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HD Compression - how do they compare?

Discussion in 'Tech Talk - Gadgets, Gizmos and Technology' started by bobvick1983, May 11, 2009.

  1. harsh

    harsh Beware the Attack Basset

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    The problem with dividing transponder bandwidth by the number of channels is that it doesn't take into account the effective bit rate after error correction and the impact of using various modulation schemes.

    Things are seldom as simple as we would like them to be.
     
  2. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    [God, I can't believe I'm doing this]
    I have to agree. Channels/bit-rates/transponders/bandwidth are way too complex to use 1 + 1 +... to know what is what. Each transponder statistically adjusts allotted bandwidth for the bitrates of all the channels on each. Since MPEG-4 bitrates vary by the changes in the programing [frames], the VOD 1080p/24 will vary from 2-16 Mb/s [as I've monitored it].
     
  3. Zellio

    Zellio Icon

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    My point is specifically about theoretics, esp. when you talk hd compression. Fios can hold alot more data, and fiber optics themselves are the only things capable of showing data beyond 1080p.

    Potential bandwidth is a huge subject to talk about, esp. when going beyond 1080.
     
  4. harsh

    harsh Beware the Attack Basset

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    FIOS can hold a lot of data, but due to their choice of modulation schemes, much of it cannot be used for conventional video.

    Bandwidth existed long before fiber.
     
  5. Reaper

    Reaper Godfather

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    Compare D* SD to DVD video quality. That's about the same as comparing D*'s SD to FiOS'.
     
  6. DarinC

    DarinC Hall Of Fame

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    In an attempt to get this back on topic...
    8PSK actually provides 50% more bandwidth over QPSK. That is significant. However, it is much more succeptible to noise, and generally requires more error correction, which takes away from that 50% advantage (though it should take away 48-49% of it). But there are a lot of variables at play, so we have no way of knowing WHY they aren't using 8PSK.

    Everything I had heard when they were first talking about hte new Ka sats was that they'd be using 8PSK. And DirecTV's own channel capacity numbers seemed to suggest it. But for whatever reason, they apparently aren't using 8PSK on the CONUS transponders, and they still aren't at their claimed channel capacity. The best answer I can come up with is simply that it didn't work out as well as they'd hoped. Ka is new, and their initial expectations may have been a bit optimistic. I'm guessing that they simply don't have the power to produce a reliable CONUS signal with a full transponder load. They are now claiming that D12 will improve their channel count, when technically, it shouldn't, UNLESS they have a power issue. To the best of my knowledge, they are already using all the Ka frequencies that we can currently receive. D12 can't go to 101, because our dishes don't have a 101 Ka LNB, and I believe they are using all the 101 frequencies for uplink. So the only obvious explanation to me is that D12 will co-locate with either D10 or D11, and some of the content of one of those will be offloaded to D12. If they need to do that to get more capacity, then that would indicate that D10 and D11 don't have enough power to drive that many transponders with a high enough output for a robust 8PSK signal, but splitting the transponders between two satellites gives them enough power to increase the power per transponder to the level needed for a reliable 8PSK encoding, which will increase their bandwidth.

    Or, maybe they can do 8PSK now, and just haven't because they don't yet need all that capacity, and are simply saving power.
     
  7. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Some DirecTV SD actually looks fairly good on my Sony XBR.
    [again] I'm not praising DirecTV's SD.
    I've posted what others have reported the [raw] resolution to be.
    A crappy scaler won't help it either, while a good scaler can make it look "not so bad".
    With a 1080 display, the "made up" pixels will be nine times the "real pixels". "The best" FiOS could do is to reduce this from 9 to 6.75 and I'd bet it's more like 7.
    At seven times "made up" to "real", the scaler quality is still improtant.
    DVD = 6 x "made up" to "real".
    Not matter how you slice or dice it: 480 resolution [SD/DVD] on a 1080 display is more "made up" than "real".
     
  8. Reaper

    Reaper Godfather

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    Well, in general I agree with your statements (I'm not going to do the math right now but it seems reasonable). However, a true 480 signal should be 480x640. D* downresses theirs to 480x480 so there's even more information that has to be "made up" by the scaler.

