Can LCDs can change display refresh rates? Is true 24p possible in Europe? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 25 Old 01-19-2010, 02:18 AM - Thread Starter
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I'm trying to get to the bottom of whether any LCDs can actually change their refresh rates, and therefore whether European LCDs can actually display a 24fps signal in a true manner (i.e. with a even pulldown ratio of n:n at 24Hz, 48Hz, 72Hz, 96Hz, 120Hz etc). Please, please help! I've searched and searched and found no definitive answer on this - I can't believe no one seems to know when it's such a major point!

Are the TVs that are sold in Europe as 50Hz/100Hz (and in the US as 60Hz/120Hz) actually the same? i.e. Can a UK TV sold as a 100Hz alter its refresh rate to 120Hz when input with a 60Hz or 24Hz signal (at 5:5 pulldown) or does it do some kind of uneven pulldown to get it to 100Hz?


I've seen arguments both ways - those who say LCDs can't change their diplay refresh rate insist all LCDs simply always run at their max refresh rate - in which case even 50Hz Euro TVs that claim to be able to display true 24p refresh rates are actually using some kind of 3:2 pulldown. Those who claim this also say that the only TVs available that can truly display a 24p output correctly are 120Hz or 240Hz TVs that display 24p on a 5:5 or 10:10 pulldown. If this is the case - how does the fact that US 120Hz TVs are clocked at 100Hz in Europe affect this? If the advocates of LCDs only have one refresh rate are correct, then surely the European 100Hz TVs will not be able to perform 5:5 pulldown (neither will UK 200Hz TVs be able to perform a pure 24p pulldown) and therefore no one in Europe can really see 24p output!

Then there are those who claim that certain LCDs can change their refresh rate. In which case you have 50Hz TVs that can run at 48Hz to show true' 24p, and 100Hz TVs that can run at 96Hz to do the same).

I currently own a Samsung LE40N87BDX which I was always under the impression could take a 24p input and display it correctly (at 48Hz I believe). Reasons I take this to be the case include the facts that:
1) The TV display indicates 24Hz when the TV is being force fed a 24p signal (though this could of course merely refer to the input signal)
2) I'm fairly sure I can detect a difference in the picture/judder when playing Blu-Ray via a PS3 on the forced 24p mode and the 50Hz mode. 24p is smoother - 50Hz has 3:2 pulldown judder..
3) The presence of the infamous Samsung hum bars during 24Hz mode - they are only present during this mode, indicating something certainly is different with the TVs display.
But I may be wrong of course!

Some background on this argument (with no definitive answers!) can be found here:
http://www.avsforum.com/avs-vb/showthread.php?t=1161285

Can anyone who really knows their stuff (or thinks they might!) help settle this once and for all?

Help! Help! Help! Please!
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post #2 of 25 Old 01-19-2010, 11:14 AM - Thread Starter
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Can anyone help with this?
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post #3 of 25 Old 01-19-2010, 01:58 PM
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I can help a little.
The INFO button on your Samsung remote is telling you what resolutio the Samsung is receiving.
3:2 pulldown only occures with 60Hz TVs when 24fps content is converted to 60fps content,
The electronic circuits and the refresh rate of the screen are based on the your countrys electrical power. Which is why in the US we have 60HZ, 120Hz and 240Hz models we have no models that can refresh at more then one rate. And in Europe you have 50Hz and 100Hz model.
If BR disks were encoded in 1080p/25 your 50Hz model would use 2:2 pulldown.
Hopefully one of the Brits that frequent these Forums will answer your options for 1080p/24 BR disks.
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post #4 of 25 Old 01-19-2010, 05:24 PM
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A german magazine says:48hertz would not work with plasma/lcd you would
get troubles with picture-quality,it should be 72,96,120.

On a dutch forum someone told me yesterday that
the tv changes 24(ps3 1080P24) into 72 hertz .

