My experiences with ATSC HDTV

[dr.ido]

Originally Posted by MRX37

Ah yes. I have come across this as well. The program may be in 16x9, but the commercials are 4x3. Sometimes my screen is surrounded by a black border on all sides of the video.

That is one glitch they need to work out.

That is annoying. I had thought that perhaps a TV tuner card would allow for greater flexibility in the this respect as the decoding is done in software. If even they suffer from aspect ratio glitches then it does suggest that the stations themselves are hard encoding content in the (sometimes wrong) aspect ratio.

It may be a side effect of the source video being reencoded several times at points in the distribution chain. I have seen a similar effect when a video file is converted from one format to another on a PC prior to burning to DVD.

I guess I'll just stick to analog and SD digital for now, it's not like I watch that much broadcast TV anyway.

[colortrakker]

That's "postage stamping." It's a problem for the industry to work out...has nothing to do with your gear. It's a side effect of transmitting a letterboxed 4:3 signal in a 16:9 ratio. SMPTE has a study group working on this one.

One other weird side effect I notice sometimes, kinda the opposite of this, is that there are spots done in 16:9 that get smushed back to 4:3 so everything looks painfully narrow. When spots like this air at work they tell me that's how they're delivered to us. So apparently there are some post houses that also need skoolin' on this stuff.

[old_tv_nut]

Originally Posted by colortrakker

That's "postage stamping." It's a problem for the industry to work out...has nothing to do with your gear. It's a side effect of transmitting a letterboxed 4:3 signal in a 16:9 ratio. SMPTE has a study group working on this one.

Actually, it has been worked out and the means to transmit it was just recently standardized as "active format description". However, it will take a while for everyone to get it into their encoders, and for all the receiver manufacturers to get it into the receivers; and some video streams that are in the can may never be corrected. If a station follows good practices, the problem should not appear in the main program even on older digital receivers, but will still pop up occasionally on commercials, etc.

[MRX37]

Some shows are taking advantage of the extra sides on a 16x9 screen, and poke fun at the 4x3 format. On Wheel of Fortune, I saw a sign in the corner of the screen that said "HD zone ahead" or something like that. This sign is not visible on the 4x3 aspect ratio to my knowledge.

I built a better antenna, and now I'm getting all our local channels in HD. 2,4,7,38,50, 56, and 62. No canadian stations yet...

The digital channel numbers are something like 2.1, 7.1 and 56.1, but according to the physical channel number, Channel 2 is actually channel 58, channel 4 is channel 45, and channel 50 is channel 14. Most of the other channels are close to their analog couinterparts, in channel number anyway...

[andy]

The whle aspect ration thing is a real disaster. Leaving it up to the viewer was a big mistake. It should have been made fully automatic right from the start of 16:9 sets. Almost every wide screen TV I see is set wrong. Most people don't notice when it's wrong and don't understand how to set it up correctly. My mom was surprised when I told her that everyone isn't supposed to look fat on a wide screen TV!

[wa2ise]

You can query the FCC database to find out what TV signals are licensed to be seen in your town http://www.fcc.gov/mb/audio/tvq.html
If you live in the middle of nowhere, you can enter latitude and longitute.

It will tell what channels the digital channels are really on.

[MRX37]

Originally Posted by wa2ise

You can query the FCC database to find out what TV signals are licensed to be seen in your town http://www.fcc.gov/mb/audio/tvq.html
If you live in the middle of nowhere, you can enter latitude and longitute.

It will tell what channels the digital channels are really on.

That helps quite a bit.

You wouldn't happen to know the Canadian equivelant, would ya?

[ChrisW6ATV]

Originally Posted by MRX37

Some shows are taking advantage of the extra sides on a 16x9 screen, and poke fun at the 4x3 format. On Wheel of Fortune, I saw a sign in the corner of the screen that said "HD zone ahead" or something like that. This sign is not visible on the 4x3 aspect ratio to my knowledge.

This is what I am looking forward to, more TV directors actually composing for the 16:9 screens. Probably not a single HD show today does that, since the majority of viewers are still using 4:3 displays. There are, or have been, a few shows (such as Conan O'Brien's show) that letterbox their SD broadcasts and therefore may take advantage of the 16:9 format.

Football games in HD are starting to make use of the wide screen; it is nice to see both wide receivers/cornerbacks and the offensive and defensive lines on screen all at once, while still being able to read the numbers on all the visible players' uniforms.

