Mailing List Archive: MythTV: Mythtvnz

50Hz vs 60Hz refresh rate

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mark.van.dijk at ihug

Dec 15, 2010, 2:18 AM

Post #1 of 11 (4368 views)
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50Hz vs 60Hz refresh rate

This is in response to a few messages in the last couple of days about the refresh rate of the TV. In the info below, note that i have an HDMI connection from a GT220 (VDAPU) to a 1080p LCD panel.

I have used the INFO button on my TV remote which verifies that my MythBox is connected at 1080p [at] 60Hz I have a very new TV and a new GT220 graphics card (only had it about 2 months), and ever since
i installed them, I have been fairly dissapointed with noticable judder during screen pans. I have always just thought that this unavoidable...

After seeing the messages about potential issues while trying to display FreeviewHD (50i) on a 60p TV connection, i have done a couple of experiments. I went into the MythTv frontend -
Utilities/Setup - Setup - Appearance. In the "Video Mode Appearance" I have manually selected "Different Modes for GUI and TV Playback", and specified both the GUI and TV playback to be 1920x1080
with a refresh rate of "any".

When i try to play back FreeviewHD content, there is a visible screen mode change on my TV - clearly indicating that the TV mode is now 1080p [at] 50

Results are that the judder is greatly reduced!!!! This is fantastic!! I have flipped back and forth between the two different settings (60p and 50p) and FreeviewHD content is absolutly better with
the refresh rate of "any". Judder is *substantially* reduced. It is not completely eliminated, but it's a lot better. If I enable "motion flow" on my TV, then there is no perceptable judder at all,
however this also introduces an unacceptable "daytime soap" feel to movies which i can't stand (see one of my previous posts), so I'm going to keep motion flow disabled.

A previous poster mentioned that this "euro judder" when displaying FreeviewHD at 60Hz was likely to be 5Hz, and just from my experiments, this appears to be correct.

--

Mark van Dijk

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nick.rout at gmail

Dec 15, 2010, 11:07 AM

Post #2 of 11 (4308 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

On Wed, Dec 15, 2010 at 11:18 PM, Mark van Dijk
<mark.van.dijk [at] ihug> wrote:
> This is in response to a few messages in the last couple of days about the refresh rate of the TV. In the info below, note that i have an HDMI connection from a GT220 (VDAPU) to a 1080p LCD panel.
>
> I have used the INFO button on my TV remote which verifies that my MythBox is connected at 1080p [at] 60Hz I have a very new TV and a new GT220 graphics card (only had it about 2 months), and ever since
> i installed them, I have been fairly dissapointed with noticable judder during screen pans. I have always just thought that this unavoidable...
>
> After seeing the messages about potential issues while trying to display FreeviewHD (50i) on a 60p TV connection, i have done a couple of experiments. I went into the MythTv frontend -
> Utilities/Setup - Setup - Appearance. In the "Video Mode Appearance" I have manually selected "Different Modes for GUI and TV Playback", and specified both the GUI and TV playback to be 1920x1080
> with a refresh rate of "any".
>
>
> When i try to play back FreeviewHD content, there is a visible screen mode change on my TV - clearly indicating that the TV mode is now 1080p [at] 50
>
> Results are that the judder is greatly reduced!!!! This is fantastic!! I have flipped back and forth between the two different settings (60p and 50p) and FreeviewHD content is absolutly better with
> the refresh rate of "any". Judder is *substantially* reduced. It is not completely eliminated, but it's a lot better. If I enable "motion flow" on my TV, then there is no perceptable judder at all,
> however this also introduces an unacceptable "daytime soap" feel to movies which i can't stand (see one of my previous posts), so I'm going to keep motion flow disabled.
>
>
> A previous poster mentioned that this "euro judder" when displaying FreeviewHD at 60Hz was likely to be 5Hz, and just from my experiments, this appears to be correct.
>
http://www.mythtv.org/wiki/User_Manual:JudderFree

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alick.wilson at braithwaite

Dec 15, 2010, 5:13 PM

Post #3 of 11 (4331 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

For reference, my MagicTV DVR manual says:

Video Output Format 50/60Hz As New Zealand DTT programmes will normally be
broadcast in 50Hz, selection of a 50Hz format from the list below is
recommended. However, some TVs (perhaps from Japan or America where
broadcasts are in 60Hz) may not happily accept a 50Hz signal. In this case
choose from the list of 60Hz formats provided.'