    Again, compare DVD to D* SD. Are they close in quality? They weren't for me. In contrast, DVD and FiOS' SD are close in quality.
     
  9. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    If you did "the math", you'd get the same numbers and I did use 480 x 480 for DirecTV, 480 x 640 for FiOS, though Broadcast SD clips this down slightly.
    Do some DirecTV SD channels look like crap? sure.
    Some SD programs don't seem to though. History International & a couple of the HBO channels, come to mind, have had programs that don't look that bad. No, they're not HD [duh], but they've looked "fairly good".
     
  10. MountainMan10

    MountainMan10 Icon

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    D* SD is much better on my Sharp 1080p 46" than it is on my Samsung 720p 32". Part of it is on my Sharp I use native on and view SD in 480p. It is watchable.
    DVD's from my bluray player in 480p look much better than D* SD, but not near as good as D* HD or bluray disks.

    In the end I really don't care if FIOS SD is better than D* SD. I don't watch SD unless I have to.
     
  11. Reaper

    Reaper Godfather

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    Thanks MountainMan10, you've made my point for me: when I had D* I did not watch any SD unless I had to. Now that I have FiOS, I occasionally watch SD and I'm not as distracted by poor video quality.
     
  12. Reaper

    Reaper Godfather

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    I was agreeing with you. Geez!
     
  13. evan_s

    evan_s Hall Of Fame

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    As it stands FIOS's TV bandwidth is essentially the same an all digital cable system with no QAM channels used up for VoD or Cable internet because their VoD is handled via Ip and comes over the separate wavelengths of light. The net result is they have plenty of bandwidth to handle ~150 hd channels at broadcast bitrates and plenty of SD channels. From the looks of things they have a good amount of bandwidth available to cover their needs and plenty of options for future expansion.

    DirecTV on the other hand has 12 500mhz blocks (3 on each of the 4 switch options) but can't compare that directly to FIOS or other systems because of different encoding, error correction and compressions used. DirecTV isn't anywhere using all of the 6ghz worth of bandwidth for delivering content to any individual customer for various reasons. Currently DirecTV is able to provide 140 hd channels and a large number of SD channels and has another stat launch pending that should increase that. DirecTV does use MPEG4 and by nature has to recompress any OTA signals and at least some if not most of the other channels but it is at a bit rate that should be visually transparent when compared to the original OTA signal because of MPEG4's increased efficiency.

    Over all both providers look to be in a pretty good place when it comes to bandwidth. Neither is available to everyone. Fios has limited deployments areas and DirecTV has LOS issues. If someone happens to be able to choose between the two they are pretty lucky.
     
  14. Doug Brott

    Doug Brott Lifetime Achiever DBSTalk Club

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    Seems we've moved way beyond the original topic .. rather than close it, I'm moving it. Seems the thread was never really about DIRECTV anyway.
     
  15. evan_s

    evan_s Hall Of Fame

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    There are a number of possibilities on what DirecTV is doing with D12.

    There are 2 blocks for Ka frequencies at each spot. Each has 1 sat in it. Ka Hi has the 2 spaceway sats and the Ka Lo has d10/11. So while we are receiving something from each of the 4 blocks I wouldn't say they are fully loaded up by any means with 2 blocks doing nothing but providing spot beams from 1 sat each.

    One possible option is DirecTV could move one of the spaceway sats to the other orbital slot and operate both spaceways from a single Ka Hi slot. This shouldn't be problem given the flexibility of the phased array used by these stats and leaves a completely empty Ka Hi block for d12 to be used in the same way as d10/d11 are. This would require some changes to the sat before launch and would limit future flexibility some also since D12 wouldn't be configured the same as d10/d11.

    DirecTV could also co-locate D12 with either d10 or d11 in a Ka Lo slot. DirecTv has broken the Ka Lo blocks into 24 transponders. Currently they use 14 tps for Conus channels and 10 for Spot beams. That is most likely more transponders than are needed for spot beams since 101 only uses 4tps and 119 only uses 3. D10 also ran 16 conus tps for a while before D11 launched. A second sat co-located at either slot could definitely run a few more Conus TPs. Potentially when combined with 8psk/lower error correction rate to get more usable bandwidth per TP but still maintain good reception by running them at a higher power.

