HOME

TOPIC 4 : CABLE AND NEWER MEDIA

Analog to Digital

In analog technology, a wave is recorded or used in its original form. So, for example, in an analog tape recorder, a signal is taken straight from the microphone and laid onto tape. The wave from the microphone is an analog wave, and therefore the wave on the tape is analog as well. That wave on the tape can be read, amplified and sent to a speaker to produce the sound.

In digital technology, the analog wave is sampled at some interval, and then turned into numbers that are stored in the digital device. On a CD, the sampling rate is 44,000 samples per second. So on a CD, there are 44,000 numbers stored per second of music. To hear the music, the numbers are turned into a voltage wave that approximates the original wave.

The two big advantages of digital technology are:

  • The recording does not degrade over time. As long as the numbers can be read, you will always get exactly the same wave.

  • Groups of numbers can often be compressed by finding patterns in them. It is also easy to use special computers called digital signal processors (DSPs) to process and modify streams of numbers

  • Till 1980 – broadcast transmission utilized analog signals

  • Today- most of the excitement in broadcasting concerns digital recording and transmission. Recording of pictures or music signal is electronically sampled and converted into strings of digital bits.

    • Transmission technology

  • Early advances : Multiplexing ( where each telephone conversation was combined with a slightly different high frequency signal called carrier wave . The same method was used for radio program transmission on a different channel.


  • After WW2 – microwave systems that allows multiple radio signals to be transmitted simultaneously on adjacent channels through the air. Instead of broadcasting the transmission in all directions, microwave system use directional transmission located on top of tall buildings or towers


  • 1951 – Microwave became an effective method of transmitting TV signals between cities, coast to coast. Also used by cable TV companies


  • Coaxial cable – a wire-line technology that improved the telephone lines by using flatter wires ( less outside interference that and carry more information).
    - used for high capacity telephone trunks to connect early TV stations into networks


  • Satellites – are antenna towers in the sky that transmit television in 2 signal path:
      1. uplink - the signal path from the ground station to the satellite (hardware used)
      2. Essentially, a microwave relay device launched into each orbit to the downlink connected to the cable head end . It is a signal path from the transponder to the ground station. The downlink signal is reflected by the parabolic dish to a central focal point.
    • Many TV stations or organization operates a stationary Ku-band uplinks/ antenna ( 10-14 GHz)

    Cable TV

  • The earliest cable systems were, in effect, strategically placed antennas with very long cables connecting them to subscribers' television sets. Because the signal from the antenna became weaker as it traveled through the length of cable, cable providers had to insert amplifiers at regular intervals to boost the strength of the signal and make it acceptable for viewing.

  • In a cable system, the signal might have gone through 30 or 40 amplifiers before reaching your house, one every 1,000 feet or so. With each amplifier, you would get noise and distortion. Plus, if one of the amplifiers failed, you lost the picture. Cable got a reputation for not having the best quality picture and for not being reliable. In the late 1970s, cable television would find a solution to the amplifier problem. By then, they had also developed technology that allowed them to add more programming to cable service.

  • In the early 1950s, cable systems began experimenting with ways to use microwave transmitting and receiving towers to capture the signals from distant stations. In some cases, this made television available to people who lived outside the range of standard broadcasts. The addition of CATV (community antenna television) stations and the spread of cable systems ultimately led manufacturers to add a switch to most new television sets.

  • In both tuning systems, each television station was given a 6-megahertz (MHz) slice of the radio spectrum. The FCC had originally devoted parts of the very high frequency (VHF) spectrum to 12 television channels. The channels weren't put into a single block of frequencies, but were instead broken into two groups to avoid interfering with existing radio services.

  • Later, when the growing popularity of television necessitated additional channels, the FCC allocated frequencies in the ultra-high frequency (UHF) portion of the spectrum. They established channels 14 to 69 using a block of frequencies between 470 MHz and 812 MHz.

  • Because they used cable instead of antennas, cable television systems didn't have to worry about existing services. Cable equipment is designed to shield the signals carried on the cable from outside interference, and televisions are designed to accept signals only from the point of connection to the cable or antenna; but interference can still enter the system, especially at connectors. When the interference comes from the same channel that's carried on the cable, there is a problem because of the difference in broadcast speed between the two signals.

  • Radio signals travel through the air at a speed very close to the speed of light. In a coaxial cable like the one that brings CATV signals to your house, radio signals travel at about two-thirds the speed of light. When the broadcast and cable signals get to the television tuner a fraction of a second apart, you see a double image called "ghosting."

