In the future, how many sub-channels could be put into one 6-mhz space?

[Frank-0-Video]

Greetings ...

At present, it seems (in my own experience, anyway) that one 6-mhz digital channel can hold at least 4 sub-channels, one offerring HDTV, the other three SDTV.

Looking to the future, will improvements in digital compression technology allow for more sub-channels to be included within the same 6-mhz space? If yes, what do you think will be the potential number of HDTV and SDTV sub-channels occupying the same 6-mhz space?

Keep answers simple and give examples, such as -- 2 HDTV & 4 SDTV -OR- 3 HDTV & 1 SDTV

Thanx-A-Lot, Frank-0-Video

[guns1inger]

The broadcasters will always attempt to fit more into the available space by over compressing and reducing quality to the end user

[MOVIEGEEK]

There is no limit to subchannels but the broadcasters in the US are limited to 2.38Mbps,none of the channels have to be HD.I have one broadcaster in my area that transmits four SD channels and the compression artifacts are very noticable.

[gadgetguy]

My local PBS station broadcasts 1 HD, 2 SD, and 1 that's just a still picture. I have no idea how the bandwidth is allocated, but I assume the still picture doesn't take much.

[SLK001]

I've seen as many as 5 subchannels from one broadcaster - all video.

[filmboss80]

If no one watches the subchannels, the stations won't be devoting too much of their operating budgets toward them. Most stations devote one subchannel to live weather radar, which is useful to viewers and cheap to the stations. Some also loop reruns of local news and community affairs programs on a subchannel. A station in my area also devotes a subchannel to Spanish language programming. So far, I've not seen anyone go beyond three subchannels, so it is kind of impressive to hear that one station is doing five in SLK001's area.

[SLK001]

In case anyone is interested, the call letters are:
WHFTDT Chan 45.1
WHFTDT2 Chan 45.2
WHFTDT3 Chan 45.3
WHFTDT4 Chan 45.4
WHFTDT5 Chan 45.5
broadcasting from the Miami - Ft. Lauderdale transmitter farm in Hollywood, FL. It is a religious station, so I only skim through the channels on my way "somewhere else"! I don't know if any channels are being broadcast in HD (I doubt it).

I also have two additional stations that broadcast 4 separate channels.

All these channels are great! Now if they would only put something on them worth watching!

[Frank-0-Video]

Greetings ...

Here is a page on sub-channels from Wikipedia. Scroll down and you will find a chart showing various sub-channel scenarios.

I took particular interest in these two scenarios ...

»» 0 HDTV & 4 SDTV (480p or 480i)
»» 0 HDTV & 5 SDTV (480p or 480i)

... as well as this ...

»» 0 TV of any kind & 120 mono radio sub-channels (does this imply that you can alternatively have 60 stereo radio channels?)

Some articles I've read seem to suggest that 480p "progressive" resolution (as opposed to 480i - interlaced) is adequate enough for digital TV channel viewing, and that resolutions of 720p may be unnecessary icing on the cake.

If all this is indeed so, I have concluded (hindsight, of course) that perhaps the "Big Plan" should have been to start off digital OTA TV with four 480p sub-channels. Next, over time slowly develop the proper technologies that would allow for either (A) additional 480p sub-channels -OR- (B) to allow one or more of the four 480p sub-channels to have at least 720p resolution without compromising the quality of the other sub-channels.

Thanx-A-Lot, Frank-0-Video

[edDV]

The major network stations seem to be mostly running one 1080i plus one 480i (usually weather). KGO-DT (ABC O&O) is running 720p plus two 480i.

The ION network stations out here run four 480i SD subchannels. KTEH-DT (PBS San Jose) runs five 480i subs. KHSL-DT in Chico,CA runs CBS network in 1080i and CW network in 480i on the same channel. Major PBS channels (KQED and KVIE) seem to be running the main channel 720p with two 480i subs.

Looking to the future, will improvements in digital compression technology allow for more sub-channels to be included within the same 6-mhz space? If yes, what do you think will be the potential number of HDTV and SDTV sub-channels occupying the same 6-mhz space?

MPeg2 is fairly mature. Also for ATSC, the minimal target tuner needs to be generation 5 and 6 chipsets because of installed base. Future TV tuners may improve quality but not necessarily be used for higher compression.

Current FCC policy says MPeg2 (18 permitted formats) is only required for the primary channel. At a minimum this would be one 2.38Mb/s primary 480i MPeg2 leaving 17Mb/s for any kind of data. Some stations use this data for h.264 or VC-1 encrypted movie distribution to hotels/motels for example. The hotel rooms use proprietary STB tuners.

At some point there may be an ATSC II supported by home tuners where subchannels use an agreed advanced codec. The primary would remain MPeg2. This would allow many more SD or HD subchannels. Home users would need a new tuner to receive these advanced ASTC II subchannels.

[Frank-0-Video]

Greetings ....

At some point there may be an ATSC II supported by home tuners where subchannels use an agreed advanced codec. The primary would remain MPeg2. This would allow many more SD or HD subchannels. Home users would need a new tuner to receive these advanced ASTC II subchannels.

"A new tuner" would mean a new TV set if not a new set-top box. In this era of plug-and-play, current ATSC/QAM-tuning Televisions and DVD recorders don't have an upgrade slot (as far as I know) which would accomodate such future improvements. A slot such as that would save consumers the cost of having to purchase a new set and/or recorder.

Thanx-A-Lot, Frank-0-Video

[edDV]

Greetings ....

At some point there may be an ATSC II supported by home tuners where subchannels use an agreed advanced codec. The primary would remain MPeg2. This would allow many more SD or HD subchannels. Home users would need a new tuner to receive these advanced ASTC II subchannels.

"A new tuner" would mean a new TV set if not a new set-top box. In this era of plug-and-play, current ATSC/QAM-tuning Televisions and DVD recorders don't have an upgrade slot (as far as I know) which would accomodate such future improvements. A slot such as that would save consumers the cost of having to purchase a new set and/or recorder.

Thanx-A-Lot, Frank-0-Video

I agree. I'd like to see a standardized tuner slot for HDTV. You could plug in an ATSC, QAM(cablecard) or Sat tuner module and upgrade over time. The way it is now most tuners will be external.

PS: Lets add tuner slots in media servers as well. The Microsoft vision for home networking is a centralized home server with attached cable card tuners that can be distributed as needed to all TV's and computers in the house including PDA/Phones.

[Frank-0-Video]

Greetings ....

There is no limit to subchannels but the broadcasters in the US are limited to 2.38Mbps,none of the channels have to be HD.I have one broadcaster in my area that transmits four SD channels and the compression artifacts are very noticable.

If I correctly interperet what MovieGeek says about 2.38Mbps, as well as what this »» Sub-Channel Scenario Chart says, are we talking about 6, 7 or even 8 480i-type sub-channels in one 6-mhz space under current standards??

Thanx-A-Lot, Frank-0-Video

[edDV]

704x480i 2.38Mb/s MPeg2 would be very low quality but legal. Works out to 8 subs including the primary.

Typical SD averages 3 to 5 Mb/s

[usually_quiet]

In addition to the HD primaries (some 720p and some 1080i), 5 of my locals have SD sub-channels. PBS and NBC each have 2 SD subchannels, in addition to the HD primary, ABC, MyNetwork, and Fox have one SD subchannel in addition to the primary,

Sadly, all the SD sub-channels are so starved for bitrate, that their crystal-clear picture looks worse than SLP mode on my VCR. I'm not sure if that is really progress.