[MRX37]

An update: I have been looking for Canadian digital TV stations, and have been puzzling as to why I can't find any. I now know why. Apparently stations such as CBET in Windsor aren't broadcasting in digital yet. Canada's analog cutoff isn't until 2011, so I guess that's a reason for me to keep my Analog system going after 2009.

[Duane]

Originally Posted by andy

The whle aspect ration thing is a real disaster. Leaving it up to the viewer was a big mistake. It should have been made fully automatic right from the start of 16:9 sets. Almost every wide screen TV I see is set wrong. Most people don't notice when it's wrong and don't understand how to set it up correctly. My mom was surprised when I told her that everyone isn't supposed to look fat on a wide screen TV!

Even tho' my set has options for different screen sizes on 1 16x9 screen, non of them can really do a 4x3 image very well,for all non HD sources.For HD,it locks to the "full" mode and that cannot be changed.This is what I use exclusively now with digital cable.

But,just like the old saying for NTSC, the images that are displayed on the HD channels are so inconsistant,it really makes you wonder what the engineers are smoking.On some channels,all that's being done is blowing up a 4x3 image to fill a 1.78:1 screen.Not true HD by any stretch..they're just passing it as such.Very little true HD programing on the HD channels..it seems to be mostly SD.At least I know what to expect on the 4x3 channels. So,it's not just the viewers who haven't a clue.

[MRX37]

It's snowing here right now, so I thought it'd be a good idea to go through and check signal strengths. Even on my weakest channel, the video plays without hiccups. Here's a screenshot:


Just as a note, I don't like Springer. I just watched him long enough to see if the video would pixelate or drop out. It didn't, though apparently there were a few correctable errors in the video stream.

On another note: My antenna is still only about 6 feet off the ground, and is currently not pointing in the best direction, as I have been trying to pick up other digital stations. I therefore conclude that at least for local channels, OTA reception should not be too much of an issue regardless of weather. Rain and snow don't seem to have a great affect on the local channels.

[MRX37]

One small update to add:

I have been further testing the cutoff point for signal strength. One of the major issues with HDTV being how well will people be able to receive OTA reception, I've been testing to see just how weak a signal can be before it cuts off.

I initally said a signal strength of 50% was as low as you could go before the video began to cut out, then I revised it to 70%. Based on more extensive tests, I am re revising the cutoff point to about 65% strength.

My updated signal strength meter (as seen in the screenshot in my above post) is more accurate then the one I was using when I started my tests. It has a range from 0 to 30 (Dunno why it's not 0 to 100, but whatever...) I have had smooth video with a signal as low as 18.7, BUT since signal strength fluctuates, a strength of 20, IE: ~65% seems to be as low as my tuner can accept without dropping the video at some point.

For my tuner anyway: if the signal strength is above 65% during a rainstorm or snowstorm, I can be very confident that I won't lose the signal.

If I get ahold of a better antenna and start bringing in distant stations, I'll examine how reliable they are and post my findings.

[wa2ise]

Reception of HDTV is driven by a combination of factors. Signal to noise, ghosting and interference are major ones. A windy day can make for rapidly changing ghost conditions, and the ghost cancelling system in the receiver might not be able to keep up. The transmitter tower bouncing around in the wind, trees swaying and so on. Movement can be a substantial fraction of the carrier wavelength up in the UHF TV band.

[MRX37]

Originally Posted by wa2ise

A windy day can make for rapidly changing ghost conditions, and the ghost cancelling system in the receiver might not be able to keep up.

I just confirmed that today...

Yes, I finally found something that affects the digital signal: Winds of 25MPH or more...

I had to point my antenna directly at the transmitter of the channel I was watching to eliminate the dropping out.

I hope this problem is solved when the stations go all digiotal and hopefully increase their output power...

[peverett]

I have seen the same issue in high winds. However, I am not sure the power increase will fix this. What is happening is that the digital locking circuit(probably some sort of PLL) is losing lock temporarily(and dropping data) due to the incoming wave varying. The variance is due to the distance from the transmitter to the receiver changing as the transmission tower moves in the wind. This is a basic problem with all broadcast digital transmissions.

At least for older analog TVs this is not an major issue, as their is no PLL in the tuner. However, there are effects in the analog picture such as varying levels of snow, ghosting, etc. in windy condtions also. In some cases, the analog TV is still viewable (with snow, etc). while the digital has frozen.

There are error correction circuits available for digital systems that can fix some of this. Of course, the transmitted signal must have enough error correction built in(this takes extra digital bandwidth) and the receiver must have the ability to use this error correction.