large-screen dispays.
for large-screen displays of video image, LCD, DLP, and D-ILA projectors are commonly used. flat-panel displays (flasma dispalys) are available in limited sizes with the largest current models limited to about 61 in (1,549 mm) diagonal. for the legible display of intructional material where the viewing distance exceed 15 to 20 ft (4.5 to 6m) , video projection technology is required to produce an adequate size image. For intructional uses, video display technology is supplanting film-based display technology (slide, motion fixture film, and overhead transparencies) because the newest film-to-video transfer devices preserve the resolution of the film media.
digitalecho cancellers are used with the microphones and loudspeaker system to help provide an echo-free and nonreverberant sound quality. in distance learning applications, a camera that can automatically track the movements of the intructior is often employed
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