How does digital TV broadcast prevent ghosting effects?

[Tim Williams]

1366x768?

Ar you kidding me?
I was under the impression HDTV was 1920x1080 these days,
and 50 and 60 Hz capable too (for Euope the 50).
The cannot even sell it here as HDTV with that few pixels.
Even my monitor has more.

Does that mean we will soon be able to read Amy's tattoo?
http://en.wikipedia.org/wiki/Amy_Wong
"One "obscene tattoo" (which appears blurred because its design requires a
resolution unmatched by modern TVs) was shown to be on her upper left
arm..."
:^)

Tim

 

[AZ Nomad]

Good morning world!

I've been reading about the new digital TV standards (8-VSB, DVB-T,
ISDB-T) and they all mention that the standards are more robust
compared to the analog standard. For example, all state that
practically ghosting effects are eliminated with DVB-T and ISDB-T
providing more robust response to mulitpath effects than 8-VSB.

How do these standards eliminate ghosting effects?

step 1) get a clue at what ghosting is

When you've done this then you'll understand why ghosting is impossible
with digital transmission.

 

[Joel Koltner]

I'm assuming that the error correction portion is dependent on the
modulation scheme.

Yes, although it's also dependent on the intended transmission path -- getting
video to a cell phone in, e.g., someone's moving car is a worse environment
than just getting it to a stationary TV antenna with decenet gain.

Where I work the way we choose the amount of error correction is to take a
prototype with no error correction, transmit known test patterns, collect
error statistics while operating the receiver in the intended environment
(e.g., at someone's home, driving around in a car, etc.), and then play around
with the amount of error correction to try to balance data rates with
robustness.

If you're looking at "well known" over-the-air standards, it's probably a safe
assumption that someone came up with a model of the environment and did plenty
of simulations before committing anything to silicon -- for high data rate or
highi volume devices, that's where the error correction is implemented
(whereas, at least to date, everything we've done has been slow enough to do
it in software).

So, am I right in assuming that the COFDM technique
being describe as more robust to multipath effects than 8-VSB plays a
part in implementing the error correction scheme?

Well, it's supposed to be, but I don't personally have enough familiarity with
them to say.

---Joel

 

[Joel Koltner]

1366x768?

Ar you kidding me?

Joerg is just going to be using it for over-the-air and DVDs, I believe, in
which case...

-- DVDs are 720x480 -- no problem
-- No one but no one is planning on transmitting 1080p over-the-air at this
point; everyone is 720p or 1080i... and to many people 1080i actually looks a
skosh worse than 720p in typical TV scenes. Granted, it *can* look better,
but the point is effectively there's "nothing to lose" by displaying 1080i on
a 1366x768 display.

I suspect that Joerg is going to be pretty happy..

I was under the impression HDTV was 1920x1080 these days

Some people like to refer to this as "true" HDTV. 1366x768 is generally
referred to as "EDTV" (enchanced...) vs. the 720x480 of "SDTV" (standard...).
The names are all pretty meaningless by the time the marketing guys get
through with them... something like "near CD quality" can still mean a
compressed 32kbps bitstream it seems!

The only "true" HDTV source material you'll see any time soon is BlueRay and
HD DVDs... something I expect you'll probably adopt much quicker than Joerg
will.

Wal*Mart did have those Toshiba HD-DVD players for $99 last month... but I
really think it's going to be next Xmas that's the year of the cheap
BluRay/HD-DVD player.

---Joel

 

[Jan Panteltje]

Does that mean we will soon be able to read Amy's tattoo?

Probably, not, probably made with filt pen, and long gone.

http://en.wikipedia.org/wiki/Amy_Wong
"One "obscene tattoo" (which appears blurred because its design requires a
resolution unmatched by modern TVs) was shown to be on her upper left
arm..."
:^)

The high resultion will cause plenty problems with makeup and props.
But wait a few years, and all actors will be simulations
Well, perhaps....

 

[StickThatInYourPipeAndSmokeIt]

-- DVDs are 720x480 -- no problem

Sure there is a problem. It will look like shit as most DVDs do.

Step up to the pump and get an HD disc format.

I have many discs that clearly show how sad the encoding of the original
DVD format is.

Full Metal Jacket is a good example of a piss poor telecine session at
the time the master was made. The new Blu Ray remaster is great!

Others I have respond to up-conversion beautifully.

"All of Me" looks great as a std DVD through an up-converting player.

Your player upconverting a DVD output is NOT the same as your display
up-scaling was it gets fed.

 

[Jan Panteltje]

HD starts as 720, so it qualifies, regardless of what you, or your
lawmakers do "over there".

Not exactly, there are 2 'terms' that can be used:
http://en.wikipedia.org/wiki/HD_ready#HD_ready_and_HDTV_1080p
<quote>
An updated spec of the standard was introduced in summer 2007. For a display to bear the HD Ready 1080p logo it must:

* have minimum native resolution of 1920x1080 pixels

* receive, process (pass through) and display video signals of 1920x1080 @24,50 and 60 hz

* display them at native or higher refresh rates.

Not all Full HD tv sets qualify for this logo.

