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60Hz vs 240Hz

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by jlsohio, Feb 20, 2011.

  1. jlsohio

    jlsohio AllStar

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    I have a Samsung series 8000 TV. I have a HR21/700 box. The TV displays 60Hz as the signal coming in.

    Question: is the 60Hz a function of the how the broadcasters send the signal? Or is it a function of the box that I have. Do any broadcasters brodcast at 120 or 240 Hz?
     
  2. Davenlr

    Davenlr Geek til I die

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    Satellite video comes in two flavors, 24 FRAMES PER SECOND, and 60 FRAMES PER SECOND, seen usually as 1080/24 or 1080/60.

    Your TV refreshes the screen either 24 times per second, 60 timees per second, 120 times per second, or 240 times per second. It can also process the signal, such as taking those 24 frames per second, doing math on them, and outputting them as 60, which means your tv would need to refresh its screen 120 times per second (120 hz) to do that.

    Basically, the signal you cannot change. The TV you can. 60hz is ok for normal tv. 120 hz will make sports look better, and allow the tv to display 24 Frame/Sec VOD downloads without flicker. 240 hz just does what 120hz does twice as fast.

    Select the rate on your TV that looks the best to you while still delivering a picture. Since 24 wont go into 60 an even number, you cannot usually display 24 frame per second video on a 60 hz tv.
     
  3. dpeters11

    dpeters11 Hall Of Fame

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    A lot of the reviews I've seen, they suggest there is diminishing return as well. Big difference going from 60 to 120, fairly small difference from 120 to 240 though it can be a larger difference when it's a 3D TV.
     
  4. BattleZone

    BattleZone Hall Of Fame

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    Higher refresh rates for LCD TVs allow for several things, not all of which are necessarily implemented by the manufacturer.

    - More refreshes of the screen reduce visible artifacts common to LCD panels of motion "blur" or "smear", due to the pixels taking longer to change. This was the primary reason for higher refresh rates, but as pointed out, there is a diminishing return as refresh rates are increased.

    - "Motion Enhancement", called AMP by Samsung and MotionFlow by Sony, is where a processor in the TV "creates" intermediate frames in between the actual frames delivered by the source device to smooth out motion. This is similar to how animation is drawn: a lead artist will draw a character at the beginning of a motion (Frame 1 in the pic below), and another frame at the end of that motion (Frame 10). Those two frames will then be sent to lower-paid artists called "Tweeners" who draw the frames in between.

    [​IMG]

    Motion Enhancement gives you the "looking through a window" effect, which most people agree is a positive thing when watching something like a live sports broadcast, but a negative when watching movies. As such, you'll need to get used to turning it on and off depending on what you are watching.

    - True 24-frame support. Nearly all film is shot at 24 frames per second, and both directors and many movie viewers feel strongly that 24 fps gives film a very distinct feel that is destroyed when converted or changed. With SDTVs, which were fixed at 60 fps (in the US; 50 fps for much of the rest of the world), all film had to be converted using a 3:2 ration of odd to even frames, causing "judder" as odd-numbered frames would be displayed for a longer duration than the even-numbered frames.

    With modern HDTVs capable of refresh rates other than 60 Hz, it is possible to offer true 24 fps capabilities by using a refresh rate that is evenly divisible by 24, such as 120 Hz (divisible by both 60 and 24) or 240 Hz. Plasmas, which generally can't refresh at such high rates, but also don't need to due to a difference in display technology, may offer refresh rates of 72 or 96 Hz in addition to the standard 60 Hz, to accomplish the same goal of being able to display 24 fps content at an even 24 fps.

    This is done by simply repeating each frame the same number of times that 24 is a multiple of the refresh rate. For example, a 120 Hz panel will repeat each frame of a 24 fps movie 5 times. 5 x 24 = 120 frames per second. Your eye can't tell the frames are being repeated, so it just seems that that frame is on the screen for 1/24th of a second. The result is judder-free 24 fps content on your home TV. For a plasma running at 72 Hz, each frame would be repeated 3 times. 3 x 24 = 72 frames per second.

    Note that this display mode is also called different things by different manufacturers; often some variation of "Cinema Mode", and more importantly, note that virtually all TVs that support this mode require their Motion Enhancement to be turned OFF. And some lower-end 120 Hz and even 240 Hz TVs do NOT offer correct 24 fps support, even though they probably could have, so a higher-than-60 Hz refresh rate isn't itself a guarantee that 24 fps content is properly supported.
     
  5. bpratt

    bpratt Godfather

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    Actually, DirecTV broadcasts 3 different signals. They broadcast 1080I, 1080P and 3D. 1080I is broadcast 60 half frames per second. They broadcast all the odd lines then all the even lines so the actual full frame rate is 30 frames per second. 1080P is 24 full frames per second. I'm not sure about 3D, but I believe it is currently 2 pictures of 1080I broadcast alternatively.

    If you own a 60 Hz TV, it will show 1080i with no change to the way it is broadcast. Some TVs will accumulate the odd and even frames and will show the accumulate picture 2 times. 1080P or 24 frames per second is displayed by showing the first frame 2 times, the second frame 3 times, the third frame 2 times, the fourth frame 3 times ......... Doing this creates a thing called Judder which some people can see, but most can not.

    The advantage to a 120 Hz TV is it will display 1080P by showing each frame 5 times and thus eliminating Judder. There really is no advantage in 1080I because these TVs just show the accumulated 1080I frames 4 times.

    Many of the 240 Hz TVs have a processor which can do motion smoothing. On these sets a 1080I accumulated frame is shown 8 times, and a 1080P frame is shown 10 times. Lets say an object is moving across the screen (like a football), at 1 inch per frame. Normally, the first frame received would show the football. The second frame received would show the football 1 inch to the right. Since the frames are each going to be displayed 8 or 10 times, the processor can do motion smoothing. The processor would display the first frame, then move the football 1/8 or 1/10 inch to the right then display next frame etc. The end result is that 240 Hz TVs give you a much smoother picture.

