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Discussion Starter · #1 ·
Provided as a courtesy to Hap Griffin, SCETV.


"OK, here is the scoop. On Thursday night at 7:00 PM straight up, we'll reconfigure our HD encoder to one of four test modes. I won't give away the modes here because I want those of you who can participate to give me objective feedback on the picture quality. We will be testing 1080i and 720p at two different bandwidths. If your receiver has the ability to show you the scan mode, please don't let that sway your rating one way or the other. I hope that TW cable will be able to track the changes...so far they have.


We will run Mode 1 from 7;00 to 7:10, Mode 2 from 7:10 to 7:20, Mode 3 from 7:20 to 7:30, and Mode 4 from 7:30 to 7:40. Then we'll begin over with Mode 1 at 7:40 and run through them once more. The test will end at 8:20. Please takes notes and forward your opinions to me of the picture quality of each mode...rating them worst to best along with any comments as to how your equipment performed at the mode changes. Also please list your equipment. "


"Many thanks for your participation. I will share the results with PBS and all of the DTV stations on my SC DTV Engineering mailing list.

Hap Griffin
SCETV "



Comments may be made to Mr Griffin via email at SCETV Besides comments posted here(if any) I will ask Hap for the overal findings to provide here as well. Unfortunately I am out of town and cannot participate in tonights test.


Bruce
 

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Discussion Starter · #2 ·
Again, from Hap Griffin:


"OK the test session is complete. We had a problem during the first mode

from 7:00 to 7:10 because of a loss of the PBS satellite signal during a

frog choking downpour, but otherwise things went as planned.


Please give me your comments if you were able to participate."


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Bruce
 

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Discussion Starter · #3 ·
First the latest I have heard from Hap Griffin:


"As you say, there are still unknown variables in the equation. I'm sure we'll be doing further tests. Part of what I really wanted was somefeedback as to how the various receivers handled the mode changes...in particular those watching via cable. I don't have TW cable here at the center (they don't have drops in this area) so I have to rely on external feedback to tell me how they are handling things."

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So if any TWC users watched the test please drop Hap some comments . Now here is what he had to say post test:


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"I had hoped to have some participation from this list in our encoder

tests, but so far there have been no comments...so here's mine.


The tests came out pretty much as I had suspected. We had two identical Panasonic 30" HD monitors fed by two identical IRD's...one tuned to the PBS satellite source material that would be used as reference and the other tuned to the WRLK-DT off-air signal on channel 32. The encode/decode delay of just over a second was obvious. The two monitors had been carefully matched for color, brightness, gamma and contrast earlier in the day.


The 720p tests at both 12.6 Mb and 15.6 Mb showed a much greater ability to handle motion and scene cross fades than the 1080i tests. At 15.6 Mb, motion artifacts were not very noticable, and only marginally more so at 12.6 Mb. Unfortunately, the lower resolution of the 720p mode was obvious, exhibuting a noticeably softer image than the 1080i source material. This came as somewhat of a surprise to me since I have viewed many demos of 720p and have always been impressed...even to the point of stating that I preferred 720p to the interlaced 1080i mode due to the smoother motion rendition of progressive scanning. Thinking back though, I can't remember seeing the two HD modes side by side with the same source material, as I was seeing here.


The 1080i tests at both 12.6 Mb and 15.6 Mb showed very noticable motion artifacts, with scene fades being very "busy" in the narrow bandwidth mode. This is partically due to the shear number of pixes per frame that have to be processed (2,073,600 for 1080i vs 921,600 for 720p)as well as the interlaced scanning. However, at both bandwidths, the resolution was indistinguishable from the original source material. When there was not much motion, the picture was outstanding.


At this point, I am inclined to configure the encoder to run in the 720p mode while we have two SD services in the mix and only 12.6 Mb of bandwidth available. I believe the much better motion performance overcomes the slightly lower resolution. The fact that I have always had a good impression of 720p indicates that without a side by side comparison, the resolution tradeoff may not be noticeable to most viewers. If and when we change our operation to include only a single SD channel, giving more bandwidth to the HD service, the 1080i mode will again be appropriate.


Encoding algorithm software upgrades will continue to improve encoder performance, so this will remain an evolving situation for a while. We will continue to research the most appropriate encoder configurations to meet the twin goals of providing the increased number of services we are obligated to provide from our funding commitments as well as providing the highest quality video and audio to our viewers."


Hap Griffin
SCETV
 
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