    Current math is 14 tps * 5 channels per tp = 70 channels per sat. Lets say they do 18 tps with 7 channels thanks to running 8psk that would result in 126 channels or 56 more channels. Right around where they are talking about.

    I don't think they are simply saving power because they can. When it comes to a Sat the power for things like the Conus TPs comes from the solar panels not from some sort of fuel. So running at lower power now isn't going to leave more fuel to run it for longer later. The fuel on sats is for position keeping/movement. Later in a sats life after solar panels have failed or aren't working as well running a sat at lower power/less tps can allow you to continue using the sat with in the reduced power budget. More likely they just don't have the power budget to do so. If you look at 101 for example DirecTV has 3 sats there providing the conus and spot coverage.

    Ultimately only time will tell what they do. I've changed my mind a few times but currently I think we will see D12 in Ka Lo with D10 running a few more TP total at a higher power level allowing 8psk and thus more channels per tp.
     
  16. Reaper

    Reaper Godfather

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    Good call Doug, thanks for not closing the thread. And sorry for all the off-topic posts - but when discussing video quality it's hard not to interject comments about FiOS.
     
  17. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Since this got moved, this may be my last post and is more just a comment.
    I just finished watching a Boston Legal recording from WGN. Color, clarity all looked pretty good. During one of the fast panning outside screen shots of the buildings, I noticed some [slightly] jagged edges on them. All and all though the general PQ looked pretty good.
    Now "the funny thing" was when I ended the recording and switched back to my local HD NBC. I instantly looked at something so blurry and washed out color, it looked like I was looking through a fish tank. This was "Martha Stuart" [not that I planned to watch it, just what was on] and on the OTA feed, so DirecTV had nothing to do with it, but was "simply" upcoverted SD broadcast on the OTA HD channel.
     
  18. DarinC

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    Yes, they could jumble them around in several different combinations. The point being, however, that they currently have enough satellites in position to use all the licensed frequencies that we can currently receive. Some have suggested that they are essentially out of CONUS bandwidth until D12 launches. D12 doesn't give them an ability to transmit on any more frequencies than they already can. So if they need D12 to push their bandwidth higher, that suggests that they need more power. Obviously, power alone doesn't increase bandwidth, but it does allow tighter encoding and less error correction, which results in more bandwidth for a given amount of spectrum.

    Yes, and no. Outside of some type failure, there are two "consumables" on the satellite that limit their lives: thruster fuel and battery longevity. Any time they in the earth's shadow, they have to operate on batteries. The life of a battery is affected not only by the frequency of discharges (fixed, in this case), but also by how heavily they are used. Higher currents when discharging and recharging, as well as deeper discharges, can reduce their life. So even though the power source is "free", that doesn't mean that there's no consequence of using power unnecessarily. If they don't have enough content to saturate their bandwidth potential using 8PSK, then they can use less power by using QPSK and/or more error correction.

    Technically, this can also help them save thruster fuel. Once the sat is in position, it's only needed for housekeeping. But IF they are in a position where they just don't yet NEED all their potential bandwidth, they can run looser housekeeping, which uses less fuel. Using QPSK and high error correction can help with the lower signals that can result from poor dish alignment, regardless of whether that's due to the dish not being aimed properly, or the sat just not being exactly where it's supposed to be. So whether your saving sat fuel, or saving money on truck rolls, there's still an advantage to using QPSK over 8PSK in cases where you just don't need all of your potential bandwidth.

    I too am leaning towards the possibility that they may simply not have the power to use 8PSK reliably on the CONUS transponders. But the fact that they AREN'T using 8PSK doesn't necessarily mean they can't. It could just mean that they don't yet have enough content lined up, so QPSK could make more sense for their current situation. A lot of that comes down to whether or not you believe they haven't rolled out more HD because they can't, or because it's just a business decision.
     
  19. Drew2k

    Drew2k New Member

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    Thanks for the closure, if you know what I mean ... Now I can unsubscribe, as I was interested int he Dish/DIRECTV comparisons, but not in the Fios discussion.
     
  20. Brandon428

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    Dish vs Directv picture quality has been done to death. I much rather talk about the technological possibilities of Dish,Directv and FiOS(or fiber optics in general).
     

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