What is sensible programming for ATSC sub-channels?

[roger1818]

They could alternate between radar and traffic every 5 or 10 seconds. If they timed the switch with a screen redraw frame it wouldn't take any more bandwidth than displaying only one or the other.

[99gecko]

Came across this from BroadcastEngineering and couldn't resist posting.

Texas station may be first to transmit two HD, one SD stream in single channel

Dec 5, 2006 8:00 AM

KXII TV, the Gray Television-owned station in Sherman, TX, has launched what may be the world's first live ATSC service with two HD channels and one SD channel in the allocated 19.4Mb/s spectrum.

The station is simultaneously broadcasting CBS in 1080i HD, Fox in 720p HD and MyNetwork, branded "MyTexoma," in 480i SD. The station is using Harmonic DiviCom MV 500 MPEG-2 HD encoders and MV 100 MPEG-2 SD encoders for its digital upgrade to deliver the three channels in its 6MHz spectrum allotment. Statistical multiplexing is being done with Harmonic’s DiviTrack, and the whole system is being managed by its NMX Digital Service Manager.

I guess seeing is believing. I would definitely tune this in if I ever get to Texas. Somehow I think the PQ would be pretty blocky.

[rob50312]

We have seen first hand with multifeeds on WNED and WIVB how just 2 sd sub channels can wreck the HD channel.Wivb is great now with no sub channels.

[Walter Dnes]

Originally Posted by rob50312

We have seen first hand with multifeeds on WNED and WIVB how just 2 sd sub channels can wreck the HD channel.Wivb is great now with no sub channels.

The problem with WNED isn't 2 SDTV channels, it's 2 EDTV sub channels. EDTV (852x480) has approximately 1/3rd more pixels than SDTV (640x480). So WNED is effectively carrying 2 and 2/3rds SDTV channels worth of video in the sub channels.

Actually, there is a much better way to do things. There's almost 2/3rd of a century of SDTV shows lying around. There are networks like RTN that show them, not to mention PBS. After the analog shutdown, 3 or 4 SDTV-resolution stations could share one DTV transmitter. It would be a lot less wasteful than using 6 mhz for one SDTV signal. On the economic side, splitting the cost of the transmitter 3 or 4 ways is economically attractive.

[roger1818]

Originally Posted by Walter Dnes

On the economic side, splitting the cost of the transmitter 3 or 4 ways is economically attractive.

Especially if after the the analog shutdown, one or two transmitters in every market were permitted to transition to shared SDTV transmitters. Much of the infrastructure would already be there and it would just be a matter of replacing the analog equipment with digital equipment.

[stampeder]

The argument I've heard against pooling several different or competing stations into one channel's sub-channels is the "all the eggs in one basket" problem, in which several different broadcasters have their signals going to just one transmitter/tower. Some stations would not be comfortable with that, because a set of technical problems could take them all down at once. Companies would have to weigh out the economic and technical benefits/risks.

[Walter Dnes]

Originally Posted by stampeder

The argument I've heard against pooling several different or competing stations into one channel's sub-channels is the "all the eggs in one basket" problem, in which several different broadcasters have their signals going to just one transmitter/tower. Some stations would not be comfortable with that, because a set of technical problems could take them all down at once.

I don't understand that argument. Why is the shared transmitter likely to be less reliable than one you own outright? Besides, if your station goes off the air, do you really care that your competitors go off too?

I'm reading between the lines here, so correct me if I'm wrong. Are you suggesting that the combined ownership will cheap out on maintenance versus a single-channel-owned transmitter? Think of the condominium model, applied to TV transmitters.

Besides, if I was Industry Canada or the FCC, I would look very unfavourably at the concept of wasting 3/4 of the capacity of a DTV channel to broadcast one SDTV-only signal. 4 SDTV "stations" teaming up to use one DTV channel would be more reasonable.

[stampeder]

Maybe some correspondence with stations would help you get answers to your questions, I'd be curious to see what they have to say on this topic. I don't speak for them - I just relayed an argument I'd heard in relation to shared sub-channel transmitters.

