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<blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid"><br>But then comcast goes and tries to cram 3 HD signals in that bandwidth.<br><br></blockquote>
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<div>QAM256 has ~38Mbps total bandwidth compared to just over 19Mbps for 8VSB this is correct. However in the 19Mbps OTA networks usually run 1 HD and usually multiple SD streams so the actual bandwidth that they use is more like 12-15Mbps and then it's not that hard to put 3 HD OTA channels in the same Cable channel with virtually no loss in quality and I imagine you'd only have issues if all three of these show simultaneously high action scenes where the total bandwidth of the three would exceed 38Mbps.<br>
<br>Here are the actual values for SF Bay Area broadcasters that one person provided on the SFBayHDTV Yahoo group about a year ago (the numbers are all in Mbps). As you can see only few of these ever go beyond 12Mbps (I don't have numbers for Cable/Satellite only HD channels so there the bandwidths may be different) and this is during prime time:<br>
<br>2-1 = variable 14 - 14.5<br>2-2 = 2.05<br><br>4-1 = 3.62<br>4-2 = 14.32<br><br>5-1 = variable 11 - 17.5<br><br>7-1 = variable 11 - 12<br>7-2 = variable 4 -5<br>7-3 = variable 1.5 - 1.7<br><br>9-1 = variable 9 - 11.5<br>
9-2 = 3.03<br>9-3 = 2.84<br><br>11-1 = variable slightly 12.7 - 12.8<br>11-2 = variable slightly 3.2 - 3.4<br>11-3 = variable slightly 2.3 - 2.4<br><br>20-1 = 14 -15<br>20-4 = 2.46<br><br>36-1 = variable 9.5 to 13.5<br>
36-2 = 3.22<br><br>44-1 = 16 - 17<br><br>48-1 = 3<br>48-2 = 15<br><br>65-1 = variable 9.5 - 11<br>65-2 = slightly variable 2.4 - 2.5<br>65-3 = variable 2.5 - 3<br>65-4 = 1.9<br></div></div></blockquote>
<div>Thanks for the numbers, however that doesn't change the fact that Comcast and other cable providers compress the content further before transmitting it to you. Its a necessary evil due to the "more channels is better" mentality that forces them to offer more to be competitive.</div>
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<div><a href="http://www.pcworld.com/article/144800/is_hdtv_compression_damaging_picture_quality.html">http://www.pcworld.com/article/144800/is_hdtv_compression_damaging_picture_quality.html</a> is a good read.</div>
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<div>As it stands, OTA is the highest quality signal available for HD as it is the final format the broadcaster is concerned with and thus their production path is designed to maximize it's quality. Though some distribution paths will achieve equal quality by sending an unadulterated signal, none should be able to exceed it as they should all be using the same feed as their source material.</div>
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