  • By the late 1970s, fiber optics had progressed considerably and so were a cost-effective means of carrying CATV signals over long distances. The great advantage of fiber-optic cable is that it doesn't suffer the same signal losses as coaxial cable, which eliminated the need for so many amplifiers.

  • Decreasing the number of amplifiers made dramatic improvements in signal quality and system reliability.

  • Another benefit that came from the move to fiber-optic cable was greater customization. Since a single fiber-optic cable might serve 500 households, it became possible to target individual neighborhoods for messages and services. In the 1990s, cable providers found this same neighborhood grouping to be ideal for creating a local-area network and providing Internet access through cable modems.

    • SATELLITE

  • Satellite television solves the problems of range and distortion by transmitting broadcast signals from satellites orbiting the Earth. Since satellites are high in the sky, there are a lot more customers in the line of site. Satellite television systems transmit and receive radio signals using specialized antennas called satellite dishes.

  • The television satellites are all in geosynchronous orbit. In other words, the satellite keeps pace with our moving planet exactly.

  • 1st communication satellite – TELSTAR 1 went into orbit in 1962.

  • Each satellite is launched into space at about 7,000 mph (11,000 kph), reaching approximately 22,200 miles (35,700 km) above the Earth. At this speed and altitude, the satellite will revolve around the planet once every 24 hours - the same period of time it takes the Earth to make one full rotation.

  • Some satellite owners still seek out this sort of programming on their own, but today, most satellite TV customers get their programming through a direct broadcast satellite (DBS) provider, such as DirecTV or the Dish Network. The provider selects programs and broadcasts them to subscribers as a set package.

  • Basically, the provider's goal is to bring dozens or even hundreds of channels to your television in a form that approximates the competition, cable TV. Unlike earlier programming, the provider's broadcast is completely digital, which means it has much better picture and sound quality .

  • Early satellite television was broadcast in C-band radio -- radio in the 3.4-gigahertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (12 GHz to 14 GHz ).

    • The Components

    There are five major components involved in a direct to home (DTH) satellite system:

  • Programming sources are simply the channels that provide programming for broadcast. The provider doesn't create original programming itself; it pays other companies (HBO, for example, or ESPN) for the right to broadcast their content via satellite. (Cable television companies work on the same principle.)

  • The broadcast center is the central hub of the system. At the broadcast center, the television provider receives signals from various programming sources and beams a broadcast signal to satellites in geostationary orbit.

  • The satellites receive the signals from the broadcast station and rebroadcast them to the ground.

  • The viewer's dish picks up the signal from the satellite (or multiple satellites in the same part of the sky) and passes it on to the receiver in the viewer's house.

  • The receiver processes the signal and passes it on to a standard television.

    • Digital TV

  • The term "digital TV" is used in many different ways right now, depending on who you are talking to. There is also the term "HDTV," which is the most advanced form of digital TV in use in the United States. The reason it gets confusing is because digital TV in the U.S. combines three different ideas. This section examines those three ideas.

  • Digital Signal : The first idea that is new to digital TV is the digital signal.

  • Analog TV started as a broadcast medium. TV stations set up antennas and broadcast radio signals to individual communities. You can put a pair of rabbit ears on your TV and pick up channels 2 through 83 for free. What you receive, as described earlier, is a single, analog composite video signal and a separate sound signal.

  • Digital TV has started as a free broadcast medium as well.

    • Digital TV’s Format

    Digital TV standards allow several different formats. Broadcasters can choose between three formats:

  • 480iThe picture is 704x480 pixels, sent at 60 interlaced frames per second (30 complete frames per second).

  • 480pThe picture is 704x480 pixels, sent at 60 complete frames per second.

  • 720p The picture is 1280x720 pixels, sent at 60 complete frames per second.

  • 1080iThe picture is 1920x1080 pixels, sent at 60 interlaced frames per second (30 complete frames per second).

  • 1080pThe picture is 1920x1080 pixels, sent at 60 complete frames per second.

    • Newest Technologies

    MP3

  • The MP3 movement is one of the most amazing phenomena that the music industry has ever seen. Unlike other movements -- for example, the introduction of the cassette tape or the CD -- the MP3 movement started not with the industry itself but with a huge audience of music lovers on the Internet. The MP3 format for digital music has had, and will continue to have, a huge impact on how people collect, listen to and distribute music.

