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Digital TV Basics

DTV stands for digital television, and by June 12, 2009, it will be the only television signal on the airwaves. Although the switch to all-digital TV marks an important shift in the way television is created and transmitted, it doesn't have to be a great change from the way you currently watch TV. Here's what you need to know about the switch from analog to digital television.

Analog vs. digital signals

The difference between an analog and a digital television signal is the way in which the information is encoded:

  • Analog signal: Since the first television broadcasts hit the airwaves in the late 1920s, television shows have been sent through the air using an analog signal. An analog signal theoretically has an infinite number of variations, which means that it can (theoretically) transmit an infinite number of subtle variations. If you think of a slide whistle (an analog instrument), as you pull in the slide, the pitch goes up. If you pull the slide in very slowly, the pitch rises smoothly, and you don't hear definite changes from one pitch to the next. Those infinitely smooth gradations of pitch mirror the smooth gradations in an analog television signal.
  • Digital signal: A digital signal stores information in the form of a gazillion 1s and 0s. Because each variation in the signal must be represented by 1s and 0s, the number of variations is finite, so a digital signal doesn't have the infinite variability that an analog signal has. To return to the slide whistle example, if you slowly pull in the slide and record it with a digital recorder, the pitch will not rise as smoothly. The pitch will "jump" from one tone to the next, leaving microscopic gaps between any two tones. If the recording is of any decent quality, though, the human ear won't be sensitive enough to hear those tiny jumps, and the recording will sound like a smooth rise in pitch.

Although it may sound like an analog signal is better than a digital signal (and in theory, this is true), analog signals suffer from degradation in a way that digital signals do not. In TV-land, that analog signal degradation comes through as television "snow." You won't get snow from a DTV signal.

Is DTV the same as HDTV?

No — DTV isn't the same as HDTV. DTV stands for "digital television." HDTV (high-definition television) is a specific DTV quality standard, but definitely not the only one. Here are the three most popular DTV quality standards, in order of quality:

  • SDTV — Standard Definition Television: SDTV is the most basic quality level for television display and resolution for both analog and digital signals. TV stations already transmit their shows as SDTV-quality analog signals. In fact, many channels have already started transmitting digital SDTV signals alongside their standard analog signals. But many of these analog signals have already gone away, and the great majority of them will be off the air by June 12, 2009.
  • EDTV — Enhanced Definition Television: EDTV was a short-lived enhanced format that has a higher resolution than SDTV, but isn't as clear as HDTV. Early adopters of enhanced television quality may have EDTV-quality sets, but you don't see them sold much anymore.
  • HDTV — High-Definition Television: This is the highest quality digital signal out there — at least for now. An HDTV signal not only carries enhanced video, but also digitally enhanced sound, so you can get theater-like surround sound from over-the-air HDTV signals. Although HDTV broadcasts are becoming more common (especially for sporting events), most DTV broadcasts will not be high definition, at least for the foreseeable future.

You won't need to get rid of your older analog TV when the time comes to switch to a digital signal; you'll just need to get a set-top box that converts (SDTV and HDTV) digital signals to (SDTV) analog signals that your TV set can understand. If you have a cable or satellite connection, your signal provider should take care of all of that for you, and you won't need a converter box.

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