Tried 48Hz last night - some questions

Discussion in 'Projectors, Screens & Video Processors' started by tryingtimes, Jan 11, 2002.

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  1. tryingtimes

    tryingtimes
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    I tried 48Hz last night (not 47.952 - I'll try that tonight)
    Watched Phantom Menace (various bits) (and also the desktop!)

    I was aware of the flicker on white highlights (especially if against dark edges) and on very bright scenes.
    Did this improve or harm the experience?
    Well - in a way i can see what people are raving about.
    It does have a more 'analogue' look, 'authentic', even.
    Will I stick with it? - maybe - I'll certainly keep a shortcut to it on my desktop (once I've sorted 47.952).

    So - to my questions.

    1. Am I helping my projector to live longer by running at 48/50 instead of 72/75?

    2. Will my graphics card be optimised for any particular frequencies.

    3. Am I damaging my eyes in any way?

    4. The picture was about 30 pixels to the right even after I had copied from my usual [email protected] memory block. Does this point to a problem or is it ok to just to move it back across.

    Many thanks in advance
    Alex
     
  2. ROne

    ROne
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    I've had some success with 48hz over other suggested frequencies. I don't think there is one ideal frequency for all material, epsecially taking into account the fixed internal hz of a LCD projector.

    1. I can't see any reason providing you are driving your projector in spec why it will last any longer. However this may not be the case for CRT. Roland or Gordon or one of these other CRT experts would advise, but certainly shouldn't damage an LCD.

    2. Graphics cards as far as I know are multi-scanning devices, and the best frequency is usually an attribute of your projector/graphics card combo.

    3. Well we watch films as 24/48 FPS so if these don't give you a headache, why should your projector? I think high refresh rates of 75hz + are required when you are reading text or studying small print etc, not necessary to recreate what is essentially limited by the 24fps material. However you may still detect flicker.

    I think this whole issue of FPS/refresh rates, is a complicated situation, we have film at 24 , NTSC video at 30, PAL at 25 ... I personally don't like the inherant jitter on film material especially on PANs and tracking shots, however if we start to speed up frame rates to 60 FPS, we may lose some of films blurry texture but will gain clarity on faster moving shots. It would be nice to standardise across the board though, so we haven't got all this silly conversion nonesense.

    However we may not be moving away from it to soon, the new digital SONY CINE-ALTA format (Hidef film), can shoot in 24fps which it did on MIKE BASSET, however its capable of shooting other framerates, I will be interested if this format keeps the 24fps or eventually alters perhaps to suit TV or HDTV broadcast
    to make easier conversion.
     
  3. tryingtimes

    tryingtimes
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    I guess this will depend on the proliferation of digital projectors that are capable. Are the current digital projectors (trafford centre for example) capable of high frame rates?

    Tough one this - the flicker on the projector seemed more than the cinema (will do some more viewing tonight and over the weekend). I wonder if this is to do with the scanning nature of the crt as opposed to the full-frame-at-a-time cinema approach.

    Even if they were the same I watch my HC far more often than I've ever gone to the cinema and it is a slight worry.
    If I notice any ill effects after watching a full movie then I guess I'll know!

    Cheers
    Alex
     
  4. Steve at NMI

    Steve at NMI
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    The following text is the content of an interesting post by Mark Rejhon on <another> forum (as they say in Parliament) that you might find interesting. I do not think Mark would mind it being posted here .........

    ***********************************************

    This is in response to emails I received, including from well-established industry professionals as well as ROCK customers, First, let me say that I really like 48 Hz -- both on CRT and on DILA. I agree with many people about 48 Hz, including very knowledgeable people.

    THE ADVANTAGES OF 48 Hz

    Basically, when you go to the movie theater, you are seeing 48 Hz there. Today's 35mm projector show each film frame two times. In the early days of film, each film frame was shown once, which produced excessive flicker even in the darkness, since it was only 24 Hz! This is where the term 'flick' was coined, as in "Let's go see the latest flick.". This is far less of a problem nowadays now that today's 35mm projectors show each frame of film twice.

    Also 48 Hz on a CRT yields a flicker frequency exactly identical to your local movie theaters, which can heighten the film-like feel because the flicker frequency is exactly the same.

    Additionally, 48 Hz on a CRT can yield sharper looking pans than 60 Hz or 72 Hz, because using a lower frequency can reduce the "motion blur" sensation.

    When showing 48 Hz on either a CRT or DILA, you are using less bandwidth than at 60 Hz or 72 Hz. This in itself, can yield a sharper and better picture because of better utilization of bandwidth. This is more pronounced on certain setups than on others, since equipment vary. This is prevalent at really high resolutions, especially when dealing with high-def images, where bandwidth limitations can become clear at different refresh rates.

    THE DISADVANTAGES OF 48 Hz

    The biggie is the potential for flicker. Some people are overly sensitive to flicker -- and dislike going to the movie theater for this reason. These people can see flicker 48 Hz, either at home or at the cinema.

    If the room is made completely dark, then this can be eliminated for many people -- but not for everyone. Some people are still sensitive to 48 Hz.

    Also, there is a segment of people who are more sensitive to flicker on a CRT. This small segment of people, when presented with the same conditions for both CRT and 35mm, are more sensitive to flicker in the CRT than with the 35mm This is due to a phenomenon called duty cycle.


    WHY CERTAIN PEOPLE DETECT DIFFERENCE BETWEEN CRT AND 35mm AT SAME REFRESH

    There is no difference in the frequency of the 48 Hz.

    However.... There is a difference in the light-dark duty cycle in a 1/48th second interval. Put a high-speed photodiode at one fixed point on the screen (And test with a white field on a 35mm and a CRT), and connect its leads to an oscilloscope, set the oscilloscope to show a 1/48 second interval, and you will see that there is a much briefer period of light and a much longer period of dark in a single 1/48 second interval, for a single point on the screen, when using CRT rather than film.

