Comcast XFINITY TV → Re: Why does my SD channels look terrible on Comcast in South FL

Irrelevant.

How - a Digital SD picture looks much better than an analog one.

The SD i'm referring to are Digital SD channels through the set top boxes. For an example BBC America which is exclusively only available on the Digital Tiered line up and it looks really bad.

Right which is still thrown in with the analog mix. as beach said dish has ABSOLUTLY ZERO(0) Analog. Everything comes over a STB or receiver.

Dishes spectrum

Digital
More Digital
Master

Comcast's

Digital
Internet
Analog
Masters

Where exactly did you say that in your post? Yeah that's right, you didn't. So, go back to your Dish

I have Mediacom Cable at my home, and BBC America looks awful there as well.

One rough way you can check compression, if you have the Comcast DVR, is to see how much it buffers. Just leave it on a channel for an hour or 2, then look at the time bar when you hit PLAY, or see how far you can rewind.

For BBC America on my system, it buffers OVER 2 hours. On the other hand, most of the local and expanded channels are about 60-90 minutes. True analogs used to buffer a fixed 45 minutes.

HD's vary from about 20 minutes (WBBM, a CBS station with no subs), to nearly 45-50 minutes (WLS, an ABC station that also broadcasts LiveWell HD and a weather channel.) Remember that broadcast HD on cable is typically the same bandwidth as used for OTA broadcast. Based on some of the old manuals, a full bandwidth (about 18Mbit?) HD would buffer about 15 minutes.

It has to do with the compression rate of channels in your area. I also live in South Florida and some digital channels look beter than others, it just depends how many digital channels they are sending per "stream". Analog channels will actually look better than most digital ones as the compression rate Comcast uses is far to high and the channel quality suffers. I'll explain it in layman's terms so everyone can fully understand.

You'll notice some digital channels look better than others. You can really tell the difference between HBO (digital 302) and G4TV (digital 162). Comcast figures G4TV is less important, therefore they compress it much more than a more widely watched channel. Just think of it as the channels that are most watched are going to be least compressed and won't be paired with as many channels in the same "stream", while less watched channels will be chunked together with the highest compression rate they can fit into a "stream".

A good explanation is what the above user posted:

said by andyross:

One rough way you can check compression, if you have the Comcast DVR, is to see how much it buffers. Just leave it on a channel for an hour or 2, then look at the time bar when you hit PLAY, or see how far you can rewind.

For BBC America on my system, it buffers OVER 2 hours. On the other hand, most of the local and expanded channels are about 60-90 minutes. True analogs used to buffer a fixed 45 minutes.

HD's vary from about 20 minutes (WBBM, a CBS station with no subs), to nearly 45-50 minutes (WLS, an ABC station that also broadcasts LiveWell HD and a weather channel.) Remember that broadcast HD on cable is typically the same bandwidth as used for OTA broadcast. Based on some of the old manuals, a full bandwidth (about 18Mbit?) HD would buffer about 15 minutes.

Basically what he means is that channels like BBC America are compressed to the max therefore they use the least amount of DVR space and can be buffered longer. The local and expanded channels are compressed less requiring more DVR space and therefore again losing buffer time depending on the compression level. SD channels are not compressed which is why the picture is actually the best, although they take up the most amount of DVR space and buffer time is the shortest.

HDTV works in the same manner and some HDTV (most watched) content is compressed more than others which causes some HDTV channels to look better than others just the same as digital compression. Basically Comcast only has X=Bandwidth to work with and they have to fit Y=Channels through that bandwidth. Say they put certain groups of channels on different "streams" which are all compressed at different ratios. Less watched SD channels might be compressed at 12:1, while watched SD channels might use a 6:1 ratio to improve picture quality.

Same goes with HD in which less watched are pushed through "streams" of 3/4:1 while more watched are using 2:1 or less. The only way to get better picture quality for all channels is for Comcast to improve their X=Bandwidth with infrastructure and network investments, which would result in more Y=Channels. Now it might just blow your mind to know that even with all of that you now have to fit On Demand streaming, Internet and Phone over the same pipe (network). That one coaxial cable running through your home has a lot of potential doesn't it!?

A great article (with images) about the issue can be found at the link below from the AVS forum. Again I tried to explain this all in layman's terms, so as many people as possible could understand it.

»www.avsforum.com/avs-vb/ ··· =1008271

Should also add that broadcast channels are typically passed on as-is. That usually means all their subchannels will share the same frequency as the main, just like the original broadcast. If a broadcaster carries more than one HD (like some Disney-owned ABC's), then both will share the allotment. Because 256QAM has double the bandwidth of ATSC, they can fit two broadcast channels into one frequency on cable. If two broadcasters both carry multiple HD's, then you could see 4 or more HD's on one frequency. Here in the Chicago area, both WLS and WYIN [a PBS station] have dual 720p channels, although they don't share a frequency on my system.

Even with the 3:1 compression of non-broadcast HD, it's not always even. I've noticed that Syfy is not very compressed, and only buffers about 20-25 minutes. Others on that same frequency are more compressed.

It's variable, it depends on the requirements of the 3 channels at the time you are watching it. That was the sole innovative motivation for the 3:1 at the time it was sold to distributors, VBR through the mux action rather than prior to it.

SD as a whole is becoming aweful, even on Sat. The content providers have upped the compression before they send out as well, the signal coming into Comcast/Dish/Direc/etc. is much more compressed than it used to be. Bandwidth isn't just starving at the last mile, the limited transponder space that BBC, Fox, Universal, etc. have to bounce multiple HD and SD signals off of is getting squeezed. Those on Comcast may also be noticing the MPEG4 overcompressed master -> MPEG2 add-more-compression artifacts as well, so much color blending it comes off really "soft". A good solution for Comcast is to rid ourselves of analog allowing more space for the HD version of all of the popular channels, clean out all of the SD duplicates, freeing up bandwidth utilizing STB's to downconvert HD to SD (Broadcom is releasing a new DTA chipset that can do this that at first reports is CHEAPER than the current DTA chipset) and allow those "SD only channel" MASTER -> last mile conversion enough breathing room that even if it is an MPEG4 -> MPEG2 transcoding, quality will not be effected. It has cost benefits to Comcast as well as quality benefits to the end-user.