Additionally, devices that carry the HDTV 1080p logo must be able to decode compressed 1080p video.

<end quote>

 

[StickThatInYourPipeAndSmokeIt]

Wal*Mart did have those Toshiba HD-DVD players for $99 last month... but I
really think it's going to be next Xmas that's the year of the cheap
BluRay/HD-DVD player.

Even then, they will be low end. Likely NOT capable of the Audio
capacity that the discs they playback will contain.

The bottom line players will concentrate on delivering 1080p video to
grab the dopes that want to enter the market. Best bet is to get a PS3
for BluRay, because you get so much more than a fully capable BR disc
player (great value for one thing), and the high end Toshiba players for
HD DVD because you will truly get the best audio processing with them as
well as the video. The low end will always have full res video, but many
will have decreased capacity in the audio dept.

One gets what one pays for.

 

[StickThatInYourPipeAndSmokeIt]

Not exactly, there are 2 'terms' that can be used:
http://en.wikipedia.org/wiki/HD_ready#HD_ready_and_HDTV_1080p
<quote>
An updated spec of the standard was introduced in summer 2007. For a display to bear the HD Ready 1080p logo it must:

* have minimum native resolution of 1920x1080 pixels

Read what you just wrote, idiot. It has to be 1080p to state that it is
1080p. NO SHIT, SHERLOCK. However, what I SAID is what the industry has
stated, and that is that the HD format BEGINS at 720, and THAT is a fact.
Why would a 720 display have ANYTHING related to 1080 written on it, you
idiot?

* receive, process (pass through) and display video signals of 1920x1080 @24,50 and 60 hz

* display them at native or higher refresh rates.

Not all Full HD tv sets qualify for this logo.

Yeah, and they get the HDTV logo, NOT the "HD Ready 1080p" logo. There
is a difference, but BOTH are HD, dingledorf.

Additionally, devices that carry the HDTV 1080p logo must be able to decode compressed 1080p video.

<end quote>

Jeez, you're a dope. Nearly ALL 720 sets will downconvert 1080i and p
signal content. Mine is 3 years old, and can do so.

wiki is not always right on the mark.

http://www.hdpictures.com/hdtv.htm

Just one example of a site that got it right.

 

[[email protected]]

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.

 

[Jan Panteltje]

BURB.

Na, you have no clue.

There 2 'terms' that can be used:
http://en.wikipedia.org/wiki/HD_ready#HD_ready_and_HDTV_1080p
<quote>
An updated spec of the standard was introduced in summer 2007. For a display to bear the HD Ready 1080p logo it must:

* have minimum native resolution of 1920x1080 pixels

* receive, process (pass through) and display video signals of 1920x1080 @24,50 and 60 hz

* display them at native or higher refresh rates.

Not all Full HD tv sets qualify for this logo.

Additionally, devices that carry the HDTV 1080p logo must be able to decode compressed 1080p video.

<end quote>

 

[StickThatInYourPipeAndSmokeIt]

Na, you have no clue.

There 2 'terms' that can be used:
http://en.wikipedia.org/wiki/HD_ready#HD_ready_and_HDTV_1080p
<quote>
An updated spec of the standard was introduced in summer 2007. For a display to bear the HD Ready 1080p logo it must:

* have minimum native resolution of 1920x1080 pixels

* receive, process (pass through) and display video signals of 1920x1080 @24,50 and 60 hz

* display them at native or higher refresh rates.

Not all Full HD tv sets qualify for this logo.

Additionally, devices that carry the HDTV 1080p logo must be able to decode compressed 1080p video.

<end quote>

YOU keep adding 1080p AFTER YOUR HORSESHIT, BOY!

That is ONLY for the "HDTV 1080p" LOGO, NOT HDTV itself, you fucking
retard!

The HDTV industry definition starts at 720 lines.

Get it through your thick skull, BOY!

 

[Joel Koltner]

Even then, they will be low end. Likely NOT capable of the Audio
capacity that the discs they playback will contain.

Sure, but keep in mind that someone upgrading from a $49 DVD player to a $49
BluRay or HD-DVD player is still going to see a huge improvement. Some of
those uber-cheap DVD players (I've seen them as low as $19!) have quite crappy
DACs in them anyway, but I don't see people complaining.

 

[StickThatInYourPipeAndSmokeIt]

There 2 'terms' that can be used:

snipped retarded WRONG wiki reference.

The NAB and the ATSC declares what is, not wiki, you retarded ****.

HDTV starts at 720 lines. Wake the **** up, asswipe.

 

[StickThatInYourPipeAndSmokeIt]

Sure, but keep in mind that someone upgrading from a $49 DVD player to a $49
BluRay or HD-DVD player is still going to see a huge improvement.

They won't be $49 for a LONG time. You may see $150 players. The $100
WalMart thing was nothing more than an overstock closeout fluke. Last
year's model. There is a difference.

Some of
those uber-cheap DVD players (I've seen them as low as $19!) have quite crappy
DACs in them anyway, but I don't see people complaining.

