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Pixelation on TiVo when uploading over cable modem?

Discussion in 'TiVo Roamio DVRs' started by drawz, Jun 15, 2014.

  1. drawz

    drawz New Member

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    Aug 1, 2011
    I'm having a bit of an unusual issue. I noticed seemingly random pixelation on FoodHD (854 on Comcast Boston/Brookline) for several months and finally investigated. Other channels seem fine.

    From DVR diag:
    • Signal level is 98-99% with SNR 39dB
    • Some RS uncorrected errors on this channel only (241149 in 8 hours)
    • Lots of RS corrected on this channel only (3004420 in 8 hours)

    Equipment:
    • Roamio Pro
    • Motorola SB6121 cable modem
    • 2-way splitter to cable modem/Roamio Pro

    The interesting part is that running a speedtest causes the uncorrected errors to sky rocket during the upload phase of the test. This also instantly causes terrible pixelation. I get 3260 uncorrected and 4986 corrected errors during a single speedtest, all uncorrected and the vast majority (99%) of corrected errors occurring during upload. I suspect that the seemingly random pixelation I've been getting coincides with random upload bursts from the various computers and other internet connected devices in the house.

    Even without the speedtest involved, I get some uncorrected errors on this channel, but 0 on others that I checked. Doesn't seem to matter which tuner is used. I did get random pixelation on the same channel with my old Premiere XL4, but it seemed much less common. I never tested the upload thing since I just stumbled upon that last night.

    Any ideas what might be going on here? Anything else I should check?
     
  2. ThAbtO

    ThAbtO TiVoholic by the bay

    6,726
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    Apr 6, 2000
    SF Bay Area
    You might need to add a 5-10 dB attenuator to your cable to bring the SNR down to at least 37dB. Cable source is a bit too strong.
     
  3. drawz

    drawz New Member

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    Aug 1, 2011
    Any idea why it would only affect one channel (as far as I can tell)? Or why uploading over the cable modem would make it worse?
     
  4. nooneuknow

    nooneuknow TiVo User Since 2007

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    Feb 5, 2011
    Cox Cable...
    That depends on the frequency the problem channel is operating on.

    Check DVR Diagnostics to find it. Then check what frequencies your cable modem is using. You may find an overlap, or that the frequencies are close to each other.

    If not, and a TA is in use, there may be some overlap in the frequencies the TA communicates on.

    If one device is pushing too strongly upstream, or one is receiving too high of a signal, it can cause an overpowering interference.

    Often, devices will boost power as they are pushed to operate at higher throughput, as opposed to being idle, or operating at low throughput.
     
  5. HarperVision

    HarperVision TiVo's Italian Cuz!

    5,275
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    May 14, 2007
    Paradise...
    It could also be a harmonic of the modem's frequency effecting your TV channel's freq.
     
  6. nooneuknow

    nooneuknow TiVo User Since 2007

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    Feb 5, 2011
    Cox Cable...
    Could be any number of factors, really.

    This is a situation where one would want to make sure all unused coax ports on splitters are terminated, and terminators are placed at every unused wall-plate.

    That's just best practices, anyway. In the digital age, there shouldn't be any ports or wallplate barrels without a terminator, if not in-use.

    The list of possibilities is a long one. This is a good starting point. Unterminated splitter ports allow ingress/egress, and signal reflection (bad). This is compounded when there's a run of coax with an open end.
     
  7. drawz

    drawz New Member

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    Aug 1, 2011
    Thanks everyone! I'll try the terminators and/or attenuators first.
     
  8. drawz

    drawz New Member

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    Aug 1, 2011
    Finally got around to troubleshooting this some more.

    Tried a 6dB attenuator from Smarthome, which knocks down the signal strength to 87-90% and SNR to 35-36dB on the effected channels. Unfortunately, I still get tons of pixelation when running the upload portion of an internet speed test, along with tons of RS uncorrected and some RS corrected errors. The splitter I'm using is from the cable company and appears to be high quality.

    Haven't tried the terminators yet, but I do also have those and will try them tonight hopefully.

    Any other ideas?

    *edit* I now get 75k uncorrected errors with one speedtest run, all on the upload side, although this is in the setting of having my QoS off on my router. With QoS on, slowing down my upload speed by about 5%, I get fewer errors, but still an unwatchable picture.
     
  9. huntermaz

    huntermaz Member

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    Feb 18, 2014
    Have you had any luck getting this fixed?
     
