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AV Glossary
Ambient Light:
The level of lighting in a room such as daylight, artificial light etc. The more light falling on the screen, the brighter the projector needs to be.
ANSI Lumen:
A measurement system used to measure the brightness of a projector.
Created by the American National Standards Institute.
Aspect Ratio:
This is the ratio between the width and height of the screen. Typical ratios are 4:3 (1.33:1) and 16:9 (1.78:1)
Audio Conferencing:
Voice only technology to enable groups of people at different locations to communicate.
Beamer:
A term sometimes used for a data projector.
Blue-Ray:
High Definition (HD) optical disk format, backward compatible with Standard Definition (SD) DVD disks.
BNC:
A type of connector used on high end video equipment which provides a connection for shielded coax cable and uses a bayonet lock arrangement.
C:
Letter used to denote the Chrominance signal in S-video system.
Candela:
Unit of luminous intensity of a light source in a specific direction.The cd/m2 brightness specification used for flatpanel displays means Candela per metre squared.
Cat 5:
A category of twisted pair (4 pairs to be exact) cable widely used in IT networking and also, with suitable equipment, used to send Audio Visual signals longer distances economically. It supports frequencies up to 100 MHz. It can be used for networks with speeds of 10 to 100Mbps.
Cat 5e:
An enhanced version of Cat 5 supporting frequencies up to 350MHz and can handle data speeds up to 1000Mbps (1 Gigabit per second). It also has reduced crosstalk (electrical interference).
Cat 6:
Similar to Cat 5e but produced to a higher standard.
Cat 7:
A twisted pair cable, again 4 pairs, but each pair is individually screened. The Cat 7 standard has been designed to allow 10Gbps Ethernet over 100m of copper cabling.
Chrominance:
The colour part of the signal (encoded) that is used in S-video. The same type of signal is also combined with the monochrome signal in a composite signal.
Component Video:
Analogue video format whereby the monochrome and 2 colour components are kept separate. Connection of this type of signal between equipment is done using three separate coax cables. (See Y, U and V terminology). DVD players often have this sort of output.
Composite Video:
An analogue video format whereby the monochrome and colour parts (Chrominance) of the video signal are combined. Connection of this type of signal between equipment is done using a single coax cable.
CRT:
Cathode Ray Tube. A glass envelope with a vacuum through which an electron gun fires three beams at a phosphor layer behind the front glass to create an image for display. A technology quickly being replaced by LCD and Plasma flatpanels.
DLP:
A type of data projector using a rotating colour wheel and micro-swivel mirror technology.
DVI:
Digital Visual Interface. This is found on a number of devices including computers, monitors, video cards and TVs. It is a standard for high speed transfer of data to high resolution digital displays.
Note:
HDMI is compatible with the digital video part of DVI. DVI does not carry digital audio, unlike HDMI.
Edge Blending
A term used for the seamless blending of the edges of projected images from two or more projectors.
HDMI:
High Definition Multimedia Interface. A digital connection standard supported by the majority of manufacturers. It has a bandwidth of up to 5GBs and can support all current HDTV standards. It also carries Dolby Surround Sound and is backward compatible with DVI video.
Horizontal Frequency:
This is the speed at which the electron beam in a CRT moves across the horizontal phosphor dots. The horizontal frequency can be calculated by multiplying the vertical resolution by the vertical refresh rate. For example 1024 x 768 (XGA) @ 75Hz. 768 x 75Hz = 57KHz horizontal frequency, rounded down to the nearest KHz.
Interlace:
The TV picture frame is built up with two fields, one with odd lines the other with even lines. 25 frames per second (or 25Hz) would have a field rate of 50Hz.
Keystone:
A geometric distortion on data projectors that results in the projected image being narrower at the bottom than the top. Most data projectors have some form of correction adjustment for this.
Metal Halide:
Type of lamp used in the vast majority of data projectors, mercury being the metal used.
Mini-optical:
This is a connector physically the same size as a 3.5mm jack socket, but using optical connection instead of electrical.
OHP:
Overhead Projector – these have largely been superseded by visualisers used in conjunction with data projectors.
Phase:
In projectors this is often referred to as clock phase. It can be adjusted to align the projector clock phase with the pixels of the image. This helps reduce edge disturbances, particularly on text.
Phono:
An unbalanced audio connector commonly used on domestic consumer equipment as well as AV equipment. It can also be used to connect video. Sometimes called an RCA connector.
Pixel:
A picture element. This is the smallest piece of information in an
image, in digital imaging. Each pixel is a sample of the original
image, and the intensity of it is variable. In projectors and flatpanel
displays the pixel has three components, red, green & blue.
Progressive:
This is a method of building up a picture frame by displaying the lines sequentially, with line 1 followed by line 2 and then line 3 etc, as opposed to interlace.
Refresh Rate:
A term describing the progressive scan frame rate used on computer displays.
RGB:
A colour system using Red, Green and Blue. In computer VGA outputs this is a five channel analogue system with horizontal syncs and vertical syncs as channels 4 & 5. Other systems, broadcast etc use a 4 channel analogue system using composite sync. There is a 3 channel system known as ‘sync on green’. Although not very common these days, it can still be found in medical television. The abbreviation RGsB is used for this.
S-Video or Y/C:
A two channel analogue video format. Connection between equipment is usually done by a miniature 4 pin connector lead. Monochrome connects via one channel and the colour signals (encoded Chroma) connects via the other. Connections can also be done using Scart connectors. A third method uses two BNC video coax leads, although this method is not as common.
Skew Errors:
Signal timing errors introduced to video signals when sent down Cat 5 cable. A lot of AV Cat 5 transmitter/receiver equipment on the market has adjustments for this.
Toslink:
A fibre optical connector used for connecting digital stereo audio and digital dolby 5.1. (See also Mini-optical)
U:
Letter used to represent the B-Y (Blue minus the Luminance) colour difference signal in component video.
V:
Letter used to represent the R-Y (Red minus the Luminance) colour difference signal in component video. Note, There is no G-Y (Green minus the Luminance) as this can be mathematically obtained from the Y, U & V signals.
Vertical Frequency:
This is the rate at which picture frames are displayed on a screen. Interlace frame rate in the UK is 25Hz or 25 times per second. The field rate is 50Hz or 50 times per second.
Video Conferencing:
Video & Audio technology to enable groups of people at different locations to communicate.
XLR:
A balanced audio connector used with professional audio and video equipment.
Y:
Letter used to denote the monochrome or luminance part of a video signal in S-video and component systems. (See also U, V and C)
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