Re: How does digital TV broadcast prevent ghosting effects?

ChairmanOfTheBored wrote:
On Thu, 22 Nov 2007 17:10:51 GMT, Joerg
<notthisjoergsch@xxxxxxxxxxxxxxxxxxxxx> wrote:

a7yvm109gf5d1@xxxxxxxxxxx wrote:
On Nov 21, 4:21 pm, ChairmanOfTheBored <RUBo...@xxxxxxxxxxxxxxx>
wrote:
On Wed, 21 Nov 2007 20:01:01 GMT, Joerg



<notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx> wrote:
Jim Thompson wrote:
On Wed, 21 Nov 2007 11:42:14 -0800, Joerg
<notthisjoerg...@xxxxxxxxxxxxxxxxxxxxx> wrote:
Joel Koltner wrote:
"MRW" <mr.whate...@xxxxxxxxx> wrote in message
news:caa438d0-efc3-495c-926e-e44ffe1b3293@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
How do these standards eliminate ghosting effects?
The basic idea is that, since they're transmitting a digital signal, if the
reflections (ghosts) aren't strong enough to start "flipping bits" (or only
flip a few), the resultant signal is still "digitally perfect" (at least once
error correction is performed) and thus the picture displayed is exactly what
the transmitter started with.
An improvement can be had with a so-called "rake receiver" (see:
http://en.wikipedia.org/wiki/Rake_receiver):Assuming the ghosting is
relatively constant, you're just getting delayed copies of the original signal
at various points in time. If you start sampling at those various points in
time and summing up the result, you can faitfully reconstruct the original
signal. (Of course, finding the correct "various points" is not so
trivial...) Hence you're you're "raking in" all the copies of the original
signals to build up the result.
Supposedly first-generation ATSC receiver chipsets didn't do any of this
active ghost cancellation, whereas second- and (the current) third-generation
chips do.
I also read a similar scheme for analog TV using Ghost Canceling
Reference (GCR) signals from both transmitter and receiver. Is this
pretty much the same idea?
Somewhat, yes, although with a rake receiver you don't (necessarily) need a
reference signal -- you just try out the various sample points until you get
one that produces the "best" result. Unlike an analog system (where all you
really have to measure are signal to noise ratios) in a digital system usually
there are plenty of synchronization and test data patterns at known locations
within the signal, so it's usually easy to determine how well the system's
performing.
Oh, forgot one thing: This new set has an anti-ghosting comb filter.
Finally! I've used that technique since the 80's and I wonder what took
them so long.
What brand?
Vizio VX37L, which is a 37 incher, at Costco.
Jeez. Vizio SUCKS. You should have flipped for the extra bucks for one
of the big players ion the industry.
Sharp Aquos Full HD for me.

I didn't post this. Learn to quote properly.


Huh? Read again: Sez " a7yvm109gf5d1@xxxxxxxxxxx wrote:". AFAIK that ain't you.


So, what's usually playing in HD these days?

HD offerings grow continually.

Tried it out yesterday, it gets some HD channels, others drop out a lot, and yet others it can't decipher on account of multipath. But all the DTV stuff was standard def. Some of it wide screen though.

If it was in wide format over the air, it was HD.


But it read 480SD in the OSD. When I turned the set to "normal" the format on the digital channel switched a lot depending on what played. News in standard with the black strips left and right, unless I switched to "wide" but then everyone appears overweight.


HD starts at 1280 x 720
The picture is nice and crisp BTW. No complaints here.

There is a link in this thread that declares what is and what is not HD.
You should give it a read.

I know, however, that over cable signals get compressed, and even
though many are wide aspect, few are true HD streams. The dirty bastards!

Sad too, since they fit onto a std 6MHz wide slot, and the
cable/satellite twits didn't need to re-compress a goddamned thing, yet
the idiots do it anyway.


Well, we have neither cable nor satellite. It's only what's available OTA. I am not a ballgame fan but I'll check this afternoon just to see how HD might look like on this set. Our vicar said the Packers play the Lions (he roots for Detroit) today so hopefully that will be in HD.

BTW, someone mentioned the Sharp Aquos: Costco has the 42" for around $1200 after rebates. Says the ad.

--
Regards, Joerg

http://www.analogconsultants.com/
.

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