1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Audio dropouts on one specific OTA channel

Discussion in 'DIRECTV HD DVR/Receiver Discussion' started by Indiana627, Aug 21, 2010.

  1. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    For the last 2 weeks, I've been having audio dropouts on my local Fox channel which my HR21-100 gets via the AM21. Audio is output via HMDI to my Sony AV receiver for 5.1 audio. This setup has not changed in months, and this channel (40.1) has come in fine for the 2 years I've lived here.

    Now when watching either live or recorded content, I get a half second audio dropout about every 60 seconds or so. The video is fine, just the audio is effected. I've been in contact with the station engineer and he says he hasn't experienced the same dropouts at his home, nor do his station logs show any errors. I rebooted the HR21 but that didn't help. I then went into the HR21 audio settings and turned off the DD so that it was only outputting PCM. I then rewound to a point where I know a dropout occurred with DD on and the dropout was not present. I then turned DD back on a rewound to the same point and the dropout was again present. I want to keep DD on for obvious reasons.

    I'm only having this problem on this one OTA channel; all other OTA channels and all SAT channels are fine. Any ideas what could be causing this? Any ideas of how to fix it?
     
  2. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    No one has any ideas or thoughts on this?
     
  3. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    Could I have a tuner or tuners going bad in my AM21? But if that was the case, wouldn't all 9 of my OTA channels be affected and not just my 40.1 channel? (And sub-channel 40.2 is fine, just main channel 40.1 is having problems.)
     
  4. MysteryMan

    MysteryMan Well-Known Member DBSTalk Club

    8,514
    532
    May 17, 2010
    USA
    Wow...57 views and none of us can help.
     
  5. Davenlr

    Davenlr Geek til I die

    9,139
    28
    Sep 16, 2006
    No ideas, but it obviously is recorded that way, since you can play it back and repeat it.
    Im also guessing running the antenna in to your TV and tuning in that way doesnt have the same problems... so my first question would be, is this station actually transmitting on VHF where short static spikes could be causing a glitch in the HD audio stream?

    Have you tried removing all your OTA (reset), and then rebooting your DVR, and then doing an Initial setup again?

    Is this station available on DirecTv (if so, does it have the glitches on the satellite downlink?).

    Weird problem. I have only seen this happen to me during thunderstorms where lightning spikes caused audio dropouts, but actually didnt affect the picture for some reason.

    Might try reseating the USB cable...

    Those are my best guesses. Since 40.2 (which probably is SD) doesnt have the problem, its gonna be a weird one.
     
  6. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    To answer some questions: Yes, the channel in question is actually broadcasting on 8.1, with 40.1 being its virtual channel. BUT I am only a few miles from the tower with a clear line of sight, and my current antenna and equipment has worked fine for 2 years with them being on 8.1.

    I had not tried resetting the OTA settings and rebooting (more on that later) but I had simply rebooted the HR21 to no avail.

    My locals are not yet available yet on D* (scheduled for October), so no help there.

    So I just finished resetting the OTA settings and rebooting and then reruning the OTA setup and that seems to have worked - so far. Watching about 5 minutes of The Simpsons and had no audio dropouts. I'm hoping my problem is solved, but I won't claim case closed until after a few more problme free days (I did have one night last week watching preseason NFL with no audio dropouts only to have them return the next day, so that's why I'm a little cautious).

    Thanks so much for the help! Keeping my fingers crossed...
     
  7. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    Well it turns out I was right to be cautious about resetting the OTA settings to fix my problem as when I tuned to 40.1 this morning the dropouts were back again.

    Does anyone think the AM21 could be going bad? Is it feasible that it would only be acting up on channel 40.1, and not 40.2 nor any of the other OTA channels I get?

    How hard is it to get D* to send me a replacement AM21 at no charge?
     
  8. texasbrit

    texasbrit Well-Known Member

    5,170
    92
    Aug 9, 2006
    It's very likely the problem is actually in the station signal, not the AM21. Fox affiliate often have these sort of problems with their audio. Just because the station engineer's equipment does not show the problem does not mean it isn't there. Fox affiliates often send out missing, duplicate or corrupted audio frames. some A/V receivers are sensitive to these and some are not.
     
  9. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    So how do I convince the station engineer of this? I guess that is the $64,000 question at this point.

    I was going to swap my two AM21s and see if that helps or not. I think there's just a power cord, USB cable and antenna input on the back of the AM21 to disconnect right? It will be a hassle to do, but I'll give it a shot.

    Still haven't heard back from the station engineer. One thing that makes me think it's not the signal is that no one else in my market's Local HDTV Info and Reception forum at avsforum.com is reporting the problem - it's just me.
     
  10. n3ntj

    n3ntj Hall Of Fame

    5,773
    13
    Dec 18, 2006
    Lancaster,...
    Is everything clean on the feed directly through the TV's ATSC tuner?

    I've had some issues with my HR20-700 that when I rewind live TV, the audio cuts out. No rhyme or reason..
     
  11. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    Well unfortunately I don't have the antenna hooked up to the TV's ATSC tuner. I used to have it split to the TV and to the AM21, but that resulted in some pixelation on the AM21, so I removed the splitter to the TV. It would be somewhat of a hassle to connect the antenna to the TV again, but I guess I could try that at some point too.

    I do have the Roadrunner line split to the QAM tuner and when I check that, there is no audio dropouts. The station engineer says that Time Warner picks up his signal via OTA, so I would think if the problem is with his OTA signal, then the dropout would be present in the cable feed too, right?