The best lcd's for stuff like this are the high-end SONY's.
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post #5 of 25 Old 01-20-2010, 01:34 AM - Thread Starter
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Thanks for this - but right away you see the problem? Two posters - both giving different answers to the title question - 8mile claiming that TVs can change the refresh rate while walford claims they can't.
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post #6 of 25 Old 01-20-2010, 02:57 AM
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My Sharp LC46D64U LCD TV (US model) can switch between 60 Hz refresh (broadcast TV) and 48 Hz refresh (1080p24 from a blu-ray using 2x2 pulldown). This means that LCD TVs with variable refresh rates are definitely doable. Also, you do not get any flicker from an LCD running at 48 Hz due to the sample & hold nature of the LCD display (A plasma TV would flicker unacceptably).

In Europe, they usually speed up the movie by 4% so the player outputs 1080p50 using 2x2 pulldown. There probably are some European TVs that can switch between 48 and 50 Hz (or between 96 and 100 Hz).

Daniel Lang
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post #7 of 25 Old 01-20-2010, 04:18 AM
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Quote:
Originally Posted by dblang View Post

My Sharp LC46D64U LCD TV (US model) can switch between 60 Hz refresh (broadcast TV) and 48 Hz refresh (1080p24 from a blu-ray using 2x2 pulldown). This means that LCD TVs with variable refresh rates are definitely doable. Also, you do not get any flicker from an LCD running at 48 Hz due to the sample & hold nature of the LCD display (A plasma TV would flicker unacceptably).

True - but you have the inherent LCD blur at lower frame rates because of the hold-type-nature.

Quote:


In Europe, they usually speed up the movie by 4% so the player outputs 1080p50 using 2x2 pulldown. There probably are some European TVs that can switch between 48 and 50 Hz (or between 96 and 100 Hz).

One needs to differentiate two things in Europe: SD and HD material.

For SD material all European sets have to accept 50 Hz material because the color systems (PAL or SECAM) are based on 50 Hz similarily like NTSC is based on 60 Hz.
Examples for SD are tuner reception or DVDs - the latter indeed suffer from the (in Europe) well-known "PAL speedup" like Daniel described above. While the movie is sped up by 4% and, unless electronically corrected, the audio is higher pitched compared to movies in the cinema, us Europeans don't have the inverse 3:2 pulldown with the well-known judder.

Many manufacturers made their TVs also accept 60 Hz video (to use the same components or software) so there is an unofficial video format called "PAL 60". When fed with RGB video from a good DVD player one can show US DVDs on such a European set (or setup a games console/PC to use 60 Hz mode).

For HD the whole affair is different:
To get a "HD ready" logo in Europe the manufacturer has to make the TV set accept 720p and 1080i with 50 and 60 Hz!
Most (all?) Full HD sets also accept 1080p with 50 and 60 Hz - 24p was added later, too, as us Europeans, not used by the 3:2 pulldown, protested drastically and didn't buy many HD sets...

While not required I'm assuming that the LCDs offering 100 Hz modes in Europe will also switch to 120 Hz to simplify matters (as they have to accept 60 Hz anyway).

The implications are clear: The manufacturer can use the same methods to display HD material like on a bog-standard US HD-TV set. The same results should be achieved and are expected because, like above, manufacturers try to use the same tech in different territories to save costs.
AFAIK all European Blu-ray players are also capable of playing 60 Hz material.

Therefore one should be able to watch all US Blu-ray disks on European equipment like a person in the USA would. If the Blu-ray has 24p-material on it but the TV can't accept 24p then it would have to use the inverse 3:2 pulldown, too.

(Everything above to the best of my knowledge, please correct if necessary!)

bye
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post #8 of 25 Old 01-20-2010, 06:27 AM
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Quote:
Originally Posted by dblang View Post

My Sharp LC46D64U LCD TV (US model) can switch between 60 Hz refresh (broadcast TV) and 48 Hz refresh (1080p24 from a blu-ray using 2x2 pulldown). This means that LCD TVs with variable refresh rates are definitely doable. Also, you do not get any flicker from an LCD running at 48 Hz due to the sample & hold nature of the LCD display (A plasma TV would flicker unacceptably).

