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Select the first letter of the word from the list above to jump to appropriate section
of the glossary. If the term you are looking for starts with a digit or symbol, choose the
In audio-visual, unwanted light or sound
- American National Standards Institute (ANSI)
Organization responsible for most standards used for US audio-visual and computer
A Device which supplies power to and strengthens an incoming signal for output
Represented as a continuous signal or quantity, continuous, as opposed to
digital; represented by discrete numbers with an extremely wide range of values
A type of lens adapter designed to produce a wide screen image from an equally condensed
image on the film
See American National Standards Institute
Automatic Sensitivity Control; detects light intensity and keeps the camera in
working conditions as it applies to light input.
The proportions of a projected picture area. In the US, standard video aspect ratio is 4
units wide by 3 units high, usuallu shown 4:3
Input jack witch delivers a signal to piece of equipment or a jack that receives a signal
using a cable with the proper connectors.
Output jack witch brings an audio signal from a piece of equipment of one which delivers
an audio signal using a cable with the proper connectors.
An MS-DOS file that is automatically executed when a computer is powered up. The file may
contain commands to load and run other programs an the disc.
- Automatic Level Control (ALC)
A circuit used in audio and video recorders to control the level of the record signal
automatically to provide uniform level of the record signal without distortion due to
overloading. Also called automatic gain control.
A 1/2 inch video cassette format
A direct current (DC) or a high frequency alternating current (AC) signal fed to a
magnetic recording head with the audio in order to minimize distortion. AC Bias ordinarily
provides higher fidelity.
- BNC Connector
A locking type if industrial connector commonly used in professional video systems.
To raise of strengthen the signal
Achromatic intensity, relative lighting without regard to color.
- Brightness Ratio
The difference between the brightest and darkest areas in an image. The wider the
brightness ratio the wider the contrast ratio.
- Broad band
A circuit which can operate over a wide range of frequencies. An example is cable TV.
Extra bright images which remain on the surface of a camera tube as a ghost image when
other images are being shown.
An InFocus product; a single cord connection to plug your computer/video, audio,
monitor, and mouse into an InFocus projector. The unit is Mac and PC compatible. See CableWizard in the Equipment guide for more information.
A lens mounting system for video cameras and 16mm movie cameras which accepts certain
A component in circuitry which stores and releases voltage within the circuit. Also a type
of microphone. See also microphones.
A rotating shaft or spindle which moves tape at a constant speed during recording or
playback in tape recorders and players. A pressure roller squeezes or pinches the tape
tight against the capstan to provide traction.
- Cathode Ray tube (CRT)
the video display tube used in video monitors, receivers and computer terminals. Contains
a cathode and heater element at one end which produces electron beams that hit a phosphor
coating on the face of the tube and make it glow or hit an oxide coating and produce
Community Antenna Television, usually referred to as cable television.
- Ceramic Microphone
Color Graphics Adapter
- Character Generator
A device which displays letters and numbers electronically on a video screen for use in
In video, the hue and saturation of color of an object as differentiated from the
brightness value or luminance of that object. Without the chrominance signal, the received
video picture would be in black and white. Compare with luminance.
One of the first widescreen movie formats, presenting a 2.35:1 aspect ratio with a 2:1 anamorphic squeeze.
- Closed Circuit Television (CCTV)
A distribution system which limits reception of an image to those receivers or monitors
that are directly connected to the origination point by coaxial cable or microwave link.
- Closed Loop
A continuous loop of film or tape for repetitive playing, often in a cartridge.
- Color Burst
The portion of the composit video signal which aligns the color decoder of the display
- Color Bars
SMPTE standard test bars used to match playback with the original recording levels. Often
accompanied by a 1000Hz audio tone.
- Composite Video Signals
Single signals with picture and sinc information.
- Condenser Lens
On projectors; one or more lenses between the projection lamp and slide or film aperture
to concentrate the light in the film and lens apertures.
- Continuous Loop
A loop of film or tape made by splicing the ends together for continuous projection or
- Contrast Ratio
The ratio of brightness of the brightness of the brightest possible area to the darkest
possible area of an image.
How much brighter the white areas are than the black areas.
