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PVR-150 No sound on some channels
http://forum.linhes.org/viewtopic.php?f=2&t=6778		 Page 1 of 2
Author:  gamelyn31 [ Fri Nov 04, 2005 9:45 pm ]
Post subject:  PVR-150 No sound on some channels
I'm running a straight forward setup of myth (no unusual configuration settings, etc.) using a PVR-150. Things are working pretty well, but on some channels I am not getting any sound. The video comes in clearly on all available channels, but some channels (specifically: 7, 12, 16, 30, 31, 39, 42, 48, 52, 54, 96) are soundless. On all the rest of the channels the sound is perfect. Any ideas? I've tried changing the input source type from us-cable to us-cable-hrc, but that didn't seem to help (actually, it made things worse by adversely affecting the video). I'd be happy to provide additional information, but I'm not sure what would be useful in this case.
Author:  gamelyn31 [ Sat Nov 05, 2005 9:51 am ]
Post subject: 
Update: Well, this seems to have been a tuning problem. The cable company "tightened up" some of the outside connections and now I'm getting sound on all but 4 channels (12, 16,42, 48). I'm going to assume those are tuning problems as well.
Author:  tjc [ Sat Nov 05, 2005 10:51 am ]
Post subject: 
You can make fine tuning adjustments and see if that helps. While upgrading my system I had to redo this, and noted that the picture could look fine while there wasn't any sound because the tuning wasn't quite right yet..
Author:  gamelyn31 [ Sat Nov 05, 2005 2:08 pm ]
Post subject: 
Thanks for the tip, tjc. Using the web interface, I was able to fine tune the remaining few channels and now all channels have sound.

I fine tuned the channels by adding a 107 to each of the fine tune fields on the web interface. It worked, but I'm not sure why (maybe someone knows?). The only reason I tried 107 was because someone else posted in the forums that it worked for them. I don't know if there's something "magical" about 107 or if I just got lucky.

One other thing - in case anyone is wondering - you do not need to restart mythfrontend to get the fine tuning to take effect. All I had to do is switch to another channel and then switch back after saving the web page (SAVE button at the bottom of the page). I'm sure most of the folks here probably know that, but I thought maybe it was worth mentioning.
Author:  tjc [ Sat Nov 05, 2005 2:27 pm ]
Post subject: 
gamelyn31 wrote:
I fine tuned the channels by adding a 107 to each of the fine tune fields on the web interface. It worked, but I'm not sure why (maybe someone knows?). The only reason I tried 107 was because someone else posted in the forums that it worked for them. I don't know if there's something "magical" about 107 or if I just got lucky.

Just lucky I suspect, unless your provider has some kind of standard offset. One of the things I saw on this topic had a link to the frequency charts... Hang on...
OK, here is the message I found in the MythTV Users mailing list archive: http://www.gossamer-threads.com/lists/mythtv/users/152716
And here is the link to the frequency tables mentioned: http://www.jneuhaus.com/fccindex/cablech.html
It looks like there is an offset of 125 Khz (the current fine tune increment is 1Khz) between some of the Brodacast and IRC (standard cable) frequencies, so 107 would be close to that.
Author:  gamelyn31 [ Sun Nov 06, 2005 10:14 am ]
Post subject: 
I tried the 125 offset. That actually worked even better. Using 107, there was a 1-2 second delay before the audio kicked in. Using 125, the audio comes in instantly.
Author:  tjc [ Sun Nov 06, 2005 10:38 am ]
Post subject: 
Note that the 125 wasn't across the board, unless the MythTV frequency tables are screwed up. Who is your cable provider?

OK, I just went and checked the MythTV source code and the US-Cable frequency table is 125 below the IRC frequencies across the board, aside from channels 5 and 6 which are both 2125 below where the IRC chart says they should be. Think I'm going to go whip up a little chunk of SQL to fix this...
Author:  tjc [ Sun Nov 06, 2005 11:36 am ]
Post subject: 
OK, here is my hack for applying finetune settings to go from the US-Cable frequencies to the IRC standard ones used by Comcast in Eastern MA. Note that you should ONLY try this if you can answer YES to ALL of the following questions.

