Monday, May 2, 2011

Revenge of the Rabbit Ears – The Digital Transition

The broadcast spectrum changes – and so does the picture on your TV screen.

Up until now, you could take that old black-and-white TV out of the attic, plug it in and sure enough you could watch a show or two. Why? Well, television broadcast technology hadn’t changed much since the advent of colour TV. Even then it was based on the same standards and resolutions as the early heydays. Sure the vacuum tubes were gone, clunky dials were replaced with remote controls and flat screens appeared … but the underlying tuner technology just didn’t fit in with the digital age.

Cue the digital transition. Across the world, governing bodies and TV technological consortiums planned the new standards for terrestrial digital broadcast (fancy term for “not the analog broadcasting we used when TVs still came as wooden floor models”). The result: the biggest change in television history. Out goes the old analog (NTSC) tuner, in comes the new digital (ATSC) tuner.

As I mentioned in my last post, think of an old vinyl record being compared to a CD. With a record, every scratch, fleck of dust and jump of the needle resulted in the famous hisses and pops, while a CD provides clear, crisp sound even with a few scuffs here and there on the surface. That’s sort of how analog and digital TV stack up against each other. The old analog tuner had no choice but to follow the incoming signal line for line, much like the needle going along the groove of the record. Any disturbance, reflection or interference resulted in the static, snow and ghosting that plagued antenna-based TV. With the new DTV signal, the analog waves are gone and replaced with a digital data stream beaming from the tower to your TV. So much extra picture information is contained in the broadcast that the digital tuner is able to process even the most contaminated signals to display the images cleaned and refined. (Look up “forward error correction” on Wikipedia if you’re interested in how the signal gets “fixed”) In the end what does this mean? Goodbye fuzzy pictures, hello crisp 1080i HD image… all from an antenna.

Same TV, same antenna, two different worlds. Check out the difference between the analog (top) and digital (bottom) signal. Now you can watch Don Cherry in glorious 1080i and Dolby 5.1 (don’t say we didn’t warn you).

To see the difference in action, simply do a YouTube search of “NTSC vs ATSC” and watch various examples of how your TV can almost miraculously pull HD TV off the airwaves where there was only static and snow before. My favorite video is this one that does a split screen side-by-side comparison of the analog signal vs the digital signal, you can access it here:

Here are some other key things you should know about digital broadcast TV:

Believe it or not, it’s still free!

The biggest advantage with OTA DTV is that besides the initial cost of equipment (which for some people may already be zero) it’s free to watch. Try asking your cable or satellite company about switching from analog to digital and you know the drill – you’ll have to buy all new receivers and of course sign up for the HD package and pay the wonderful HD fees that come with it. So with OTA, you can’t beat that deal.

DTV does not necessarily have to be only HDTV

DTV does not necessarily mean HD. Sure DTV can deliver uncompressed 1080i signals that are crisper than satellite and cable, but the DTV requirement is only that stations broadcast digitally (For USA: June 13th, 2009 and for Canada :August 31st, 2011). This means that in certain cases your TV set will still benefit from the “clean” digital signals but the resolution may be 1080, 720 or even 480.

DTV is the base of HDTV. While all 3 mean digital TV, the 2 top logos are to identify equipment that is ready for terrestrial DTV broadcasts. HDTV refers exclusively to the highest quality of DTV possible.

So why is this important? Well, if your TV has the DTV logo on its casing or in its user manual, that means you’re ready to go for digital OTA right out of the box. In this case, your TV is your receiver - just slap on an antenna and no additional cost is required.

Digital means binary: 1 or 0. Just like your image will either be on or off, but not in between.

With digital signals there are no more “snowy, but watchable” channels – either you get crystal clear reception ... or nothing. Most new TVs and OTA receivers will have a built in signal strength meter to help you point your antenna and maximize DTV signal reception. Obviously, you want the signal as strong as possible as it means you are getting a clear, strong stream of digital data from the transmitter tower and the tuner is doing minimal corrections.

Ready, aim and fire - unlike the analog days, new TVs have built-in signal meters to help point your antenna and maximize DTV signal reception.