- Contrast Range
The range of grays in a video image, usually a ratio of light to dark.
Proper alignment of the vertical and horizontal lines, as in video projection.
Approach, using an X axes (horizontal) and Y axis (vertical). For 3D images, a Z axis is
Central Processing Unit; the portion of a computer which reads and executes programming.
Cathode Ray Tube; the display on any video or computer monitor.
Canadian Standards Association.
- Cue Control
A device for rapidly advancing or rewinding a tape or film to sample the contents or find
a desired section.
- Curved Screen
A section of surface of a large sphere. Curved screens have viewing angles less than 180
degrees and gains greater than 1 percent.
Digital Audio Tape
- Decibel; a measurement of sound. See Decibel.
dB rating which indicates the number of decibels a signal is higher or lower than 1mW
Direct current; maintains a steady flow and does not reverse directions (as in alternating
current); usually provided by battery power.
- Decibel (dB)
A relative comparison of two signal amplitudes in a manner which roughly corresponds to
human sensory response to the signals. In audio work, 0 dB is the threshold of hearing and
120 dB is the threshold of pain. A change of 3 dB doubles or halves the apparent loudness.
A value or parameter which is assumed, unless the user supplies an alternative. Many
software programs supply default values and options.
The sharpness/resolution of a picture.
See Head Demagnetizer or Eraser.
To remove or erase a file.
A character which is used as a boundary or separator between two data elements.
A triangle-shaped grouping of 3 electron guns in a color CRT (Cathode
Resolution or definition; the clarity of a picture
Usually refers to a device such as a disc drive, display screen, terminal, printer or
The element in a microphone activated by sound wave vibrations. These vibrations are then
converted into voltage vibrations which then produce an audio signal.
A type of reflector, mirror or filter which reflects and transmits different wavelengths
of light selectivity, permitting a projector to provide more visible image light with less
heating of the slide or film.
A system of recording data and images with discrete, noncontiguous codes; provides signal
reproduction with little noise or distortion.
- Digital Light Processing (DLP)
The core of the DLP system from Texas Instruments Inc., is the Digital
Micromirror Device (DMD), a semiconductor light switch controlling 480,000 tiny mirrors on
a single microchip. The mirrors are digitally controlled and individually activated to
create very high definition, high contrast images with absolute picture uniformity and
full color saturation from middle to all edges.
- Digital Micromirror Device (DMD)
See Digital Light Processing
- Digital Recording
Advanced method of recording which involves a sequence of pulses or on/off signals rather
than a continuously variable of analog signal; advantages are increased frequency range
and lower tape noise. May be used for control, audio and video purposes.
The process of converting analog signals to numeric values (ones and zeros) that can be
processed by computer.
Output device, for presenting legible information often a Cathode Ray Tube (CRT)
of Liquid Crystal Display (LCD).
A change from one scene to another in which the outgoing and incoming visual images are
superimposed or blended together for a discernible period of time as one scene fades out
while the other fades in.
- Dissolve Control
A device which controls the illumination from 1, 2 or more projectors in such a manner
that the images fade from one to another at a fixed or variable rate.
See Screen Borders & Drop
During playback, the instantaneous loss of a recorded signal due to imperfections in the
- Dual Channel
A device with two separate paths that do not interfere unless deliberately mixed. Stereo
equipment is an example.
- Dynamic Microphone
- Dynamic Range
The highest and lowest signal levels on a given device.
Enhanced Graphics Adapter
- Eight Pin Connector
The jack often used for VCR-to-monitor connection.
- Electronic Viewfinder
- A small picture tube (CRT) or liquid crystal display (LCD)
built into a video camera and connected to the system to enable the camera operator to see
exactly what is being scanned by the camera.
- Encoder (Multi-Image Devices)
A signal generator or pulsar used with a tape recorder or other information storage device
to produce the synchronizing signals or pulses for later decoding to operate combinations
of devices (often Projectors) in synchronization.
- Encoder (Video)
Devices that change an individual component signals into composite signals. For example,
an encoder combines y (luminance or light) and C (chrominance or color) signals to provide
a video image. All video cameras contain encoders.
