microphones. Electronic instruments, AM-FM tuners, audio CD players, cassette
decks, MP3 players and personal computers are also audio sources.
The visual part of an audio visual system also has several sources:
n Cameras
n VCRs, DVDs, VTRs, DVTRs
n Cable television
n Satellite television
n Broadcast/cable/satellite
n Document cameras
n Personal computers
n Data networksThe wide range of video sources also means a wide range of video signal
types and methods with which they connect to an audio visual system.
Emerging video sources include electronic whiteboards and the Internet.
Speakers and instructors use personal computers as part of an audio visual
system in meeting rooms, conference rooms and classrooms where presentations
often rely on Microsoft PowerPoint software. The personal computer serves as a
video input to an audio visual liquid crystal display (LCD) projector.
Document cameras have replaced the older, bulky overhead projectors. The
document camera, which contains a video camera, is also typically connected
to an LCD projector. Document cameras can handle a variety of materials
including x-rays and even three-dimensional objects.
Interactive or electronic whiteboards can be used to display an electronic
presentation but can also be used as an A/V source where everything written
or displayed on a whiteboard can be recorded for electronic retrieval later.
One application is in the classroom where an instructor utilizes the electronic
whiteboard and the content on the whiteboard can subsequently be electroni-
cally retrieved by a student via a data network or the Internet (Fig. 15.2).
Audio and Video Processing
Audio signals may be processed in a multitude of ways with the most familiar
being equalizers which are also used on many car and home stereo systems. An
equalizer processes the audio signal by increasing or decreasing the low-, mid-,
and high-level frequencies to provide the most pleasing audio sound possible.
Brief descriptions of other common audio processors follow.
Audio Visual Systems 171