There are published glossaries of audio-visual terminology so this guide is by no means comprehensive and represents a basic guide.
- ANSI lumen
- A unit of measurement of projector brightness, calibrated and clarified by the American National Standards Institute.
- Analogue
- Signals that are recorded in analogue format are modulated, ie their information is contained in amplitude or amount of signal. Digital, conversely, is either on or off, and amplitude is identified in a different way.
- Aspect ratio
- The relationship between the height and width of an image, usually described as a ratio with the width first eg 4:3 or 16:9.
- Audio In (stereo input)
- The jack or jacks (eg standard RCA jack, to plug in sound coming from an external source.
- Audio Out (stereo Out)
- The jack or jacks to hook up external amplification systems.
- Betacam
- Analogue, component video format ie broadcast rather than domestic quality. Uses ½” cassette. Now includes Betacam SX and Digital Betacam.
- CD
- Compact disk, digital storage medium, invented by Philips.
- CD-ROM
- Compact disk-read only memory.
- CD-RW
- Compact disk-rewritable, editable after final ‘save’.
- Codec
- An electronic circuit that converts analogue signals to digital and digital to analogue.
- Compressed Resolution
- A process in which a projector accepts a higher resolution signal and compresses the data down to fit its true resolution.
- Composite video
- A video signal that combines all the color and timing components of the image into a single input line.
- Component video
- System of signal recording and processing that maintains the original video elements separately rather than combined (encoded) into a single, composite video signal.
- Contrast ratio
- A method of measuring the dynamic range. A contrast ratio of 15:1 (passive matrix LCDs), offers washed out colors, little detail, and images that can barely survive with significant ambient light. Projectors with Active matrix TFTs have ratios to 100:1, DLPs from 125:1 and Poly-Si LCDs 200:1. By comparison transparency film (i.e. 35mm slides) have contrast ratios over 500:1.
- Colour temperature
- The measure of the colour of a light source by relating it to a theoretically perfect black body source of radiant energy, measured in degrees Kelvin (°K).
- Contrast
- The degree of density difference between tones in an image or the ratio between the maximum and minimum brightness values. A high contrast image will have deep or intense blacks and detailed or spectral whites which may or may not include a full range of middle value tones. A low contrast image is generally an image with all its tones placed in the short middle values and may only contain various shades of grey.
- Crosstalk
- Crosstalk is the leakage of a signal into adjacent channels or into another part of a system. Crosstalk may occur through electrical, mechanical, magnetic, capacitive or other forms of coupling, for example, between adjacent heads in a multitrack recorder, in analogue disc recordings, or in electronic circuits, such as when wires or tracks on a printed circuit board are close together.
- Cue light
- Cue button on lectern, which generates a signal to the technician who moves on the slide.
- Data Rate
- The rate at which data is transmitted, usually stated in bits per second.
- Data/video projector
- A projector that handles common computer and video signals, often associated with the Microsoft software, PowerPoint.
- Decibel
- The unit of measure used to indicate relative changes insignal intensity or sound volume.
- Digital
- Binary format.
- Digital Betacam
- Digital VTR recording format, developed by Sony.
- Device driver
- Software that allows a computer to communicate with an internal or external peripheral device, such as a printer, scanner or CD-ROM player.
- Diagonal Screen
- The method of measuring the size of a computer or television image. Measured from one corner to the diagonally opposite corner, a 9 FT high by 12 FT wide projected image has a diagonal of 15FT. Typically, in computer and video we assume that the diagonal dimensions are for the traditional 4:3 aspect ratio as in the previous example. Remember, the 4:3 aspect ratio is standard for Video and computer images, but some screens are square, others particularly wide.
- Digital compression
- Encoding data or digital information to use less storage space or to require less bandwidth for efficient transmission.