    I don't know what to think. There seems to be evidence pointing to the problem in the signal and to the problem being on my end.
     
  12. TomCat

    TomCat Broadcast Engineer

    4,153
    100
    Aug 31, 2002
    Very likely? Based on what, other than your suspicions? And what do you base the assertion that FOX affliliates have these sorts of problems? Hearsay on a forum? There's something you can take to the bank.:rolleyes: While you are correct that "station logs", which probably refers to splicer logs that only the FOX corporate engineers can access, don't show issues doesn't mean there aren't issues, not showing issues also does not mean that there are any, and usually implies that there aren't.

    That is totally unsubstantiated. What orifice could you have possibly pulled that out of? Transmission of AC-3 audio is sophisticated, but it is not plagued with issues, otherwise the phones at the TV stations would never stop ringing. Audio issues like these affect a very microscopic fraction of the viewing audience, and are usually based on a failure or incompatibility of the error correction in decoding, which is a customer-based function, not a transmission-based function. Broadcasters adhere to rigid standards but unfortunately receiver manufacturers don't, which includes DD decoders as well as ATSC tuners.

    As a broadcast engineer working intimately with transmission of digital audio since 1999 (and working in the field since the 70's) I can assure you that TV AC-3 audio typically is transmitted with virtually zero errors. Oh, there are always plenty of errors, they just do not very often come from the transmission itself. The errors creep in due to atmospheric and multipath interference, and are usually masked by error correction, but the important part of that process is that the errors do not occur at transmission, which typicaly vanquishes the source as being the problem.

    It is true there are slight differences in technique for transmission of AC-3, and a FOX affil may do it slightly different than a CBS station. In my area, the CW station is the one with the dropouts, and that is rare (and I chalk that up to reception rather than a failure of the station to transmit it properly). Here, the PBS station had problems over sat for weeks after moving channels, but that is a completely different type of problem even though also confined to a single station, and was related to how DTV received it before backhaul. And it is also true that some ATSC tuners will react slightly differently, and that some are more compatible with a certain station's technique than others may be, especially in marginal reception areas.

    The fact that the audio is there in PCM proves that the problem is not with the audio, but with decoding of the DD 5.1 metadata (there is only one audio sent for PCM and DD, it is handled differently by each).The audio is there, is not corrupted, duplicated (how in the heck does that happen naturally as a function of transmission?), and not missing. If there is a particular incompatibility between a particular source and a particular DD decoder, this is exactly how it will manifest, PCM OK, DD problematic. Further decoding is needed for DD beyond decoding the PCM, as PCM is a direct track to channel translation while DD needs to map the channels on the fly according to the DD metadata. If the metadata is not decoded properly, it will mute the audio for those frames, even if the audio (the information that contains the audiio) is really there.

    For the OP, I would post in the local reception forum for your city on AVS, which will tell you if you are the only one with this issue. Be sure to mention what DD you are using.
     
  13. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    Yes I have done that already - actually did that before starting this thread here. So far no one has posted they are having the same problem.

    I think I'm going to call D* today and try to get a new AM21 sent to me for free. Wish me luck!
     
  14. CCarncross

    CCarncross Hall Of Fame

    7,058
    60
    Jul 19, 2005
    Jackson
    You said a few posts ago you were going to swap your AM-21's, what was the result of that test?
     
  15. texasbrit

    texasbrit Well-Known Member

    5,170
    92
    Aug 9, 2006
    Tomcat - I am sorry you were so upset by my post.
    1. If only one station is showing this problem, it is highly likely that the problem is with the signal coming from that station. Occam's razor - the simplest solution is usually the most likely
    2. If you read all the hundreds of posts on audio dropouts (and before those, with the "brrrp" issue) you will find that Fox affiliates have been by far the worst (although not the only) offenders. My quote on the audio frame issue comes directly from a DirecTV insider who was involved in monitoring the signals. Speculation (I will use that word) is that the problem is related in some way to the equipment Fox uses. Maybe also the Fox-affiliated national channels use some of the same equipment since they also seem to be more prone to the problem. And often with the affiliates it does not occur on locally-derived programming, only on national programming. Even switching to local commercials makes the problem go away.
     
  16. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    Haven't had a chance yet to be honest. During various 5 minute testing periods since last night, I've not heard the dropouts. Go figure. I was going to call for a new AM21 just to be proactive as I've had a few other periods of time where the dropouts stopped only to return. I've not gotten any feedback from the station engineer saying they found/fixed the problem, so I still feel in limbo.
     
  17. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    New AM21 ordered at no charge. It took a little anger in my voice, but they were nice enough to help out a 7+ year loyal customer.
     
  18. Indiana627

    Indiana627 Hall Of Fame

    3,266
    4
    Nov 18, 2005
    So the new AM21 arrived today. I have to work this afternoon and hope to install it tonight. This is my plan on making the switch. Does it sound like the right order?

    1. Reset OTA settings.
    2. Do a menu reboot and when it powers down unplug from the wall.
    3. Remove the old AM21.
    4. Install new AM21.
    5. Plug cord back in.
    6. Once rebooted, rerun the OTA settings by entering ZIP code.
    After the removing the old AM21 in step 3, should I power the HR21 back up with no AM21 connected, let it boot all the way up, then do another menu reboot and unplug cord when it powers down, and then proceed to step 4 and install the new AM21?
     

Share This Page