What HDTV Is Digital describes electronic technology that generates, stores, and processes data in terms of two states: positive and non-positive. Positive is expressed or represented by the number 1 and non-positive by the number 0 (Lasica). Data that is transmitted or stored with digital technology is expressed as a string of 0’s and 1’s. Each of these digits is referred too as a bit (and a string of bits that a computer can address individually as a group is a byte). Prior to digital technology, electronic transmission was limited to analog technology, which conveys data as electronic signals of varying frequency or amplitude that are added to carrier waves of a given frequency (Lasica). Broadcast and phone transmission has conventionally used analog technology.
Digital technology is primarily used with new physical communications media, such as satellite and fiber optic transmission. The first digital transmission was Morse code. A modem is used to convert the digital information in your computer to analog signals for your phone line and to convert analog phone signals to digital information for your computer. Newer distribution technologies-such as direct broadcast satellites (DBS), videocassette recorders (VCRs) and cable-are in heavy competition with over-the-air broadcasting for audiences of over 600 million television viewers worldwide (Lasica).
In the United States, the political and economic stakes have changed since the beginning of the development of television. The standardization and commercialization of new television technologies affect culture through social, political, economic, institutional, industrial, and aesthetic factors that influence the strategies and policies of both industry and government. Technological developments in television have brought new products and processes for manufacturers, broadcasters, and regulatory agencies (Television Standard). For example, looking specifically at economics, new technological developments in reception will change the stakes of that market.
Advanced forms of television receivers capable of displaying higher definition pictures will probably be available as early as. HDTV is defined as a television system that differs from current television systems-such as the North American and Japanese NTSC System-in the following ways: five times the increase in visual information detail, 10 times the color information, more than double the horizontal and vertical resolution, substantial improvement in picture brightness, over a one-third increase in aspect ratio (from 4:3 to 5.33:3), and sound quality equivalent to digital compact disc audio (Television Standard). Although the term HDTV is now used to refer to a new development in television technology, the term “high definition” has historically been used to define a number of advances in television picture quality. RCA first used the term “high definition television” in its 1934 Annual Report, identifying the role HDTV would play in the commercialization of television. Also in 1934, Vladimir Zworykin-a leading pioneer in the development of electronic television-defined the parameters for HDTV “regarding 240 scanning lines as a minimum.” Overseas, a British engineering report from the Royal Television Committee in London offered a similar technical definition for HDTV.
In this article, Zworykin’s HDTV definition of 240 lines or greater will be used (Kuhn). There are many different formats associated with High Definition TV. The ATSC recommendations have been characterized by the computer industry as “a confusing collection of 18 different standards that will be unnecessarily difficult and expensive to implement by set manufacturers”(Television Standard). However, the computer industry does not build or market television sets like other set manufacturers do. These manufacturers believe that sets can be made and sold to consumers that will accommodate all of these standards, similar to the way that multi-sync monitors accommodate the many incompatible computer display formats in use today (Kuhn). The formats listed below are production and transmission formats.
For example, when displaying a 24-Fr/sec transmission, the display might be 72-Fr/sec. The basic formats (in pixels) are (A pixel or picture element is a digital sample of the color intensity values of a picture at a single point). 1920H x 1080V 16H x 9V Aspect Ratio, Square-Pixel, Progressive-Scan at 24-Fr/sec and 30-Fr/sec, Interlace-Scan at 60-fields/sec; 1280H x 720V 16H x 9V Aspect Ratio, Square-Pixel Alignment, Progressive-Scan at 24-Fr/sec, 30-Fr/sec, and-60 Fr/sec; 704H x 480V 4H x 3V or 16H x 9V Aspect Ratio, Non-Square Pixel Alignment, Progressive-Scan at 24-Fr/sec, 30-Fr/sec, and 60-Fr/sec, Interlace-Scan at 60-fields/sec; 640H x 480V 4H x 3V Aspect Ratio, Square Pixel Alignment, Progressive-Scan at 24-Fr/sec, 30-Fr/sec, and 60-Fr/sec, Interlace-Scan at 60-fields/sec. Another type of format will be in the way HDTV will bring sound to the sets. AC-3 compression is the most popular format that will be used. AC-3 also known as Dolby digital will be the new medium for stereo sound.
Dolby digital consists of five channels or speakers and a single sub-woofer. All five channels will be able to receive a full frequency response of 20hz-20,000hz. The sub-woofer will receive its own frequency typically below 120hz. On November 10, 1994, AC-3 Elementary Streams in an MPEG-2 Multiplex was approved by the Technology Group on Distribution. On February 23, 1995, and by the full ATSC Membership on April 12, 1995.
Annex B, “AC-3 Data Stream in IEC958 Interface,” and Annex C, “AC-3 Karaoke Mode,” were approved by the Technology Group on Distribution. “Digital Television Standard for HDTV Transmission”, references this document and describes how the audio coding algorithm described herein is applied in the U.S. ATV standard (Compression Standard). In order to more efficiently broadcast or record audio signals, the amount of information required to represent the audio signals may be reduced. In the case of digital audio signals, the amount of digital information needed to accurately reproduce the original pulse code modulation (PCM) samples may be reduced by applying a digital compression algorithm, resulting in a digitally compressed representation of the original signal. The term compression used in this context means the compression of the amount of digital information, which must be stored or recorded, and not the compression of dynamic range of the audio signal (Compression Standard).
Digital compression of audio is useful wherever there is an economic benefit to be obtained by reducing the amount of digital information required to represent the audio. Typical applications are in satellite or audio broadcasting, delivery of audio over metallic or optical cables, or storage of audio on magnetic, optical or other storage media(Compression Standard). A typical problem in audio programming is that different members of the audience wish to enjoy different amounts of dynamic range. Original high quality programming (such as feature films) are typically mixed with quite a wide dynamic range. Using dialogue as a reference, loud sounds like explosions are often 20 dB or more louder, and faint sounds like leaves rustling may be 50 dB quieter(Compression Standard).
In many listening situations it is objectionable to allow the sound to become very loud, and thus the loudest sounds must be compressed downwards in level. In many listening situations the most quiet sounds would be inaudible, and must be brought upwards in level to be heard (or a higher volume). Since most of the audience will benefit from a limited dynamic range, soundtracks which have been mixed with a wide dynamic range are generally compressed: the dynamic range is reduced by bringing down the level of the loud sounds and bringing up the level of the quiet sounds. While this satisfies the needs of much of the audience, it removes the ability of some in the audience to experience the original sound program in its intended form. The AC-3 audio coding technology solves this conflict by allowing dynamic range control values to be placed into the AC-3 bit stream.
In order for this dynamic range control method to be effective, it should be used by all program providers. Since all broadcasters wish to supply programming in the form that is most usable by their audience, nearly all broadcasters will apply dynamic range compression to any audio program which has a wide dynamic range(Compression Standard). High Definition Television will be the next step television development. The formats are more accurate,the scanning lines are greater, and the picture just looks better. In essence the picture will look as if you are looking at a computer screen, but you will not have to sit 6 inches in front of the monitor.