  • The MP3 format is a compression system for music. It helps reduce the number of bytes in a song without hurting the quality of the song's sound. The goal is to compress a CD-quality song by a factor of 10 to 14 without affecting the CD-quality sound. With MP3, a 32-megabyte (MB) song on a CD compresses down to about 3 MB. This lets you download a song in minutes and store hundreds of songs on your computer's hard disk without taking up that much space.

  • MP3 format uses characteristics of the human ear to design the compression algorithm. For example:
      1. There are certain sounds that the human ear cannot hear.
      2. There are certain sounds that the human ear hears much better than others.
      3. If there are two sounds playing simultaneously, we hear the louder one but cannot hear the softer one.

  • Using facts like these, certain parts of a song can be eliminated without significantly hurting the quality of the song. Compressing the rest of the song with well-known compression techniques shrinks the song considerably -- by a factor of 10 at least. When you are done creating an MP3 file, what you have is a "near CD quality" song. The MP3 version of the song does not sound exactly the same but it's very close.

  • The MP3 movement –consistingof the MP3 format and theWeb's ability to advertise and distribute MP3 files -- has done several things for music:
      1. It has made it easy for anyone to distribute music at nearly no cost (or for free).
      2. It has made it easy for anyone to find music and access it instantly.
      3. It has taught people a great deal about manipulating sound on a computer.

    • Virtual Reality

  • Virtual Reality is a way for humans to visualize, manipulate and interact with computers and extremely complex data"

  • The visualization part refers to the computer generating visual, auditory or other sensual outputs to the user of a world within the computer. This world may be a CAD model, a scientific simulation, or a view into a database. The user can interact with the world and directly manipulate objects within the world. Some worlds are animated by other processes, perhaps physical simulations, or simple animation scripts.

  • The applications being developed for VR run a wide spectrum, from games to architectural and business planning. Many applications are worlds that are very similar to our own, like CAD or architectural modeling. Some applications provide ways of viewing from an advantageous perspective not possible with the real world, like scientific simulators and telepresense systems, air traffic control systems.

    • Types of VR systems

  • Window on World Systems (WoW)
    Some systems use a conventional computer monitor to display the visual world. This sometimes called Desktop VR or a Window on a World (WoW). This concept traces its lineage back through the entire history of computer graphics.

  • Video Mapping
    A variation of the WoW approach merges a video input of the user's silhouette with a 2D computer graphic. The user watches a monitor that shows his body's interaction with the world. At least one commercial system uses this approach, the Mandala system. This system is based on a Commodore Amiga with some added hardware and software. A version of the Mandala is used by the cable TV channel Nickelodeon for a game show to put the contestants into what appears to be a large video game.

  • Immersive Systems
    The ultimate VR systems completely immerse the user's personal viewpoint inside the virtual world. These "immersive" VR systems are often equipped with a Head Mounted Display (HMD). This is a helmet or a face mask that holds the visual and auditory displays. The helmet may be free ranging, tethered, or it might be attached to some sort of a boom armature.
    A nice variation of the immersive systems use multiple large projection displays to create a 'Cave' or room in which the viewer(s) stand. An early implementation was called "The Closet Cathedral" for the ability to create the impression of an immense environment. within a small physical space.

  • Telepresence
    Telepresence is a variation on visualizing complete computer generated worlds. This a technology links remote sensors in the real world with the senses of a human operator. The remote sensors might be located on a robot, or they might be on the ends of WALDO like tools. Fire fighters use remotely operated vehicles to handle some dangerous conditions.Surgeons are using very small instruments on cables to do surgery without cutting a major hole in their patients. The instruments have a small video camera at the business end. Robots equipped withtelepresence systems have already changed the way deep sea and volcanic exploration is done.

  • Mixed Reality
    Merging the Telepresence and Virtual Reality systems gives the Mixed Reality or Seamless Simulation systems. Here the computer generated inputs are merged with telepresence inputs and/or the users view of the real world. A surgeon's view of a brain surgery is overlaid with images from earlier CAT scans and real-time ultrasound. A fighter pilot sees computer generated maps and data displays inside his fancy helmet visor or on cockpit displays.
    The phrase "fish tank virtual reality" was used to describe a Canadian VR system reported in the 1993 InterCHI proceedings. It combines a stereoscopic monitor display using liquid crystal shutter glasses with a mechanical head tracker. The resulting system is superior to simple stereo-WoW systems due to the motion parallax effects introduced by the head tracker.

    • About Us | Site Map | Privacy Policy | Contact Us | ©2005 mayu.com