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Guest Message by DevFuse

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CBS HD on 61.5 now being down converted!!!


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88 replies to this topic

#21 OFFLINE   Stewart Vernon

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Posted 17 December 2005 - 03:39 PM

By my calculations:

1280x1080 = 1,382,400 / 2 (interlaced) = 691200
1280x720 = 921,600 (+33.3%)

Yes I know compression makes these numbers not very accurate but the same compression affects both and it seems to me that 720p is clearly superior.


About seventy-zillion (ok that's an exaggeration) time in various threads several folks, including myself, have tried to explain the above erroneously incorrect type of information.... so I can't bring myself to do it all over again.

But I will take the opportunity to say no... 1080i is superior resolution of image to 720p, period. And even a scaled down 1280x1080 instead of native 1920x1080 contains more resolution than a 1280x720 picture.

No arguments, just facts. All the strange math and wrong assumptions that folks keep jumping on are making my head hurt.

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#22 OFFLINE   n0qcu

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Posted 17 December 2005 - 03:59 PM

By my calculations:

1280x1080 = 1,382,400 / 2 (interlaced) = 691200
1280x720 = 921,600 (+33.3%)


-JB

Dividing by 2 is WRONG.

Just because interlaced only gives "half" of the frame at a time the WHOLE frame is still 1080 'lines' which is 360 more than 720.

Forget the funny math just use simple math.
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#23 OFFLINE   James Long

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Posted 17 December 2005 - 04:43 PM

JL: I could see how that equal bandwidth rule could come into play, however they currently have abc,nbc,cbs on one TP and fox on its own TP. Fox is averaging ~14mbit/s, while cbs/abc/nbc average between 9-12mbit/s.

There is no way they are cramming 4 HD channels per TP unless they want some really pissed off HD customers. 9Mbit/s even for 1280i is cutting it pretty low. So, what I think we'll see is maybe abc/cbs on one TP and nbc/fox on the 2nd. Having fox by itself doesnt make sense, unless they plan on adding the local pbs and WB in HD :lol:

I must have misread Tony's charts ... seeing 9483, 9936, 9937 and 9938 on R1 TP17. One of those numbers must be a mirror (two numbers, same content).

BUT - CBS at 10.98 Mbps times four channels is 43.92 Mbps. 8PSK transponders can handle 41.2 Mbps (FCC filing for E10). It is not inconcievable that four HDs would be tried on a TP (average 10.3 Mbps each). If E* was planning on giving the channel 1/3 of a transponder the bitrate could be closer to 13.7 Mbps.

Eventually we are going to have to let go of the numbers games. When HD channels go MPEG4 (and the encoders get up to speed) it is likely that we will see lower bit rates per channel.

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#24 OFFLINE   JohnH

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Posted 17 December 2005 - 04:53 PM

Too bad we can't get natural scan anymore. We have to put up with these 60 or 30 freeze frames per second and the motion just jumps across the screen.

I am waiting for someone to tell them they cannot change the digital OTA signal when providing it on satellite. That is they have to mirror it. No additional compression or any format changing.

#25 OFFLINE   JohnH

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Posted 17 December 2005 - 04:57 PM

I must have misread Tony's charts ... seeing 9483, 9936, 9937 and 9938 on R1 TP17. One of those numbers must be a mirror (two numbers, same content).

JL


Someone who can see the PAT, PMT and PIDs made note of that somewhere. It is CBS and CBS are the same channel.

#26 OFFLINE   JohnH

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Posted 17 December 2005 - 05:06 PM

Dividing by 2 is WRONG.

Just because interlaced only gives "half" of the frame at a time the WHOLE frame is still 1080 'lines' which is 360 more than 720.

Forget the funny math just use simple math.


Yep, but the flicker is different.

#27 OFFLINE   boylehome

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Posted 17 December 2005 - 05:55 PM

I'm trying to find the exact wording of the FCC requirement that stations within a market be given equivilent bandwidth. I keep finding the rule as it refers to distant channels not getting more bandwidth than the local version and significantly viewed channels not getting more bandwidth than the local version but not the rule I'm looking for.

I
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I have read it also and I have read the latest letters to the FCC. As I have said in other posts, it is a HARD read. I believe that the FCC basically gives the satellite broadcasting industry to do as they feel fit within reason. It is so general and ambiguous that it is open to just about any interpretation.

Here is a reference point for the report to congress: http://www.fcc.gov/

#28 OFFLINE   kb7oeb

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Posted 17 December 2005 - 07:12 PM

Do we know that its 720p? Maybe its 720i since the original signal is interlaced.

#29 OFFLINE   BrettTRay

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Posted 17 December 2005 - 07:38 PM

its is 720p

#30 OFFLINE   Stewart Vernon

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Posted 18 December 2005 - 12:54 AM

Too bad we can't get natural scan anymore. We have to put up with these 60 or 30 freeze frames per second and the motion just jumps across the screen.

I am waiting for someone to tell them they cannot change the digital OTA signal when providing it on satellite. That is they have to mirror it. No additional compression or any format changing.


A lot of folks also don't seem to grasp that moving to digital from analog threw out a lot of resolution too. Japan has analog 1000 scanline TV, so we could have done that here in the US too... but when the move to HD was discussed the powers-that-be also decided to go digital at the same time.

We gain a bunch of stuff... but one gain is in digitizing the signal, they can compress it and even at a minimal level of compression the digital HD signal takes less bandwidth than an analog HD signal would have.

We could have done analog HD digital, and *that* would have been an awesome sight!

#31 OFFLINE   BoisePaul

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Posted 18 December 2005 - 01:17 AM

We could have done analog HD digital, and *that* would have been an awesome sight!


