The Dual HD Subchannel thread

Aaron62

Contributor
Staff member
#1
Do any of you have a station with dual HD subchannels in your local market? How is the picture quality between the two subchannels?

I'm in LA, and I just found out today (thanks to Trip's page here RabbitEars.Info) that KABC broadcasts two 720p signals plus a 480i. I mostly watch DirecTV for local channels so this new discovery has me a bit intrigued.

Throughout the week I'll be checking to see the quality of picture broadcasted on both KABC subchannels. :drinks:
 

Eureka

DTVUSA Member
#4
On a decently size screen, it looks like crap.

Between stubbornly clinging to VHF wherever possible and cramming too much data into too little bandwidth, ABC is trying hard to kill the quality of OTA DTV.
 

Trip

Moderator, , , Webmaster of: Rabbit Ears
Staff member
#5
(thanks to Trip's page
Beware that some of my bandwidth numbers on that page are outdated. Some of them date back to before the launch of LiveWell HD.

Basically, if the LiveWell stream is lower than about 3.5 Mbps, it's probably outdated.

- Trip
 

Aaron62

Contributor
Staff member
#6
Someone needs to update this part of the wiki for "Digital Subchannels".

Tradeoffs
As the amount of data which can be carried on one digital television channel at one time is finite, the addition of multiple channels of programming as digital subchannels comes at the expense of having less available space for other purposes, such as high-definition television. A station carrying multiple subchannels will normally limit itself to one high-definition channel, with the additional channels being carried in standard definition. Because of the tradeoffs, stations owned by CBS Corporation that are a part of CBS Television Stations (which include CBS O&O's, CW O&O's, and some independent stations) are not permitted to have digital subchannels.

It is, however, possible for stations to carry two subchannel feeds in HD, though it is still extremely rare. Currently, at least three stations broadcast in this format:

KXII, the CBS affiliate in Sherman, Texas, airs Fox programming in HD on its third subchannel in addition to airing its main CBS programming in HD. The station also has a myNetworkTV affiliate in SD on subchannel 12.2.
WKBN-TV, the CBS affiliate in Youngstown, Ohio which also owns & operates low-powered Fox affiliate WYFX-LP & simulcasting sister station WFXI-CA of nearby Mercer, Pennsylvania, simulcasts WYFX/WFXI on its second digital subchannel while broadcasting its main CBS feed on its first subchannel. Both subchannels are broadcasting in 720p HD, a reduction from CBS's preferred 1080i transmissions although Fox has a preference for 720p.
WPVI-TV, the ABC O&O in Philadelphia, simulcasts two channels in 720p HD, and a third weather channel in 480i standard definition. WPVI is also one of the few stations broadcasting digital television in the VHF spectrum (channels 2 to 6) below the FM radio band.
 

CptlA

DTVUSA Member
#7
On a decently size screen, it looks like crap.

Between stubbornly clinging to VHF wherever possible and cramming too much data into too little bandwidth, ABC is trying hard to kill the quality of OTA DTV.
That's what I've always said, yet people argue with me all of the time in other forums about how they can't tell the difference between 720p and 1080i. On my dad's 55" DLP Sony, it's definitely noticeable. I remember watching a few football games on ESPN a few years back on that TV and thinking "This is HD lite" with the 720p.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#8
That's backwards. 1080i takes more bandwidth.

========

I have a PBS that is 720p using 9.88 mbps. This is close to half and to me on a 32 inch 720p screen doesn't look that bad, but I am not that picky.

That is false. 1080(interlaced) requires a 540 line draw every cycle.....720(progressive) requires a 720 line draw every cycle (more information = more bandwidth)

720p is better for lots of fast motion, 1080i has better resolution on static or slow moving images.
 
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Piggie

Super Moderator
#9
Once you get into Picture Quality it becomes a subjective discussion, although technical specifications can be directly applied. What a person considers good enough is different. It's also based on money. To buy a 52 inch TV I would need not to eat for 3 months (probably do me good). It's also a matter is content king or picture quality?

Even though you can apply technical standards to picture quality this still falls in he realm of religious and political discussions.


On a decently size screen, it looks like crap.
Speaking to the "religious nature" of PQ, I could take this offensive that I can't afford a decent size screen, but I am not. I bought a 32 in over 2 years ago for $400, or I probably would not have had an LCD so soon.


That's what I've always said, yet people argue with me all of the time in other forums about how they can't tell the difference between 720p and 1080i. On my dad's 55" DLP Sony, it's definitely noticeable. I remember watching a few football games on ESPN a few years back on that TV and thinking "This is HD lite" with the 720p.
I won't argue, there is not point in that, it's much better to discuss.

I am sure on a larger screen with higher resolution the difference can be seen.

=======

In all cases watching any HD source, you really need to know the mbps as well as the resolution.

This can lead to then is content king or picture quality? This also goes directly into my opinion that is not shared by everyone.

Take a 1080i OTA signal. It needs at least 15.5 mbps to not break up during fast fades, wipes or motion across the entire screen (like a field of wheat in the wind or waves on the ocean). This only leave about 2.5 for an SD channel. If it's more than just a weather or news feed then the SD look bad.

