Digital Cable

People are confused about digital cable. If it's digital, isn't that the same as digital TV? Well...no.

We discussed the current analog television system in a prior post. It has been around in the US seemingly forever. It is based on the NTSC standard (just the standard we use on this side of the world, as opposed to the many varieties of PAL, used in Europe and elsewhere) and has lately become also known as "standard definition television" or SDTV. This all worked pretty well except for reception issues of course, so the cable companies aimed to fix that problem. In a typical cable system, you can simply plug the cable into the back of most TV's produced in the last 15 years and see all the channels the tuner will allow. The NTSC tuner is capable of viewing analog channels 02-125. The fact that it's so simple is the reason cable has become widely available throughout the US.

But we always want more, don't we? With the demand for more channels, bandwidth problems began to crop up. The answer to this was "compression", taking a native analog video signal and squeezing it a bit to fit into a smaller slot on the cable. It still works by just plugging it into your TV, but of course, it has led over time to lower picture quality. And yet the demand for more channels still grows. So what next?

The obvious answer is to digitize the signals. As we learned earlier, digital signals are much more efficient than analog, but he downside is that they require a new kind of tuner...one that will digitally tune the new channels added by this new signal structure. This gave the cable companies the opportunity to provide us with a new billable item - the set-top box (STB). For a small additional charge, we are not just limited to the first 125 channels (most cable services only broadcast about 80, anyway), but now you can see channels all the way up to the 900's! Lots of great new services here too, like Video On Demand (VOD), which allows you to see almost whatever you want almost whenever you want to see it.

Today these STB's are actually hybrid devices. They still tune the first 80 or so channels in NTSC analog, then switch to QAM, the digital cable standard, for the remainder. But remember that we started out talking about picture quality? The signals passed on digital cable are for the most part still standard definition (480i, for those who read the previous post). Turns out that there is a somewhat better quality picture in the digital cable world, but in our view it is marginal compared to what's coming next. What it's all about is really money - profits for the cable companies for the extra equipment and services they can provide with this digital format. Don't get me wrong - this is not bad news. We're capitalists here and are happy to see reasonable compensation for good services. But, you just need to know that the economic model is what will ultimately dictate the services you are able to receive.

With the advent of DTV, the cable companies are scrambling to add local digital stations and even the high definition capability. This will require transmitting the newer standard 480p, 720p, 1080i etc. signals, something QAM was designed to do, but this takes lots more bandwidth. People want the great HDTV picture, and the cable companies have to provide it to survive, so just like the situation in off-air broadcasting, they are petitioning to be allowed to stop passing analog signals. This will give them back lots of bandwidth to cover the new digital and HD channels. This will happen eventually, just like on the off-air side, and cable companies will be able to sell us all set top boxes because we will no longer be able to just plug into the cable and get the channels we are used to seeing.

Once again, however, technology has come to the rescue in the form of a a new device - built-in digital cable tuner which can be put into televisions, DVD players or just set-top boxes. Many TV's now coming to the market have all three standards built in: NTSC, ATSC and QAM. What this means is that you can provide an antenna and/or cable signal to the set and once again receive what is available either free, in the case of off-air, or unscrambled in the case of CATV, just like we are used to from the old analog days.