An electronic device which compensates for frequency inaccuracies in an audio or video
- Erase Head
A separate head on an audio or video tape recorder which erases a previous signal on the
tape before it is recorded on. An electromagnet which disturbs the signal previously on
- Eraser, Tape, Bulk
A device that produces a strong alternating electromagnetic field which almost instantly
erases an entire reel, cassette or cartridge of tape. Also called a bulk demagnetizer or degausser.
- European Television
The standard television system in Europe currently has 625 scanning lines and 50 fields
per second (as opposed to the NTSC system used in the US, which is
- Expansion Slots
Open connectors for the attachment of various computer peripheral devices, such as modems
Varying the strength of a picture - either from black to full strength (fade in) or from
full strength to black (fade out).
The regeneration of sound caused by a system's microphonic pickup of output from it's own
speakers causing a ringing sound or signal.
One half of a standard television frame, containing every other line of information. Each
standard video image contains 2 fields interlaced. In the NTSC video
system, a field contains 262.5 lines, a frame contains 2525 lines. There are 2 fields per
frame in standard video.
- Field Frequency
The number of fields per second; NTSC field frequency is 60 per
second, PAL and SECAM frequencies are 50.
A series of still pictures on a strip of film (usually single frame 35mm). The filmstrip
may be silent or provided with a accompanying sound program. Filmstrips may be advanced
manually as desired or in response to an audible beep in the audio source, or, if so
equipped, automatically by a cue tone on a tape.
- Filmstrip Projector
A device containing a lens system which focuses an image from a filmstrip onto a viewing
- Flat Screen
A flat reflecting surface with 180 degree viewing angles and gains
approximately equal to 1.
- Fluid Head Tripod
A tripod whose camera mount consists of two metal plates separated by a layer of fluid
making movement is very smooth.
Rapid change in frequency of an audio or video signal due to variations in tape or disc
speed. AWOW is usually considered a lower frequency speed variation.
- Flying Erase Head
A combination record/erase head found on video camcorders and recorders which provides
- Focal Length (FL)
The distance between a focal point of a lens or mirror of projection equipment and the
corresponding principal plane. Shorter focal length means larger image size on the screen
for given projection distance.
- Focus (Automatic)
A device on slide projectors whereby after focusing the first image, remaining similarly
mounted slides are automatically focused.
Sharpening a blurred image on a screen, monitor or any display; adjusting picture to
achieve the greatest possible resolution.
The amount of light reflected by a surface one foot from a lighted candle. Metric
equivalent is LUX.
One Lumen or one Foot candle of light over a one square foot surface.
In Video, a single image on a display created by storing a continuous sequence of scan
lines. In film, action and movement are depicted by a series of still frames shown very
The rate of repetition in cycles per second (Hertz) of musical pitch or electrical
signals. Low frequencies are base; high frequencies are treble.
- Frequency Response
The frequency range in audio and video systems over which signals are reproduced within a
stated amplitude range. Generally expressed in dB versus Hz for example 100-5000Hz + 5 dB.
A flat glass of acrylic lens in which the curvature of a normal lens surface is collapsed
into small steps in an almost flat plane, resulting in concentric circle forms impressed
or engraved on the lens surface. Because of lower cost, less weight and compactness, it is
often used for the condenser lens in overhead projectors and in studio spot and floor
- Front Screen Projection
An image projected on the audience side of a light-reflecting screen. See also Rear Screen.
Feet per second
- Gain or Screen Gain
The ability of a screen to amplify incident light. A matte white wall has a gain of
approximately 1. Screens with gain less than 1 attenuate incident light, screens with gain
more than 1 amplify incident light. For example: An image reflecting off a 10 gain screen
appears 10 times brighter than it would if it reflected off a matte white wall. Curved screens usually have larger gain than flat screens. Dual
purpose rear/front screens often have gains of about 0.5 in each direction. See Screen Surfaces for descriptions and gains of each type of
The amplification of a unit of system. May be expressed in dB for electronic equipment or
a factor (times) for screens.
A device which locks the frequency of it's internal sync generator to an external source.
The ability of a projector to accurately reproduce the border around a rectangle image.
