What to Expect from Digital TV

There are three main differences you’ll see from digital TV:

  1. More Channels
  2. All or Nothing Reception
  3. Deeper Coverage

More Channels

While analog TV has channels such as 2, 5, 7, 9, digital TV has 2.1, 2.2, 2.3; 5.1, 5.2, 5.3; 7.1, 7.2, 7.3; and 9.1, 9.2, 9.3. Digital signaling can reliably pack more information (and distinguish the sub-channels) than analog signaling. As a result, instead of broadcasting just one stream, there can be 3 streams—essentially 3 independent channels running on the same frequency.

It should be noted that analog channels refer to specific frequencies. For example, channel 2 is the lowest frequency in the TV band (from 54 MHz to 60 MHz). However, the wise professionals deciding standards for ATSC (that’s the digital TV standard in the US) decided that it would confuse people if all their favorite stations switched numbers all of a sudden—especially while they were told they needed to buy a new converter box to receive TV that they’ve been watching for over 60 years. At the same time, digital TV is being phased in side-by-side with analog TV. So, they couldn’t just turn off the analog channels and give them to the digital channels.

So, they came up with a scheme to allow channel numbers to remain the same: basically, the channel number has been separated from the frequency it is transmitted on. So, for example, in the Chicago area, digital channel 7.1 is transmitted from 698 MHz to 704 MHz—the equivalent of analog channel 52. This confuses me, since I thought channel 52 went up for auction recently. If anyone cares knows the answer, post it in the comments. Your TV is smart enough to display channel 7.1 regardless of which frequency it’s listening to.

All or Nothing Reception

I don’t want to panic anyone, but digital TV will be all or nothing in terms of your ability to receive it.

In the analog days, when things were bad, you’d see a fuzzy or snowy picture, but you’d see something. This is because your TV simply received the signal over the air and put it on your screen. The electron gun just did whatever the antenna said to do—without interpretation.Watch Full Movie Online Streaming Online and Download

Now, your digital TV (or the digital converter box next to your analog TV) does a lot of interpreting. It makes millions of judgement calls a second, taking the signal it receives from your antenna and deciding if it’s a 1 or a 0. When things are good, the judgement is right close to 100% of the time and you get a perfect replica of what the station is broadcasting (with no degradation whatsoever).

However, when things are bad, the judgement calls that your TV (or converter box) makes get worse. Instead of putting a 0 out, it might put out a 1, and vice versa—flipping bits at random. If a large enough percentage of these 1’s and 0’s are flipped, the TV can’t make heads or tails of the signal (pun intended) and you basically get nothing.

The digital TV signal is compressed at the broadcaster in exactly the same way that your CD (which takes up 660 MB of space) can be squeezed down to 10 MP3’s (taking up around 30 MB of space) by removing artifacts that most can’t hear.  In fact, the term MP3 means MPEG layer 3. MPEG is the Motion Picture Experts Group, which defined the compression for video (including DVD’s and digital TV). Audio MP3’s merely inherited the benefit of their work. When your TV receives the signal, it needs to decompress it. If enough of the bits are wrong, the digital stream looks nothing like a compressed video to the MPEG decoder. So, the MPEG decoder gives up and shows nothing.

Deeper Coverage

This last expectation—deeper coverage—is merely my expectation. It is basically based on the idea that the analog TV that we receive now is approximately 60 years old. As a result, sophisticated processing techniques (digital signal processing being the most notable) weren’t available to the designers of the analog TV standard. However, we have gained 60 years of research. As a result, starting with a new standard means more advanced reception techniques built into the standard. Such things as forward error correction should make the signal more resilient for more people.

These advanced techniques are already built into the digital TV standard. There’s little much you or I can do along the lines of digital signal processing to improve your picture quality with digital TV. However, all the old analog techniques of boosting power and minimizing noise still apply. At home, you can still use these techniques so that you can fall into the All rather than the Nothing category. I’ll post my advice for maximizing your signal quality (if you live on the fringe) sometime soon.


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