Twelve standard quality forms of the digital television standard adopted for the United States featuring AC-3 digital surround sound, wide (16:9) and “square” (4:3) aspect ratios, and high-quality (though not high definition) digital video capable of interlaced and progressive scan images with 480 horizontal lines (vertical resolution) by 704 vertical lines (horizontal resolution) at 24, 30 and 60 Hz refresh rates and video capable of interlaced and progressive scan images with 480 horizontal lines by 640 vertical lines at 24, 30 and 60 Hz refresh rates. he 704 by 480 resolution format uses a 16-by-9 widescreen aspect ratio. The 640 by 480 resolution format uses a traditional, “square” 4-by-3 aspect ratio. The 640 by 480 format (4:3 aspect ratio) is essentially equivalent to analog NTSC video in its resolution. However, due to its digital nature and capability to use progressive scan technology, SDTV video will feature a significant quality improvement over NTSC video. he digital nature of DTV (digital television – the digital television standard that encompasses the 6 forms of HDTV and the 12 forms of SDTV) eliminates many of the problems encountered with analog televisions such as “snow,” poor color reproduction, color bleeding, etc. SDTV uses AC-3 encoded sound resulting in the ability to transmit excellent quality surround sound audio in a 5.1 digital format. he wider aspect ratio featured with some forms of SDTV (16 units wide by 9 units tall versus the more square 4 units wide by 3 units tall used with NTSC analog television programming) allows movies to be presented in their full width, widescreen format. Movies for theater release are filmed in a wide aspect ratio different from that used in analog television sets. In order to fit a movie picture on a “square” television screen, portions of the image are cut off and discarded (pan-and-scan) or the movie is presented in its full width with black bars above and below the image (letterbox). The wider aspect ratio of SDTV in some of its forms will allow movies to be presented as intended without the use of black bars while still retaining their original information. This will also result in “wide” television programming making television shows more like movies. ue to the smaller bandwidth required to broadcast SDTV signals compared to that required for HDTV signals, there is the possibility to broadcast multiple SDTV programs over a single HDTV channel. Such a use of bandwidth would result in lower picture quality compared to HDTV but more channels to choose from. he primary disadvantages of digital television are cost and limited programming availability. For the near future, DTV is a costly proposition with most DTV sets (big screens in the 60 inch diagonal measurement area) starting at or above $7,000. Limited programming is related to how many cities receive DTV broadcasts. The ten largest television markets will have digital television in November 1998 with an additional 30 markets (the next largest ones) getting broadcasts in November 1999. onsumers will be able to watch DVDs, laserdiscs, VHS tapes and analog television signals on digital television sets. DVD will work particularly well with SDTV thanks to its digital storage of video and audio and its resolution closely matching that of SDTV. While there are currently no DVD players or other video sources capable of full HDTV output, SDTV will immediately benefit from digital video from DVD players and digital satellite transmissions.