Gigahertz; 1 billion cycles per second
- Glass Beaded
See Screen Surfaces
The electronic and mechanical components of a computer system.
High Definition; often meaning HDEP and HDTV
High Definition Electronic Production
High Definition Television, a term used top describe advanced production and delivery
A small electromagnetic which places magnetic signals onto a video of audio tape as it
moves by; also reads those signals off a tape.
- Head Demagnetizer (Degausser)
A device which provides an alternating magnetic field used during routine maintenance or
remove the residual magnetism from recording or playback heads.
A device consisting of one or two electro-acoustic receivers attached to a headband for
private listening to audio sources, sometimes called an earphone.
A headphone with a built in microphone on an adjustable boom. It is audio active, meaning
the wearer can both listen and respond.
- Helical Scan Video Tape Recording
A type of video recording in which the video heads and the tape meet at such am angle that
the resulting pattern on the tape is a long, diagonal series of tracks from the video
heads, each diagonal stripe containing the full information for 1 field of video picture.
Also called slant track.
- Hertz (Hz)
The frequency of an alternating signal. Formerly called cycles per second.
Hercules Graphics Adapter
- High Fidelity
Accurate and faithful reproduction of the original image; absence of distortion.
- High Resolution
Camera, monitor or projector with a great number of scanning lines (1000-2000) which
produces a very sharp, detailed image.
- Homing (also Resync)
A projector feature which causes the projector to automatically return to it's starting
- Hot Spots
Central part of a reel on which tape or film is wound.
Color; Value (red, green, blue, yellow) rather than intensity or brightness.
Audible disturbance caused by the power supply.
- Image Buffer
Electronic circuitry which converts 625-line 50Hz video signals to 525-line 60Hz standards
and visa versa.
Resistance to the flow of alternating current electricity. Measured in ohms. Low impedance
circuits are 600 ohms or less, and high impedance circuits may be 50K ohms or more.
- Infared (IR)
Heat rays or waves just beyond (longer than) the visible spectrum; often filtered out to
reduce heat on film or slide.
The program that enters a unit or system; the jack or receptacle into which a signal if
Energy from an outside source which interferes with a specific signal.
Increasing video resolution by doubling the number of horizontal scan lines; NTSC video is interlaced.
Inches Per Second; more properly written in/s. Standard method for measuring the speed of
An adjustable aperture in a lens made of moveable metal parts which change the diameter of
the lens opening in order to control the amount of light passing through the lens.
Openings are shown in f-stops.
Receptacle for a plug connector for the input or output circuits of an audio or video
device. These are several common sizes and formats, including: Standard (1/4") phone,
0.25" or 6.35mm; Small phone, 0.206 or 5.23mm; Mini, 0.140" 0r 3.6mm; Micro or
Submini, 0.097" or 2.5mm.
- Jack Box
A device with one plug and several jacks to permit the connection of a number of units
such as headphones to one output jack. Some models are available with variable volume
The distortion (usually of a wide-top narrow-bottom effect) of a projected image caused by
improper projector-to-screen angle.
- Kilohertz (kHz)
Ghost image of an object or subject which remains on screen after the image of
object is no longer on the screen.
Local area network; a computer system that allows PCs, terminal, mainframes and
peripheral devices to interconnect and exchange files.
- Lantern Slide
A once common slide, often glass, 31/4" x 4".
Light Amplification by Stimulated Emission of Radiation; often used in pointers.
- Lavalier Mike
A small microphone worn on a cord around the neck or clipped to the lapel. Also see microphone.
Liquid Crystal Display; liquid crystals exist in an intermediate state between liquid and
solid, and realign under electrical stimulation. Exceptionally slim and light, they are
ideal in computer and TV displays.
- LCD Panel
An LCD device which allows text and graphics from a personal computer to be displayed onto
a large screen using an overhead projector as the light source.
- Learning Center
A device into which several people may plug headphones so they may all listen to the same
Light Emitting Diode; a semiconductor diode that converts electrical energy into visible
electromagnetic radiation. Often used in VCRs and other equipment displays.
