or Connect
AVS › AVS Forum › HDTV › HDTV Programming › Comcast HD Quality Reduction: Details, Screenshots
New Posts  All Forums:Forum Nav:

Comcast HD Quality Reduction: Details, Screenshots - Page 18  

post #511 of 2079
Quote:
Originally Posted by maxman View Post

Coax network? They're running ads all day long saying they're fiber optic!

LOL, if they had fiber then this thread would probably not exist!!!!
post #512 of 2079
Quote:
Originally Posted by maxman View Post

IN WHAT AREA??? Could you include it when you say "in my area" please.

Salem, Oregon.
post #513 of 2079
Quote:
Originally Posted by impala454 View Post

I don't think this is correct. OTA is broadcast at full bandwidth, and that could be the case with the cable channel, although the signal passes through a lot more equipment before arriving at your home. The QAM cable signal will use the same amount of bandwidth whether you're transmitting 9Mbps or 1305723057023570Mbps. It does not necessarily indicate that the original signal was that high.

OK, let my try to explain a little different way.

The term "bandwidth" when talking about channels means the channel width - in all cases in the US, that is 6Mhz. Analog and digital TV stations OTA have a 6Mhz bandwidth. Cable channels also are 6Mhz. A single SD analog station takes 6Mhz, and a digital QAM occupies 6Mhz.

There are different modulation techniques used for OTA (8VSB) and cable (QAM) channels. ATSC is capable of carrying around 19Mbps data rate. With various "overhead" elements it is claimed that the actual "payload is about 18Mbps. So, if a ATSC station devotes it's entire payload to a single HD program, then that program can be up to 18Mbps. Each SD digital sub-channel typically takes 2-3Mbps. So if there are 3 such SD subchannels, that will leave 9-12Mbps (usually on the lower end) for the HD. That's the case with many PBS stations.

QAM is twice as efficient (doesn't have to worry about ghosts, etc.), so can carry a payload of about 38Mbps. Many cable systems put 2 HD channels on a single QAM (they do here), giving each channel about 18Mbps. Of course, the topic of this thread is that Comcast is putting 3 HDs on a QAM, thus carrying only about 11-12Mbps.

Now if the local PBS station feeds cable via fiber and sends them the full bit-rate, and cable is only putting 2 HD channels per QAM then that PBS hd channel will go out to cable customers at about 18Mbps. Yet, the same station, because of the 3 subchannels is sending out the HD signal OTA at only 9-12Mbps.

That's correct, and happens more than you think. Many stations feed their local cable head end via fiber or microwave so that their cable viewers still get the signal if the stations transmitter has problems.

Now, in regards to "the signal passes through a lot more equipment before arriving at your home". That is true. But when talking about QAM channels we are talking about DIGITAL, and (up to a point) degradation of the signal from all those amplifiers (and there are less than you think in a modern cable system - see my next post) does not effect the quality of the received DIGITAL signal.

I do hope that this clarifies the situation. Just keep "bandwidth" and "bitrate" separate.
post #514 of 2079
Quote:
Originally Posted by maxman View Post

Quote:


Originally Posted by bidzer
...Now they're at a huge disadvantage as their old coax network has reached it's limit....

Coax network? They're running ads all day long saying they're fiber optic!

The odds are (particularly in Boston) that the cable system is what is known as HFC (Hybrid Fiber-Coaxial) where the signals are brought into the neighborhood (node) via fiber and only the "last mile" (or so) is via coax. (Incidentally, FiOS is only fiber to the house - signal distribution in the house is via good old fashioned CoAx as well). This hybrid architecture is what makes high speed internet, digital phone, On Demand and, eventually, SDV practical.
post #515 of 2079
Quote:
Originally Posted by jcouvret View Post

The cable box (required for digital cable) already downconverts. I can hook my HD cable box up to an SD TV and watch it letterboxed. Of course this is an HD cable box, but a software change to even SD cable box might allow this to work.

i realize this, the key word in my post was EVERYONE. the point is the problem right now is that every single TV would need a box and that is what people are pissed about.
post #516 of 2079
Quote:
Originally Posted by davehancock View Post

The odds are (particularly in Boston) that the cable system is what is known as HFC (Hybrid Fiber-Coaxial) where the signals are brought into the neighborhood (node) via fiber and only the "last mile" (or so) is via coax. (Incidentally, FiOS is only fiber to the house - signal distribution in the house is via good old fashioned CoAx as well). This hybrid architecture is what makes high speed internet, digital phone, On Demand and, eventually, SDV practical.

