Glossary

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Ambient
In audio-visual, unwanted light or sound

Amplifier
A Device which supplies power to and strengthens an incoming signal for output

Analog
Represented as a continuous signal or quantity, continuous, as opposed to digital; represented by discrete numbers with an extremely wide range of values

Anamorphic
A type of lens adapter designed to produce a wide screen image from an equally condensed image on the film

ANSI
Automatic Sensitivity Control; detects light intensity and keeps the camera in optimum working conditions as it applies to light input.

Aspect Ratio
The proportions of a projected picture area. In the US, standard video aspect ratio is 4 units wide by 3 units high, usually shown 4:3

Audio-In
Input jack witch delivers a signal to piece of equipment or a jack that receives a signal using a cable with the proper connectors.

Audio-Out
Output jack which brings an audio signal from a piece of equipment of one which delivers an audio signal using a cable with the proper connectors.

AutoExect.Bat
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.

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  F to H  

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Fade
Varying the strength of a picture - either from black to full strength (fade in) or from full strength to black (fade out).

Feedback
The regeneration of sound caused by a system's microphonic pickup of output from it's own speakers causing a ringing sound or signal.

Field
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.

Filmstrip
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 screen.

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.

Flutter
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 cleaner edits.

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.

Focus
Sharpening a blurred image on a screen, monitor or any display; adjusting picture to achieve the greatest possible resolution.

Footcandle
The amount of light reflected by a surface one foot from a lighted candle. Metric equivalent is LUX.

Footlambert
One Lumen or one Foot candle of light over a one square foot surface.

Frame
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 quickly.

Frequency
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.

Fresnel
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 lights.

Front Screen Projection
An image projected on the audience side of a light- reflecting screen. See also Rear Screen.

ft/s
Feet per second

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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 screen surface.

Gain
The amplification of a unit of system. May be expressed in dB for electronic equipment or a factor (times) for screens.

Genlock
A device which locks the frequency of it's internal sync generator to an external source.

Geometry
The ability of a projector to accurately reproduce the border around a rectangle image.

GHz
Gigahertz; 1 billion cycles per second

Glass Beaded
See Screen Surfaces

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Hardware
The electronic and mechanical components of a computer system.

HD
High Definition; often meaning HDEP and HDTV

HDEP
High Definition Electronic Production

HDTV
High Definition Television, a term used top describe advanced production and delivery systems.

Head
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.

Headphone
A device consisting of one or two electro-acoustic receivers attached to a headband for private listening to audio sources, sometimes called an earphone.

Headset
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.

HGA
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 point.
Hot Spots

Hub
Central part of a reel on which tape or film is wound.

Hue
Color; Value (red, green, blue, yellow) rather than intensity or brightness.

Hum
Audible disturbance caused by the power supply.

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  M to O  

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Masking Borders
See Screen Borders and Drop

Master
Original, as in recording.

Matte White
See Screen Surfaces

Menu
The display of user options at any given point in a program

MHz
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.

Microphone
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
Omnidirectional
- 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
Bidirectional
- Picks up sound in front and behind itself and rejects sounds from the side

Microphone Generating Systems
Ceramic
- Uses a piezo-electric element to generate voltage when it is deflected by sound.
Crystal
- similar to ceramic, no longer used in A-V applications
Carbon
- 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.
Electret
- 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

Microphonics
Audio signals (noise) caused by the mechanical vibration of elements within a system.

Mirror
A device for reflecting light; may be plane or curved. Used in projectors behind lamps to concentrate and distribute light, to reverse images for correct viewing (such as rear screen projection), and to fold light beams for more compact or more convent systems.

Monitor
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 video.

Muse
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.

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NAB
National Association of Broadcasters

Noise
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.

Noise-Canceling
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.

NTSC
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".

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Objective Lens
See Projection Lens

OEM
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 cassette.

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.

Output
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 Equipment Guide

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PAL
Phase Alternate by Line; 625-line 50-field composite color transmission system, used in England, Western Europe, Scandinavia, South Africa and Australia

PAL-M
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.

Pixel
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 discernable pixels.

Projection Lens (Objective Lens)
A convex lens or system of lenses that recreates an enlarged image on a screen.

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(empty)

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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.

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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 presentations.
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 white.

Screen Surfaces
Matte White
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

Glass Beaded
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 mildew resistant.
Gain 1.5 Viewing Angle - 40 degrees

High Power
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
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

Lenticular
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 Page.

Super Wonder-Lite
See Screen surfaces

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Video Spectra 1.5
See Screen Surfaces

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WOW
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 are combined.