1080i (50Hz) The default setting - accepted by all HDTVs

1080p (50Hz) A good choice if your TV accepts a 1080p HDMI input

720p (50Hz) A good choice if your 'HD Ready' TV has 720 or 768 lines of
resolution

576i (50Hz) Use only if your TV is Standard Definition

576p (50Hz) 1080i (60Hz) 1080p (60Hz) 720p (60Hz) 480i (60Hz) 480p
(60Hz) Use these only under special circumstances

Alick Wilson

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mythicalbeast at slingshot

Dec 16, 2010, 8:08 PM

Post #4 of 11 (4306 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

The really issue that was being discussed in the other hijacked thread
was that:

TV VGA inputs not supporting 1080p50 or 60.
TV VGA inputs not supporting full HD 1920x1080 (at any video mode).
TVs only allowing full HD p50 p60 over HDMI.

And ..
PC monitors typically do not support any 50Hz mode.

IMO
Using a more appropriate video mode is worth the effort.
Using the video card to do all processing/scaling is best (if GPU is up
to it).

> Video Output Format 50/60Hz As New Zealand DTT programmes will normally be
> broadcast in 50Hz, selection of a 50Hz format from the list below is
> recommended. However, some TVs (perhaps from Japan or America where
> broadcasts are in 60Hz) may not happily accept a 50Hz signal. In this case
> choose from the list of 60Hz formats provided.'
>

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nick.rout at gmail

Dec 16, 2010, 9:12 PM

Post #5 of 11 (4291 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

On Fri, Dec 17, 2010 at 5:08 PM, Brett <mythicalbeast [at] slingshot> wrote:
> The really issue that was being discussed in the other hijacked thread
> was that:
>
> TV VGA inputs not supporting 1080p50 or 60.
> TV VGA inputs not supporting full HD 1920x1080 (at any video mode).
> TVs only allowing full HD p50 p60 over HDMI.
>
> And ..
> PC monitors typically do not support any 50Hz mode.

which is a shame, because the tuners in the tvs in this house are
never used. but clearly a good tv is not just a monitor with a tuner
added on...

>
> IMO
> Using a more appropriate video mode is worth the effort.

yes i am going to play around with the "any" video refresh rate
setting on my gt220 paired with sony 46" tv.

> Using the video card to do all processing/scaling is best (if GPU is up
> to it).
>
>
>
>
>> Video Output Format 50/60Hz As New Zealand DTT programmes will normally be
>> broadcast in 50Hz, selection of a 50Hz format from the list below is
>> recommended. However, some TVs (perhaps from Japan or America where
>> broadcasts are in 60Hz) may not happily accept a 50Hz signal. In this case
>> choose from the list of 60Hz formats provided.'
>>
>
>
>
> _______________________________________________
> mythtvnz mailing list
> mythtvnz [at] lists
> http://lists.ourshack.com/mailman/listinfo/mythtvnz
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>

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tortise at paradise

Dec 17, 2010, 12:10 AM

Post #6 of 11 (4290 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

>> IMO
>> Using a more appropriate video mode is worth the effort.

Intuitively this makes sense. Its hard to do better than the data in
the recording, although it seems possible, e.g. de-interlacing.

>
> yes i am going to play around with the "any" video refresh rate
> setting on my gt220 paired with sony 46" tv.

I've a brief go, referring to
http://www.mythtv.org/wiki/User_Manual:JudderFree
adding

Option "FlatPanelProperties" "Scaling = Native"

into xorg and doing the 1920x1080 / any settings.

TV still says its getting 1080i [at] 60H Hmmm I'll try a change to a
digital cable (from component) and see if that makes the difference, as
was suggested earlier.

Its interesting to consider PC monitor refresh rates, that 60Hz are
generally the minimum, and can be inadequate for a comfortable viewing
experience, with 75-85Hz having significant success in tricking our
brains into perceiving better image quality. Come along LCD's and 60Hz
is suddenly fine. (And we have a raft of new measurement dimensions to
compare problems that did not need to be measured as they were not an
issue in earlier technologies - speed, blacks, whites, viewing angles etc)

Yet 50Hz freeview is seen to be very good. Go figure. I think the
explanation is that the video images are generally moving, compared with
static flashing images, and also the underlying technologies, with CRT
screens being much faster gave them the ability to show the flashes much
better also.

Then add into the picture 24 fps videos, which is even less intuitive,
bearing the previous comments, I can only assume these are shown at 48Hz
or possibly other multiples to provide the necessary quality?

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mythicalbeast at slingshot

Dec 17, 2010, 3:37 PM

Post #7 of 11 (4297 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

> the recording, although it seems possible, e.g. de-interlacing.
>
The de-interlacing & vdpau hq scaling are features of the GT220 you
should expt with...

> http://www.mythtv.org/wiki/User_Manual:JudderFree
> adding
>
> Option "FlatPanelProperties" "Scaling = Native"
>
> into xorg and doing the 1920x1080 / any settings.
>
This forces all scaling (in GPU) of all output to 1920x1080 which is
good if your TV is full HD capable (inc connection).
> TV still says its getting 1080i [at] 60H Hmmm I'll try a change to a
> digital cable (from component) and see if that makes the difference, as
> was suggested earlier.
>
Just don't pay to much for what should be a $10 2m cable.

