The greatest differences between digital and analog lines lie in the quality of the signal received and the volume of traffic that can be sent. Differences are basically the same for digital subscriber lines (DSL) into the home, television cable and high density cables running between cities connecting telephone switching offices. In all cases, the digital line outperforms the analog line to such a degree that soon there may be no analog lines left.
The Digital Difference
Basic Differences
An analog line is like a speaker cable, carrying audio information in a sine wave. The wave varies in frequency and amplitude to drive your speaker, which is simply a motor moving a piece of paper, to move the air exactly as did the voice or musical instrument that created the sound in the first place. A digital signal sends a code made up of "1's" and "0's," that only describes the signal as it was originally created. The receiving end decodes the "1's"and "0's" and creates a new signal equivalent to what was originally coded.
Example
If a singer performs into a microphone and the signal is amplified and sent across town on a wire before being amplified again through a speaker, that final sound could be highly distorted by the losses in the wire and the noise picked up along the way from AC power lines and radio interference. But if the signal were sent to the other end using a code, to be read by a second performer at the opposite end, the sound would be created anew and be much clearer. Thus is the ideology of digital technology. It is not sending the pure information susceptible to distortion. It sends codes, and as long as they can be recognized out of the noise, it recreates the signal anew
Subscriber Lines
Telephone subscriber wires that once carried only phone calls and fax signals into your home can now carry internet traffic and can support a hub in your home to operate several computers at the same time. All of this is due to digital technology. Literally billions (gigabytes) of "1's" and "0's" can be sent, received and distributed over the same lines that would have had a difficult time carrying two telephone conversations at the same time. The reason: far more digits can be sent and identified than waves.
Television Cable
The same technology also works for television cables. Your digital cable will not only carry far more channels, you will never see "snow" on your digital signal. "Snow" represents distortion or noise. But since code digits recreate your picture, no digit will create "snow." So even if your digital signal gets weak over a long distance of cable, it will still recreate a perfectly clear picture, down to the point where the signal is so weak that the picture breaks up and disappears.
Industrial Lines
Telephone lines between cities have the same noise, volume and quality improvements as subscriber lines and television cables, with the added advantage of being able to go farther distances. Repeaters can pick up weak signals at the end of a cable section and recreate them to be sent anew, whereas analog cables could only pick up the signal as it was received, noise and all, and amplify the whole mess. On an analog cable, after so many amplifications, the signal could be so distorted that it would be unusable.
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