StooMonster
Prominent 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)
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)