In Europe, they usually speed up the movie by 4% so the player outputs 1080p50 using 2x2 pulldown. There probably are some European TVs that can switch between 48 and 50 Hz (or between 96 and 100 Hz).

Daniel Lang

I could not find a link to the user manual for your TV and could only determine from the Sharp Website that it was a 1080p 60Hz model. Which would mean that it would use 3:2 pulldown to play 24fps content from a BR disk.
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post #9 of 25 Old 01-20-2010, 06:38 AM
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Quote:
Originally Posted by 8mile13 View Post

A german magazine says:48hertz would not work with plasma/lcd you would
get troubles with picture-quality,it should be 72,96,120.

On a dutch forum someone told me yesterday that
the tv changes 24(ps3 1080P24) into 72 hertz .

The best lcd's for stuff like this are the high-end SONY's.

There have been some 72Hz Plasma models sold in the US which use 3:3 pulldown when playing 24fps content in order not to have "3:2 puilldown" Judder.
I agree the top end Sony models appear to handle 24fps content as good or better then other models.
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post #10 of 25 Old 01-20-2010, 07:09 AM
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Unlike plasma and CRT (which have to constantly refresh an image by illuminating the pixel), there is no inherent refresh rate in an LCD. Once an LCD pixel is set to a color, it stays that way until it changes. This is why LCDs have response times (4ms, 2ms, etc) whereas response times aren't really relevant for plasma and CRT.

As long as the refresh rate doesn't exceed the panel's minimum response time, it can theoretically be varied however the manufacturer wants. So a 50Hx/100Hz set and a 60Hz/120Hz set can have the exact same panel, and it's up to the video processing electronics in the set to tell the LCD when to change the color being displayed by each pixel.

So it all comes down to how the video processor in the set handles source material. Depending on how the video processing circuitry has been designed, a PAL set can definitely display 24Hz content at its native cadence. It's possibly easier on an NTSC set since there are common multiples like 120Hz, but it can be done on a PAL set.

It just depends on how each manufacturer implements it. Maybe one of the UK or European home theater magazines that does testing verifies this like many North American magazines and reviewers do.
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post #11 of 25 Old 01-20-2010, 07:28 AM - Thread Starter
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Quote:
Originally Posted by scottacus View Post

Unlike plasma and CRT (which have to constantly refresh an image by illuminating the pixel), there is no inherent refresh rate in an LCD. Once an LCD pixel is set to a color, it stays that way until it changes. This is why LCDs have response times (4ms, 2ms, etc) whereas response times aren't really relevant for plasma and CRT.

As long as the refresh rate doesn't exceed the panel's minimum response time, it can theoretically be varied however the manufacturer wants. So a 50Hx/100Hz set and a 60Hz/120Hz set can have the exact same panel, and it's up to the video processing electronics in the set to tell the LCD when to change the color being displayed by each pixel.

So it all comes down to how the video processor in the set handles source material. Depending on how the video processing circuitry has been designed, a PAL set can definitely display 24Hz content at its native cadence. It's possibly easier on an NTSC set since there are common multiples like 120Hz, but it can be done on a PAL set.

It just depends on how each manufacturer implements it. Maybe one of the UK or European home theater magazines that does testing verifies this like many North American magazines and reviewers do.

Hey Scottacus - thanks for your post (and all the rest of you too!). I'm now leaning more to the idea that LCDs CAN have different display refresh rates (which i obviously hoped was true). You'd think this would be more talked about or clarified in reviews etc but it is usually glossed over - and people seem to know very little about it. I have posed this same question on the UK forum AVForums several times and had no sensible replies!
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post #12 of 25 Old 01-20-2010, 07:38 AM - Thread Starter
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Quote:
Originally Posted by Benny42 View Post

True - but you have the inherent LCD blur at lower frame rates because of the hold-type-nature.



One needs to differentiate two things in Europe: SD and HD material.