- Digital Light Processing (DLP)
- The technology inside is sometimes referred to as either “micro-mirrors”, or DMD: It works with a powerful lamp and uses hundreds of thousands of rotating mirrors, lined up in 800 rows of 600 mirrors each. Attach each of those 480,000 hinges to its own motor. The motors tilt their mirrors up to 20 degrees at incredible speeds. allowing the mirrors to modulate light from the lamp, and send the “modulated signal” out through a lens, on to a screen. The 480,000 mirrors (actually 580,000 are used), hinges and motors are packed onto a “wafer” a bit larger than your thumbnail.
- Digital Video
- Video where all the instructions for the images are in computer data form, i.e. bits.
- Digitise
- Process of converting analog information into digital information.
- Distribution amplifier
- An amplifier used to maintain a clean noise free signal to the projector over significant distances. Even with heavily shielded cables, the range of video and computer signals is limited to a few dozen feet before noticeable degradation. Often projection using ceiling mounted equipment, a distribution amp may be needed even with shorter distances to eliminate the interference caused by electric conduits and equipment in the ceiling near the signal cable. Many distribution amps can also split the signal into 2 or more amplified signals for driving multiple projectors, projectors and monitors.
- Dolby Stereo Sound
- Dolby Laboratories’ original motion picture film soundtrack system that encodes four channels of sound (left, center, right and surround) into a two channel photographic sound track, incorporating Dolby A-type noise reduction and extended frequency response.
- DVCAM
- A relatively low cost broadcast Digital VTR format based on the consumer DV standard using 6.35 mm tape recording a 4.2.0 component signal sampled at 8 bits and compressed at a ratio of 5:1 on metal evaporated tape.
- DVD
- Digital Versatile Disk (Digital Video Disk): a video format for storing full length motion picture images on a 5” (120mm) compact disc (CD) using MPEG-2 compression for “better than VHS” quality. It is the same size as a CD but stores from 4.38 GB (seven times CD capacity) on a single sided, single layer disk. DVDs can also be double sided or duel layer – storing even more data.
- Dynamic Range
- The ratio of the maximum to minimum level of a signal or number.
- Electronic Whiteboard
- A whiteboard that has the ability to electronically scan itself and the images can then be transferred to computer, edited, printed, emailed or faxed. Many electronic whiteboards will interface with projectors, allowing annotating of presentations and some control of the computer.
- Encoder
- A circuit that combines the primary red, green and blue signals into a composite video signal.
- EPS
- Encapsulated PostScript. A method of storing and interchanging high resolution vectorised graphics of unlimited resolution in PC and Macintosh environments.
- Focal length
- The optical property of a lens. In projection terms, the smaller the focal length, the larger the projected image is likely to be.
- Frame store
- A digital device designed to store and display a single television frame as a freeze frame.
- Freeze frame
- An optical printing effect in which a single frame image is repeated so as to appear stationary when projected.
- Frequency
- The rate of vibration of an electrical or mechanical oscillation. Measured by the number of complete cycles executed in 1 second. In audio terminology, frequency range is considered to be from 20 cycles per second, or 20 Hertz (Hz), up to 20,000 cycles per second, or 20 kilohertz.
- Front Projection
- Projecting onto a reflective surface of an opaque screen material for viewing from the same side, as opposed to rear projection.
- Fresnel lens
- Used to focus light. The lens is virtually flat.
- Gradation
- The slow change of a colors density; a change in tone or texture, etc., between adjacent areas of an object or the corresponding image.
- Graphics standards
- These determine the number of colours and the definition you can expect to achieve.
Computer graphics standard Resolution/pixels VGA (Video Graphics Array) 640×480 VSVGA (Super) 800×600 VXGA (Extended) 1024×768 VSXGA (Super Extended) 1280×1024 VUXGA (Ultra Extended) 1600×1200 VQXGA (Quantum Extended) 2048×1536 - HDTV
- High Definition Television, a term used to describe advanced production and delivery systems.
- High Gain Screen
- A screen that uses one of many methods to collect light and reflect it back to the audience. This results in an image which is considerably brighter than the image on a white wall or matte screen. The disadvantage of a high gain screen is often a narrower viewing angle. High Gain screens are more expensive than Matte screens.
- Hiss
- Unwanted background noise in a sound system.