720p takes in the 14.5 mbps range to look good. This leaves enough room for a moderately good looking SD feed, actually acceptable in most cases for SD.

---

What I have noticed looking at various channels on my lesser LCD TV, 1080i when you rob it of bandwidth pixelates. Where 720p seems to get blurry.

---

As TV's get cheaper those that want higher resolution will have to look away from OTA. OTA will be in a bind in a few years as more cable companies and satellite companies demand more and more stations feed them more bandwidth, that is less compressed than they transmit OTA.

Then losing 23 channels for people that want more cell phones and FloTV, there isn't enough room to put even all the networks we have now one signal per channel.

Then if ATSC-M/H takes off, that will cram a 1080i station with a single channel tight also squeezing in three streams (one program) of M/H signal as well.

OTA is in a jam to those that demand high picture quality, period. Even those that choose to run one program will lack the advertising revenue from a sub-channel. Those that run a sub-channel will loss viewers to cable and satellite where they have more bandwidth than OTA.

--------

Personally I think the future for OTA to survive is to give up the picture quality battle. Go with the concept that content is king.

Most of it's viewers for the last 20 years or more have been those that can't afford cable. Once the initial "fad" wears off it will go back to them mostly watching OTA. They also don't have the money for a great TV and again nor cable, etc. Hence to them more programming choices will most likely trump picture quality in the end. This assumes all those with large higher resolution sets have gone back to cable and satellite, as those service have less bandwidth restrictions and can and have transitioned to MPEG4.

---------

If in the future, someone comes out with a MPEG12 (made that up) that is backward compatible to MPEG2, yet allows 2 to 4 time more compression without loss of PQ, OTA is stuck with the limitation given it by the FCC.
 

Piggie

Super Moderator
#10
That is false. 1080(interlaced) requires a 540 line draw every cycle.....720(progressive) requires a 720 line draw every cycle (more information = more bandwidth)
.
The key word here is cycle. Two ways to look at this.

1080i has 30 frames/sec so yes it does have 540 lines to draw per cycle (field, not frame).
But since there are 2 fields to frame, that means a each field is transmitted 60/sec.
Hence in 1080i, in 1/60 second 540 lines are transmitted,
or 32,400 lines per second.

Since 720p, has no fields or you could say a field in 720p is equal to a frame, and it's frames are transmitted 60/sec, just like an individual field in 1080i.
Hence in 720p, in 1/60 second 720 lines are transmitted,
or 43,200 lines per second.
----------

But really this is only the lines and not the pixels.

1080i is 1920×1080 pixels on the screen displayed 30 time per second,
for a total of 62,208,000 pixels transmitted every second.

720p is 1280×720 pixels on the screen displayed 60 times per second,
for a total of 55,296,000 pixels transmitted every second.

This is also how it's displayed in a CRT. LCD's do things different since they don't have the persistence of a CRT. So they have to store in memory two fields from 1080i to form a frame, then covert it to 720 lines. But since we were talking about transmitted bandwidth this is a non sequitur aside.

---------

Hence, there is more data in OTA 1080i than 720p, thus requiring more bandwidth.

The old frame vs field has been a source of misunderstanding in TV for decades.
 

EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#11
Scratches head.

Yeah, youre right, I was confussled there for a minute.

540x1920 > 720x1280

But 720p is better for fast action.
 
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EscapeVelocity

Moderator, , Webmaster of EV's Antenna Blog
#12
I was checking with my knowledge base in CRT projector land, and there are units which have the bandwidth for 1080i but not 720p.

Which brings me back to my confussled state.
 

Piggie

Super Moderator
#13
I was checking with my knowledge base in CRT projector land, and there are units which have the bandwidth for 1080i but not 720p.

Which brings me back to my confussled state.
The OP was curious about OTA so I answered in relationship to OTA.

Maybe because they can't display 720 lines at the same time but can display 540? If that were true it would explain it.

I have a CRT TV that is wide screen and not HD. The tube while 16:9 only supports 480 lines max. If you put a DVD player that outputs 720p even into the component inputs it can't sync.
 

dave73

DTVUSA Member
#14
I know this thread is over 2 years old, but have to comment on it. In the Chicago market, there are 2 stations that run dual HD. ABC O&O WLS-TV (along with all other ABC O&O) run the main channel & Livewell Network in 720p HD, & have an SD subchannel (used to be Accuweather, but now a simulcast of Livewell Network in SD for cable systems that won't convert the picture themselves). The other station is WYIN (PBS) Gary, IN. WYIN runs 56.1 & 56.2 in 720p HD, while 56.3 & 56.4 are widescreen SD. The only channel right now WYIN programs different is 56.3, & is usually childrens programming from the PBS Kids Go library (24 hours), but occasionally air programming from the Indiana Channel on that channel (if they have Indiana Channel programming on, it's usually on Saturdays). 56.2 & 56.4 are still simulcasting the main channel after going HD in late 2009. The station itself broadcasts in 720p HD, but local programs are still not HD yet. WYIN hasn't decided what to put on the other channels, but they want those channels to also generate revenue. Supposedly, World from PBS is a free service, & wonder why they haven't taken advantage of that, since WTTW & WYCC have both taken a pass on it (Chicago being only top 5 market not carrying World)
 
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