  10. nooneuknow

    nooneuknow TiVo User Since 2007

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    Feb 5, 2011
    Cox Cable...
    It seems like you might have a bad splitter. Are you somehow the 1% that uses a single splitter for everything? That rarely works out. I haven't re-read the whole thread to try and extrapolate how everything is hooked-up.

    Try the terminators first. Then I suggest it might be time to start replacing splitters and coax, until you find the problem.

    It almost sounds like the port isolation of a splitter somewhere is too low, or it could be bad/damaged coax. Are you certain there aren't any splitters inside walls, or in places you haven't looked? Have you traced-out where all coax comes and goes?
     
  11. drawz

    drawz New Member

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    Aug 1, 2011
    Wow, I just came to give an update that I thought was brilliant, but nooneuknow beat me to it by a few hours! I think the splitter was a big contributor as it improved SIGNIFICANTLY when I swapped it. I still get pixelation and image break up if I turn off my router QoS, but it looks fine with QoS on. The random pixelation also seems less frequent, but too early to say for sure. I did not add the terminators yet.

    For clarification - the coax comes into my condo building somewhere unknown to me, so I'm not quite sure what is going on outside. In my unit, there is a 6-way splitter supplying all the rooms (two drops to most rooms). My TiVo and cable modem are connected via a single 2-way splitter from Comcast and they are the only devices in use in my unit. There is now a 6dB attenuator on the TiVo side of the split. I haven't tried taking the attenuator back out.

    I suppose I should terminate the unused ports either at the 6-way splitter or at the open ports in each room. My next move was going to be trying new coax cables in case of a broken shield or bad connector. These were also supplied by Comcast and cut to length by the tech, so I could easily see them failing.

    FWIW - this exact set up worked just fine with my TiVo Elite, so the Roamio is more sensitive for whatever reason.

    Thank you all for your help! If I get time to play with it any more, I'll add anything useful that I discover.
     
  12. nooneuknow

    nooneuknow TiVo User Since 2007

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    Feb 5, 2011
    Cox Cable...
    Splitter port-isolation (high=good) is key to stopping crosstalk between OUT ports on a splitter. Used in conjunction with terminators, it can keep things running smoothly. Regardless of how something else worked before, unless the interference is coming in over the network, it seems like your Cable Modem and Cable TV signals need better isolation. You can create more isolation between the two, by using more splitters. You can also attenuate in a much better way, if you use splitters and terminators to do so. This is how Cox does it in my 1GHz market. They no longer install, or allow attenuators. Any attenuation needed must be done by using splitters with excessive OUT ports, and/or daisy-chaining more splitters in-line. I prefer to daisy-chain most of the time, and keep my cable modem as many splitters away from my TiVo, as is possible. When doing this, terminators are NOT optional.

    It also sounds like it's possible your TiVo has a defective internal filter for 5-54Mhz frequencies, which cable modems, tuning adapters, and EMTAs broadcast at high power on, to push the upstream all the way back to the cable plant. Here's the fix for that: http://www.wiredathome.com/cables-a...-by-pico-hpf-54mhz-cable-tv-high-pass-filter/
    Be warned, the only place this can be used is screwed directly to the port on the back of the TiVo. I used to have to use these with TiVo HDs, due to an issue like yours.

    Some comments on splitters:

    I recommend 1GHz. If you can get 1.2GHz for a little more, get that. 1000MHz=1GHz. Some splitters will say 5-1002MHz. Those are essentially 1GHz splitters trying to stand-out as better. Make sure it says "digital" somewhere on the splitter itself (not just the box it is in).

    Do not get higher than 1.2GHz. Do not pay extra for something that says "MoCA-enabled" or "MoCA-enhanced", etc. It's the same deal as with HDMI cables that cost more, for the brand and enhancements that are BS.

    The one real problem is: I can't buy any splitters that won't have problems like you do, from retail stores, no matter what they cost. I either have to get one from a cableco van, the local Cox store, or mail-order them. Nothing Wal-mart, or the likes-of is worth the packaging it's in. Home Depot might have some good ones, if you are lucky.
     
  13. drawz

    drawz New Member

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    Aug 1, 2011
    Thanks for the additional info. I happened to have another one from Comcast that seemed to solve the problem. I still have the 6dB attenuator inline with reasonable signal levels. If you go back to my first post in this thread, you'll see the signal was a bit strong to start. I don't think I'm going to mess with it much more at this point since it's working ok, but I'll keep your other tips in mind if issues crop up again.