So they have the bandwidth, but choose to not use it? I guess I'm confused. A small coax run inside the house is better than coax being the last mile or more. The coax in my area tends to get wet alot. A few runs have already been replaced.
post #517 of 2079
Quote:
Originally Posted by McDonoughDawg View Post

Again, here in Atlanta, at least in Peachtree City, your statements do not hold water.

But he's not watching the channels in Atlanta. The point is that in some markets, Comcast is crowding HD channels into QAM slots, so that quality suffers.

If the degradation of PQ is not happening in your area, more power to you, but if Comcast as a whole is making policy decisions that result in this, it may eventually affect you, so you may benefit from the effort made by people here to shine a light on a burgeoning problem.
post #518 of 2079
I have a theory and anyone who knows the facts, please let us know exactly what they are, please?

Recently in Nashville, we got the "Project Infinity" upgrade to the VOD service. After this supposed upgrade, I first noticed the degradation in of the HD broadcasts. This is even before seeing this thread. This upgrade took place around a month or so ago.

For those who do not know, this is what I think has happened with the "Project Infinity" upgrade. It is in fact adding more bandwidth for on demand services to add programming including HD, though it also adds more commercials in the content. It is my understanding this upgrade (at least now a downgrade in my opinion) is being done around the country at different times to be completed by the end of the year.

The reason some markets may have better quality cable than others could be the upgrade has not yet been implemented or/and the size of the market requires less bandwidth on the network.

Does anyone know what Comcast has said they are doing long-term and what the final outcome will be come February 2009? Or are they mum at the moment seeing how they can get by on the cheap or get away with with the customer being the ultimate loser. Of course, in some markets, we do not have any competition to Comcast except the dish. I had a dish 1996-97 and at the time, I was not impressed and got rid of it quickly. Surely, it has been upgraded to satisfy customers over a decade later.

My personal feelings is that states and cities should no longer have the right to govern regulations over companies that provide broadcast content that subscribers pay for but open to market to all who want to get in the game. We should have the choice to pick and choose who we give our money and determine who gives us the best quality for the dollar. Since I have been made aware of FiOS, I don't see anything better on the market, that is if you can get it in your area.
post #519 of 2079
Quote:
Originally Posted by bidzer View Post

LOL, if they had fiber then this thread would probably not exist!!!!

Most all cable systems are known as HFC, or hybrid fiber coax, meaning fiber is used to get close to the subscriber premises, and then coax is used the final leg. Depending on how "deep" the fiber is laid helps determine how much bandwidth can be utilized at the sub's home. The further the coax runs to the node, or fiber link, the less bandwidth is available at the sub's premise.

For example, one of the ways Comcast is expanding the network in my town is to lay fiber further than before as a way to increase bandwidth at the home, ultimately to be able to have 1GHz of usable bandwidth. Of course, until the newer 1GHz STBs and DOCSIS 3.0 are deployed, that extra 160MHz of bandwidth is fairly useless.

Keep in mind that Verizon is literally a company that has more money than they know what to do with, and as been noted by others, FTTH(fiber to the home) is a very expensive proposition.

I see Dave has answered the fiber question while I was composing this post.
post #520 of 2079
Quote:
Originally Posted by briansemerick View Post

i realize this, the key word in my post was EVERYONE. the point is the problem right now is that every single TV would need a box and that is what people are pissed about.

