May 22, 2017

On digital TV and natural disasters

As I’m writing this, the eye of Hurricane Ike is roughly ten hours from landfall.  The weather here, maybe 60 miles inland, is overcast with mild wind.  Meanwhile, the storm surge has already knocked out power for ten thousand homes along the coast, claims the TV news, humming along in the background as I write this, which brings me to a thought.

Next year, analog TV gets turned off, and it’s digital or nothing.  Well, what happens in bad weather?  Analog TV degrades somewhat, but is still watchable.  Digital TV works great until it starts getting uncorrectable errors.  There’s a brief period where you see block reconstruction errors and, with even a mild additional amount of error, it’s just unwatchable garbage.  According to AntennaWeb, most of the terrestrial broadcast towers are maybe ten miles from my house, but that’s ten miles closer to the coast.  However, I get TV from Comcast, my local cable TV provider.  As I’ve watched the HD feed today, it’s been spotty.  Good for a while, unwatchable for a while.  The analog feed, which we also get on a different channel, has been spot on the whole time.

From this, it would appear that Comcast is getting its feed out of the air, and thus has all the same sorts of weather effects that I would have if I bothered to put my own antenna on the roof.  Next year, when the next hurricane is bearing down on the coast, and digital TV is the only TV around, it’s an interesting question whether I’ll get something useful on my TV during a disaster.  Dear Comcast, Engineering Department: please get a hard line between you and each of the local major TV stations.  Better yet, get two of them, each, and make sure they don’t share any telephone poles.

[Sidebar: In my old house, I used DirecTV plus a terrestrial antenna for HD locals, run through a DirecTV-branded HD TiVo.  Now, I’m getting everything from Comcast, over telephone poles, into a (series 3) TiVo-HD.  In any meaningful disaster, the telephone poles are likely to go down, taking out my TV source material. I get power and telephone from the same poles, so to some extent, they make a single point of failure, and thus no meaningful benefit from putting up my own antenna.

Once the storm gets closer, I’ll be moving the UPS from my computer to our, umm, shelter-in-place location.  I don’t expect I’d want to waste precious UPS battery power running my power-hungry television set.  Instead, I’ve got an AM/FM portable radio that runs on two AA’s.  Hopefully, the amount of useful information on the radio will be better than the man-on-the-street TV newscasters, interviewing fools standing along the ocean, watching the pretty waves breaking.  Hint: you can’t “ride through” a storm when the water is ten feet over your head.]


  1. I really don’t like digital TV signals at all, even when they are coming in full quality. Sometimes I feel like I must be the only person who is really bothered by MPEG compression artifacts. Try watching the final episode of a competition reality show, when they drop bright confetti after announcing the winner. All that high-contrast motion gobbles up the available kbps until it the picture looks like an old 1995-era RealPlayer stream.

    Hope you stay high and dry!

  2. “Radio”

  3. @Mike: Your not alone. I too find digital artifacts much more distracting than analogue ones. That the FSM that my laserdisc player still works.

  4. A friend of mine has spent a lot of time debugging Codecs. He is now so “tuned in” to the digital defects that he finds digital TV unwatchable.

  5. @Adrian:
    There are 2 major reasons digital artifacts are so distressing.

    One thing the compression is particularly bad at is a simple fade up from black. So — 15 frames into a new show and your experience has already been ruined.

    And stations are greedy; they think all that extra market share (and/or ad revenue) they think they’ll get by adding yet another stream, so they divide and subdivide until all their channels are nigh onto unwatchable.

  6. Worse than blocking or edge artefacts are motion artefacts — pumping and wobbling of parts of the image relative to others, i.e. the “M” in “MPEG”. Motion prediction/encoding are sensitive to compression too.

  7. On a more general note, there is a fundamental tradeoff between “efficiency” and “robustness” — in most cases the latter comes from some sort of redundancy (assuming a reasonably efficient technology). In the case of analog vs. digital TV/phone, it’s to an approximation effective bandwidth utilization vs. signal-to-noise ratio. I get my current TV+Internet (low-res but supposedly HDTV capable AT&T Uverse) over the phone line (from a terminal on the street that gets it from fiber optic cable).

    Problems with phone service are similar — costs are down, but acoustic quality is way down too. Garden-variety international service sounds like crap, with echo or artefacts reminiscent of early cellphone technology — too much compression trying to jam more and more traffic into fixed capacity “physical” lines.

  8. How about a relevant comment?

    During the current, transitional period, digital channels are broadcast at lower-than-ultimately-intended power, and on different-than-ultimately-intended frequencies. This is because the analogue channels need to remain on the air for the time being, and they need to do so with minimal interference. Post transition, the power levels will be raised, and a number of channels will move frequencies to the more advantageous positions currently enjoyed by their analogue counterparts. As such, digital reception should improve.

    MPEG annoyances aren’t really relevant to this discussion, but perhaps the critics should compare OTA to cable and satellite. I think such a comparison will favour OTA, and maybe enough to kill this round of the “digital sucks; analogue is God” argument before it metastasizes into the full-blown cancer it is and was in the audiophile arena ever since the CD first appeared. I am certain that, as it has done with audio, equipment improvements will remedy the problem.

  9. Thomas Nast says:

    There is little reason to rely on television for emergency services. A portable AM/FM Walkman costs about $20, uses one AA battery which lasts months, and will pick up analog stations far out of range of any TV. Your implicit assumption that TV services are indispensable needs reexamination.