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Getting to an All-Digital World Saves on Slurping

One of the more magnetic topics circulating around the industry in recent weeks is the "all-digital transition."

The enormity of the topic is what, in part, makes it so captivating. This one is gargantuan.

Even the technologically elite take a deliberate, thought-collecting pause before discussing what it would take for cable to shake off its analog mantle, and make it digital. Then they qualify the answer with something like "I'm not certain we know all the questions yet." (As in, "let alone the answers.")

'No analog'

"All digital" essentially means "no analog." It necessarily begins with "less analog," and then "lesser analog," until one finally (maybe) arrives at "no analog." That's why the term "all-digital" is synonymous with "analog spectrum recapture," which also tends to pop up in conversations about the topic.

Understanding the recapture of analog spectrum for digital purposes starts with knowing the traditional bookends of cable's "shelf space."

Most modern cable systems contain 750 Megahertz of architecturally reuseable shelf space. About 5% of it, located between 5 and 40 MHz, is reserved for upstream traffic — the click of the remote to order an interactive service, or the mouse click to retrieve a Web page.

About one quarter of cable's available spectrum, located between 550 and 750 MHz, goes to digital downstream services, like digital video, video-on-demand, the broadband Internet and telephony.

The rest — roughly two-thirds of a system's available spectrum, between 54 and 550 MHz — is used by analog downstream services: basic cable.

What fits in 6 MHz

Before digital, of course, 95% of a 750 MHz system's bandwidth was slurped up by analog services. "Slurping" refers to the greediness of analog, relative to digital.

Think of it this way: If somebody magically put one analog channel in the palm of your hand, you'd be holding a clump of spectrum that is 6 MHz wide.

You could choose to populate your 6 MHz with the following things: An analog TV picture and its sound; 10 digital video pictures and their sound; two or three HDTV channels and their sound; 500 or so broadband Internet connections; or around 500 telephone lines.

So, the thinking goes, why not move the digital downstream boundary further into the analog realm, and be more spectrally efficient?

Most of the "why not" has to do with the stuff we already have in our houses. Americans collectively own something like 200 million analog television sets, and 100 million analog VCRs.

Put another way — if America's cable system serves 65 million households, and those homes each contain two TVs and a VCR, that's 195 million dark screens, if cable were to flip an imaginary switch and go all-digital right now.

Box prices

Getting those 300 million analog TVs and VCRs to display a digital picture and sound, just like they've always done with analog pictures and sound, means something has to be there to convert the signal back to analog.

Either that, or we all have to haul our analog stuff to the recycling center and replace it with its digital equivalent sometime before the imaginary "all-digital" switch flips.


Enter the digital-to-analog converter, sometimes referred to as "the $35 special" or "the $50 box that isn't a box." Pricing on this gadget obviously varies widely, depending on who's wishing.

Regardless, people interested in the gizmo agree on three things. One, it has to be small: Pager-sized or littler. Two, it has to be cheap: Hundreds of millions of them will be needed. Three, it has to let analog TVs and VCRs work exactly the way we all know them to work.

Pace Micro Technologies plc was the first to publicly display a digital-to-analog gizmo, at the recent National Show in Chicago. Others will invariably follow.

Less analog?

But a D-to-A converter gizmo is only one part of the to-do list. Lots of things change when there's no more analog. Pretty much anything that moves over a cable system — whether service or maintenance, upstream or down — needs a thorough accounting, to assure that it still works in an all-digital environment.

What doesn't change, blessedly, is the miles of fiber optic and coaxial cables that line the poles and underground conduits of the nation. That's good, because it's the most expensive part.

It's important to note that in the MSO community, not everyone is convinced that all-digital is really necessary. Less analog might be just fine, the thinking goes.

Either way you look at it, an all-digital transition is a chewy, mind-expanding journey. This one is going to go on for a while.