Generally true, BUT: not QUITE EVERY SINGLE TV. Those TV's with QAM tuners (most sets being sold today) could receive Digital signals without a box.

BUT, most of the folks that we are talking about simply have analog sets, so your statement is generally correct.
post #521 of 2079
Quote:
Originally Posted by bidzer View Post

So they have the bandwidth, but choose to not use it? I guess I'm confused. A small coax run inside the house is better than coax being the last mile or more. The coax in my area tends to get wet alot. A few runs have already been replaced.

It's not just in the house though, that coax line runs all the way back to the node, a node sometimes feeding 500+ homes, there's only so much you can squeeze in a single coax line. Smaller node size is another way cable is looking to increase bandwidth delivery.

Laying fiber all the way to the house is very expensive.
post #522 of 2079
Quote:
Originally Posted by keenan View Post

I see Dave has answered the fiber question while I was composing this post.

Both of us were busily typing
post #523 of 2079
Yeah, but I only use 2 fingers when I type...
post #524 of 2079
Quote:
Originally Posted by briansemerick View Post

i realize this, the key word in my post was EVERYONE. the point is the problem right now is that every single TV would need a box and that is what people are pissed about.

And in Feb. '09 every OTA analog set will require a STB. Currently every TV connected to Sat. service requires a STB. So why is cable held to a different standard?
post #525 of 2079
Quote:
Originally Posted by hernanu View Post

But he's not watching the channels in Atlanta. The point is that in some markets, Comcast is crowding HD channels into QAM slots, so that quality suffers.

If the degradation of PQ is not happening in your area, more power to you, but if Comcast as a whole is making policy decisions that result in this, it may eventually affect you, so you may benefit from the effort made by people here to shine a light on a burgeoning problem.


I understand that. I'll also add that I have a hard time believing that the system he's on looks as bad as some of the screen shots he has posted. I don't think people would stand for it.
post #526 of 2079
Quote:
Originally Posted by jrn23 View Post

And in Feb. '09 every OTA analog set will require a STB. Currently every TV connected to Sat. service requires a STB. So why is cable held to a different standard?

completely true. i'm all for switching to full digital right now. but the gen public isn't, and that's the problem. the thread provides very valid arguments on why we should switch and also why the uneducated public will uproar.
post #527 of 2079
Quote:
Originally Posted by jrn23 View Post

And in Feb. '09 every OTA analog set will require a STB. Currently every TV connected to Sat. service requires a STB. So why is cable held to a different standard?

It's what the customer has grown accustomed to over the years. My wife and I don't think anything about having a box as we have had cable since we were teenagers and for anything more than lifeline basic it required a box (especially for me as it was and still is a dual cable system). Also, there are a lot of people who may have had a box or two in the main viewing rooms but wired the rest of their homes with TVs without boxes (once Cable Ready TVs were the norm) in secondary locations such as kid's bedrooms and kitchens. I know people who have passed on DirecTV and Dish because of the expense of connecting 7 or 8 TVs....Cable they could put digital boxes where they wanted and just have analog on the rest. Add in a lot of the local neighborhood bars (excluding Chains and Sports Bars) also use analog to feed their multiple TVs, forcing everyone into a digital box would upset a lot of these customers.
post #528 of 2079
Quote:
Originally Posted by jmallory View Post

It's what the customer has grown accustomed to over the years. My wife and I don't think anything about having a box as we have had cable since we were teenagers and for anything more than lifeline basic it required a box (especially for me as it was and still is a dual cable system). Also, there are a lot of people who may have had a box or two in the main viewing rooms but wired the rest of their homes with TVs without boxes (once Cable Ready TVs were the norm) in secondary locations such as kid's bedrooms and kitchens. I know people who have passed on DirecTV and Dish because of the expense of connecting 7 or 8 TVs....Cable they could put digital boxes where they wanted and just have analog on the rest. Forcing everyone into a digital box would upset a lot of these customers.

