Chapter 3 - Audio- Video Technology

Broadcasting, cable, and new media make use of facsimile technology, reproducing sound and sight in other forms. The better the correspondence between the facsimile and the original, the higher the fidelity.

Transduction involves changing energy from one form to another; it is at the heart of audio and video technology. Transduction can be analog—the transformed energy resembles the original—or digital—the original is transformed into a series of numbers.

Audio and video signal processing follow five main steps: signal generation, amplification and processing, transmission, reception, and storage/retrieval.

Signal generation. Audio signals are generated mechanically, by using microphones and turntables; electro-magnetically, by using tape recorders; and digitally, by using laser optics. Television signal generation involves the electronic line-by-line scanning of an image. An electron beam scans each element of a picture, and the image is then retraced in the TV receiver.

Amplification and processing. Audio and video signals are amplified and mixed by using audio consoles and video switchers. Today’s digital technology enables sophisticated signal processing and a variety of special effects.

Transmission. Radio waves occupy a portion of the electromagnetic spectrum. AM radio channels are classified into clear, regional, and local channels. FM stations are classified according to power and antenna height. The wide bandwidth of an FM channel allows for stereo broadcasting and other nonbroadcast services. There are two types of digital radio: satellite-based and in-band, on-channel.

The traditional systems of transmitting a TV signal are (1) over-the-air broadcasting utilizing electromagnetic radiation on channels located in the VHF and UHF portions of the spectrum and (2) by wire through a cable system using coaxial cable that can carry more than 60 channels of programming. New distribution technologies include fiber optics, satellite transmissions, and new forms of digital distribution.

Television and radio are moving to new forms of digital distribution. On the TV side, the FCC has mandated a switch to digital high-definition television by 2006. That process is currently underway at the nation’s TV stations and networks. In radio, two companies provide national digital radio distribution via satellite, which is committed to providing CD-quality radio to homes and cars.

Signal reception. Radio receivers pull in AM, FM, and other signals, in monaural or stereo. New digital multiband receivers are becoming more prevalent. In TV, large and small-screen receivers have attained record sales in recent years, abetted by new digital capabilities and "smart" remote control devices.

Storage and retrieval. New technology is reshaping audio and video storage and retrieval. Phonograph records, compact discs, and videotapes are being supplemented and may ultimately be replaced by digital storage media, such as recordable CDs, digital versatile disks (DVDs), and high-capacity disk drives on computers. A comparatively new phenomenon, audio and video streaming, permits radio and TV stations to send their complex signals onto the Internet. Today, any home computer with a soundcard, a CD-ROM drive, and a microphone can produce and distribute its own radio and TV programs. The impact of this development on traditional radio, TV, and cable is unclear.