Rogers Signal Compression Question

[otown47]

Does anyone know if Rogers uncompresses the OTA HD signals it picks up and then compresses them again for distribution thru their system, or do they pass the signals thru as received?????

Thanks...

[hugh]

I was under the impression OTA signals are sent uncompressed.

Signals sent via cable are definitely compressed and Rogers can alter the compression rate.

[JohnnyG]

AFAIK, they simply re-modulate the 8VSB signal to a QAM signal. This would leave the MPEG2 Video/Audio untouched.

[57]

HD signals are sent OTA and via Rogers cable at 19.4 Mb/sec. No difference. I think satellite is close to this number too - can't remember for sure.

Some stations (PBS Detroit for example) simulcast their SD signal on the "same channel", so their HD "portion" of the signal is slightly lower than the 19.4 Mb/s mentioned above, but they still manage to provide one of the best pictures around.

Some US cable companies are considering sending 3 HD channels per 6MHz, but I'm not sure that's been done. This would lower the rate to 12.9 Mb/s. I think they're considering this for the non-rebuilt areas...

[JohnnyG]

Originally Posted by 57

but they still manage to provide one of the best pictures around

Not when compared to the Rogers demo channel! I caught the dying seconds of some Canadian production last week on that channel and it looked much better than the best on PBS. Has anybody else caught this? If so, what is it exactly?

[57]

Yeah, I noticed that they added something that looked like the Rideau Canal or something recently.

The "Samsung" stuff was done by Randall P. Dark if I recall.

As for the PBS comment - when you see the PBS shows on "Over Alaska" or the one on the Antarctic in HD, those really do compare well to Rogers demo. PBS has been showing a lot of upconverted widescreen lately...

See the downloadable pdfs for the true HD programmes.

http://www.detroitpublictv.org/watch/digitalsched.shtml

[hugh]

HD signals are sent OTA and via Rogers cable at 19.4 Mb/sec

Rogers does have the ability to compress the signal. Whether they do or not, I don't know. I was told that they have tested sending it at 12 Mb/sec without any discernable difference to the viewer.

[57]

Originally Posted by human

I was told that they have tested sending it at 12 Mb/sec without any discernable difference to the viewer.

With most material this is probably correct. With sports, or pictures with lots of movement, you'd notice a lot more artifacts. The 12 comes from the same number I mentioned a couple of posts up - trying to put 3 HD channels into 6 MHz instead of 2.

There is some new compression coming out that is supposed to do this job without any more artifacts at 12.9, than now at 19.4...

Edit, uncompressed HD is over a Gigabit/sec.

[otown47]

Thanks for the replies guys, however a lot of this is over my head and maybe I didn't use the right terminology.

What I meant by compressed is the encoding of the original signal into some kind of MPEG signal (like I can do on my computer or is done on a DVD). So if I change the word compressed to encode, does Rogers re-encode the OTA signals. Also are OTA broadcasts encoded MPEG ???

Thanks.....

[dialog_gvf]

Originally Posted by 57

With sports, or pictures with lots of movement, you'd notice a lot more artifacts.

So true. A nature scene with a flock of birds taking off and filling the screen can be a pixelated mess with 19.4. I've seen several examples of that and it is INCREDIBLY annoying.

Even something as simple as a babbling brook can show pixelation.

[57]

Interestingly, I've been watching a few hours of Basketball and Hockey this past week, and I don't recall seeing any pixellation whatsoever and I have been looking for it.

Same earlier this year on the CBS NCAA games - perfection - and again I was looking for it.

I do remember seeing that "flock of birds" example. I think it was in the PBS programme about Kangaroos. I'm wondering if it was the "original" and not what we received, since it's the only example of really bad pixellation I can recall...

The only other pixellation I've seen has been minor on movies, or the kind that comes from "missing information" (usually green or white pixels).

On the whole, I think the compression chosen has been an excellent compromise, providing an excellent picture the vast majority of the time.

[JohnnyG]

Interestingly, I've been watching a few hours of Basketball and Hockey this past week, and I don't recall seeing any pixellation whatsoever and I have been looking for it.

Me too, and my eye agree with yours. There are 2 likely reasons for this. One, 720p is actually easier to compress than 1080i. Two, the material looked filtered to me. Remove some detail, and the video is easier to compress.