HD picture not quite right on certain channels

[Radium99]

I have Comcast cable and all the channels look fine when I view them directly on my Toshiba LCD TV. But I have problems on two channels when I watch them with my TivoHD:

On NBC (channel 105) there is a bright yellow vertical line running down the entire left side of the TV.

On CBS (channel 107) the picture is shifted down about 1 centimeter and there is a thin 1 pixel line at the top left of the screen. The line goes about 10% of the way across the screen.

All the other HD channels (at least the ones I watch) work fine on the Tivo. I rarely watch SD, but some of those seem to have the overscan problem with a fuzzy line at the top of the screen that I read about elsewhere on the forum (this doesn't matter too much to me).

Does anyone know what would cause the problem with the HD channels? It seems to be related to Tivo because the channels look fine without the Tivo. I use the 1080i output setting, but I tried other settings and it didn't help. I did a search on the forum but couldn't find anyone describing this problem. Any help would be great because it is kind of annoying to watch the channels when they're not perfect.

[ThAbtO]

When you press the aspect button, what does it show? panel, zoom, full? Pressing aspect again will cycle these settings.

[gastrof]

How exactly to you have things connected? You said you've viewed the cable box output both thru the TiVo and on the TV. Did you disconnect the TiVo from the pathway when doing this, or is the TiVo connected to the cable box at the same time as the TV is (using different outputs)?

I also notice you say you use 1080. Does that setting affect the output feeding the TiVo? It shouldn't...

Give us as many details you can about how you've got everything connected, and what settings you're using on everything.

[DeathRider]

Are you using a different input on each?

I know on my Sony LCD, each input as it's own settings.

IIRC, my friend's Toshiba, it's Natural setting to control overscan.

[Radium99]

Thanks for the responses. I did some testing over the weekend, here is more information:

Connections:
I'm not using a cable box. I have a Cablecard installed in the Tivo. I take the Comcast cable from the wall and plug it into a splitter that splits the signal into two cables. One cable goes directly to the TV. The other cable goes to the TivoHD. I thought that the splitter might be causing problems so I removed it and plugged the wall cable directly into the Tivo, but that didn't help, the picture is exactly as it is when using the splitter.

From the Tivo I have an HDMI cable going to the HDMI input on my TV. I have video output on the Tivo set to "1080i Fixed". I tried 720 Fixed but that didn't help. I tried 480 Fixed and that actually fixed the problem, except that this isn't a solution because I lose the HD quality.

I tried changing the Aspect setting as suggested by ThAbtO. That setting didn't seem to have any affect. The Tivo help was kind of unclear on what this setting actually does. If I'm watching 16x9 content on a 16x9 screen then this setting should have no affect right?

The TV that I have is "Toshiba REGZA 52HL167". It is a 52" LCD that accepts a 1080i signal. I am using the HDMI input for the Tivo. I don't see any obvious settings to fix overscan or anything like that.

When I view the channel on the TV I tune it to channel 7.1. When I view the channel on the Tivo I set it to 107. I'm assuming that this is the same channel and it just has to do with the way that the Tivo maps the channel.

The problem occurs on the Tivo on both recorded shows on the problem channel and when viewing the channel live via the Tivo. So it seems that for some reason the Tivo has a problem with the cable input on these two channels for some reason. The other channels work perfectly and the Tivo menus display perfectly so it doesn't seem to be a problem with the Tivo connection to the TV.

Any ideas would be really helpful here because I haven't seen anyone else describe this problem and I'm not sure if it is a problem with the Tivo or with Comcast.

[ThAbtO]

Don't forget that the tv has aspect setting of its own. You said you tune the tv to channel 7.1 (most likely that is OTA), and tivo to 107 (QAM?), both should be on the exact same channel to compare.

The tv may also have a different aspect setting for each source (tuner, hdmi,video, etc)

You can tune the tivo to 7.1 by pressing the ->| for the decimal.

[Radium99]

Is there a FAQ or something to describe how HD channels work? The Tivo has CBS HD on channel 107, but when viewing directly with the TV it shows up as 7-1. If I try to tune 7-1 on the Tivo like ThAbtO suggests nothing shows up on the screen. Also if I try to tune channel 107 on the TV I just get static. Because of this I just assumed that they were the same actual channel but were somehow remapped to different numbers by the different devices.

I don't have an external antenna hooked up so I assumed everything on the TV was coming from the cable. Tomorrow I can disconnect the cable from the TV to be doubly sure I'm not getting anything from the air.