> Its interesting to consider PC monitor refresh rates, that 60Hz are
> generally the minimum, and can be inadequate for a comfortable viewing
> experience, with 75-85Hz having significant success in tricking our
> brains into perceiving better image quality. Come along LCD's and 60Hz
> is suddenly fine. (And we have a raft of new measurement dimensions to
> compare problems that did not need to be measured as they were not an
> issue in earlier technologies - speed, blacks, whites, viewing angles etc)
>
> Yet 50Hz freeview is seen to be very good. Go figure. I think the
> explanation is that the video images are generally moving, compared with
> static flashing images, and also the underlying technologies, with CRT
> screens being much faster gave them the ability to show the flashes much
> better also.
>
We need to have discussion about persistence of vision & persistence of
phosphor & perception of motion by human eye/brain...

> Then add into the picture 24 fps videos, which is even less intuitive,
> bearing the previous comments, I can only assume these are shown at 48Hz
> or possibly other multiples to provide the necessary quality?
>
Real 24fps (blueray/film) is handled by 3:2 pull down scheme (60Hz) or
speed up (50Hz).
Latest blueray players & TVs allow real 1080p24 & the TV refreshes at
48Hz or some multiple of 24.

The problem with old 24fps material is transferred/converted by
telecining to DVD etc and/or telecined wrong.
Some TVs & video card drivers detect telecined material & 'fix it'

My experience of nvidia feature set C inverse telecining DVD is that it
is excellent.
Never tried any 1080p24 24fps material.

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mythicalbeast at slingshot

Dec 17, 2010, 3:44 PM

Post #8 of 11 (4277 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

> experience, with 75-85Hz having significant success in tricking our
> brains into perceiving better image quality. Come along LCD's and 60Hz
> is suddenly fine. (And we have a raft of new measurement dimensions to
> compare problems that did not need to be measured as they were not an
> issue in earlier technologies - speed, blacks, whites, viewing angles etc)
>
> Yet 50Hz freeview is seen to be very good. Go figure. I think the
> explanation is that the video images are generally moving, compared with
> static flashing images, and also the underlying technologies, with CRT
> screens being much faster gave them the ability to show the flashes much
Remember that your old analogue TV most likely displayed NTSC material
at 60Hz (interlaced).
My old CRT displays std. video PAL at 1250i50 or 576p50 & NTSC at
1080i60 or 480p60 (these are overscanning resolutions)

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jyavenard at gmail

Dec 18, 2010, 12:47 AM

Post #9 of 11 (4270 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

Hi

On 17 December 2010 15:08, Brett <mythicalbeast [at] slingshot> wrote:
> And ..
> PC monitors typically do not support any 50Hz mode.

They may not report it in their EDID, but most of the ones I've tried
with a custom modeline, do work at 50Hz.

That includes my 20 and 24" Dell LCD monitor

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mythicalbeast at slingshot

Dec 18, 2010, 12:57 PM

Post #10 of 11 (4284 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

On Sat, 2010-12-18 at 19:47 +1100, Jean-Yves Avenard wrote:
> Hi
>
> On 17 December 2010 15:08, Brett <mythicalbeast [at] slingshot> wrote:
> > And ..
> > PC monitors typically do not support any 50Hz mode.
>
> They may not report it in their EDID, but most of the ones I've tried
> with a custom modeline, do work at 50Hz.
>
> That includes my 20 and 24" Dell LCD monitor
>

Using work PC winXP nvidia 256..custom modeline.
LG 24" 1920x1200 hdmi would not work with custom modeline 50Hz.

This was only a 15min play using the nvidia modeline generator.

Can you post your custom 50Hz modeline ?

side note: this LG monitor shows POST startup output in YUV colourspace
probably due to hdmi connection.

So we now need to reprogram the EDID eeprom in the displays..
How soon do we need to start changing the firmware to make them work
correctly..

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mythicalbeast at slingshot

Dec 20, 2010, 8:48 PM

Post #11 of 11 (4269 views)
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Re: 50Hz vs 60Hz refresh rate [In reply to]

> Using work PC winXP nvidia 256..custom modeline.
> LG 24" 1920x1200 hdmi would not work with custom modeline 50Hz.
>
For the sake of completeness.
The LG L246WH 1920x1200 16:10 supports the following 50Hz modes.
hdmi:
1080p
1080i
720p
576p
576i

vga:
n/a

component:
1080i
720p
576p

note: there are NO native resolution 50Hz modes.

1080 looks rough scaled to full screen & forgot to try letterbox
mode...this might be a solution as it may pixel map one to one.

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