    3D requires either 120 Hz or 240 Hz. New sets are being developed which run at 480 Hz. These sets allow 3D and motion smoothing to be shown.
     
  6. P Smith

    P Smith Mr. FixAnything

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    "Actually, DirecTV broadcasts 3 different signals. They broadcast 1080I, 1080P and 3D."

    Actually you mean two - MPEG-2 and MPEG-4 ;).

    Inside of that two, it's matter of controlled conversion by STB to TV output: remember those 480/720/1080 LEDs ? ;)
    It is not a broadcast per se.
     
  7. bpratt

    bpratt Godfather

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    MPEG-2 and MPEG-4 define how the transmission is compressed and has nothing to do with TV refresh rates we are discussing in this thread.
     
  8. P Smith

    P Smith Mr. FixAnything

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    That's why you wasted time and space to bring the sentence. :)
     
  9. HoTat2

    HoTat2 Hall Of Fame

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    As far as I can tell DirecTV broadcast 2D HD images in 1080P/24 Hz, 1080i/60 Hz, and 720P/60 Hz formats.

    3D HD I think is 1080P/24 Hz Side-by-Side (SbS) for film material, and 1080i/60 Hz SbS for video.

    What I don't know is that as is done with SD when DirecTV is broadcasting film material in regular 2D HD do they actually eliminate the redundant field or frame to save bandwidth and really transmit film sources in 1080i/48 Hz or 720P/48 Hz (FX HD channel, etc.) and the receiver simply adds the redundant fields or frames back in based on the repeat flags or something.
     
  10. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    I think this is done at the program provider and they're the ones sending out the "HD" signal, so any upconverting is done before DirecTV gets it.
    Think back to HD locals that were still using an SD camera, they added the side bars.
     
  11. Max Mike

    Max Mike AllStar

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    NTSC broadcast television signal is 29.97 interlaced frames of video per second or rounded up 30 frames a second. Each frame consists of 2 fields (with the half lines of the pictures full resolution) ... 2 X 30 = 60. 480p 720p and 1080p/60 broadcast 60 full non-interlaced picture frames. So you only have a max of 60 individual pictures coming to the TV each second no matter the refresh rate of the TV. A 120Hz or 240Hz TV either repeats frames or creates interpolated frames to fill out their increased refresh rates.

    Digital signals in theory could be broadcast at higher rates.

    Contrary to what they say and think many and probably most people cannot see the difference between 60Hz and 120Hz. virtually no one has really sees the difference between 120Hz and 240Hz. As stated above 120Hz does offer real benefits when watching 1080P/24 content.

    The biggest benefit of 240Hz screens is not the 240Hz refresh rate but the fact that 240Hz TV tend to have panels that have better contrast. blacks. ect...simply put 240Hz panels tend to have better pictures because they are better panels picture wise with or without 240Hz.
     
  12. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Let's not bring reality in here or the marketing departments will need to find something else to hype. :lol:
     
  13. HoTat2

    HoTat2 Hall Of Fame

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    I understand that, but what I was questioning whether or not DirecTV actually removes the redundant fields or frames when broadcasting film based material in HD as they do with SD. Thereby reducing the field/frame rate by ~20% to save on bandwidth.

    Not the up-conversion of 4:3 material to an HD format. :)
     
  14. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    I'd say the MPEG-4 is removing the redundant parts, verses MPEG-2 not.
     
  15. Rich

    Rich DBSTalk Club DBSTalk Club

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    Damn! That was a FINE post! Thanx for the clear, easy to understand info.

    Rich
     
  16. hasan

    hasan Well-Known Member

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    (much snipped)

    That is an outstanding post, a very clear and concise explanation, much better done than many other places that have tried to explain. Good job Battle Zone!

    I would add:

    Vizio calls their motion processing: Smooth Motion Technology

    As you noted my Sammy calls it AMP (Auto-Motion Plus).

    Of the motion processing implementations I have looked at, I like the Samsung the best, although that's simply a matter of personal preference. I like the Vizio as well, but it is not as "striking" as the Samsung (set to defaults...there are a ton of variables that you can play with). I have not seen the Sony implementation. Lower end Sanyo 120 hz machines also have some smoothing, but no controls, and while better than not having it, I find their approach unimpressive.

    What I have heard from the consumers with respect to motion smoothing is that they either love it, or hate it. I had one person tell me that it gave them vertigo. My wife referred to it as "super-realistic" on our Sammy.

    I very much like AMP myself. I also agree that the jump from 60 to 120 is readily observable if you have the right program material and know what to look for, and anything above 120 hz is confounded by so many other variables, that I can't tell what is what (like another poster noted, differences in the panel itself produces all sorts of "perceptions".

    Thanks for taking the time to make such an informative post.:)
     
  17. BattleZone

    BattleZone Hall Of Fame

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    Can you tell I get asked those questions all the time? :)
     
  18. P Smith

    P Smith Mr. FixAnything

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    Time to reveal truth about 480 and 960 (!) Hz refresh rates. :)
     
  19. Rich

    Rich DBSTalk Club DBSTalk Club

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    I could tell that you know what you're talking about and are able to dumb it down enough for me to understand. That alone takes a certain talent.

    Rich
     
  20. BattleZone

    BattleZone Hall Of Fame

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    I'm originally from an IT background, running Tech Support or Help Desk call centers, so a key part of those jobs is taking complex technical information and finding a way to make non-techie users understand it. Of course, that is probably why I tend to over-use analogies, but, hey, I do what works. :)
     

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