Digital TV channels carry broadcasts utilizing digital technology rather than analog technology. Digital broadcasts are superior to analog for a number of reasons, the foremost being resolution or clarity of the picture, a wider 16:9 aspect ratio, and the ability to carry 5:1 surround sound audio. Digital broadcasts make use of high-definition television (HDTV) to deliver crisper, cleaner, more vibrant and realistic images than ever before. Another advantage over analog broadcasting is that digital TV channels can be utilized to include sub-channels for additional programming ability.
Since HD is the most lauded reason for switching from analog to digital broadcasting, some people mistakenly believe that all digital broadcasts are high-definition (HD) broadcasts. A digital broadcast can be in a lower resolution that does not qualify as HD, but standard definition (SDTV) or enhanced definition (EDTV), the former being somewhat equal to traditional analog broadcasts. Why would a network choose to do this? By broadcasting in SDTV or EDTV, additional space is available on the wavelength for sub-channel programming which can be assigned to new digital TV channels.
For example, a nightly newscast does not benefit greatly by the HD format. Much of the show consists of static studio shots, filming anchors behind desks delivering the news, and field reports are typically shot in SD. By broadcasting the show in SDTV or EDTV the network leaves space on the channel’s band to create additional programming that would be assigned a sub-channel of the main channel, giving viewers more choices. This is known as multicasting.
In the US, digital TV channels are broadcast in one of four basic resolutions: 480i with a 4:3 aspect ratio (SDTV), 480p (EDTV), 720p (HDTV) or 1080i (HDTV). The number refers to the amount of scan lines, and the letter to whether the lines are progressive or interlaced. Progressive formats deliver each line to the TV progressively in a single scan, whereas an interlaced format paints every other line in one sweep, then a second sweep fills in the opposite lines.
Progressive scan is superior with less flicker, but requires more bandwidth to deliver. This is why the highest resolution (1080i) is interlaced. HDTVs with built-in tuners and the ability to display 1080 broadcasts will process a 1080i signal to display it in 1080p. HDTVs that can only display in 720p will downconvert a 1080i signal to display in 720p resolution.
To receive free-to-air (FTA) digital broadcasts, a digital antenna is needed. Depending on local topography and distance to the point of broadcast, a roof antenna might be required. Indoor digital antennas are also available for those who live in areas where broadcast signals are stronger.
An analog television cannot display digital TV channels without a digital converter box. Analog TVs are traditional cathode ray tube (CRT) displays; very deep sets with heavy footprints. Converter boxes are available from companies that provide digital TV feeds, such as cable and satellite dish companies, and converter boxes are also available as stand-alone devices for those who wish to receive FTA broadcasts only.
Digital TV channels are available worldwide with regional areas in some parts of the world still completing the switch from analog broadcasting. A few digital standards include ATCS (Advanced Television Systems Committee) used in countries that include the United States, Canada and Mexico, DVB (Digital Video Broadcasting) used in Europe, and ISDB (Integrated Services Digital Broadband) used in Japan and Brazil.