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KSTR/49 goes High Def
- Thread starter JHBrandt
- Start date
It happened in December.
And in some markets, they invert the subchannels. Example: Sacramento, where the stations are transmitting from different locations. KUVS has Univision HD on 19-1 and TeleFutura SD on its sub (maps to 64-2), while KTFK is TeleFutura HD on 64-1 and Univision SD on its sub (19-2).
Why they're doing it in Dallas and Los Angeles though, I have no idea.
- Trip
And in some markets, they invert the subchannels. Example: Sacramento, where the stations are transmitting from different locations. KUVS has Univision HD on 19-1 and TeleFutura SD on its sub (maps to 64-2), while KTFK is TeleFutura HD on 64-1 and Univision SD on its sub (19-2).
Why they're doing it in Dallas and Los Angeles though, I have no idea.
- Trip
tripinva said:
They're inverted in Houston as well.
easttxtv said:
It's just an sd version of the main channel. Just like 39.
fredcantu said:
49.1 and 49.2 appear identical on my converter-box-equipped TVs, but I suppose it depends on which converter box you use and how you have it set. So maybe channels like 39.2 and 49.2 are there to take the guesswork out of converter box setup.
I can't tell the difference myself, but I've heard many videophiles complain about carrying HD and SD subchannels on the same RF carrier, because each SD subchannel reduces the bandwidth available to the HD channel, reducing its quality. To me, this is a worthwhile tradeoff if the SD subchannel provides unique content (like This TV) but if the SD is just a copy of the HD, do the videophiles have a point?
fredcantu said:
It's a relative thing, and depends on a number of variables.
A DTV station gets a fixed-width pipe. (19.2MBPS) The FCC allows them to split that pipe any way they want. All programs on a given transmitter are co-equal. (we call 49.2, 49.3., etc. "subchannels" but really they're co-equal with 49.1, from a technical standpoint)
If you run only one program, it gets all 19.2MBPS. (whether it needs it or not... we have one station here running a single 480i SD. They're transmitting a LOT of empty "null packets"!)
If you run more than one, then no one program gets the whole thing. The bandwidth you give to .2 has to be taken from .1; if you add .3 you have to take its bandwidth from .1 and/or .2.
You can't transmit uncompressed HD even in the full 19.2MBPS. The less bandwidth you give a HD program, the more heavily it must be compressed. Most people can't see the compression in a 1080i program in a full 19.2MBPS.
My station is running a 1080i and a 480i. During sports, when there's rapid movement in the 1080i program, if you know when to look & what to look for, you can just barely see compression artifacts. It's a lot more obvious in the 480i program, because we're giving it a bit less bandwidth than it really should have.
There's something called "statistical multiplexing". It allows the transmitter to dynamically allot the bandwidth. If someone's running downfield on .2 while .1 is showing a static weather map, the "statmux" can temporarily divert some bandwidth to .2. It's an extra-cost option though, so a lot of stations don't have it.
w9wi said:
I think I've seen this effect watching football on KXII (which is insanely compressed in order to fit two HD subchannels and one SD subchannel into RF channel 12). When there's lots of motion parts of the picture get rather "blocky" for a second or two.
Out of curiosity, do you know how much bandwidth a standard SD channel requires? Also, would I be correct to assume that news/weather channels (like KXAS/5.2 and WFAA/8.2) generally require less?
JHBrandt said:
That's exactly what I'd expect to see when they run out of bandwidth..
There's no one answer to that. It depends on how much motion there is -- and how much picture quality you're willing to give up. Trinity Broadcasting is running five SDs on their transmitters, and it all looks fine to me - then again, a lot of their channels are running preachers, which compress pretty well. (not much motion) (the cartoons on their .5 compress pretty well too, large areas of solid color)
Weather channels do tend to compress fairly well too - lots of time spent on static weather maps & towercam shots.
I know of one station in Milwaukee that's running eight SDs. Three of them are basically radio stations, the only video is a still describing the (classical|jazz) selection being aired. It changes every 2-3 minutes or so. There's a LPTV in San Jose that's running even more -- twelve, if I remember properly -- and none of them are stills. I have to assume it looks like crap but I suppose if the programming is unique, someone will watch it...
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