Understanding Digital Television

The standard-analog or NTSC-TV systems that served so well in the 20th century have been replaced by a digital TV system (ATSC) that offers stunning picture quality and multi-channel surround sound.
Multiple Standards
One of the most confusing aspects of DTV is the proliferation of standards. The FCC didn't mandate a single standard, but chose to "let the market decide," so now there are 18 possible variations on the digital theme. Fortunately, only three seem to have enough support to survive:

Standard Definition: 480P, the DVD format. 480I is shorthand for analog video; the name refers to 480 visible horizontal scanning lines interlaced in alternating fields. 480P is a progressive-scan mode that basically doubles the resolution of the old  video, producing a better image.

High-Definition: 720P and 1080I are both High-Definition formats. Some video experts contend that the difference in picture quality between 720P and 1080I is negligible.

    •   720P could be thought of as a line-tripling scheme, and is favored by ABC and ESPN.

    •   1080I alternates fields of 540 lines each to create combined frames of 1080 lines. 1080I is used by CBS, NBC, and PBS.

Stereo or Multi-channel Sound
Some programming, especially shows produced by Showtime and HBO, is delivered in Dolby? Digital 5.1TM surround sound. Stereo receivers "fold down" surround signals to two channels. A DVD or broadcast movie with a surround soundtrack is still enjoyable through a two-channel system, but lacks front-to-rear localization cues.

 HDTV Introduction

  DTV FAQ, Terms, Definitions

When not transmitting in HDTV, broadcasters will be able to transmit four or more channels of standard definition television (SDTV) programming simultaneously. This is called multicasting. The option to multicast was made possible by digital technology to allow each digital broadcast station to split its bit stream into 2, 3, 4 or more individual channels of programming and/or data services. For example, on channel 55, you could watch 55.1, 55.2, 55.3 or 55.4, or if the station were  broadcasting in HDTV, you could watch a single High-Definition program.


TV Formats:

  • 480i - The picture is 704x480 pixels, sent at 60 interlaced frames per second (30 complete frames per second).
  • 480p - The picture is 704x480 pixels, sent at 60 complete frames per second.
  • 720p - The picture is 1280x720 pixels, sent at 60 complete frames per second.
  • 1080i - The picture is 1920x1080 pixels, sent at 60 interlaced frames per second (30 complete frames per second).
  • 1080p - The picture is 1920x1080 pixels, sent at 60 complete frames per second.
(The "p" and "i" designations stand for "progressive" and "interlaced." In a progressive format, the full picture updates every sixtieth of a second. In an interlaced format, half of the picture updates every sixtieth of a second.)

The 480p and 480i formats are called the SD (standard definition) formats, and 480i is roughly equivalent to a normal (old) analog TV picture.

The 720p, 1080i and 1080p formats are HD (high definition) formats. When you hear  "HDTV," this is what is being discussed -- a digital signal in the 720p, 1080i or 1080p format.

Aspect Ratio

The HD formats of digital TV have a different aspect ratio than analog TVs. An analog TV has a 4:3 aspect ratio, meaning that the screen is 4 units wide and 3 units high. For example, a "25-inch diagonal" analog TV is 15 inches high and 20 inches wide. The HD format for digital TV has a 16:9 aspect ratio. The screen is 16 units wide and 9 units high.

Digital Signal

Analog TV broadcasts you receive are a single, analog composite video signal and a separate sound signal. You can get, over the air (OTA), channels 2 thru 83 in most large cities if you live within 50 miles of the station's antenna.

Digital TV as well can be received from local  commercial digital TV stations if you have a digital TV receiver and an antenna. The FCC gave television broadcasters a new frequency to use for their digital broadcasts, so right now each broadcaster has an analog TV channel and a digital TV channel. The digital channel carries a 19.39-megabit-per-second stream of digital data that your digital TV receives and decodes. more ..

Learn about the various tv formats:
TV formats
Learn about tv features:
TV features
How do I get HDTV: