Is your Comcast HD quality up to snuff?

[PaulGo]

Is your Comcast HD quality up to snuff?

Posted Mar 20th 2008 7:25PM by Darren Murph
Filed under: Industry, Set-top boxes, Cable

It's not unusual to hear of entire neighborhoods kvetching over lackluster HD quality, but judging by the growing chorus of complaints over at AVSForum, we're beginning to wonder if this issue isn't more widespread. Reportedly, Comcast is squeezing three HD channels onto a 38.8Mbps QAM, which is typically used to handle just two HD channels. One particular user decided to pull screen grabs from shows seen on Comcast and Verizon's FiOS TV, and needless to say, the results were fairly startling. We aren't assuming that the overdone compression is being seen elsewhere, but we are curious to know if your Comcast service has taken a hit in quality. So, is your viewing experience as good as ever? Or have things become slightly less Comcastic of late?

Is your Comcast HD quality up to snuff? - Engadget HD

[PaulGo]

Is Comcast Squeezing Your HD Picture?

My thanks to bfdtv over at AVSForum for his very interesting post on the compression that Comcast is using on some of their HD channels as compared to Verizon’s FiOS service. The link is here. Comcast HD Quality Reduction: Details, Screenshots - AVS Forum.

Apparently, in order to free up more bandwidth to add more HD channels, Comcast is further compressing their HD feeds with the predictable disastrous effects on picture quality. In the past, cable operators like Comcast were putting two HD channels into one 38.8 Mbps QAM slot. This was enough for two full bit rate full resolution HD channels with no degradation in picture quality. Now, they are compressing 3 HD channels into that same QAM slot with a noticeable effect on picture quality as is evidenced in bfdtv’s screen captures.

Furthermore, you do not have to be a Comcast subscriber to note this diminished picture quality. This 3:1 compression is being performed at the Comcast Media Center’s Headend in the Sky(HITS) in Denver which feeds the cable channels to many other cable companies including Cox and Charter. The 3:1 compression does not effect all HD channels, at least not as of yet. Select channels without much in the way of motion are being grouped together in groups of three. The affected channels are as follows: Discovery HD, SciFi, USA, Food, National Geographic, Universal HD, A&E, HGTV, Starz, Cinemax, HBO, TLC, Animal Planet, Discovery HD Theater and History.

Despite the theory that compression artifacts won’t be visible or as visible on channels with static images, the screen captures show otherwise. The images from Comcast’s feed as compared to the same shows on FiOS show motion artifacts galore and a very noticeable drop in picture quality to the point of being unwatchable. I for one would be quite upset if the images on my screen were so degraded.

Frankly, this is shocking to see from Comcast who had been running ads crowing about the quality of their HD PQ as compared to DIRECTV's "HDLite." Now it appears that Comcast has jumped into the same boat as DIRECTV. In fact, Comcast’s picture quality may be even worse than DIRECTV's as DIRECTV uses a more efficient compression algorithm MPEG4 compared to Comcast’s MPEG2.

For those subscribers at Comcast and other cable companies who obtain their HD feeds from the HITS facility and who have noticed that their HD channels don’t look as good as they did a few months ago, you now know why. Those once beautiful full bit rate HD signals are being choked to death by Comcast, all for the sake of adding more HD channels. The better approach would be to spend the money necessary to upgrade their cable systems to add more bandwidth to add more HD channels. Saving a few bucks by degrading the channels you already have to add new ones is not the way to go and is a clear step backwards for all fans of high definition television.

I would suggest that those of you that care about the quality of their HD experience complain to Comcast or their own cable company about what they are doing. Otherwise, they will continue to do so and spread the practice to other channels as well. They will take your silence as a sign that you are not noticing what they are doing to the signal which will only encourage them to continue and even worse, expand the practice. Tell them you are as mad as hell and won’t take it anymore! Or, at least, that you will switch to another service if it continues. Loss of subscribers is the only thing that will get their attention! The ball is in your court, HD fans!

