Digital television

Digital television (DTV) uses digital modulation and compression to broadcast video, audio and data signals to television sets.
Introduction
A major use of DTV can be to carry more channels in the same amount of bandwidth. Another can be high-definition programming. The digital signal eliminates ordinary analog broadcasting artifacts such as "ghosting", "snow", and static noises in audio. It can restore them with new MPEG compression artifacts, such as "blocking", when transmitted at too low a data rate, and may fail to work wholly in situations where analog television would have formed an impaired but watchable picture. Depending on the sophistication and level of the error correction defined by the standard and chosen by the broadcaster, DTV may either work perfectly or not work at all.
The switch-over to DTV systems often coincides with a change in picture format from an aspect ratio of 4:3 to one of 16:9. This enables TV to get closer to the aspect ratio of movies and human vision. On traditional screens this leads to "letterbox" black bars above and below the picture due to placing the 16:9 picture in a 4:3 frame. The preceding aspect ratio of 4:3 was chosen to match the Academy standard ratio of the day.