- Lens Speed
Refers to the ability of a lens to pass light expressed as a ratio: the focal length of
the lens divided by the (effective) diameter. A fast lens which passes more light might be
rated f/1.1 or 1.2; a much slower lens which passes less light might be designated f3.5.
The f/number or f## = focal length/aperture.
A measurement of quantity of light taken at the source of the light. Lumens per square
foot are footcandles. See also LUX.
- Luminance (Video)
The relative brightness values of a particular object in a scene.
The metric measurement of light quality. The measurement is taken from the reflection off
the object illuminated. One footcandle equals 10.76 LUX. A LUX equals one LUMEN per square
- Masking Borders
See Screen Borders and Drop
- Original, as in recording.
- Matte White
See Screen Surfaces
The display of user options at any given point in a program
Megahertz; millions of cycles per second.
- Micro/Mini Cassette
One of several audio cassettes much smaller than the compact cassette; used principally
for note taking and dictation.
A device that converts sound into electrical signals usable by other pieces of audio
equipment. Microphones vary in sound quality, generating system used, directional patterns
and impedance. For examples see Shure Microphones in the Equipment Guide.
- Microphone Directional Patterns
- Picks up sound from all directions;
- Cartioid, Unidirectional
- Picks up sound primarily in the direction it is pointed, rejecting sounds from the rear
of the Mic.
Example: Shure SM57
- Picks up sound in front and behind itself and rejects sounds from the side
- Microphone Generating Systems
- Uses a piezo-electric element to generate voltage when it is deflected by sound.
- similar to ceramic, no longer used in A-V applications
- Made with a diaphragm which compresses carbon granules to vary the current, no longer
used in A-V applications.
- Microphones dynamic
A microphone with a diaphragm connected to a fine wire coil
moving a magnetic field, may be any pattern.
Condenser, Electrostatic or Capacitor
- A Mic with a conductive diaphragm that varies high-voltage electric field to generate a
signal, may be any pattern, requires a mini amp and power supply.
- Similar to electrostatic except the diaphragm is permanently charged, eliminating the
need for high-voltage supply, usually requires an internal battery for a built-in pre-amp.
Example: Shure SM58
Audio signals (noise) caused by the mechanical vibration of elements within a system.
A device for reflecting light; may be plane or curved. Used in projectors behind lamps to
concentrate and distribute light, to reverse images images for correct viewing (such as rear screen projection), and to fold light beams for more compact
or more convent systems.
A device to inspect or preview a program.
- Multi-Standard Decoder
A device that converts HTSC, PAL, SECAM or NTSC 4.43 video to RGB
Multiple sub-Nyquist Sampling Encoding; one of several HDTV
transmission methods; also one of the first. Some versions, including Muse-6 and Muse-9
are receiver-compatible while others are not.
National Association of Broadcasters
in audio systems, noise is an electrical interference or any unwanted sound. In
video it refers to random spurts of electrical energy or interference. Heavy noise is
often called snow.
A microphone designed to cancel ambient noise so it will not be broadcast or recorded. The
housing of the microphone allows noise to reach both sides of the diaphragm
simultaneously, thereby canceling each other out. A close speaking voice strikes the
diaphragm on only one side so generating a stronger signal with less background or room
noise. Also see microphone.
- Non-Linear Optical Device
A device that converts the wave length of a laser. Theoretically, recording density using
this technology could be increased by a factor of 4.
National Television Standards Committee, which established the US standard 525-line
60-field system, often referred to as just the NTSC format. This format is color
compatible. Humorously referred to as: "Never Twice the Same Color".
- Objective Lens
See Projection Lens
Original Equipment Manufacturer. Companies often buy products from OEMs for sale under
their own label.
- Opaque Projector
- Uses the principal of light reflection to create an image of any nontransparent object,
such as printed pages, coins, photographs single sheets or in book form. Screen images
ordinarily require a well darkened room.
- Open Reel
Audio or video tape or film mounted on a reel that is not enclosed in a cartridge or
- Optical Sound
Sound that is reordered by photographic means on film. The sound track is printed along
the edge opposite from the sprocket holes. The sound is reproduced by projecting a narrow
beam of light from an exciter lamp through the sound track into a photoelectric cell which
converts it to electrical impulses for amplification.
