Are You Confused With HDTV Refresh Rates, & What Is Safe: I Am

Forums › Home Theatre (including HTPC and EPG Collector) › Are You Confused With HDTV Refresh Rates, & What Is Safe: I Am

1gkar

722 posts

Ultimate Geek

#59129 27-Mar-2010 17:54

Even though I have been using PCs in the form of HTPCs for some time now, I am still confounded by what is considered safe for your TV, when using an HTPC connection.

My Samsung 32" LCDTV states in the manual that it will support 576p, 720p & 1080i on an HDMI/DVI connection @ 50hz & 720p & 1080i on the same connection @ 60hz. Yet, further into the manual it states the supported refresh rates vary from 60.317-60.015hz on resolutions between 800x600-1360x768 in VESA mode, for an HDMI/DVI PC connection.

So, what refresh rate(s) is safe to run your HTPC at, without compromising your TV's internals. The reason I have concern is I damaged my old Sony 29" CRT, a while back, from using unsupported refresh rates.

At present I am running, through Mediaportal 1.1.0RC1, the following with the aid of the Dynamic Refresh Rate Changer:

-PAL media with a FPS of 25=50hz
-HDTV media with a FPS of 50=50hz
-NTSC media with a FPS of 29.97=60hz
-Cinema media with a FPS of 23.976=50hz (2x multiple=48 which is close)

I have also begun using Reclock 1.8.6 as my referred video renderer to further assist with video judder. I am getting there, in terms of smooth & stable video playback. But, are these settings safe for my LCDTV? Cheers.

I have spent considerable time trying to research for an answer to this & there does not appear to be any info on the web concerning my query, which I find surprising. I cannot be the only one with concerns of not wanting to damage my TV investment.

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Nety

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#311922 27-Mar-2010 19:11

I think the basic difference here is that a CRT will try to display any refresh rate you feed it regardless of whether it is within it specifications or not. This is because it is analogue. On the other hand a LCD is digital so will do one of the following
Display a message to say that it cannot display the resolution/refresh rate if it is not in its limits.
Convert the signal to something it can display and show that as well as a message to say it is not able to display the signal correctly (as above).
It will simply turn off.

In short IMHO it is not possible to damage a LCD display by feeding it a incompatible signal.

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Rsmith

35 posts

Geek

#311954 27-Mar-2010 23:01

As Nety said, you don't need to worry about damaging your TV.

The VESA resolutions will be limited to 60Hz because this is the VESA standard which is a pain because it rules out running the TV in native resolution with the 50Hz frame rate of PAL tv :\ (well it does with my Sony anyway)

Yet another reason for getting a Full HD screen because at least 1080 panels are 1080 pixels tall.

1gkar

722 posts

Ultimate Geek

#312186 28-Mar-2010 20:54

Nety: I think the basic difference here is that a CRT will try to display any refresh rate you feed it regardless of whether it is within it specifications or not. This is because it is analogue. On the other hand a LCD is digital so will do one of the following
Display a message to say that it cannot display the resolution/refresh rate if it is not in its limits.
Convert the signal to something it can display and show that as well as a message to say it is not able to display the signal correctly (as above).
It will simply turn off.

In short IMHO it is not possible to damage a LCD display by feeding it a incompatible signal.

That being the case, how do you explain why I can playback in 24p when the TV does not appear to have support below 50hz? I know it is doing this as I have a notifier checked which informs me of the refresh rate information upon the media start.

It would be ideal if I was able to safely use that rate, as it would allow judder-free playback, but would need positive confirmation it won't cause hardware damage. Where can I find this info on the net? Thanks for the replies.

PS. I have just run a test & set my PAL media to run @ 100hz, well outside the stated TV support, & it played back, according to the notifier @ 100hz. What gives? Is there an app that checks what rates a media file is actually running at?

Nety

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#312314 29-Mar-2010 10:21

My guess (and it is only a guess) is that your video card is converting what it is feed to something that it knows your display can handle. Either that or the TV is converting it internally.
Is there any way you can get your display to show you what it is displaying/being sent? ie resolution and refresh rate?

Rsmith

35 posts

Geek

#312317 29-Mar-2010 10:26

hey 1gkar, As you mentioned in your first post, reclock is using a 50Hz refresh rate when displaying 24fps video so it's not using < 50hz

I don't know the exact specs of your TV, but as Nety said, it isn't going to do anything that it can't do.

What resolution are you running this at?

re the 100Hz, when you say 'set my PAL media to run @ 100hz', are you suggesting that the refresh rate of the TV is @ 100hz or that you are just playing the video back @ 100fps? I don't think that HDMI/DVI would have the bandwidth for 1080p @ 100hz, WQXGA (2650x1600) @ 60hz requires dual link DVI.