1) Do all of your video sources use the US-Cable frequency set? If not or you don't know DO NOT USE THIS CODE!
2) Do you get a picture on most of the cable channels? If not DO NOT USE THIS CODE!
3) Are channels 5 and 6 (but only those two!) fairly messed up? If not DO NOT USE THIS CODE! If the only two channels you CAN tune are 5 and 6 you have a different problem and should probably be using the US-Cable-HRC frequency set.
4) Are you experiencing other "slightly off" symptoms like flakey sound on some channels? If not DO NOT USE THIS CODE!
5) Are you running R5A22 or later? If not DO NOT USE THIS CODE! Note that the fine tune scale for the IVTV driver changed between the version used in R5A16 and R5A22. These values are only appropriate for the new drivers, and off by a factor of ~12 for the old ones.
6) Have you made a current backup of your database? If not DO NOT EVEN THINK ABOUT USING THIS CODE!

Code:
mysql -u root mythconverg <<EOF
update channel set finetune = 0;
update channel set finetune = 2000 where freqid in (5, 6);
update channel set finetune = finetune + 125;
commit;
EOF
Author:  gamelyn31 [ Wed Nov 09, 2005 11:38 pm ]
Post subject: 
Sorry tjc, I've been away from my computer lately.

For the record, Comcast is my cable provider. I'm in 60191 zip code, if it matters.
Author:  tjc [ Thu Nov 10, 2005 8:40 pm ]
Post subject: 
Sorry gamelyn31, that wasn't really intended for you. You've already made the change and had it work for you. Presumably you've tested all the channels too.

This was one of those postings that's more intended for posterity. The screaming warnings are in case posterity is a horse's posterior. ;-)

BTW - Were your channel 5 & 6 way out of whack?
Author:  ed3120 [ Sat Dec 31, 2005 3:41 pm ]
Post subject: 
I had the same problem with Comcast cable in NJ...most channel had picture and sound, but about 20 channels had picture with no sound.

I fixed it by adjusting the fine tuning for the channels with no sound via MythWeb. Most channels only required me to add a 1 to the fine tunning section. Some channels did not work with the 1 and required a 2. One channel required a 3. At this point all of my channels have working picture and sound, and none required more than a 3 in the fine tuning, so the picture isn't really effected.

I suggest everyone with this problem, try adjusting the fine tuning, starting at 1, and increase by 1 each time to get it to work.
Author:  tjc [ Sat Dec 31, 2005 6:02 pm ]
Post subject: 
This is strongly dependant on the version of MythTV and possibly the IVTV drivers. With the versions in R5A16 my offsets were also small. Between that and the versions used for R5A22 or R5A26 they changed the units and the bigger values now apply. I even mentioned that several posts back in this thread...
tjc wrote:
5) Are you running R5A22 or later? If not DO NOT USE THIS CODE! Note that the fine tune scale for the IVTV driver changed between the version used in R5A16 and R5A22. These values are only appropriate for the new drivers, and off by a factor of ~12 for the old ones.
Author:  ed3120 [ Tue Jan 03, 2006 9:26 am ]
Post subject: 
In case knowledge of this helps, I'm running R5A26.
Author:  tjc [ Tue Jan 03, 2006 7:42 pm ]
Post subject: 
So apparently the fine tuning step size change occured between the 0.18.1 version of MythTV as seen in KnoppMyth R5A16 and R5A26 and the 0.18.svn... as seen in R5A22.
Author:  jammad [ Sun Mar 26, 2006 7:15 am ]
Post subject: 
I was struggling with this same issue (Channel's 5 and 6) did not come in correctly, no sound black and white fuzzy picture. It definitely appeared to be a tuning issue. I saw this same behavior with clean installs of both R5A30.2 and R5B7 with a PVR 150. I also live in Eatern Massachusetts (Franklin) and have Comcast. The solution to my problem (after trying almost every possible combination of finetuning, and using the code in this article) was to switch from Cable Standard to Cable-IRC and re-scan for the channels. Hope that can help someone else.
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