Is there something different about WTMJ's signal? (4-1 freezing)

[Mark Strube]

For some reason our DISH ViP211 has issues viewing 4-1. We just got it replaced with a new one for this issue and a few others, and the new one has the same problems!

For some reason, only on 4-1, the picture constantly freezes up, but the sound is fine during all of this. It might happen every 2 minutes, or it might happen every 5 seconds... sometimes the freeze only lasts a few frames, other times I've seen it last for up to 5 seconds.

4-1 is perfectly fine on our Vip622, which is connected to the same antenna. Also, just to be sure this wasn't a wiring issue, I connected my old VOOM receiver to the same line that the 211 is connected to, and it had absolutely no issues with 4-1.

Is there something different about their signal that certain receivers don't like? and If so, can they switch back to whatever they were doing a month or two ago, before this problem cropped up?

I've resorted to having my mom view the standard definition version of WTMJ provided by DISH, until this problem is solved. I've left the VOOM receiver connected with a splitter, in case there's a football game she wants to watch on 4-1 in HD, but otherwise she's watching the standard version from DISH, since she's disabled and I can't always be here to switch her to the VOOM box.

Since I've had this same issue with two brand new DISH ViP211 receivers, I'd assume everyone in SE Wisconsin with this receiver is having the same issue - so this is definitely something WTMJ is going to want to look into.

Is there a WTMJ engineer on this forum, or if not, does anyone know where I might forward this info?

[REVM1M]

I thought i was the only one . I have the same problem, my 622 is fine but 211 keeps freezing (channel 4-1), every couple of days I reboot but it has not helped, I was going to call Dish to get a new 211 but based on your comments it probably will not resolve this problem.

[bubbaridesfast]

I don't have Dish but when you refer to 4-1 I assume you are referring to an OTA signal? if yes, then you should probably read the thread at http://www.milwaukeehdtv.org/forums/showthread.php?t=6273

[Mark Strube]

Looks like the problem has to do with "statistical multiplexing." I saw that thread before I posted this, but didn't think it was the same issue. Any way we can get WTMJ to simply stop using this? I'd imagine it shouldn't be too hard since they weren't doing it earlier.

[Jaxxos]

I have emailed WTMJ engineer twice now and I have received no replies, I gues they don't care. I have Dish with a 411 receiver and I'm getting that same freezing every few minutes on my OTA signal.

[Mark Strube]

I just sent an email as well. We'll see what happens. If I get no response within a week or so, I'm going to call them and ask to speak to the engineer.

[techboy]

I started the original thread about the freezing caused by the statistical multiplex signal on WTMJ-DT.  I have been in contact with the Engineer in Charge at WTMJ and I know he is aware of the issue.  But I don't believe he recognises how wide spread the issue is.  I and another member of this group who use older PC based tuner cards contacted WTMJ months ago about the freeze ups.  I also have a 1st generation Sony STB (SATHD-100). It also freezes up as described above.  Switching to statistical multiplex was done with the best intentions by WTMJ.  It should have allowed the sub WX channel to be added with little impact on the primary HD signal.  However, in practice, it seems to upset a certain unknown percentage of receivers.  Speculation is that some receivers can't handle the dynamic nature of the NULL PACKETS overflows.  I was told by the EIC at WTMJ that they are in contact with the  manufactuer of the encoder to resolve the problem.  But this has been ongoing ( 5 months ) since they added the WX 4-2 sub channel.  I can't watch WTMJ-DT on either of my receivers, but a friend has a receiver which works fine.  My take on this is that until managment at WTMJ recognises that this is a widespread and serious problem, it's not going to be a priority for them.    Tod

[Mark Strube]

Yeah I understand. In my email I linked to the 2 related threads here, making it clear that anyone in SE Wisconsin using a non-DVR DISH box to view their channel is having issues. Hopefully they check their engineering email address.

[StarvingForHDTV]

On my set top box (Samsung SIR-T151) I have the same problem.