I think my head just exploded when I read that...

#32 OFFLINE   Richard King

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Posted 18 December 2005 - 08:01 AM

A lot of folks also don't seem to grasp that moving to digital from analog threw out a lot of resolution too.

I recall seeing an analog HD display MANY years ago at an NAB convention. I have NEVER seen anything come even close since. The source material was on custom laser discs, the display was two stacked CRT projectors. I certainly wouldn't have wanted the job of converging that mess, but the end result was worth it. I always had a hard enough time back then converging my 3 tube Zenith projector. :lol:
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#33 OFFLINE   tnsprin

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Posted 18 December 2005 - 02:01 PM

I must have misread Tony's charts ... seeing 9483, 9936, 9937 and 9938 on R1 TP17. One of those numbers must be a mirror (two numbers, same content).

BUT - CBS at 10.98 Mbps times four channels is 43.92 Mbps. 8PSK transponders can handle 41.2 Mbps (FCC filing for E10). It is not inconcievable that four HDs would be tried on a TP (average 10.3 Mbps each). If E* was planning on giving the channel 1/3 of a transponder the bitrate could be closer to 13.7 Mbps.

Eventually we are going to have to let go of the numbers games. When HD channels go MPEG4 (and the encoders get up to speed) it is likely that we will see lower bit rates per channel.

JL

What is the bit rate claimed for 8psk turbo that Echostart said it was going to roll out? This was said to be happening even before they planned to go to mpeg4.
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#34 OFFLINE   James Long

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Posted 18 December 2005 - 03:03 PM

I believe the 41.2 Mbps for 8PSK is including Turbo.

JL

#35 OFFLINE   Stewart Vernon

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Posted 18 December 2005 - 04:36 PM

I think my head just exploded when I read that...


Sorry... I was just trying to be as wrong as some other people to fit in ;)

Actually, it was an honest mistake as I didn't proofread my post before (or after) I sent it... Thanks for noticing my mistake! Really, when I make a mistake even an accidental one, I like knowing so I can try not to do it again!

It does read pretty funny though... :)

#36 OFFLINE   Stewart Vernon

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Posted 18 December 2005 - 04:41 PM

I recall seeing an analog HD display MANY years ago at an NAB convention. I have NEVER seen anything come even close since. The source material was on custom laser discs, the display was two stacked CRT projectors. I certainly wouldn't have wanted the job of converging that mess, but the end result was worth it. I always had a hard enough time back then converging my 3 tube Zenith projector. :lol:


I wish I could have seen that. I seem to remember way back that when Japan introduced their analog HD there was some pressure here in the US and there were some sets designed for some of those fancy CES-type shows... but I gather either it was too expensive OR at the same time folks were looking at going digital so it never really saw the official light of day.

I believe Japan switched to digital as well at some point... but I figured it was worth noting that it was possible and spectacular. In a perfect world, we would get crisp analog signals and that would put everything else to shame!

But usually we have to choose between poor analog and passable digital... with the occasional nice HD digital signal thrown into the mix, fortunately.

To keep myself semi-on-topic here... I sincerely hope they don't decide to downconvert CBSHD or NBCHD. I know both use 1080i natively... I believe the WB does as well. I know ABC and FOX are 720p. I don't know what UPN uses, because my local UPN is the only station that doesn't use HD at all. I've read that PBS typically is 1080, but I can't be sure of that from my local PBS because it never looks quite as sharp as my CBS does.

#37 OFFLINE   BobMurdoch

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Posted 19 December 2005 - 08:38 AM

I've heard people say that 1080i looks "sharper", but that 720p handles motion better.

I tend to leave my 921 set at 1080i....
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#38 OFFLINE   LtMunst

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Posted 19 December 2005 - 09:34 AM

I've heard people say that 1080i looks "sharper", but that 720p handles motion better.



There's plenty of pro/con propaganda for both formats. I wish someone would do a double blind study comparing the two so this controversy could finally be put to rest.

#39 OFFLINE   voripteth

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Posted 19 December 2005 - 11:24 AM

I have a set that can display 1080p and I think more of that type are purchased every day. It would be a shame to throw away the extra data just to appease the 720p zealots.

I did see some odd graphic glitches this weekend on CBS HD. Every few minutes I would see a screen flash. With careful use of freeze frame I was able to see that it was a video frame shifted to the right about a half screen. Is this an artifact of DISH changing from 1080i to 720p?

#40 OFFLINE   Mike123abc

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Posted 19 December 2005 - 11:54 AM

I believe the 41.2 Mbps for 8PSK is including Turbo.

JL


What turbo coding does is use an improved error correction algorythm so they are able to cut back the amount of error correction and still get the same error rate for a given signal strength.

Dish is currently using 2/3 FEC on 8PSK. So 1/3 of the bits being transmitted are error correction. Now with turbo coding they can either keep 2/3 FEC and have less rain fade since error correction is better, or they can reduce the error correction to 3/4 or 5/6 and have more bits used for programming and keep the rain fade resonable.

At 3/4 they would have 21500 (symbol rate) * 3 (8PSK) * 3/4 (FEC) * 188/204 (RL EC) or roughly 44.58 Mbit/sec

At 5/6 they would have 21500 * 3 * 5/6 *188/204 or roughly 49.53

versus the current 21500 * 3 * 2/3 * 188/204 or roughly 39.62

It will be interesting to see what the final rates end up being. They can make adjustments in the symbol rate to balance rain fade vs bits/sec. For example if they decide that 3/4 is too little rain fade yet 5/6 is too much, they could slow down the symbol rate to lower the rain fade.




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