- Hz, (KHz, MHz)
- Hertz or (Kilohertz or Megahertz). Cycles per second. (Kilo = 1,000, Mega = 1 million). These terms are used to express the frequency of an electrical signal.
- Infra-red remote
- The traditional remote control, it transmits infrared light, like a television remote. Typical range is limited to 30 or 35 feet. Infra-red requires line of site or a bounce off of a hard surface. These signal from this type of remote control cannot pass through walls.
- Interface
- A piece of equipment which connects normally incompatible components so that the signal from one is readable by the second.
- IR (Infra-Red)
- A type of wireless transmission using infrared light waves.
- Iris
- Adjustable diaphragm controlling amount of light trasmitted by a lens.
- Keystoning
- The “wedge” shape picture caused when the projector is not even with the horizontal or vertical center of the middle of the screen. Most data and video projectors use optical and electronic methods to eliminate this problem.
The picture ‘keystones’ like the keystone in an arch. - LCD
- Liquid Crystal Display. A glass panel display that works by controlling the opacity of segments of itself by varying the electrical signal. Each individual segment called a pixel, acts as a shutter, to control the amount of light being passed through.
- LCD projector
- A projector using LCD technology.
- Lighting ratio
- Difference between intensity of key light and fill (shadow) light in a scene.
- Light Valve
- Another projection technology, found in the “big” systems, these units are extremely bright and capable of producing “stadium size” images.
- Lux
- A unit for measuring light, as methods of measurement are not standardized, numbers provided by manufacturers usually do not provide all necessary information to compare one product to another. A preferred unit of measuring light output is the ANSI Lumen.
- Megabyte
- 1 million, or 1,048,576, bytes or characters. It is abbreviated as MB or Meg.
- Memory
- The device in the computers main unit that stores information, both permanently (hard-disk) or temporarily in microchips (RAM or random-access memory).
- Metal halide
- A type of projector lamp giving out a bright, clear white light, and used in many medium and all high-end portable projectors. These lamps emit a very high amount of light for the amount of power they consume. Unlike many other types of lamp, they slowly lose intensity (brightness) as they are used. These lamps output a very “hot” temperature light, Their whites are “extremely” white and make Halogen lamps whites look yellowish in comparison.
- Modulation
- The imposing of a signal on some type of transmission or storage medium, such as a radio carrier or magnetic tape. Impressing a signal onto a carrier frequency for transmission purposes. In video, a Modulator is a section within a VTR that changes the frequency of the video signal information coming in from an external source to signal information that is compatible with the requirements of the VTR heads, while keeping the picture information basically unchanged.
- MPEG
- Moving Picture Experts Group. ISO / ITU-T. MPEG is involved in defining a standard for data compression of moving pictures. Its work follows on from that of JPEG [single pictures] to add inter field compression, the extra compression potentially available through similarities between successive frames of moving pictures. MPEG-1: Uses a data rate of 1.2 Mbps (Mega Bits per Second), the speed of CD-ROM transfer. MPEG-2: Uses a data rate (also called a bit rate) of from 2 to 10 Mbps. MPEG-2 is the format most favoured for video-on-demand and DVD.
- Non Linear
- Non-Linear (Editing) means not linear, meaning that the recording medium is not tape.
- NTSC
- National Television Standards Committee. Usually refers to the standard for video and broadcasting used in the United States, Canada and several other countries. The NTSC standard is older and produces lower resolution than other television systems used in the world. It is incompatible with other television standards.
- OHP
- Overhead projector.
- PAL
- Phase Alternate Line. The PAL television system used extensively in Great Britain and western Europe. It is incompatible with other television standards.
- Peripheral
- External devices controlled by the computer, e.g. printer, keyboard, mouse.
- Pixel
- Short for picture element. The smallest element of a raster display represented as a point with specified color and intensity.
- Polysilicon LCD
- The latest LCD technology for LCD projectors. Polysilicon is usually 3 separate layers of LCDs, for red, green and blue light. This results in increased color dynamics, with high contrast ratios around 200:1. Poly silicon is ideal for multimedia applications.