Yep, I understand that all too well. I'm one of those that has stuck with cable over the years because I didn't want to endure the cost of adding boxes to all of my TV's. But for the govt. to mandate that all analog OTA sets need a box , read upsetting a lot of people, and then turn around and mandate that cableco.'s need to provide analog to their customers just seems to be a double standard.

Yes, I understand cableco's don't want to upset customers but it appears that it's not working. Recent articles I've read seem to indicated that subscribership has actually dropped.
post #529 of 2079
Quote:
Originally Posted by jrn23 View Post

Yep, I understand that all too well. I'm one of those that has stuck with cable over the years because I didn't want to endure the cost of adding boxes to all of my TV's. But for the govt. to mandate that all analog OTA sets need a box , read upsetting a lot of people, and then turn around and mandate that cableco.'s need to provide analog to their customers just seems to be a double standard.

Yes, I understand cableco's don't want to upset customers but it appears that it's not working. Recent articles I've read seem to indicated that subscribership has actually dropped.

I agree with your statement that to mandate digital for over-the-air but not to mandate it for Cable has been one of the many problems with the whole transition to digital television that is leading to a lot of frustration and confusion to all parties involved IMO but that is a whole other thread.

Well some of those drops are related to the economy so those aren't necessarily a win for another provider. Also, when a customer moves from analog to digital (say as part of a triple-play) that is counted as a loss of a basic customer and added as a digital or triple-play customer. I don't think it is as bad as analysis tend to make it.

Something else to keep in mind, Comcast isn't strictly a Cable TV provider anymore. TV is Dish and DirecTV's only business...there is a lot more incentive for them to excel in this area. Comcast sells convenience and cost-savings as much (if not more than) the technical abilities of their product.
post #530 of 2079
Quote:
Originally Posted by jrn23 View Post

And in Feb. '09 every OTA analog set will require a STB. Currently every TV connected to Sat. service requires a STB. So why is cable held to a different standard?

FCC Chairman Martin must be a Comcast subscirber

--- CHAS
post #531 of 2079
Did bfdtv post his test procedure anywhere?

Did anyone ask him to repeat the test after switching the boxes?
post #532 of 2079
Quote:
Originally Posted by briansemerick View Post

i realize this, the key word in my post was EVERYONE. the point is the problem right now is that every single TV would need a box and that is what people are pissed about.

On top of that, even those that already have a digital cable box may need a new one that supports HD downconversion. My parents have one of those ancient DCT-24xx series. It will tune to some HD channels (mainly broadcast), but only gives audio with incomplete video.
post #533 of 2079
I've noticed on Discovery HD (not HD Theater) that even programs that are supposedly HD (or at least not showing any pillarboxing) are having text at the top or bottom clipped off. I wonder if those with FIOS/satellite can compare to see if this is a Discovery or Comcast issue?

I am aware DISHD (as it's currently named on my system) zooms up SD programs.
post #534 of 2079
i mentioned that problem here:

http://www.avsforum.com/avs-vb/showt...1#post13480711

i'm assuming it's built in overscan. blah.
post #535 of 2079
Quote:
Originally Posted by JDrider View Post

Did bfdtv post his test procedure anywhere?

Did anyone ask him to repeat the test after switching the boxes?

Did you read the first page of this thread at all. His testing methods were questioned and changed after different software recommndations.

He is doing this on TivoHDs via CableCards. There is no way to get this kind of info from Comcast or FIOS STBs. However, the newer Motorola DCH STBs just have an M-Card in them, so the testing method is sound.
post #536 of 2079
Quote:
Originally Posted by jefbal99 View Post

Did you read the first page of this thread at all. His testing methods were questioned and changed after different software recommndations.

He is doing this on TivoHDs via CableCards. There is no way to get this kind of info from Comcast or FIOS STBs. However, the newer Motorola DCH STBs just have an M-Card in them, so the testing method is sound.

Yes. I saw some challenge on the still-image capture technique, but nothing about bit-rate measurements. I'm wondering if something in the Tivo box (firmware/hardware) might be impacting the file size. He never said both boxes were the same exact model and firmware, or did I miss that?

