June 2004 — Product Watch

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Glossary of Audiovisual Terms

The audiovisual lexicon is as diverse as its technologies and applications, and is expanding and evolving just as fast. The following is a primer of terms you'll likely encounter when purchasing projectors, monitors and other presentation products.

Aspect Ratio: The ratio of width to height of a frame or screen. Television screens usually have aspect ratios of 4:3, while plasma and LCD monitors often have aspect ratios of 16:9, making them more compatible with widescreen movies and HDTV programs.

Back-Room Projector: A projector equipped with a lens designed to be used much farther away from the screen than is usual - often in a projection booth or at the back of an auditorium.

Bandwidth: In video, the range of frequencies passed along a single channel.

Cathode-Ray Tube (CRT): An analog display device using a vacuum tube that generates images on a layer of phosphors driven by an electron beam, or gun, inside the tube. It is commonly referred to as a picture tube and is often used in front-room projector models.

Digital Light Processing (DLP): A video projection technology from Texas Instruments that creates images by reflecting light off hundreds of thousands of tiny rotating mirrors (each representing one pixel) mounted on a microprocessor. Three-chip DLP projectors use separate mirror arrays for red, green and blue. Single-chip projectors use a color-filter wheel that alternates each color in front of the mirrors.

Digital Micromirror Device (DMD): The name of the micromirror microprocessor from Texas Instruments that powers a DLP projector. (See also DLP.)

Digital Television (DTV): The umbrella term for the digital transmission formats designated by the Advanced Television Systems Committee (ATSC) to replace the traditional National Television Standards Committee (NTSC) system by 2006.

Direct-Drive Image Light Amplifier (D-ILA): A video projection technology from JVC that uses a reflective LCD to create images as a light source is reflected off the LCD and sent through the lens to the screen. (See also LCD.)

Halogen Lamp: A projection lamp used in most low- and medium-priced models that lasts about 1,000-2,000 hours and delivers a consistent output throughout its life. Images from halogen lamps look very white compared to those from incandescent lamps but less white than those from metal halide lamps.

High-Definition Television (HDTV): A high-resolution broadcast and display format commonly understood to include a widescreen 16:9 image with twice the horizontal and vertical resolution of traditional NTSC video, as well as 5.1 channels of Dolby Digital audio.

High-Gain Screen: A projection screen employing one of several techniques designed to reflect an unusually bright image back to the audience.

Horizontal Scan Rate: The speed in kilohertz at which the horizontal lines of the projected image are created. The higher the scan rate, the greater the resolution at a given vertical frame rate, provided that the scan rate of the video source is within the scan-rate range of the projector.