[a68oliver]

Is there a FAQ or something to describe how HD channels work? The Tivo has CBS HD on channel 107, but when viewing directly with the TV it shows up as 7-1. If I try to tune 7-1 on the Tivo like ThAbtO suggests nothing shows up on the screen. Also if I try to tune channel 107 on the TV I just get static. Because of this I just assumed that they were the same actual channel but were somehow remapped to different numbers by the different devices.

I don't have an external antenna hooked up so I assumed everything on the TV was coming from the cable. Tomorrow I can disconnect the cable from the TV to be doubly sure I'm not getting anything from the air.

The channel numbers tuned by the Tivo and the channel numbers tuned by the TV may not match, even though both are coming over cable. Since you have a cablecard the Tivo downloads a channel map that gives the Tivo the same channel numbers that you would get if you used a cablebox. You should be able to check this by comparing the numbers to a channel list published by the cable company. Since these are local HD channels they are probably unencrypted QAM. Also, because you have a channel map, you can't enter numbers like 7-1 since they are not in the channel map.

However, the channel that you tune directly with the TV is also unencrypted QAM but since you have no cablecard in the TV, it doesn't have the same channel map. Instead, the TV get's it's channel number from PSIP info embeded in the signal. This is a virtual channel number usually provided by the broadcaster (and sometimes provided by the cable company) that matches their analog channel assignment plus a sub-channel designation. For instance, your CBS station is probably broadcasting on analog channel 7. Their digital HD staion may actually be something like 28. However, to not confuse the public, this channel 28 is rarely displayed. Instead, they broadcast a virtual channel identifier that matches their analog channel such as 7.1. If they broadcast a sub-channel of news or weather, it is usually 7.2.

Both your Tivo and TV are probably tuned to the same unecrypted QAM channel. I hope this helps you understand why they don't display the same channel number.

However, this still doesn't explain why the tuner in the TV doesn't show the offending lines in the picture and the Tivo does. All analog TVs overscanned the picture which put the edges of the TV signal off the edge of the picture tube where you couldn't see it. Some digital TVs don't. It sounds to me like your TV tuner slightly overscans the picture (throwing the offending lines off the edge of the screen) and your HDMI input does not.

I suspect that the annoying lines are present in the signal being broadcast by the station and has nothing to do with the Tivo or Comcast. The HDMI input on the TV is slightly underscanning the signal and the tuner input is overscanning the signal.

Sorry to ramble so much.

[[NG]Owner]

You might consider running Component cables to the tv from the Tivo. Maybe its an HDMI issue.

[NG]Owner

[a68oliver]

I see that the REGZA 52HL167 has 3 HDMI inputs. Have you tried all three?

[Playloud]

I have Comcast cable and all the channels look fine when I view them directly on my Toshiba LCD TV. But I have problems on two channels when I watch them with my TivoHD:

On NBC (channel 105) there is a bright yellow vertical line running down the entire left side of the TV.


I have noticed this on my TivoHD/Sharp Aquos 32" LCD via HDMI (haven't tried component) when watching any NBC HD signal. It only happens when I have the TV on dot by dot mode (zero overscan). The workaround is to allow a slight overscan, although I prefer non-overscan picture (just because I am stubborn, not because of any quality difference). I would imagine it is NBC's fault, and would hope they find a way to fix that.

[Radium99]

Thanks a68oliver for the detailed descriptions of how the channels work. It makes a lot more sense now.

I have figured out that the problem is due to overscanning. I was always looking in the TV menus for something with the word "overscan" in the name but couldn't find one. It turns out there is a setting for Natural and Native. I had it set on Native. Once I set it to Natural the picture is zoomed in slightly and the problem goes away. The TV tuner apparently defaults to Natural, but HDMI defaults to Native. Thanks for the help everyone.

I'm just wondering why overscan is still a problem. With a digital signal and a digital TV wouldn't the TV know exactly where each pixel should go on the screen? My computer monitors don't have an overscan problem.

[a68oliver]

I have figured out that the problem is due to overscanning.

A point of clarification. You have overscan and underscanned confused/reversed. Normal televisions overscan the picture, that is the picture is magnified and actualy scans off and over the edge of the picture tube. In underscan, the entire video signal is shrunk so that all of it appears on the picture tube. It looks like today's window box broadcasts, not to be confused with letter box or pillar box. Professional video monitors usually have a button that allows underscanning so that the video engineer can see every bit of the signal they are transmitting.