'The Whip': Is Comcast Squeezing Your HD Picture?

[cablewithaview]

Shaw Cable (Broadcast, StarChoice) now offers 3 HD channel per transponder on the Shaw Broadcast platform (aka Cancom), in this case they switched from QPSK to 8PSK to keep the full quality of the picture using a SR of 20000 and an fec of 2/3. I believe in the case of Comcast, they will HAVE to change the delivery of the signal from QPSK to 8PSK to keep their intergerity. Comcast currently uses a SR of 29.270/fec 3/4 combo which allows a higher rate of data granted, but the switch from QPSK to 8PSK I believe will resolve any issues and even possibly make room for at least one more HD channel without ruining the PQ.

While DirecTV is using MPEG 4, I still haven't seen anything delivered in full resolution. I think MOST providers sell the term HD instead of selling them "TRUE HD" picture. Quality means more then quanity.

[PaulGo]

I hope that Comcast does something quickly since Verizon FiOS could jump on this in an ad campaign to show their superiority to Comcast and other cable companies who use Comcast encoding.

Two definitions of terms used above:

8PSK (8 Phase Shift Keying) is a phase modulation algorithm.

Phase modulation is a version of frequency modulation where the phase of the carrier wave is modulated to encode bits of digital information in each phase change.

The "PSK" in 8PSK refers to the use of Phased Shift Keying. Phased Shift Keying is a form of phase modulation which is accomplished by the use of a discrete number of states. 8PSK refers to PSK with 8 sates. With half that number of states, you will have QPSK. With twice the number of states as 8PSK, you will have 16PSK.

Because QPSK has 8 possible states 8PSK is able to encode three bits per symbol.

8PSK is less tolerant of link degradation than QPSK, but provides more data capacity.


QPSK (Quadrature Phase Shift Keying) is a phase modulation algorithm.

Phase modulation is a version of frequency modulation where the phase of the carrier wave is modulated to encode bits of digital information in each phase change.

The "PSK" in QPSK refers to the use of Phased Shift Keying. Phased Shift Keying is a form of phase modulation which is accomplished by the use of a discrete number of states. QPSK refers to PSK with 4 states. With half that number of states, you will have BPSK (Binary Phased Shift Keying). With twice the number of states as QPSK, you will have 8PSK.

The "Quad" in QPSK refers to four phases in which a carrier is sent in QPSK: 45, 135, 225, and 315 degrees.

[PaulGo]

Cablewithaview what do you think of this technology?

"Vyyo Chief Executive Wayne Davis says his company's technology, called spectrum overlay, helps operators increase the raw bandwidth of their networks by as much as 3 GHz. It could on average cost around $125 per household."

It appears Cox is employing this technology.

Cox picks Vyyo for 3 GHz network passives :: Communications Technology

[PaulGo]

From the Consumerist:

Recently Comcast has started compressing their digital channels, including the HD ones, in order to deliver more HD channels. A thread over at the AVS Forums demonstrates the results of this by comparing the same program recorded with Comcast and Verizon's FiosTV. The differences are startling and it's obvious that Comcast is now going with quantity over quality. This is an about face to last year when Comcast was touting their superior HD image quality.

Comcast

[cablewithaview]

They may feel if DirecTV can sell being the HD leader with 1220 or 1440 x 1080i, they might could to.

[cablewithaview]

As for Cox, I feel they are going in the right direction with this. I like to see some 3 Gig line gear and see the specs on it. That's 400 plus channels to mess with!!! 450 x 12 = 5400 standard digital channels and possibly about 1400 HD channels!!! Now that's capacity.

[PaulGo]

I hope Cox sets the pace for other cable companies and the other cable companies make the investment to expand their bandwith. Last year Vyyo estimated the cost for their technology to be $125 per subscriber. Hopefully the price has come down. That's not cheap, but compared to the investment of Verizon FiOS it is cheap!

