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A digital TV broadcast is a television signal distributed in digital format as opposed to the traditional analog format. What makes a digital TV broadcast different is the use of computer code to compress picture and sound information into bits that can be transmitted over the airwaves. Digital typically provides a cleaner, crisper image.
Digital signals are called "discrete;" that is, they are not continuous but occur in individual units. Despite being broken down this way, the transmission of each unit of information is consistent, or at least less subject to fluctuation. The compression of sound and picture into computer bits also means channels can carry a great deal more information. For instance, many local network affiliates have been able to broadcast several sub-channels, each with different programs.
Digital has a greater capacity than the traditional analog format. In fact, the Federal Communications Commission (FCC) and broadcasters often tout the vastly greater number of Standard Definition (SD) channels that the digital system can carry. In addition, digital can transmit High Definition (HD) programming, which would take up a great deal of space in the broadcast spectrum if sent through traditional analog signals.
In contrast to digital, analog signals are continuous electrical signals. This continuity allows the signal to travel farther but leaves it susceptible to "noise." "Noise," in this context, refers to any electrical or magnetic interference created by the environment or the devices that send and receive the analog signals.
One compelling reason for the digital TV broadcast switchover is the amount of space that is freed on the broadcast spectrum, leaving more channels open for police, fire and rescue officials. This changeover has also allowed the U.S. government to sell off newly freed space on the spectrum. There has been no shortage of buyers, particularly among telecommunications companies.
Digital TV broadcasting has not been perfect in its early stages. Physical obstacles such as hills, buildings, trees or even the positions of viewers in their living rooms have been known to interfere with digital signal reception.
The U.S. government originally planned to have all high-power stations abandon analog transmission and begin digital TV broadcasting only on 17 February 2009, but decided the American public did not have sufficient time to prepare for the change. Viewers with cable connections would be unaffected, but those who still used antennas would need converter boxes to allow their TV sets to display digital TV broadcasts.
The official conversion date was pushed back a few months. CBS affiliate WRAL in Raleigh, North Carolina became the first TV station in the United States to transmit a digital TV broadcast on 23 July 1996. Interestingly, Luxembourg was the first nation in the world to make a complete transition from analog to digital, with the switchover taking place on 1 September 2006.