[tencom]

In my research relating to Channel 4s digital signal I came to the conclusion that the software, used by there digital encoder may be defective, in my experience of using two different ATSC decoders, each handled the errors differently I recorded a  4.1 HDTV video stream and played it back using the FUSION decoder and  had occaisional macroblock break up, where as using the ELECARD decoder at the same points were macroblock break up errors occured the ELECARD decoder either skipped those frames or had a picture freeze for a few seconds and then checking the recorded stream file with a program called "MPEG REPAIR"  at these same points the log showed what is called "MOTION VECTOR ERRORS" which the program itself  could correct and lastly if you want a clean channel 4 digital signal use  TIME-WARNER cable as your source on cable channel 103 it showed almost no errors either by eye or checking there recorded stream, with MPEG-REPAIRs log either cable has the ablity to correct the errors or they are getting a seperate digital feed. and finally stream 4.2 weather also had many "MOTION VECTOR ERRORS" errors but doesn't seem to cause problems, and other digital channels, on either, OTA or cable had virtually no errors when checked with MPEG/REPAIR.

[techboy]

Time / Warner cable gets a fiber optic feed of the WTMJ analog and digital signals.  The TW HD video and audio feed leaves the building BEFORE encoding.  TW encodes the feed to 256 QAM.  If you compare OTA TMJ DT to TW, TW is even later in time. ( more processed)   The TMJ OTA HD is of course encoded for OTA into a 19.3 mbps (mpeg) stream and modulated at the trasmitter 8VSB.  It's the 19.3 Mbps stream from the TMJ encoder that is "faulty".   Statistical multiplexing dynamically allocates bits in the stream on an "as needed" basis.  It attempts to maximize picture quality in both the main HD channel and the sub channel simultaniously.  It generally allows the sub channel about 5Mbps, leaving the HD channel with about 13Mbps.  13 Mbps is usually enough for a good HD picture if the video is not too complex or changing quickly.  But when the encoder detects that the HD picture needs more data, it decreases the bits on the sub channel and increases the bits on the main HD channel.  This constant changing of the bit rate is what is screwing up my receivers and many others as well.    BTW, about 1Mbps is used for the audio and other necessary data. ( program guide, captioning, stream ID's, etc.)   All of the other Milwaukee TV stations that have sub channels use fixed rate bit streams.  
 Tod

[tencom]

I am almost sure that cable was the first to use statistical multiplexing for there QAM 256 signals I know that SCIENTIFIC ATLANTA has statistical multiplex encoders available for the cable market and tout its advantages Isn't another name for statistical multiplexing is "VARIABLE BIT RATE" used by DVDs?
Another point according to MPEG/REPAIRs log  channel 4.1 stream is running about over 15 million bits per second  average and 4.2 is running about  2.2 million
bits per second average..  I don't agree with you on the statistical multiplexing is the source of the problem because after doing much research I can find no evidence of a change in ATSC standards  in the last several years  on this topic and that decoder software would have to reflect. I heard that buggy software is a problem in digital encoders, and in my case I was able to correct  the errors with
mpeg/repair and got seamless video, with no reported errors even the ELECARD decoder counted additional frames where the macroblock errors occurred. this is some of the evidence that I gathered and would stand corrected if you gave me good evidence to the contrary you as well a I had had contacted the engineering department at channel 4 for where do they stand on this issue?

[techboy]

I believe that the encoded  stream must always have a combined total constant bit rate of 19.3 Mbps.  The total stream is NOT variable bit rate.  It's the amount of data and compression that varies.  There will be times when the audio and video don't require all of that "bandwidth".  So, the stream is filled up with null packets.  Zero's   In mpeg GOP's, a static picture would only require updating the I frames.  B frames and P frames aren't necessary.  so lots of null packets are generated.  It's very complex.  And yes, SM encoding has been around for satellite and cable use for a long time.  Also, the TMJ problem doesn't affect all receivers.  Some handle the SM perfectly.   I also can record the stream and process the problem away; essentially stripping out the null packets and retiming the data.  My examples of bit rates in my last post was hypothetical to make it easier to understand.    The bottom line is that a lot of viewers can't watch TMJ OTA without freeze-ups and somebody needs to figure out whats wrong.

[Jaxxos]

I don't know about the rest of you but I am watching the Seahawk/Bear game tonight and for the first time this season it's not freezing up every few seconds. Perhaps WTMJ finally addressed the problem because I have changed nothing on my end.  

[Nels Harvey]

I don't know about the rest of you but I am watching the Seahawk/Bear game tonight and for the first time this season it's not freezing up every few seconds. Perhaps WTMJ finally addressed the problem because I have changed nothing on my end.  

Yeah, but now the weather warnings put 4-1 into SD!