Let's take a quick look at the main differences between analog, digital and high definition.
ANALOG TV:
An analog signal or SDTV (Standard Definition TV) is what you have been receiving since TV first went on the air. These types of television sets decode their pictures by using a signal received from a TV transmitter with varying signal voltage and radio frequencies. This format, known as NTSC (National Television System Committee) became the color TV standard in 1953 after the transition from black and white.
SDTV has 525 lines of information for every single frame of video. In one second, almost 30 frames of video are broadcast to give your eyes the perception of a continuously moving picture.
DIGITAL TV:
Digital television (DTV) is fast replacing analog TV which enables us to offer viewers a movie-quality picture and sound using digital modulation data. These are digitally compressed bits of information that require decoding by a specially designed television set or a standard receiver with a set-top box. This is known as ATSC (Advanced Television Systems Committee) and made its first appearance in the US during the early 1990s. Japan & other countries have already been using this system for many years.
DTV has many advantages over traditional TV. The most significant is DTV uses a smaller channel bandwidth. This frees up space for more digital channels, other non-television services such as pay or multimedia services and the generation of revenue from the sales of frequency spectrum taken by analog TV. There are also special services such as multicasting (more than one program on the same channel), electronic program guides and interactive programming.
All Digital TV is NOT High Definition - and that's important to know! Digital TV is simply the way the signal is broadcast and received by a TV set. HD is a by product of Digital TV.
HIGH DEFINITION TV:
High-definition television (HDTV) is a television broadcast that offers a significantly higher resolution than the traditional SDTV format.
HDTV has higher resolution: The image on a digital television is made up of small elements called pixels. The pixels in HDTV are closely packed together to provide high-resolution detail. HDTV can have 1,280 or 1,920 active horizontal pixels by 720 or 1,080 active scanning lines respectively. The total number of pixels in a high-definition image can exceed two million.
HDTV has a widescreen format: In addition to providing improved picture quality with more visible detail, HDTV is transmitted in a widescreen display commonly referred to as a 16:9 format, meaning that the picture is 16 units wide by 9 units high. A conventional analog TV display is 4 units wide by 3 units high, or 4:3 (see diagram below). Thus, the 16:9 display provides a wider image area that more closely matches the relative dimensions, or aspect ratio, of cinema.
HDTV has better sound: Many HDTV programs also contain multi-channel (5.1) Dolby® Digital surround sound to complete the realism of the viewing experience within a home theater system. Digital Television Sets & Monitors
