On 4/15/05, Phil Buescher <[EMAIL PROTECTED]> wrote: > Yeah, I was guessing the poor quality just caused larger recordings, > and decided to focus a long detailed search last night to find out > what would cause these quality problems. > Near as I can tell, the lines are almost always due to either over the > air ingress or simple RF/EM interference. > > Plugging in a small TV set directly into the coax outside of my cable > box, the channels are nearly crystal clear, but even at the shortest > run of cable inside the house, the channels begin to flake out. And > at the furthestmost cable run (where my MythTV box is) the channels > are much worse. > > So it's looking like the cable runs are not as clean as I had hoped. > I had pulled the cable through myself, and it must run alongside some > power lines behind the walls somewhere. I guess I need to re-route my > coax and try running it another way. Maybe I'll run a temporary cable > outside of the house and in through a window just to see if that > clears it up or not. And if so, I'll at least know that's the > problem. > > Still, I would think if it was just EM/RF interference, an RF filter > would have some effect! Ah well. > > If that doesn't solve it, then the only suggestion I found was to call > the cable company and get an installer to come out, and if they can't > fix it, insist that the problem be escalated, so that a special line > testing technician will look into it for > leakage/ingress/egress/interference - and all that other good jazz. > > Thanks for your input - I'll certainly post whatever works for me, > although it sounds like these diagonal lines can be cause by many > things, all having to do with the simple fact that something is in the > signal that shouldn't be there. > At least now I know I can focus on quality issues instead of wondering > what else might be causing it. > > Phil > > On 4/14/05, Joe Votour <[EMAIL PROTECTED]> wrote: > > Phil, > > > > It's because of the cable noise and its effect on the > > recording codec (in your case, RTJPEG, since you're > > using a software encoder). > > > > In order to save space on the hard disk, MythTV (in > > software) will compress the video and audio, since > > storing every frame in full detail would be enormous. > > Therefore, you'd start off with a full-frame image, > > and then you'd probably store the changes to that > > image for a period of time, and then another full > > image (this is basically how MPEG-2 works, although > > it's a bit more complicated than that - I imagine that > > RTJPEG uses something similar). > > > > The noise screws up the deltas - since the noise > > causes picture distortion, you end up with more > > changes between frames, thus increasing the filesize. > > > > The only way to fix this is to fix your cable signal, > > which may or may not be possible. I'm in a similar > > situation, and Comcast won't touch it, nor will my > > landlord (as they don't want to be digging up the > > ground or going through the walls to figure out where > > the problem is). > > > > -- Joe > > > > --- Phil Buescher <[EMAIL PROTECTED]> wrote: > > > I've been running Myth for a couple years now. I'm > > > just running it > > > with a software based encoder Happauge WinTV-Radio. > > > > > > I moved to a new town just recently, and a different > > > cable company, of > > > course - I have Comcast now. > > > Anyway, onto the problem... > > > > > > Certain channels come in pretty fuzzy, with bad > > > quality, showing > > > diagonal lines on the screen. Most channels come in > > > just fine and > > > look great. These channels come in all fuzzy on a > > > normal TV as well. > > > > > > Here's the big problem though - on those channels > > > with the poor > > > quality, the recording sizes are abnormally HUGE! > > > We're talking about 3-4 times larger than the > > > recordings should be. > > > For instance, a normal hour-long show will take up > > > 0.74 gigs, but the > > > ones on the flaky channels will take up anywhere > > > from 2.5 to 3.5 gigs! > > > It's really crazy! > > > > > > I didn't change anything besides my tvlisting feeds > > > on my MythTV box, > > > so I know it isn't something I did. I didn't change > > > my recording > > > format, I didn't change my setup, and this is > > > certainly a per-channel > > > problem. Only two channels I know of have this poor > > > quality and HUGE > > > recordings problem. > > > > > > I did get basic cable, nothing digital, no satellite > > > or anything goofy > > > - just the basic standard cable package with no need > > > for a set top > > > box. > > > > > > Could this be that these channels are actually HDTV, > > > and that's why > > > they're taking up so much room and come in all fuzzy > > > on tuners that > > > aren't HDTV-ready? Or can it just be that channels > > > with this poor > > > quality problem simply take up a ton more room to > > > record? I have DSL, > > > but could I be receiving some interferance that has > > > to do with cable > > > Internet? I don't know - I'm totally guessing > > > because I have no clue > > > anymore. > > > > > > I really need some help, as the two channels we > > > record the most shows > > > off (shows that are on while we're at work), are the > > > ones that have > > > this problem - and even with over 300 gigs of HD > > > space, I'm running > > > out rather fast. > > > > > > I really don't want to have to re-transcode/mencode > > > the shows after > > > recording them, since that's a pain - any idea what > > > the problem is? > > > The cable installer thought the poor quality was due > > > to bad wiring, > > > but between him and I, we replaced every single run > > > of cable in and > > > outside of the house with high-quality wiring and > > > ends. The installer > > > even replaced the cable running from the > > > neighborhood box that runs to > > > our house. We never did figure out why these > > > channels come in fuzzy. > > > He left, proclaiming the problem fixed - and it > > > wasn't fixed, he just > > > checked one of the channels that come in just fine. > > > I even bought an > > > expensive coax tester, and all the runs are totally > > > clean. > > > > > > I tried putting a signal booster in front of my > > > MythTV box, but that > > > had no effect. I also tried an RF filter, to no > > > effect. I'm totally > > > stumped and frustrated. > > > > > > Please help - any suggestions or insights are > > > appreciated. > > > _______________________________________________ > > > mythtv-users mailing list > > > [email protected] > > > > > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users > > > > > > > __________________________________ > > Do you Yahoo!? > > Yahoo! Small Business - Try our new resources site! > > http://smallbusiness.yahoo.com/resources/ > > > _______________________________________________ > mythtv-users mailing list > [email protected] > http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users >
Are you using the correct type of coax cable? RG6, 75 ohms. If a short run shows a noticeable signal degradation I would guess an impedance mismatch between the cables. -- Tim www.magicitx.com _______________________________________________ mythtv-users mailing list [email protected] http://mythtv.org/cgi-bin/mailman/listinfo/mythtv-users