- PostScript
- Adobe’s page description language that allows printing devices to interpret complex graphics.
- QuickTime
- A system extension for the Apple Mac that facilitates the playback of video clips.
- Rear projection
- The projector is placed behind a translucent plastic screen, out of sight of the audience. It projects onto the back screen and the audience sees on the front.
- Refresh rate
- The number of times the screen image is “painted” or refreshed per second, expressed in Hz.
- Resolution
- Number of dots or pixels per unit of area. The greater the pixels per unit area the higher the resolution, giving more detail.
- Reverse Image
- Reverse image is a feature found on many projectors which flips the image horizontally. Reverse image is needed for rear projection.
- RGB
- Red, green, blue – the description of the components fo white light that are used in varying proportions to create any colour imaginable.
- S-VHS
- Super VHS, an enhancement of the basic VHS format.
- Scan rate
- Refers to the frequency of a projector, monitor or signal. All computer signals ‘scan’ across the screen, building up the image. Expressed in Hertz (kHz).
- SCSI
- Small Computer Systems Interface, pronounced “scussy”. A device independent interface used for a wide range of peripherals.
- SECAM
- A television standard for video and broadcasting. Used mainly in France and the former East Bloc countries. Higher resolution than NTSC. It is incompatible with other television standards.
- Serial
- A method of transmitting data bit-by-bit through a single communications channel.
- Source
- An input feeding a signal to a projector.
- Subwoofer
- A speaker designed specifically to reproduce low-frequency information, usually between the range of 20 to 120 Hz. Dolby Digital soundtracks provide a separate low-frequency effects (LFE) channel specifically for playback over subwoofers.
- Surround sound
- Dolby Laboratories’ original motion picture film soundtrack system that encodes four channels of sound (left, center, right and surround) into a two channel photographic sound track, incorporating Dolby A-type noise reduction and extended frequency response.
- SVGA
- Super VGA Resolution, see Graphics Standards.
- Synchronisation
- The maintenance of one operation in step with another. Abbreviated as ‘sync’ In film a picture record and a sound record are said to be “in sync” when they are placed relative to each other on a release print so that when they are projected the action will coincide precisely with the accompanying sound. When these conditions are not met they are said to be “out of sync”. In video, this is usually refers to the synchronization pulses necessary to coordinate the operation of several interconected video components. When the components are properly synchronized, they are said to be “in sync”. A sync generator is an electronic component that generates sync pulses.
- SXGA
- SXGA refers to a monitor resolution of 1280×1024 pixel display, regardless of the number of colors available.
- TFT
- Thin Film Transistor, used in monitors to reproduce sharp images.
- TIFF
- Tag Image File Format. A method of storing scanned or graphical images on computer, for interchange between systems or software packages.
- Time code
- Standardized frame identification used in video editing or electronic indexing method used for editing and timing video programs. Time code denotes hours, minutes, seconds and frames elapsed on a videotape.
- True Colour
- A term for 24 bit color (16.7 million colors – any combination of 256 shades each of Red, Green, and Blue).
- VCR
- Video cassette recorder, normally with built-in TV tuner.
- VHS
- Video Home System. Dominant domestic video format.
- VGA
- Video Graphics Array. See Graphics Standards.
- VTR
- Video tape recorder.
- Video conferencing
- Remote conferencing to one or more specific sites with the ability to send and receive both vision and audio, live.
- Webcasting
- Means of streaming data and video via the Internet.
- Widescreen
- The term widescreen is used to describe a variety of forms of film projection in which the aspect ratio (width-to-height proportion) of the picture is greater than the 4:3 format adopted as standard. Originally, one object of the ultra-large screen was to stimulate peripheral vision and thus give an illusion of 3-D which the smaller screen lacked.
- Windows
- Microsoft’s PC architecture, based on a graphical user interface (GUI) like the Apple Macintosh.
- XGA
- See Graphics Standard
- Zoom lens ratio
- The ratio between the smallest and largest image a lens can projector from a fixed distance.
Ref: Sharp, Screensound