As the strength decreases and more errors are introduced, the tuner is working harder; it is replacing missing bits of info needed to build the picture. Once your reception drops down to 10-20% the sound may start to degrade and you will begin to see freezing or “marcoblocking” - large coloured squares that will make the hockey game look more like a Picasso painting. Marcoblocking is what happens when there are large chunks of contaminated data in the signal and the tuner does not have enough info to clean the image. Any signal degradation beyond this and you’ll have no picture at all.

The various stages of DTV reception: Perfect picture (top) until the signals drops to about 10-20%, at which point your TV will go neo-cubist on you and macroblocking occurs (middle). At this point as well the audio will start to sound like a T-Pain song. Anything below this and you'll get the “signal screen of death” (bottom) … which I guess is still better than the old blast of black and white static of the analog days.

Virtual channels – and you thought imaginary numbers didn’t exist

While it would be great to think that the government and TV manufacturers pushed all these upgrades because they wanted to give the consumers a better television experience, fact is that wasn’t the only reason for the shift. Here's a bit of background info so bear with me:

The FCC and other governing bodies that assign and allocate the bandwidth for aerial transmission is using the digital transition to move some things around in the broadcast spectrum. One goal is to make room to sell the airwaves for more wireless products and emergency communication and to make more efficient digital use of the suddenly crowded broadcast frequencies. Like an old industrial building being knocked down to put up new condos, the FCC has taken a wrecking ball to the low VHF bands. As part of the digital transition, all VHF-Low stations are required to vacate and broadcast on a different frequency. That means no more channels 2 through 6, the new digital stations have to be either VHF-Hi (7-13) or UHF (14-69).

What this resulted in was a shuffling of the broadcast spectrum. However, because the relocated stations didn’t want to spring for new letterhead, if desired they were allowed to broadcast on one frequency but the TV would “re-map” them to the old channel number, now called the “virtual channel” number. For example, good old Channel 3 from northern Vermont shows as channel 3.1 on the TV … but is actually broadcasting on UHF channel 22.

This relocation and remapping may not really matter on the TV remote, but the shuffle can mean that certain channels may be broadcasting on new frequencies that may be easier (or harder) to receive in your area. A station you could not get in the analog days may suddenly come in at the new frequency, but also vice versa.

Sub-channels – and no, I don’t mean a channel dedicated to Philly steak sandwiches

One advantage with digital signals is that the data transmissions are more efficient than analog. As a result, for the same bandwidth DTV stations can broadcast more channels: a primary and multiple “sub-channels”. Sub-channels are represented by the number that comes after the decimal place or hyphen in the DTV channel number. For example 4.2 or 4-2 is the second sub-channel on channel 4 (which may not actually be channel 4 as per above… confusing, eh?) This means two things: first, you’re getting more channels than the analog days if the stations around you are using their sub-channels. (By the way: these sub-channels, since they are not real channels, will not show up for cable or satellite subscribers, another OTA advantage.) Second, your remote now has a cool hyphen so that you can dial in 4 – 2 for channel 4.2

No, it’s not to do math – it’s to cruise sub-channels.

The number of sub-channels per station is dependent on the image quality. Usually only the primary channel is broadcast in 1080 or 720 while the sub-channels will be in standard 480 definition, or audio only. The less the resolution of the channels, the more channels can be crammed into the digital signal. Most stations will stop at about 1 to 3 subchannels as a result, but there are exceptions.

One example of sub-channel use is WANN-TV in Atlanta, which currently has a whopping 15 sub-channels and still room to spare under its primary channel (which ironically is just a program guide for all its sub-channels). Screenshot and more info courtesy of

Guide and program info – just like the big boys have

DTV signals are full of so much data that not only is there enough info crammed in there to correct all the blips and errors as mentioned above, but there is also enough to provide program info. Most TVs will interpret this as on-screen info and as a built-in channel guide or list.

No more flipping through the pages of TV Weekly - the DTV on-screen info and guide is right at your fingertips. How much is this costing me again? Oh yeah, nothing.

So that’s your digital transition background info. I’ll be going into the various DTV tuners, receivers, antennas and what to do if your TV is an old clunker in the coming weeks. If you can’t wait, feel free to browse the following DTV sites for more info:

The American version that guided viewers through the US transition in 2009 contains tons of excellent info presented in a simple format:

And here is the poorer, Canadian version of that website from Heritage Canada in case anyone is interested… *sigh*

Next episode: Can an OTA Setup be right for you?