The situation of the cable companies cutting corners could be become permanent if their is no pushback from the customers or if Verizon and / or the satellite companies do not advertise that they have a superior picture quality. Cable companies currently have a limited bandwidth unless they go to advanced spectrum usage techniques. Even after they eliminate most analog channels they will be under pressure to add more and more HD channels since currently more customers are interested in that than picture quality.

Since cable has to share their bandwidth with telephone service and internet service they need to employ better technology to have excellent picture quality. Cable companies are reluctant to invest the money to upgrade their infrastructure unless the customers demand it or they loose customers because enough people switch to a better quality service.

[PaulGo]

In the HDTV Recorders forum of AVS I asked James Doster, Digital Coordinator, Charter Communications about the reduction in HD quality , here is his response:

It's a little off-topic, however there's alot of people on the DVR threads on others who have asked alot of questions about the Digital Transition, ADS and other issues.

MSOs (including dish and IPTV operators) are going to get more and more competitive about having more services, the two ways they are going to compete is to reduce analog and compress / encrypt Digital / HD channels.

Personally I would think the entire point of having HD channels is improved picture quality, so if the picture quality is sacrificed, they are going to push away the very customers they are trying to convince to stay.

More than likely I would think that would only be a temporary measure until more bandwidth can be made availible. - But then again, I don't think they'd be doing it so systematically if that was the case...

There are also newer standards (I want to say MPEG4 but it could be 6) that will allow for greater compression without degredation, however that requires equipment upgrades (and some boxes are not compatible) - I think HBO is pushing hard to switch to hardware that will allow them to put all their feeds in HD quality while using the same amount of bandwidth from their Sat feeds (we'd have to either downconvert them or upgrade out boxes to decrypt - for most boxes that would be a firmware upgrade I believe)

I know within Charter the general plan is to migrate Analog channels (expanded basic) over to Digital and use the freed up bandwidth to launch new HDs. Generally you can get 2 to 3 HD networks PER analog that's converted. - I know most of our markets that have HD now should be seeing 10 more HD channels being added by the end of the year. If we drop to only 20 Analog channels, that should free up bandwidth enough for us to have all 71 expanded basic in Digital (up to 10 digitals per analog)

So I'm thinking in your better systems you should expect to have about 20 QAM channels dedicated to Analog and probably another 30 for SD Digital (yielding a max of 300 Digital SD Channels) and if used responsibly, probably 50 for HD (which should give 100 to 150 HDs) Of course getting from here to there will be the bumpy road.

The big bumps in the road will be the fact that cable companies are trying to do alot of upgrading and changes and none of them are really making a huge profit at this time (most of them are still paying off major debts from the dot-com boom when they were laying down fiber like there's no tomorrow...)

Time Warner and Comcast are in the best position - they're #1 and #2 in the nation with plenty of room before #3 (which was Charter at last check)

TW and Comcast also have major advantages as they are also Media holders (Comcast owns several sports networks and the InDemand PPV networks)

One thing that was a major point in that thread is that all major MSOs have made commitments to keep *SOME* analog access for three more years -

however as I understand it here, in our case it will be Basic only... most expanded will be migrated to digital only and require the use of a box or Card*.

It's important to note here that a very large population of "Digital" tuners including alot of the new ones coming out now for people wanting to decode digital broadcast are limited QAM tuners without CARD access - as such they will only show what's unencrypted - which will be the basic channels, local HDs and Digital feeds and if the market so chooses - Music feeds (Music Choice etc)

Digital tuner boxes without Cable Cards may be even more limited as the ones I've seen will only do about 60 channels (as they are intended for broadcast only) and therefore won't pick up the channels outside of that range, even if they are unencrypted.

But again I'm going more off topic - on the HDs, I think they made the wrong decision to sacrifice PQ to squeeze more in and I'd hope (for the customer's sake) that it's a short term issue that is only occuring until they can get more bandwidth in place.
__________________
James Doster
Digital Coordinator
Charter Communications; Hickory, NC