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Discussion Starter · #1 ·
I would like to know how many people out there that receive HDTV via Cable(not DBS) can tell a noticeable different between HDTV via cable Vs. via OTA.


Here in Tampa FL most people receive HDTV via cable that is provided by Bright House Networks. One of the engineers has been so adimate that they don't reshape or re-compress in any way, that they have had Tours in Orlando to show some of the non believers that they don't own any re-shapers.


Personally I have done a A/B comparison between Cable and OTA, utilizing an E86 D* receiver via component to my Mitsu ws55711. Vs BHN Pace hd550.

I have to say that I can not tell a difference.

I have also captured the QAM stream and the OTA stream to my hard drive and the bit rates are the same.


Here is the thread over at TampaHDTV.com
http://www.tampahdtv.com/modules.php...iewtopic&t=186


Here is a post from that thread, from the BHN associate.
Quote:
First, the home show guy is (looking for a polite term here...) wrong. BHN passes the signal to the settop in the format it's presented to us. Then, depending on what box you have, the output resolution is determined. If you have a S/A 3100HD, everything coming out the component outputs is 1080i. If you have a Pace 550HD, then you have the choice to specify output resolution at 1080i, 720p, 480p, or 480i, or just let whatever resolution the broadcaster adopted pass through.


Regarding the Stereophile Guild to Home Theater article, it's full of misleading assertions. First, every cable company, and indeed, almost every cable operation in the country is different -- you can't paint them all with the same brush. Heck, I think the differences in BHN in Central Florida vs. Tampa alone would prove my point.


Secondly, does BHN remove bits from the HD stream -- yes. Because the 8VSB modulation scheme is intended for OTA broadcasts, its designed to deliver an intact signal despite the "challenging" environmental conditions the signal must traverse. QAM modulation, conversely, is designed to travel in the protected path a Hybrid Fiber Coax cable plant provides. Therefore, the robust error correction data the 8vsb signal sends along with the video/audio is unnecessary, and even more so, unused at the receiving end. The short version is that we don't need to send a full 19.4mbs to deliver the exact same signal -- the bits that are the signal come through untouched.


We've been accused of compressing signals time and time again. All I can say is that it isn't true. We don't own any compression equipment. Heck the other day I was trying to get some locally produced video encoded to put it on our iControl platform, and I had to send the tape to inDemand to get them to pitch it back via satellite.


I finally convinced the Orlando High Definition Society folks that we don't compress by giving them a tour of our headend. We can't do it, because we don't have the equipment to do so. Period.


The final thing the Stereophile guide complained about was a device that performs "rateshaping". While there are companies trying to sell these to us, we haven't bought any.
Are we lucky here in Tampa? What is your experience with your local cableco?
 

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Quote:
Therefore, the robust error correction data the 8vsb signal sends along with the video/audio is unnecessary, and even more so, unused at the receiving end. The short version is that we don't need to send a full 19.4mbs to deliver the exact same signal -- the bits that are the signal come through untouched.
Quoting from within the quote, perhaps this was a typo. OTA 8vsb is delivered at ~32 Mbps, with data beyond ~19 Mbps being forward error correction data that is stripped away by cable companies because it's not needed for cable delivery. The much smaller PSIP data for each station may also be removed, with the cable system's on-screen guide substituting.


Yup, my Time Warner Cable system, the country's largest contiguous one, admits to using rate-shaping gear with digital TV to conserve bandwidth. Adelphia joined them recently. I've attempted A-B comparing OTA versus rate-shaped digital cable on my 64-inch RPTV, but the results were dubious because my last two cable converters (SA2000HD and SA3100HD) unfortunately have a faint image fog that spoils contrast which in turn diminishes resolvable details--just what I'd be comparing.


Those marketing and using rate shaping may--not surprisingly--claim it doesn't visibly affect image quality. Perhaps it doesn't with most displays. But the process of altering bits representing high-frequency detail must influence fidelity, and perhaps will become more evident with giant images or emerging displays capable of 1080p (1920X1080), even though resolvable detail this great can't be achieved in homes currently--other then test patterns.