    *edit* the product you linked is very interesting. going to bookmark that one...
     
  14. catburt

    catburt OldGeek

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    Aug 14, 2014
    You might want to keep a eye on the RS corrected and corrected errors. I get less than 100 a day. I had to get the cables in my house perfect to make my original Tivo HD work because of a bug in the internal tunner firmware that did not terminate the line correctly inside the Tivo years ago. That bug was eventually fixed by tivo but taking the time to correct the cable issues means I almost never have internet or TV issues.

    You might want to log into your cable mode at 192.168.100.1 and look at the signal tab. The weaker or more noisy signal the modem gets the louder it has to transmit to get back to the mother ship increasing the noise on the line. Dslreports has a good section on what the numbers should be.

    In my case I just had to get comcast to replace all the old crimp connectors on my cables with the newer O-ring sealed two part weather tight connectors and removed all the old unneeded taps in my 25 year old house.

    Comcast will not care about the errors on the cablecard but you should be able to get them out to fix errors on the cable modem if you have slow internet response and you say the right things.

    The quality of internet service is a big deal for me because I work from home. My wife also is quick to point out any issue.
     
  15. drawz

    drawz New Member

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    Aug 1, 2011
    So I moved some things around to clean behind my TV and the pixelation is back! :( Makes me suspicious of bad cables or a bad crimp that was a little positional. Same channels, same cable modem upload issue.
     
  16. nooneuknow

    nooneuknow TiVo User Since 2007

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    Feb 5, 2011
    Cox Cable...
    Time to get some new RG-6 "patch" cables. It's not easy (for the typical person) to put new ends on, nor are the tools to strip and secure the ends, cheap (the ones worth using). I have all the tools, know what I'm doing, and still would rather replace the "patch" coax cable, than spend the time to put new ends on one. The ends aren't cheap, either, unless you buy in bulk.
     
  17. kbmb

    kbmb Active Member

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    Jun 22, 2004
    NH
    I'm on Comcast up in Southern NH. I can tell you that 854 is one of the channels that I've had issues with in the past (along with channels like 832, 872, 823), both on Tivo's and Comcast DVRs. It's something about how Comcast sends the signals for these that I think tends to have them had more issues.

    You can certainly try to reduce your SNR if you want, but I know that the Plus/Pro Roamios boost the signal compared to the Basic. I had nothing but problems when I tried reducing my levels (right now I'm around 41 SNR), so I left it alone. Initially when I was attenuating my signal, it's the above channels that consistently had signal issues where none of the other channels did.

    In fact, back when I had a Comcast DVR, at one point I would get all the channels except for the ones above where I would get no signal. Comcast tracked it down to a bad coax connector. So I guess I'm saying I think a channel like 854 is more prone to have issues if you have coax/line problems.

    I just ran a speedtest while viewing 854 and didn't notice any issues here, so you might want to replace cables to see.

    -Kevin
     
  18. nooneuknow

    nooneuknow TiVo User Since 2007

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    Feb 5, 2011
    Cox Cable...
    What could be of more use to know, is what frequencies the channels you list are carried on, and if any of they share the same frequency. It's also great to know what frequencies any cable modems, TAs, or EMTAs are operating on.

    I avoid speaking about channel numbers, and try to focus on what frequency range they are in, if I'm going to bring up problem channels.

    I get that a common provider might use the same channel numbers in all markets. Some might even carry the same channels on the same frequencies. It's just not that simple, most of the time.

    It's also helpful for newcomers that might find a thread, and think a mention of channel 1018 and/or or TNTHD, will apply the same with them. The only time network channels might help others, is if people in multiple markets are having issues with TNTHD, none on the same frequency, but all seeing a problem. Then, it tends to point to that network channel.
     
  19. drawz

    drawz New Member

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    Aug 1, 2011
    Thanks for the tips guys. Any advice on where to get some decent, but reasonably priced, RG6 patch cables? Can I go to my local Comcast office and get some freebies? :)

    I'll look up and post the frequencies for the effected channels later this weekend.
     
  20. ThAbtO

    ThAbtO TiVoholic by the bay

    6,726
    8
    Apr 6, 2000
    SF Bay Area
    The local Radio Shack, Best Buy, any electronics store, even Walmart or Target.
     

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