I would assume that your graphics card is only ever outputting 50hz or 60hz, and I assume you're using standard HD resolutions and not the native 1366x768 as none of the TV's seem to do anything other than 60hz @ VESA resolutions.

1gkar

722 posts

Ultimate Geek

#312522 29-Mar-2010 18:02

"hey 1gkar, As you mentioned in your first post, reclock is using a 50Hz refresh rate when displaying 24fps video so it's not using < 50hz"

That was correct in my original post. However, I also set the dynamic refresh rate changer plugin (DRRC) in Mediaportal to set Cinema 23.976FPS to 24p mode. The notifier states it is displaying the playback @ 24hz.

"re the 100Hz, when you say 'set my PAL media to run @ 100hz', are you suggesting that the refresh rate of the TV is @ 100hz or that you are just playing the video back @ 100fps? I don't think that HDMI/DVI would have the bandwidth for 1080p @ 100hz, WQXGA (2650x1600) @ 60hz requires dual link DVI."

According to the DRRC it is notifying me that upon media playback start, it is running @ 100hz. OK. I just reset the DRRC to 100hz & it won't open the media file. Did it yesterday, just can't remember which file I tried it on originally. So maybe the LCDTV is fucntioning properly. Am still unsure why it will display @ 24hz

"I would assume that your graphics card is only ever outputting 50hz or 60hz, and I assume you're using standard HD resolutions and not the native 1366x768 as none of the TV's seem to do anything other than 60hz @ VESA resolutions."

This is what is confusing me. Is it the TV, the graphics card, or other controlling the actual refresh rate?

fahrenheit

757 posts

Ultimate Geek

#312871 30-Mar-2010 15:59

Your TV is one of the many that accepts a 24p signal, but internally converts to 60Hz.
You would need a TV capable of 48, 72, 120 or 240Hz refresh rate to support proper 24p playback.

How elegantly your TV handles the 24p source - 60Hz output equation is the real question. You can either let it convert, or send 60Hz (not 50Hz) in the first place so that it doesn't have to.

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1gkar

722 posts

Ultimate Geek

#313576 31-Mar-2010 18:32

fahrenheit: Your TV is one of the many that accepts a 24p signal, but internally converts to 60Hz...

Thank you. This is the kind of confirmation I am after, but where is there documented statements to that effect, that confirm that is how LCD-TVs scale media & adjust refresh rates and operate with no danger to its internal hardware. That is the gist of my query?

How elegantly your TV handles the 24p source - 60Hz output equation is the real question. You can either let it convert, or send 60Hz (not 50Hz) in the first place so that it doesn't have to.

If I don't use the DRRC, then the media file playback contains significant judder. However, if I do activate the DRRC with the standard defaults (ie.24p=24hz), then it is much more watchable. I assume this would indicate the TV cannot adjust the media file for good playback, & the PC is much more suited for this task, I guess??? Also assuming that other factors are not also modifying the media file.

At the end of the day, all I'm after is a simple documented statement from some authority on digital TVs that state using these non-standard refresh rates with media file playback (in NZ, at least) are not damaging to the set.

With all the proliferation of information available on the internet, I would have thought that shouldn't be too hard to find. My mistake.

fahrenheit

757 posts

Ultimate Geek

#313594 31-Mar-2010 19:50

1gkar:
Thank you. This is the kind of confirmation I am after, but where is there documented statements to that effect, that confirm that is how LCD-TVs scale media & adjust refresh rates and operate with no danger to its internal hardware. That is the gist of my query?

Your TV has an EDID that devices and OS' can query to see what is an acceptable resolution and refresh rate to send the TV. Generally this will stop any wayward resolutions and timings from getting in the door. I don't know how LCDs deal with non-standard resolutions and timings as far as dangerous voltages go, because generally speaking I wouldn't want to feed them something they have to convert.

If I don't use the DRRC, then the media file playback contains significant judder. However, if I do activate the DRRC with the standard defaults (ie.24p=24hz), then it is much more watchable. I assume this would indicate the TV cannot adjust the media file for good playback, & the PC is much more suited for this task, I guess??? Also assuming that other factors are not also modifying the media file.

'Judder' needs to be qualified. Is it 3:2 pulldown judder, is it 25fps - 60Hz conversion judder? Is it motion interpolation settings on your TV judder?

What you have suggested in this thread is that you are making alterations that deviate away from common standards and that makes things all the more difficult to diagnose.

eXDee

4032 posts

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#313614 31-Mar-2010 21:29

Our Sony won't take anything except 60hz at 1360x768.
I dont actually see tearing either, running windows 7 and it seems all fine interestingly enough. I dont see tearing when i watch TV or video (PAL or NTSC) on my 60hz monitors either.