Bullshit. I bought a SHIT COBY player that claimed 5.1, and even had 6
RCA ports on the back for the 5.1 out, BUT the damned thing would stop
playing the audio track at random points in the film ALL THE TIME. One
would have to stop, and then restart the flic and browse to the point in
the film they were at.

I will NEVER buy a no name El Cheapo Chinese-o brand again.

I will ALWAYS buy the name brands, and I don't care if they were made in
China as well, at least they utilize some modicum of QA control over
their designs and manufacturing processes.

**** El Cheapo. You get what you pay for.

Why would someone buy a nice display, and have a nice stereo system and
speakers, and then compromise everything on the video playback device
just to save $50 to $200 bucks?

The video might be there, but the sound will be 100% utter CRAP.

Very lame. I'll spring for the best in all arenas, thank you.

 

[Joel Koltner]

Bullshit. I bought a SHIT COBY player that claimed 5.1, and even had 6
RCA ports on the back for the 5.1 out, BUT the damned thing would stop
playing the audio track at random points in the film ALL THE TIME.

OK, I guess I should have said that I don't see _many_ people complaining.
Coby definitely is the low-end of low, although we have one in the exercise
room and it's been fine (it's hooked to some old 19" TV). I'm pretty sure I
know the exact model you're discussing up there -- seen'em in stores and once
even had one in a motel room -- but I've never used one.

I will NEVER buy a no name El Cheapo Chinese-o brand again.

Perfectly understandable.

Why would someone buy a nice display, and have a nice stereo system and
speakers, and then compromise everything on the video playback device
just to save $50 to $200 bucks?

Well... not everyone will find the better quality worth the extra money, and
(more likely) not everyone has a nice display/stereo/etc. to begin with. Or
you have situations like a friend of mine, who has another friend who
hands-him-down all of his nice A/V equipment but only "piecemeal" so said
friend was once out buying a $99 DVD player to hook up to a $3,000 stereo.

Very lame. I'll spring for the best in all arenas, thank you.

Be thanksful that you have that option.

---Joel

 

[Paul Hovnanian P.E.]

Good morning world!

I've been reading about the new digital TV standards (8-VSB, DVB-T,
ISDB-T) and they all mention that the standards are more robust
compared to the analog standard. For example, all state that
practically ghosting effects are eliminated with DVB-T and ISDB-T
providing more robust response to mulitpath effects than 8-VSB.

How do these standards eliminate ghosting effects?

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?

Thanks!

With analog video signals, ghosting is caused by mutipath distortion,
where a 'second copy' of the signal arrives at the receiver delayed by a
small amount of time. That second copy is displayed as a second image,
offset on the screen by a distance equal to the path delay times the
horizontal scanning rate of the CRT.

With digital video, the broadcast is sent in several types of frames.
Each frame is labeled with a sequence number indicating where in time it
should be displayed. While mutipath distortion can still interfere with
digital signal reception, it does not manifest itself as a second image
offset on the screen spatially from the original. The only way to
produce a ghost in a digital stream would be to spoof the packet timing
data.

 

[Glenn Gundlach]

step 1) get a clue at what ghosting is

When you've done this then you'll understand why ghosting is impossible
with digital transmission.

Multipath is a large problem in digital transmission though it doesn't
manifest itself as trailing edge smears in the picture. It shows up as
lumps in the RF response (comb filtering) that make it difficult to
impossible to extract the data. There are active equalizers that can
correct some pretty bad reflections. The newest chipsets (#6 coming
soon) can correct a broader range of errors and do it faster - almost
to the point of working in a moving car.

http://www.hdtvprimer.com/ISSUES/what_is_ATSC.html

GG

 

[Tim Williams]

The high resultion will cause plenty problems with makeup and props.
But wait a few years, and all actors will be simulations
Well, perhaps....

Nah, what they need is sentient computers so they can kick the striking
screen writers.... at least right now.

I'd imagine robotic actors would sell better in the personal porn industry,
at least first. You know, when personality doesn't matter.

Tim

 

[Jan Panteltje]

With analog video signals, ghosting is caused by mutipath distortion,
where a 'second copy' of the signal arrives at the receiver delayed by a
small amount of time. That second copy is displayed as a second image,
offset on the screen by a distance equal to the path delay times the
horizontal scanning rate of the CRT.

Correct so far, but not delays are in the microsecond rang.
Always there is a HORIZONATL shift (ghost), never a vertical one.
For exaple in a NTSC 64 uS line 1 uS is about 1/60 of the screen width.

With digital video, the broadcast is sent in several types of frames.
Each frame is labeled with a sequence number indicating where in time it
should be displayed.

'Frames' are in the millisecond range (one every 40mS for example for
25 fps), at the speed of light the refecting object would
have to be about 300 000 000 000 * .04 / 2 meters away = 6 000 000 000 or
6 million kilometers.
Not likely, and the signal strength of that reflected signal would be very very low...

While mutipath distortion can still interfere with
digital signal reception, it does not manifest itself as a second image
offset on the screen spatially from the original. The only way to
produce a ghost in a digital stream would be to spoof the packet timing
data.

No, even if you changed the frame time stamp, the frame would be displayed
at the same position.
But the decoder may well abort.

Digital will simply take the strongest signal in the simplest case.