Cable company head ends compressing video? Perhaps not with hardware designed specifically for that. Of course, you also have to examine what their program sources have done in the way of compression before it's downlinked. And, since MPEG-2 automatically 'throws out' higher-frequency detail, especially when motion is involved, what happens when one cable company puts 10 or more non-HD cable channels in each 6-MHz-wide, ~39-Mbps cable slot, providing ~3.9 Mbps per cable channel, versus another putting only 8 channels in the slot, providing ~4.9 Mbps per channel? Lots of tinkering is possible, of course, such as variable bit rate delivery and using statistical multiplexing, as outlined in the 'rate-shaping' link above. -- John
 

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Discussion Starter · #3 ·
John, thanks for clearing that up, it is very interesting.

So how did you vote?
 

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Comcast does not alter the image or sound of HDTV they provide.
 

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Doing an A/B of Wide Open West I also could see no difference from OTA. But I can't say conclusively what they do.


- Tom
 

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The other problem you throw into the mix is that in most a/b comparisons you'll be using 2 different box's.


I think the only true way you could do an a/b comparison would be to use say an LG QAM capable tuner where you could do OTA and Unencrypted QAM on the same box so that you're seeing the same picture through the same circuitry.
 

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I cannot tell any difference between D*, Comcast or OTA HD. It is all WOWTV.
 

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Discussion Starter · #9 ·
Quote:
Originally posted by Jeremyfr
The other problem you throw into the mix is that in most a/b comparisons you'll be using 2 different box's.


I think the only true way you could do an a/b comparison would be to use say an LG QAM capable tuner where you could do OTA and Unencrypted QAM on the same box so that you're seeing the same picture through the same circuitry.
I have done this using my integrated tuner in my Mitsu ws55711. It will recieve both OTA and QAM.


I could not tell the difference.
 

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Quote:
The other problem you throw into the mix is that in most a/b comparisons you'll be using 2 different box's.


I think the only true way you could do an a/b comparison would be to use say an LG QAM capable tuner where you could do OTA and Unencrypted QAM on the same box so that you're seeing the same picture through the same circuitry.
Agree using nearly the same video-processing circuits for comparing 8-VSB OTA versus QAM cable delivery would be the ideal method--but nearly impossible for most. You just want to know if an OTA signal looks equivalent, with instant A-B switching, to the cable-delivered signal. You'd want your display adjusted as equally as possible for the two sources.


And you'd also want to check results from several persons using different OTA STBs but A-B comparing video from the cable system with the same-model cable converter. As mentioned above, I've discounted my OTA/cable comparisons because of converter image-fogging/detailing-spoiling problems. Unless it's an organized test, having everyone use the same display model also isn't practical. For likely subtle image variations caused by rate shaping, maybe you'd need 120-inch screens. -- John
 

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Discussion Starter · #11 ·
Quote:
Originally posted by John Mason
Agree using nearly the same video-processing circuits for comparing 8-VSB OTA versus QAM cable delivery would be the ideal method--but nearly impossible for most. You just want to know if an OTA signal looks equivalent, with instant A-B switching, to the cable-delivered signal. You'd want your display adjusted as equally as possible for the two sources.


And you'd also want to check results from several persons using different OTA STBs but A-B comparing video from the cable system with the same-model cable converter. As mentioned above, I've discounted my OTA/cable comparisons because of converter image-fogging/detailing-spoiling problems. Unless it's an organized test, having everyone use the same display model also isn't practical. For likely subtle image variations caused by rate shaping, maybe you'd 120-inch screens. -- John
I agree that this would make for the most accurate results.


Although for this poll, if you know they "reshape" and you have to go to these measure to see the difference then I would vote "If they do, I can't tell"
 

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Good Evening,


While John may have received information from TWC NY that they 'reshaping' compression rates, that is not the definitive word for all TWC Divisions around the country.


Time Warner Cable in South Carolina is absolutely not following this policy.

We pass through the signal exactly as we receive it. We pass through bitrates exactly as we receive them from programmers.


I'm not arguing that it doesn't happen, just that it is not universal and should not be assumed as a given. In addition, I 'think' in some cases people measure reduced bitrates on certain programming and assume their local cable company is 'throttling the bandwidth', when in actuality, it is because the programming is sent in a lower bitrate.
 

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I think some of the problem may be that the SA Cable equipment I have seen definitely has less contrast and less resolution.


When I watch an OTA Sports event, and they show the announcers, I can CLEARLY tell if their suit is cotton, polyester, or wool blend. With Cable HD I cannot see that level of detail, at least not with the SA box I have auditioned so far.


-- Cain
 

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Discussion Starter · #14 ·
I know there are not alot of HD cable watchers here at AVS, but I am very impressed with the results. I would of thought that there was more compresion going on.
 
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