Glossary of Technical Terms

Compact Disc

Compact Disc is a stereo digital audio system based upon a 12cm single sided disc made from a polycarbonate material with an internal reflective layer of aluminium or occasionally gold. The information is read by sensing the presence or absense of reflected light from a tightly focused Laser beam pointing at the pits and bumps in the reflective surface within the disc. The digital audio signal is sampled to 16 bits per channel at a rate of 44.1KHz. The major developers were Philips electronics of Holland and Sony of Japan; it was largely based upon optical disc technology developed for Philip's VLP video disc system which later became LaserDisc, and the digital Pulse Code Modulation (PCM) work done by Sony.

CCIR

The CCIR is a standards body that originally defined the 625 line 25 frames per second TV standard used in many parts of the world. The CCIR standard defines only the monochrome picture component, and there are two major colour encoding techniques used with it, PAL and SECAM. The CCIR standard uses 1:2 interlace which means that each 625 line TV image is composed from 2 video fields, each consisting of 312 lines of picture information. The first video field contains just the odd numbered lines from the 625 line picture, the second field contains just the even ones.

EIA

The EIA (Electronic Industry Association) is the standards body that originally defined the 525 line 30 frame per second TV standard used in North America, Japan, and a few other parts of the world. The EIA standard, also defined under US standard RS-170A, defines only the monochrome picture component but is mainly used with the NTSC colour encoding standard, although a version which uses the PAL colour encoding standard does also exist. It is similar to the CCIR TV system in that it uses 1:2 interlace and has two fields per video frame.

LaserDisc

LaserDisc is a laser read optical disc system used for the reproduction of video and audio signals. The system reproduces a full bandwidth analogue video signal with around 7MHz response, along with dual FM coded analogue audio signals. Subsequent revisions have seen the addition of two 44.1KHz 16bit digital audio channels in the NTSC version, and the replacment of the two analogue channels with digital ones in the PAL version. Originally developed by Philips as the Video Long Player (VLP) during the 1970s, it eventually reached the NTSC video market in 1978 as DiscoVision. By the time it reached the European market in 1981, it was appearing under the name LaserVision. LaserDisc was adopted as the current format name in 1990 when Pioneer offered the use of its trademark to allievate the confusion created by the move to digital soundtracks in the PAL markets.

NTSC

NTSC is a colour encoding system named after the US National Television Standards Committee which developed it. NTSC colour is usually used on top of the EIA TV standard. It has received a nickname of 'Never Twice the Same Colour' due to problems it has with colour errors caused by phase shifts in the transmitted signal. These problems do not occur in a cable TV or video environment.

PAL

PAL stands for Phase Alternate Lines. It is an enhanced version of the NTSC colour encoding method which reverses the phase of the colour signal every other line to ensure that any phase errors are immediately countered by an equal and oposite phase error. PAL is usually used in conjunction with the CCIR TV standard, but is used in a few countries (notably Brazil) in conjunction with the EIA TV standard.

RGB

Literally, Red Green Blue. RGB is used to describe the transfer of colour video signals as three seperate picture signals, one for each of the primary colours of the TV picture tube. It is a raw, decoded form of the TV picture used internally within the TV set immediately prior to display. The SCART connector allows for future TV system changes by allowing the TV to display a pre-decoded RGB signal; originally intended for text display applications, it has also been used to allow for S-Video style input to non S-Video connector equiped TV sets.

SCART

The SCART is a 20-pin rectangular connector fitted to the vast majority of PAL market TV receivers. It provides composite video inputs and outputs, stereo audio in and out, and RGB input. Modified versions can also support S-Video style Y/C operation on some sets. It is also known as Euro-connector and PERI-tel.

SECAM

SECAM stands for SEqential Couleur Avec Memoire. It was developed in France as an alternative colour encoding system to PAL, and was adopted extensively throughout eastern Europe to ensure incompatibility with nearby western European PAL transmissions. It is always used in conjunction with the CCIR TV standard.


B.King@ee.surrey.ac.uk
19th June 1994