For SD material all European sets have to accept 50 Hz material because the color systems (PAL or SECAM) are based on 50 Hz similarily like NTSC is based on 60 Hz.
Examples for SD are tuner reception or DVDs - the latter indeed suffer from the (in Europe) well-known "PAL speedup" like Daniel described above. While the movie is sped up by 4% and, unless electronically corrected, the audio is higher pitched compared to movies in the cinema, us Europeans don't have the inverse 3:2 pulldown with the well-known judder.

Many manufacturers made their TVs also accept 60 Hz video (to use the same components or software) so there is an unofficial video format called "PAL 60". When fed with RGB video from a good DVD player one can show US DVDs on such a European set (or setup a games console/PC to use 60 Hz mode).

For HD the whole affair is different:
To get a "HD ready" logo in Europe the manufacturer has to make the TV set accept 720p and 1080i with 50 and 60 Hz!
Most (all?) Full HD sets also accept 1080p with 50 and 60 Hz - 24p was added later, too, as us Europeans, not used by the 3:2 pulldown, protested drastically and didn't buy many HD sets...

While not required I'm assuming that the LCDs offering 100 Hz modes in Europe will also switch to 120 Hz to simplify matters (as they have to accept 60 Hz anyway).

The implications are clear: The manufacturer can use the same methods to display HD material like on a bog-standard US HD-TV set. The same results should be achieved and are expected because, like above, manufacturers try to use the same tech in different territories to save costs.
AFAIK all European Blu-ray players are also capable of playing 60 Hz material.

Therefore one should be able to watch all US Blu-ray disks on European equipment like a person in the USA would. If the Blu-ray has 24p-material on it but the TV can't accept 24p then it would have to use the inverse 3:2 pulldown, too.

(Everything above to the best of my knowledge, please correct if necessary!)

Hey Benny42,

Thanks for your post. I'm trying to distinguish here between input signals and display - I'm aware that HD TVs can accept pretty much any input frequency below upto their Hz clocking, I'm talking about what the display refresh rate will actually be.

On another note if we're all agreed (seemingly) that the technology inside a US 60Hz (or 120Hz) model is, on the whole, the same as a Euro 50Hz (or 100Hz) model then are the UK and US models actually identical? I.e. Can a model sold in the UK as 100Hz can actually DISPLAY at 120Hz when necessary? I have heard this suggested by many UK posters on forums - they claim that 50Hz/100Hz is used to sell TVs in UK because it relates to the native TV frequency, and that they are in fact identical in display capabilities to their US counterparts.
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post #13 of 25 Old 01-20-2010, 07:50 AM
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Quote:
Originally Posted by snowdon-goat View Post

I.e. Can a model sold in the UK as 100Hz can actually DISPLAY at 120Hz when necessary? I have heard this suggested by many UK posters on forums - they claim that 50Hz/100Hz is used to sell TVs in UK because it relates to the native TV frequency, and that they are in fact identical in display capabilities to their US counterparts.


I believe a 100 hertz flatscreen means 100 hertz is its maximum.
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post #14 of 25 Old 01-20-2010, 08:11 AM - Thread Starter
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Quote:
Originally Posted by 8mile13 View Post

I believe a 100 hertz flatscreen means 100 hertz is its maximum.

Cheers 8Mile,

Why would they do this though - surely it would be easier for them just to manufacture 120Hz LCDs instead of two different kinds? Couldn't a 120Hz LCD which was input a 50Hz signal just switch to a 100Hz display rate? Though, if what Scottacus says is true, this would require some additional modes to be added to the circuitry (like the availablity of a 48Hz mode on a 60Hz TV) - so I guess that's why they make two different versions!?
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post #15 of 25 Old 01-20-2010, 09:33 AM
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Quote:
Originally Posted by snowdon-goat View Post

Cheers 8Mile,

Why would they do this though - surely it would be easier for them just to manufacture 120Hz LCDs instead of two different kinds? Couldn't a 120Hz LCD which was input a 50Hz signal just switch to a 100Hz display rate? Though, if what Scottacus says is true, this would require some additional modes to be added to the circuitry (like the availablity of a 48Hz mode on a 60Hz TV) - so I guess that's why they make two different versions!?

