Conference hydra::amiga_v1

    
    
    	Yes the flicker fixer cards work. I have used the Flicker Fixer
    by Microway for many years and the display is great. You will need
    a Multi sync or VGA monitor to use a flicker fixer.
    
    		Steve P.
    

Check out other notes for more info, but with a 2000 you've got at least
3 choices.

MicroWay flickFixer
Commodore A2320 (I think that's the model)
Flicker Free Video

All of them are functionally pretty equivalent.  The MicroWay and CBM 
boards typically take up the video slot.  The "Flicker Free Video" sits 
under the Denise chip.  The Commodore and "Flicker Free Video" offer some 
features above and beyond the MicroWay board - PAL support, pass-through, 
scan doubling, etc. (or so I remember). 

I initially owned a MicroWay flickerFixer, then traded in for a CBM
board since I wanted proper PAL support.  The CBM board has a few quirks,
but they're well documented and easy to live with (for me).  I was very
happy with the MicroWay board, except for the PAL support.

All of them are in the $220-270 range new, and can often be found used 
if you check comp.sys.amiga.marketplace.

A good multi-synch is recommended, although you might get by with a VGA
monitor (depending on what you choose to get).  All of these will produce
the rock-solid display you're looking for. 

Steve

    So far nobody has bitten the bullet and responded to the question:-
    
    	"How does it work?"
    
    
    		Paul (Curious Cat)
    

    Re .0:
    
>   Anyway, all I want to know is, do the flickerfixer cards that are
>   available completely eliminate the flicker and how does it work?
    
    I'm sure this has been covered elsewhere, but here we go again.  To
    understand the cause and cure for display flicker, you need to know
    something about how the screen is scanned in the first place.  I'll
    assume NTSC (the North American standard) for the following.
    
    Start with your TV screen at home and the "non-interlaced" medium
    resolution (640x200) Amiga display that many of us consider "normal". 
    During each 1/30 second, the screen is painted top-to-bottom TWICE,
    scanning the "odd" lines on one pass and the "even" lines on the other. 
    Whereas the NTSC standard calls for 525 lines total, the 200 lines of
    the Amiga medium resolution display are simply displayed twice.  Since
    the screen is repainted every 1/60 second, there is no apparent flicker.
    
    Now shift to the 640x400 "interlaced" high resolution screen.  At this
    point, alternate lines are TRULY painted in alternate 1/60 second
    intervals.  This means that any GIVEN line is only painted once each
    1/30 second, long enough for it to "fade" before being repainted.  That
    fading is what we perceive as flicker.
    
    A "flicker fixer" uses a monitor that scans at twice the normal speed. 
    It buffers the "even" and "odd" lines and paints the whole screen from
    top to bottom every 1/60 second.  The result is a rock-solid display. 
    
    Yes, these display enhancers work.  They even make medium resolution
    screens look better by filling in the gaps between the 200 displayed
    lines.  The only "fluke" comes when there is rapid motion.  Then the
    fact that the lines being painted from the buffer are 1/60 second older
    than the ones being taken directly from the custom chips can cause
    "tearing".  Since this usually affects games more than anything else,
    it's hardly a serious problem.
    

    
    Right Bill, what you said in .4 is the oft quoted "standard answer"
    for the question "why does the Amiga flicker in interlaced mode?"
    and your answer implied that the standard broadcast TV picture was a
    single uninterlaced picture. However this is not the case as both
    NTSC and PAL broadcasts are also interlaced so both TV transmissions
    AND the Amiga have IDENTICLE waveforms. So why Does the Amiga
    flicker.
    	For reference sake I will point out I served my apprenticeship
    as a TV and Radio engineer and I am also a licensed Radio Amateur
    (or HAM to you)
    
    
    
    			Paul
     

    Paul,
    
    read the note in AMIGA_V2 which describes the AMX emulator. The author
    has a long internet reply in .1 I think. A section in there describes
    why the Amiga flickers.
    
    Greg

    Re .5:
    
>   Right Bill, what you said in .4 is the oft quoted "standard answer"
>   for the question "why does the Amiga flicker in interlaced mode?"
>   and your answer implied that the standard broadcast TV picture was a
>   single uninterlaced picture. However this is not the case as both
>   NTSC and PAL broadcasts are also interlaced so both TV transmissions
>   AND the Amiga have IDENTICLE waveforms. So why Does the Amiga
>   flicker.
    
    I confess to having overloaded that part of the discussion.  Let's
    separate the Amiga from standard broadcast for a moment.  A standard
    broadcast picture is referred to as "interlaced" because it alternately
    transmits screens of ODD lines and EVEN lines.  There's a phase lag at
    the beginning of the EVEN screen so that its first line appears between
    the first two lines from the previous ODD screen.
    
    The Amiga's "medium resolution" mode (640x200) OMITS this lag, so the
    even screen is painted directly over the odd screen.  From the Amiga's
    point of view, the whole display is painted, so it is NON-interlaced.
    
    The Amiga's "high resolution" mode (640x400) IS interlaced, meaning
    that the even lines and odd lines are painted in separate screens. 
    Computer graphics tend to have MUCH higher contrast and sharper edges
    than television pictures, so the 1/30 second decay in the intensity of
    a pixel that is displaying a light color and is adjacent to a dark
    pixel is that much more evident to the human eye.  There are four
    solutions to the problem:
    
    	1.  Reduce the contrast (thereby discarding signal information)
    	2.  Use a higher-persistence monitor (introducing "smearing" of
    	    rapid motion)
    	3.  Increase both scan frequencies together (interlace artifacts
    	    remain, but decay is reduced so flicker is less evident)
    	4.  Double the horizontal scan frequency and deinterlace the
    	    picture (this is what the Flicker Fixer, et al, do)
                                      

re .5

You seem to be implying that broadcast TV doesn't flicker. This isn't the
case - it does, if you catch it showing the right kinds of images.

Watch people wearing plaids, preferably with contrasting colors and and a
fine mesh. It's not uncommon for there to be flicker in such patterns during
a broadcast.

	<mike

    Right.  Remember that computer screens tend to use high contrast line
    elements which are only *one* pixel high, and are aligned perfectly
    with the raster scan lines.  Images for television are usually
    designed specifically to AVOID these conditions, because it causes
    that annoying flicker effect!

Re: .5

To continue what Mike was saying in .8, display a nice digitized
interlaced HAM picture on your Amiga.  Now step back about three feet
from the monitor.  You probably will not be able to see any flicker.
This situation is equivalent to a TV displaying a still picture.
Like the TV, the Amiga will not exhibit much flicker because the image
being displayed has smooth color shading and low contrast.

If you want an example of flicker on TV, just watch for text displays and look
at the top and bottom edges of characters; flicker should be evident there.