

Do I notice it on my LCD television, not really too much ... except when there's movement, or scrolling text then it's horrible (regardless of the convertor).

Not the best way to view PAL.

And no it doesn't reduce "ringing" or "solarisation" viewing PAL at 60Hz either -- to anwer an email in a thread.

Some people don't notice adding the extra frames, example is the Pioneer MXE that have 70Hz internal frame buffer they frame convert PAL and NTSC to 70Hz and add judder.

The brain easily becomes accustomed to anything.

Originally posted by GarethH
Do you still see the pulldown effect with NTSC on Plasmas then?
Yes.

Unless you have the likes of an DVDO iScan HD that plays NTSC movies at 48Hz with 2:2 pulldown and no judder ... hurrah! (Assuming your plasma has an internal frame buffer that allows 48Hz).

StooMonster
 

StooMonster

Well-known Member
When I wrote the first post in this thread I was hoping it would be a Sticky, and people would post details about the internal frame rates of the screens... guess testing it is beyond the skills or inclination of most. :blush:

I thought it was down to Spectre or the moderators to make things sticky -- I don't know how to do it.

StooMonster
 

StooMonster

Well-known Member
Originally posted by Urotsukidoji
Is the judder worse than pal at 60hz?
Yes it is because the scaler is upping PAL to 75Hz, then the internal frame buffer is downing that to 60Hz and not necessarily picking the correct frames.

This will look much more juddering than converting PAL to 60Hz, which is what you have to put up with if you want to use DVI (at the moment).

StooMonster
 

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