Of course it has been reported that the Tivo HD re-encodes to save file size on the HDD:

Quote:


The ATI Theater 314 demodulator chips handle digital channels, while the Philips/NXT ADC chips handle analog channels. They run in parallel, feeding a ViXS XCode-2115. This appears to be a dedicated encoding/transcoding chip

http://www.gizmolovers.com/a-review-...edia-recorder/

From the Vixs web site on the XCode 21xx series:http://www.vixs.com/sections/product...uct_sheets.htm
Quote:


Transcode/Transrate HD -> HD

With the transcoding/transrating inside the box I'm not sure how meaningful the bit-rate measurements are from the HDD.
post #537 of 2079
Thread Starter 
JD,

The TiVos are the same model with the same firmware/software. The recordings are downloaded in MPG (MPEG-2) format direct from each TiVo. They are bit-for-bit identical to the signal delivered by FiOS and Comcast.

There is no transcoding or transrating of any kind. The XCode encoder is only used on analog channels.

I attended the Nationals games this weekend so I didn't have as much time as I had hoped to do more comparisons. I am transferring more recordings now, but it is a rather slow process because recordings only download at ~1.5MB/s.
post #538 of 2079
Thanks for the clarification. Just to eliminate any possibility of box-related impact on your measurements, you should reverse the boxes. I realize it means re-initializing the Cablecards, but it would be better science.

Quote:


There is no transcoding or transrating of any kind. The XCode encoder is only used on analog channels.

And how do we know this?
post #539 of 2079
Quote:
Originally Posted by JDrider View Post

Yes. I saw some challenge on the still-image capture technique, but nothing about bit-rate measurements. I'm wondering if something in the Tivo box (firmware/hardware) might be impacting the file size. Ken never said both boxes were the same exact model and firmware, or did I miss that?

Of course it has been reported that the Tivo HD re-encodes to save file size on the HDD:


http://www.gizmolovers.com/a-review-...edia-recorder/

From the Vixs web site on the XCode 21xx series:http://www.vixs.com/sections/product...uct_sheets.htm


With the transcoding/transrating inside the box I'm not sure how meaningful the bit-rate measurements are from the HDD.

The Tivo is not transcoding the video data. It should be the exact digital version of what Comcast is sending, after being decrypted in the cablecard. The R5000-HD system also enables the capture of the native digital stream too. I may look for artifacts in my recordings as well, though I don't have FIOS to compare it with. :-( We don't do 3:1 here yet the the SF Bay Area, but since the feed is coming from HITS we should be seeing the exact same problem.

I think bfdtv's testing methodology is solid, but if Comcast wants to try and disprove the impact by showing some countervailing information, I'd be all ears. I don't think that exists however.
post #540 of 2079
Quote:
Originally Posted by JDrider View Post

Thanks for the clarification. Just to eliminate any possibility of box-related impact on your measurements, you should reverse the boxes. I realize it means re-initializing the Cablecards, but it would be better science.


And how do we know this?

I asked a tivo engineer I know about it, and it is consistent with the system design. Note that bfdtv is not looking at the video output on his TV from the Tivo. All he's doing is using it to capture the raw mpeg information, and then doing the analysis with tools on his PC.

If you doubt my statement too, go to the tivo discussion forums and post a query in one of the groups the tivo engineers frequent and ask them.

Another way to verify this would be if someone had 2 R5000-HD's in service, on on comcast and the other on FIOS. Then it would be possible to do this and cut the Tivo completely out of the process. However, it wouldn't make any difference. Perhaps even a couple different R5000-HD equipped SageTV users could record the same program, one in FIOS and the other from Comcast, and upload the files to bfdtv to analyze them and look for differences?

I'm happy to do that since I have an R5000-HD on Comcast, but because I don't have FIOS it'll take awhile to upload the files...
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: HDTV Programming
This thread is locked  
AVS › AVS Forum › HDTV › HDTV Programming › Comcast HD Quality Reduction: Details, Screenshots