Rather than speak for them, I'm just going to say that in my opinion broadcasters need to be on the air to make money so if a technical glitch forces several competing stations off the air, the economic hit is that much wider than if only one competitor's station goes down.

Also, in times of emergency it would be best if stations were not all subject to technical problems at one site. If there is a chance that one or more of them can take to the air, that is preferable and logical to me.

[99gecko]

Multiple stations multicasting on the same frequency might make economic sense in terms of bandwidth efficiency. However, different stations multicasting on the same frequency would run into branding issues. What existing station would want to have to re-market themselves as Channel X.2 (or .3 or .4) of their competitors? Every unique SD station would want to be the highly visible .1 designation.

Where network stations are co-owned or otherwise aligned it might make sense. However, I can't think of any Canadian subsidiary station that should be a sub of a non-HD station. I don't like the idea of SD subs sharing a channel allotment with an existing HD channel.

Perhaps new stations might accept a .2 or .3 channel designation if they were given license allowances (monetary incentives?) from the CRTC.

[stampeder]

But PSIP remapping would allow existing channel brands to show up (i.e. 27.1 remaps to 8, 27.2 remaps to 3, 27.3 remaps to 10) so is that what you meant?

[roger1818]

But PSIP remapping would allow existing channel brands to show up (i.e. 27.1 remaps to 8, 27.2 remaps to 3, 27.3 remaps to 10)

Is it possible to map different sub channels to different channel numbers? I would have thought this would be done in the US where two analog channels share a digital channel if it was possible.

[stampeder]

Actually I'd better check the PSIP documentation to see if its just major numbers that can be remapped or whether the decimal numbers an be individually remapped too...

[stampeder]

Well, the PSIP documentation (A69/Annex B) says that in the U.S. all Digital OTA major numbers must correspond with the station's NTSC channel number. I interpret that to mean that an NTSC station on Channel 8 that is on Channel 36 digitally is not going to be able to assign 36.x sub-channels to other NTSC stations in the market. I'll keep reading to see if its any clearer.

[roger1818]

Originally Posted by stampeder

in the U.S. all Digital OTA major numbers must correspond with the station's NTSC channel number.

I susspect this rule was created with the assumption that all stations would revert to their NTSC channel number after the analog shutdown to ensure that no two channels in a given market would have the same virtual channel number. This rule has probably been changed to permit stations to now use the physical channel number that they will use after the analog shutdown (I think some stations have started to do this) and require them to use this number after the analog shutdown.

[99gecko]

Originally Posted by stampeder
so is that what you meant

Sorry, as roger1818 suggested no. You are correct in pointing out that I erronously made an assumption that subs could only remap to the same channel designation as the major channel. Although that might actually be the case, it was an assumption, and should be considered that until we dig up the goods on atsc.org. I made it considering all the confusion in 2006 summer with the realignment of the Buffalo networks and the transmission site changing hands. I can't remember for sure, by I think WNLO was subbing on WNYO, or did I mess that up too ?
Regardless, the likelyhood of this is apparently nil in the US because of:

Originally Posted by stampeder
...in the U.S. all Digital OTA major numbers must correspond with the station's NTSC channel number.

These are rules created for the US. Would Canada carbon copy the US policy?

Originally Posted by roger1818
I susspect this rule was created with the assumption that all stations would revert to their NTSC channel number after the analog shutdown to ensure that no two channels in a given market would have the same virtual channel number....

WUTV-DT (FOX) applied to revert to 29 after analog shutdown and was denied - they must stay on 14.

With respect to the content of my post:

Every unique SD station would want to be the highly visible .1 designation.

I was basing that on if subs cannot remap to a different major number. The Samsung T-451 tuner for example goes directly to the .1 sub if you enter a channel number directly entering using the number buttons, as opposed to surfing up/down to it. You cannot enter the subchannel designation.
for example:

If I'm on channel 5, and press [4] [3] [enter], it will take me to 43.1, even though 43.2 and 43.3 are valid. In fact to get to 43.3 directly, I would have to enter [4] [3] [enter], and then surf to 43.3 through 43.2.

To me, that means 43.1 gets a higher hit count.
confused yet?... I know I am