They have to make different versions anyway so they can include the proper NTSC or PAL tuner (or they choose to do so, in any case). The panels are the same but the video processor circuitry is different.

100Hz is the "maximum" in that type of set because the circuits are doubling the number of frames in the source material, which happens to be at 50Hz. It's very likely the same processor is used as for 120Hz TVs, just with slightly different timing. in fact some manufacturers may just use the same 5:5 pulldown method as on 120HZ TV's (repeating each frame 5 times) to properly display 24p material.
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post #16 of 25 Old 01-20-2010, 09:58 AM - Thread Starter
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Originally Posted by scottacus View Post

They have to make different versions anyway so they can include the proper NTSC or PAL tuner (or they choose to do so, in any case). The panels are the same but the video processor circuitry is different.

100Hz is the "maximum" in that type of set because the circuits are doubling the number of frames in the source material, which happens to be at 50Hz. It's very likely the same processor is used as for 120Hz TVs, just with slightly different timing. in fact some manufacturers may just use the same 5:5 pulldown method as on 120HZ TV's (repeating each frame 5 times) to properly display 24p material.

Meaning those "100Hz" LCDs are actually displaying at 120Hz (for 24p)?
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post #17 of 25 Old 01-20-2010, 11:00 AM
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No Electroning timing circuits in 100Hz sets and the refresh rate corrections are all based on 2x the 50HZ.(the electric power souce frequenc)
A 100Hz set would uses 2:2 pulldown for 50Hz source materal and would use 4:4 pulldown for 25Hz material if available.
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post #18 of 25 Old 01-20-2010, 11:05 AM
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Quote:
Originally Posted by snowdon-goat View Post

Thanks for this - but right away you see the problem? Two posters - both giving different answers to the title question - 8mile claiming that TVs can change the refresh rate while walford claims they can't.

The problem is no one here really knows how these things work. There's been a ton of speculation, and a ton of 'experts' that have read nothing but the speculation. This forum needs some real engineers working in the field to drop by and educate us on how these LCDs work. I'd wager that 99% of the people here are all talking out their ass.

Back off man, I'm a scientist.
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post #19 of 25 Old 01-20-2010, 11:26 AM
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Well, there have been some straightforward facts presented.

Fact 1: LCDs don't have refresh rates in the same sense that other technologies do, they have response times. The liquid crystals change state, they're limited by response time, not refresh rate.

So, fact 2: If the video processing technology feeding the LCD tells them to change state every 1/24ths of a second (okay, 1/23.97th, whatever), they're happy to do so. This is exactly what goes on in 120hz TVs doing a 5:5 pulldown anyway, from the LCD panel's perspective. Just because the video processor deals with it in terms of "okay do 5 repeats of this frame, now 5 of this frame, now 5 of this frame" and so on until it has served up 120 frames in a second doesn't mean the LCD is serving up 5 repeats then 5 repeats then 5 repeats - it just stays the same for all 5 of those frames that it is given, for a total of 24 actual state changes in a second.

Finally fact 3: The panel itself does not impose a technological limitation that would prevent 24p content from being shown at 24hz. The only question is what the actual supporting hardware and software in the TV itself can feed the screen. Here it would be helpful to know some more about the specific engineering problems faced in serving lower framerate content. For example, A-series Samsung TVs had a visual banding problem when displaying 24p content. It got fixed in a firmware update. Who knows what was going on there?

So it isn't that people are "talking out of their asses" about all this. There are clear facts, and there are questions. I'd like to have some of the questions answered, that would be great.
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post #20 of 25 Old 01-20-2010, 11:27 AM
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There is a frequent poster to these fourms from the UK whose ID is "Sneals2000" who is an engineer in the TV broadcast industry. Hopefully, he will see this thread and respond since I have seen some excellent posts of his concerning the playing of 24fps BR DVDs in Europe and trust them since my own display engineering experience is limited to 60Hz units.
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post #21 of 25 Old 01-20-2010, 11:31 AM
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Quote:
Originally Posted by Agreed View Post

Well, there have been some straightforward facts presented.

