teia de ideia [mídia e tecnologia]

Francisco Rolfsen Belda

Exercício 1. O que é digital?

com 2 comentários

Proposta: Leia os trechos a seguir. Se necessário, consulte um dicionário ou páginas específicas na internet de modo a esclarecer termos técnicos relacionados aos princípios físicos e às tecnologias citadas. Reflita sobre as aplicações desses conceitos ao universo da comunicação digital. Redija um verbete de até 3 linhas com uma definição do termo “digital”.

Objetivos deste exercício: Apresentar conceitos introdutórios de mídia digital; familiarizar os alunos com hábito de leitura em inglês; estimular a capacidade de síntese e de definição.

Trecho 1. 

Data transmission

Data transmission, digital transmission, or digital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibres, wireless communication channels, and storage media. The data is represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.

While analog transmission is the transfer of continuously varying analog signal, digital communications is the transfer of discrete messages. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying wave forms (passband transmission), using a digital modulation method. The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment. According to the most common definition of digital signal, both baseband and passband signals representing bit-streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital-to-analog conversion.

Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an Analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. This source coding and decoding is carried out by codec equipment.(…)

Applications and history

Data (mainly but not exclusively informational) has been sent via non-electronic (e.g. optical, acoustic, mechanical) means since the advent of communication. Analog signal data has been sent electronically since the advent of the telephone. However, the first data electromagnetic transmission applications in modern time were telegraphy (1809) and teletypewriters (1906), which are both digital signals. The fundamental theoretical work in data transmission and information theory by Harry Nyquist, Ralph Hartley, Claude Shannon and others during the early 20th century, was done with these applications in mind.

Data transmission is utilized in computers in computer buses and for communication with peripheral equipment via parallel ports and serial ports such us RS-232 (1969), Firewire (1995) and USB (1996). The principles of data transmission is also utilized in storage media for Error detection and correction since 1951.

Data transmission is utilized in computer networking equipment such as modems (1940), local area networks (LAN) adapters (1964), repeaters, hubs, microwave links, wireless network access points (1997), etc.

In telephone networks, digital communication is utilized for transferring many phone calls over the same copper cable or fiber cable by means of Pulse code modulation (PCM), i.e. sampling and digitization, in combination with Time division multiplexing (TDM) (1962). Telephone exchanges have become digital and software controlled, facilitating many value added services. For example the first AXE telephone exchange was presented in 1976. Since late 1980s, digital communication to the end user has been possible using Integrated Services Digital Network (ISDN) services. Since the end of 1990s, broadband access techniques such as ADSL, Cable modems, fiber-to-the-building (FTTB) and fiber-to-the-home (FTTH) have become wide spread to small offices and homes. The current tendency is to replace traditional telecommunication services by packet mode communication such as IP telephony and IPTV.

Transmitting analog signals digitally allows for greater signal processing capability. The ability to process a communications signal means that errors caused by random processes can be detected and corrected. Digital signals can also be sampled instead of continuously monitored. The multiplexing of multiple digital signals is much simpler to the multiplexing of analog signals.

Because of all these advantages, and because recent advances in wideband communication channels and solid-state electronics have allowed scientists to fully realize these advantages, digital communications has grown quickly. Digital communications is quickly edging out analog communication because of the vast demand to transmit computer data and the ability of digital communications to do so.

The digital revolution has also resulted in many digital telecommunication applications where the principles of data transmission are applied. Examples are second-generation (1991) and later cellular telephony, video conferencing, digital TV (1998), digital radio (1999), telemetry, etc. (…)

Fonte: Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Digital_communication

Trecho 2. 

Analog. Digital. What’s the Difference?

Analog phone lines. Analog signals. Digital security. Digital PBX. Analog-to-digital adapters. What does it all mean? In the telecom world, understanding analog versus digital isn’t as simple as comparing one technology to another. It depends on what product—and in some cases, which product feature—you happen to be talking about.
As a technology, analog is the process of taking an audio or video signal (in most cases, the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of “1”s and “0”s. Simple enough when it’s the device—analog or digital phone, fax, modem, or likewise—that does all the converting for you.

Is one technology better than the other? Analog technology has been around for decades. It’s not that complicated a concept and it’s fairly inexpensive to use. That’s why we can buy a $20 telephone or watch a few TV stations with the use of a well-placed antenna. The trouble is, analog signals have size limitations as to how much data they can carry. So with our $20 phones and inexpensive TVs, we only get so much.

The newer of the two, digital technology breaks your voice (or television) signal into binary code—a series of 1s and 0s—transfers it to the other end where another device (phone, modem or TV) takes all the numbers and reassembles them into the original signal. The beauty of digital is that it knows what it should be when it reaches the end of the transmission. That way, it can correct any errors that may have occurred in the data transfer. What does all that mean to you? Clarity. In most cases, you’ll get distortion-free conversations and clearer TV pictures.

You’ll get more, too. The nature of digital technology allows it to cram lots of those 1s and 0s together into the same space an analog signal uses. Like your button-rich phone at work or your 200-plus digital cable service, that means more features can be crammed into the digital signal.

Compare your simple home phone with the one you may have at the office. At home you have mute, redial, and maybe a few speed-dial buttons. Your phone at work is loaded with function keys, call transfer buttons, and even voice mail. Now, before audiophiles start yelling at me through their PC screens, yes, analog can deliver better sound quality than digital…for now. Digital offers better clarity, but analog gives you richer quality.

But like any new technology, digital has a few shortcomings. Since devices are constantly translating, coding, and reassembling your voice, you won’t get the same rich sound quality as you do with analog. And for now, digital is still relatively expensive. But slowly, digital—like the VCR or the CD—is coming down in cost and coming out in everything from cell phones to satellite dishes. (…)

Fonte: Paul Wotel, Hello Direct

http://telecom.hellodirect.com/docs/Tutorials/AnalogVsDigital.1.051501.asp

Trecho 3. 

Digital

Digital information is stored using a series of ones and zeros. Computers are digital machines because they can only read information as on or off — 1 or 0. This method of computation, also known as the binary system, may seem rather simplistic, but can be used to represent incredible amounts of data. CDs and DVDs can be used to store and play back high-quality sound and video even though they consist entirely of ones and zeros.

Unlike computers, humans perceive information in analog. We capture auditory and visual signals as a continuous stream. Digital devices, on the other hand, estimate this information using ones and zeros. The rate of this estimation, called the “sampling rate” combined with how much information is included in each sample (the bit depth), determines how accurate the digital estimation is. (…)

Fonte: TechTerms

http://www.techterms.com/definition/digital

Escrito por Francisco Rolfsen Belda

31/10/2011 às 12:37

Publicado em TV Digital

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2 Respostas para 'Exercício 1. O que é digital?'

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  1. Exercício 1. O que é Digital?

    Numa definição mais imediata, o termo coloca-se em oposição à transmissão analógica de sinais usada na radiodifusão tradicional, ou seja, indica a digitalização ou codificação binária do sinal nas transmissões multimídia em banda larga.

    Aluna: Tatiana Garcia

    alunoppgtvd

    04/01/2012 em 0:07

  2. Digital é um sinal codificado pelo sistema binário e está associado à tecnologia.

    Postado por: Eliane Gushiken

    alunoppgtvd

    10/02/2012 em 23:41

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