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In Reply to: The bandwidth to pass full HD is 35kHZ posted by floyd on March 29, 2002 at 05:19:58:
1080i, outputs at a rate of 1920 x 1080 x 30 = 62 Mpixel/sec. I though one needs 1.5 - 3x the bandwidth to transfer properly, which would work out to be 100-200Mhz.1080p would need double that bandwidth.
Follow Ups:
Video systems don't generally use pixels; they use video samples. This means that the bandwidth of a reconstructed signal will really only be half the sampling frequency.Pixels are good for computers, because they're mathematically easy to work with and conceptualize, and the harmonics let you get cleaner edges, at a given resolution. The price you pay is that aliases get into your signal. So, for example, when a full-bandwidth image is being slowly panned, you'll notice a certain amount of popping and noise. To compensate for this, people have developed "anti-aliasing" techniques, which selectively limit the bandwidth of the signal, in order to reduce these display artifacts. Pixels are also a fairly accurate model for the limitations of image reproduction, on LCD or DLP-based displays. (Note that this doesn't mean you need higher bandwidth cables, between your DVD player and LCD projector - only between your computer and LCD projector.)
Conversely, pixels aren't good for video. Within a scanline, a video signal is reconstructed from samples using a sinc reconstruction filter (as opposed to a box). This means you can freely use the full theoretical bandwidth, without having to worry about artifacts introduced by aliasing. For signals along the vertical axis of the screen, more aggressive pre-filtering should be done, since the result is reconstructed with a gaussian (the beam shape) FIR, which does admit a certain amount of aliases.
Therefore, you should only need nominally more bandwidth than 31 MHz, in order to account for horizontal and vertical blanking. When you're looking at bandwidth specs, be sure that the passband is qualified by the amount of allowable attenuation (i.e. -3dB). Otherwise, the number is meaningless.
This whole issue seems to be the greatest single point of confusion, between the general public (and even some professionals and reviewers) and the engineers who write the specs and build the equipment. I guess basic signal processing concepts really need to find their way into high-school curriculums.
the minimum spec. for the new mass-market receivers (ie Denon AVR 5803 ) seems to be 100 mHz. I just ordered a video switch from Extron...i believe the guy said something about "three times that".but maybe he was talking about the price...
it's a video switch, selects my DVD player or my HD tuner/receiver
that's $736.00 (discount price)
plus another $550 for a meter of a true 75 ohm RGB cable
yes, i did say a meter of video cable, but it's over an inch thick!
you can tell it's good because you can't bend it at all.
when did high-end become a plumbing nightmare?
the horror...
Pete,Since I have a Panny 42" on order, I'm likely to be investigating a switcher for the same reasons you are. Would you mind telling me what convinced you to go with the Extron switcher over any others? (For instance, I know you can by many brands of switchers that are much cheaper). Also, which model did you go for?
Thanks,
Rich.
but I do believe I'm going to cancel the order later today. The bill came to $1110.00, and all I want to do is select between the HDTV receiver or the DVD player.even that was a savings, because for a while there they had me buying a $5000 Runco PFP-11 (or -7, I forget which) for fixed pixel displays, only we couldn't figure out what the native rate is on the panny...
i did some research on video switching and it seems as if 100mHz is the industry standard sized pipe for doing it. all the video processors I've seen use this spec., which is the same spec on the new Dennon AVR 5803, which costs alot less than a video processor.
i'm pretty happy with the scaler/line doubler built into the Panny.
I think I'm going to sell all my seperate components in the video system and just have one massive box to do it all. It's so retro.
Pete,Looks like we're going the same route! The Denon looks fabulous. But here's my solution:
I see the Pioneer is already available, and at about half the cost of the Denon.The local dealer says the Denon might arrive in a few weeks. I'm going to check it out.
still, I'd like to think again about an outboard video processor...
there's so much going on in home video today--nothing is clear, not even to the "experts"
I paid about 90 cents a foot for my Belden 1406B RGB cable(makes a cheap and fine component video cable-all in one sleeve too). But it's not an inch thick and you can bend it. I'm thankful I'm not into high def and plasma yet! I can only imagine what Kurtz would think of all this!
Joseph Conrad was very into high end!sheesh!
what...no wait...let me quote:
HEART OF DARKNESS
by Joseph Conrad
Chapter One
"The "Nellie," a cruising yawl, swung to her anchor without a flutter of the sails, and was at rest. The flood had made, the wind was nearly calm, and being bound down the river, the only thing for it was to come to and wait for the turn of the tide."
****
that's the opening, written by a guy who learned English as a third language.
compare that prose to that of any person living or dead, ever.(the horror...)
and look, read it again.
is that about adventure?
he's telling us we are at rest, we are to wait...but what? are we not filled with the urge to continue? can you possibly sleep without ever knowing the next line ?
is that not a monumental rent in the very fabric of wonder?
oh, how can you not take the next step into that gaping maw?
so subtil, it's almost not apparent
he's telling us to wait, right at the moment when we are most ready for action
he's telling us there's a moment, not now
he's telling us we are "bound down the river"
what a beautiful turn of phrase: "bound" as in "traveling"
and "bound"...a forboding against free will...a hint at enslavement...
the inevitablity of the union dance of fate and character...waiting for the turning
on "our cruising yawl"...a lark, we're on a cruise, our free will brought us to this place...this threshold
"without a flutter of the sails"
we are becalmed, at peace, and yet
on the edge of something, are we not?
there's a change beneath the surface of things
the force of our soul has "swung to her anchor"
something so vast, so mysterious, so unknowable
has made itself known to us
is that not the very essence of the high end?
yes
oh god,
yes!
(deep in the heart
of darkness)
.
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