Fact 1: LCDs don't have refresh rates in the same sense that other technologies do, they have response times. The liquid crystals change state, they're limited by response time, not refresh rate.

So, fact 2: If the video processing technology feeding the LCD tells them to change state every 1/24ths of a second (okay, 1/23.97th, whatever), they're happy to do so. This is exactly what goes on in 120hz TVs doing a 5:5 pulldown anyway, from the LCD panel's perspective. Just because the video processor deals with it in terms of "okay do 5 repeats of this frame, now 5 of this frame, now 5 of this frame" and so on until it has served up 120 frames in a second doesn't mean the LCD is serving up 5 repeats then 5 repeats then 5 repeats - it just stays the same for all 5 of those frames that it is given, for a total of 24 actual state changes in a second.

Finally fact 3: The panel itself does not impose a technological limitation that would prevent 24p content from being shown at 24hz. The only question is what the actual supporting hardware and software in the TV itself can feed the screen. Here it would be helpful to know some more about the specific engineering problems faced in serving lower framerate content. For example, A-series Samsung TVs had a visual banding problem when displaying 24p content. It got fixed in a firmware update. Who knows what was going on there?

So it isn't that people are "talking out of their asses" about all this. There are clear facts, and there are questions. I'd like to have some of the questions answered, that would be great.

Thank you - that was a very clear summary of what is known by those of us who are familiar with LCD technology but aren't the engineers who actually implement it.
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post #22 of 25 Old 01-21-2010, 02:52 AM
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Quote:
Originally Posted by walford View Post

I could not find a link to the user manual for your TV and could only determine from the Sharp Website that it was a 1080p 60Hz model. Which would mean that it would use 3:2 pulldown to play 24fps content from a BR disk.

The newer models with the S firmware switch from 60Hz refresh to 48Hz using 2:2 pulldown:
http://www.avsforum.com/avs-vb/showt...7#post15913147
This is not documented in the user manual as it is a later addition.
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post #23 of 25 Old 01-21-2010, 10:45 AM
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Quote:
Originally Posted by dblang View Post

The newer models with the S firmware switch from 60Hz refresh to 48Hz using 2:2 pulldown:
http://www.avsforum.com/avs-vb/showt...7#post15913147
This is not documented in the user manual as it is a later addition.

Score!

Thanks

So we have at least one manufacturer doing it. LG advertises that their 60hz panels can display 24p natively for at least the 2009 lineup as well. That's two. I believe that Samsung does this on at least the 5-series TVs as well but that is strictly supposition and my own experiences with 24p content versus the same content in 60hz (3:2 pulldown pre-applied on the DVD). But it's good to see that at least one manufacturer just comes out and remarks on it, lends some more credence to the Samsung tech who said that the displayed refresh rate/framerate is in fact what is being played.
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post #24 of 25 Old 01-21-2010, 02:47 PM
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Here is a good discussiion about 48fps mode on the G10 and 96 fps mode on the V10 Panasonic 60Hz plasmas.

http://www.amazon.com/review/R1P7WSX...=cm_cr_pr_cmt?

What is not explained is how it is being implemented.
Possibly the 48fps mode is being implemented after 24fps source has been upgraded to 48fps using 2:2 pulldown and then every 5th frame is being blanked out before being displayed. This would enable each 24fps frame to be displayed the same number of times but could easily cause flicker just like the old CRT multisscan PC monitors when run at 48fps.
I do not have a hypothetical implementation method for 96fps mode.
Hopefully someone seing this thread does know how these modes are being implemented and can provide the implementation method.
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post #25 of 25 Old 01-21-2010, 03:42 PM
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Plasmas are different. They rely on the phosphors being excited to produce the picture. Not comparable to LCDs in the implementation of refresh rates - moreso to CRTs; at 48hz there would be mad flicker, so 96hz makes a lot more sense.
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