Signal delivery from any audio or video device; also a jack, connector or circuit which
feeds the signal to another piece of equipment such as a speaker or headphones.
- Overhead Projector
A device which produces an image on a screen by transmitting light through a transparency
or LCD panel lying on the face or stage of the projector. The
lens and mirror arrangement in an elevated housing makes it possible to project a bright
image in a semi darkened room. For examples see Overheads in
Phase Alternate by Line; 625-line 50-field composite color transmition system,
used in England, Western Europe, Scandinavia, South Africa and Australia
Phase Alternate by Line; Brazilian broadcast standard which consists of 525 lines and 60
fields per second.
- Peak White
The whitest portion of a picture signal.
- Phone Plug
Jack or plug type most often used for microphones.
- Phonon Plug
Jack or plug type most often used with audio amplifiers, also known as RCA Plug.
picture Element; the smallest element to create an image in computer graphics; a dot.
- Pixel Resolution
A measurement of resolution of a television image defined in terms of
- Projection Lens (Objective Lens)
A convex lens or system of lenses that recreates an enlarged image on a screen.
- Rear Screen
A translucent screen of glass or plastic with a specially formulated coating on which the
image is projected through the screen for viewing. The screen is between the projector and
the viewer. The image must be reversed or a mirror used to correct
the image for viewing.
- Screen Borders and Drop
Black masking borders are a black area around the edge of a projection screen. Borders
enhance the perceived brightness of an image on a screen. The human eye perceives the
image to have more contrast and a sharper picture with brighter colors. Borders also allow
the projected image to "bleed-off" the screen for professional appearing
- Drop is extra fabric added to the top or bottom of the screen to adjust the screen
surface to within normal viewing heights. Drop can usually be specified in either black or
- Screen Surfaces
One of the most versatile screen surfaces and the number one choice for
situations where ambient light is controllable. It's surface evenly distributes light over
a wide viewing area. colors remain bright and life-like, with no shift in hue. Screen
surface may be cleaned with mild soap and water. flame retardant and mildew resistant.
Gain - 1.1 Viewing Angle - 50 degrees
A glass beaded screen surface has the ability to achieve a higher gain by
reflecting more of the projected light back along the projection axis. glass beads
impregnated in the screen's surface provide additional reflectance providing a screen
surface for vibrant, life-like color reproduction at moderate viewing angles. Not
recommended for areas where screen will be subject to abuse or soiling.
Gain - 2.5 Viewing Angle - 30 degrees
Video Spectra 1.5
This screen surface is especially designed for demanding video and LCD projection
applications where a balance of higher gain and greater viewing angle is required. The
special Pearlescent surface may be cleaned with mild soap and water. Flame retardant and
Gain 1.5 Viewing Angle - 40 degrees
This screen is a technological breakthrough. The multi-layered surface provides
the high reflectivity of a glass beaded surface with the unique ability to clean the
surface when required. It's smooth textured surface provides the highest gain of all typed
of screen surfaces with a moderate viewing angle. Can be cleaned with mild soap and water
and is flame retardant and mildew resistant.
Gain - 2.8 Viewing Angle - 30 degrees
Super Wonder-Lite employs a scientifically designed ridged lenticular pattern,
embossed into an aluminum vinyl and textile laminate. It's free from objectionable glare
and hot spots, even in partially darkened rooms. It's washable and mildew resistant. Not
available in all screen types since the material needs to be tensioned.
Gain - 2.5 Viewing Angle - 50 degrees
A screen surface characterized by a lens-like embosses and sliver or aluminized surface to
reflect maximum light over a wide horizontal and narrow vertical angle. Must be held very
flat (tensioned) to avoid "Hot Spots")
For rear projection screen surfaces see the Da-Lite Screen Surface
- Super Wonder-Lite
See Screen surfaces
- Video Spectra 1.5
See Screen Surfaces
A low rate periodic disturbance in sound usually caused by regular variations in the
rotation on some mechanical component of the system. Usually WOW and Flutter
A division of Ozarks Audio Visual
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