High-definition television is a new format for broadcasting TV programming. The existing analogue formats are NTSC and PAL, which have been used for decades. The new digital formats, or DTV, are replacing analogue. DTV is broken down into two subcategories, SDTV, and HDTV. SDTV is higher quality than analogue, and is the format that free digital television services will be broadcast in for the foreseeable future. HDTV is the top tier of digital television providing the best quality picture and sound.
Yes. You must have a high-definition tuner and screen to properly decode HDTV signals and display them accurately. HD channels are also broadcast in standard format, so today, no programs are ONLY for HDTV users. A regular television set simply ignores HDTV signals that are being broadcast. When you want to step up to watching HDTV, you'll need to get a new HD Ready TV set.
The HDTV signal is digital resulting in crystal clear, noise-free pictures and CD quality sound. For the technophile, there are about 20 megabits per second of information per broadcast channel. HDTV has many viewer benefits.
Most televisions manufactured before a couple of years ago are manufactured in a 4 by 3 aspect ratio, which means the screen is 4 units wide by 3 units high. But theatrically released movies are usually in a much wider aspect, taking advantage of the human field of vision (which is wider across horizontally). HDTV signals are sent in a 16 by 9 aspect ratio, mimicking the wide scope of movies. HDTV's aspect ratio makes for a more immersive and intense viewing experience.
Resolution is a measure of picture sharpness. Current analog television contains about 480 active scanning lines resulting in a picture resolution of about 330 lines of resolution. By comparison today's VHS VCR's have about 240 lines of resolution which is why VHS recordings don't look as sharp as the original picture. DVD's offer higher resolution typically on the order of 400-480 lines of resolution. (Note the number of scanning lines does not equal resolution. For example, both the VHS and DVD formats have 480 active scanning lines but have different resolutions.) HDTV offers resolution that is at least twice that of analog television. You can expect razor sharp images from HDTV.
Regardless of the HDTV format being broadcast, all new HDTV receivers can receive both formats. New HDTV televisions will convert any received signal to a format that is compatible with your new display. The 720p format uses progressive scanning, which is just like your computer monitor. Progressive scan offers crystal clear images that virtually eliminates those scanning lines that are visible on most large screen televisions. The 1080i format uses interlace scanning just like today's analog televisions. Scanning lines are less visible on big screens due to the number of lines. Most older projection HDTV's use 1080i.
Just as your CDs sound better than your old audiocassette tapes, HDTV's digital audio signal sounds better than standard television's analogue sound. Also, some HDTV programs include Dolby Digital 5.1 surround sound. Properly decoded, each audio track can be sent to a different speaker, creating a three-dimensional sound field in your living room. Many prime time programs contain Dolby Digital surround sound for your listening pleasure.
In most areas, HDTV is only available as an over-the-air broadcast signal. This requires the use, in most cases, of an outdoor aerial pointed in the direction of the broadcaster's tower. You will also need a new HDTV receiver that can decode the digital signals. HDTV channels are typically different than your cable or over-the-air channel.