    With 35mm film projectors, many of them are designed to maximize the length of time that light is shone on the screen (mainly for efficient use of the light output). This can mean that light may be frequently shining most of the time, with only a brief period of darkness. At the very least, it's 50-50 in today's movie theaters.

    With CRT, once an electron beam stops hitting phosphor, that point on the screen nearly immediately loses most of its brightness. By the time the electron gun is a few scanlines down, most of the brightness is typically already lost a few scanlines up. It depends on the amount of persistence in the CRT. It takes only a brief period for phosphor to lose most of its brightness (typically, mere milliseconds, or even several microseconds, for 90% of the brightness to be gone from the phosphor after the electron beam has moved on), although a much longer period for all the detectable visible light to dissappear from the phosphor (This is why sometimes you notice a ghosting, especially with bright highlights in dark video games or street lamps in nighttime video -- typically because of the higher persistence of green). This means that when someone is watching CRT, they are staring mostly at darkness with brief flashes of brightness. The principle of rapid decay makes CRT a very good technology for 3D applications with LCD shutter glasses -- because of the short decay of phosphor. Although an electron beam is usually shining a dot somewhere on the CRT screen at nearly all times, most of the other parts of the screen (above and below the beam spot) is now already black.

    Note: Both CRT and 35mm images can be roughly the same brightness, often because the CRT beam spot is super bright and focussed (literally), which makes up for the longer relative period of darkness in a single refresh interval (1/48th second at 48 Hz).

    Human eyes are more sensitive to flicker when there's a longer period of darkness and shorter period of brightness in a single refresh. So this explains why some are more sensitive to 48 Hz in one situation than another (assuming everything else equal -- average brightness, ambient light, viewing distance, etc).

    In other cases, when the person is not sensitive or bothered by the flicker in either case, motion and pans on 48 Hz on CRT can look sharper than on film due to the shorter duty cycle -- a briefer bright duty cycle frequently means less perceived ghosting (additional motion blur on top of the already-existing motion blur built into the film material). So it is possible for a person to prefer watching the same material on a 48 Hz CRT than on a 48 Hz 35mm.

    Not everybody is affected by the difference in flicker between CRT and 35mm -- but some people are.

    BOTTOM LINE

    48 Hz is an excellent choice for consumers who aren't sensitive to the flicker in their home theater conditions. The customer should decide whether to use 48 Hz. We know some people dislike 48 Hz, while we know some people love 48 Hz. (I have no idea of the relative proportion of these two audiences, however) Personally, I like 48 Hz, while I do find 72 Hz provides a good compromise between filmlike and flicker, at least on equipment that is sufficiently good enough to resolve 72 Hz without noticeable degradation in either scenario. Additionally, 48 Hz is also good for digital projectors that like the refresh rate -- such as DILA, since for these types of digitals, there is no such thing as flicker. (Lack of flicker has other types of disadvantages too - ranging from ghosting to unsuitability for 3D shutter glasses applications, etc)


    __________________
    Thanks,
    Mark Rejhon
    www.marky.com/hometheater

    ***********************************************
     
  5. tryingtimes

    tryingtimes
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    Thanks Steve
    I've read an awful lot about 48Hz on the AVS forum - enhanced detail especially in the near-blacks, improved contrast, more 3d-like, smoother pans, more natural colours, etc etc etc.
    I can certainly say that I noticed an improvement in some of these areas and I will be trying it out far more over the next couple of days.
    Even though I've heard that the projector finds it a bit easier I didn't know if this had a direct relationship with longevity. If so then it's yet another point on the plus side.

    One of the reasons I'm going to look very carefully at the flicker is that I'd like to cater for a wide number of people. I don't want to put my movie on and then find that someone is particularly sensitive to it! That's one of the things that put me off early dlp!
     
  6. Roland @ B4

    Roland @ B4
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    I'm still not convinced on the 48Khz front. I've tried it a couple of times on Barco 808 and 1209 projectors and the flicker gets to me.

    At first I thought it was hype becasue the Teranex couldn't cut it at 72 and it was the latest box of tricks

    The other thing that in the UK we must bear in mind is the mains frequency of 50hz I would not be surprised to see interferance creaping though from the power supplies.

    Also your DVD player is out putting at 50 or 60 hz so there is a lot of up down conversion going on in the scaller again

    At the end of the day if it works for you.

    Interestingly a lot of UK cinemas are now triple flashing the frames (72Hz)

    Alex to answer your questions the projector will set up a new memory block so I would just use H Phase on the projector to get it back into possition. Alternativly you could use power strip to adjust the picture position.

    The PJ will be fine at either setting and either resoloution.
     
  7. tryingtimes

    tryingtimes
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    Cheers Roland

    With regard to the pq thing. I'm starting to find the flicker does annoy me. A few freinds are coming around to watch The Fast and the Furious tonight so I might try it out on them.

    I moved from Powerdvd 4 to Theatertek only a couple of evenings before trying 48Hz and I starting to think that I may have been seeing improvements because of that rather than the refresh.
    At least it's been easy to try!
    Nothing to lose except my sanity!

    I just keep getting drawn in to the films whatever the frequency and keep forgetting to look for differences. Good news I suppose.

    I'm really starting to sink in to the picture now and forget everything else. Those small TT improvements and the elimination of the studder have really made a difference.

    The next thing for me to try is just to eek out the last bit of black level detail. The 48Hz did help but I don't think the pj is getting the info from the hcpc so I think the solution may lay with gamma.

    Thanks again
    Alex
     
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