curring oscillations that are created when objects vibrate at a certain frequency, and thereby compress the air molecules around them and cause these molecules to seek equilibrium by decompressing outward. During decompression dynamic energy is expended, thereby causing neighboring groups of molecules to compress. This starts a chain reaction. Compressed air is pushed in all directions from the source. If the resulting waves are between 50 and 20,000 Hz humans can hear them as sounds. spatial Compression/coding that is performed on a single frame of video data as opposed to temporal (time) coding that is performed by comparing successive video frames to each other. spectrum A range of wavelengths or frequencies of acoustic, visible or electromagnetic radiation. Also refers to a display of visible light radiation that is arranged in order of wavelength. SpectrumSaver Compression Labs compression system designed to digitize and compress a full-motion NTSC or PAL analog TV signal SO that it can be transmitted via satellite in as little as 2 MHz of bandwidth. splitter In CATV networks, multiple feeder cables are attached to splitters that match the impedance of the cables. square wave A term typically used to refer to a digital signal comprised of only two voltage values, that represent on and off (or one and zero). SQCIF H.263, a scalable version of H.261, Sub-QCIF, a 128- by-96 pixel image resolution format. SQCIF was also added to the H.261 recommendation, to allow low- resolution picture coding. S/T-Interface The ISDN Subscriber/Termination (S/T) Interface uses two pairs of wires to deliver an ISDN signal from a wall jack to an ISDN adapter or other ISDN equipment. standards conversion The process of adapting a television or video production from one set of standards (e.g., NTSC) to Glossary of Terms another (e.g., PAL). This is necessary when programming that was developed for one part of the world (e.g., North America), is viewed in another (e.g., Europe). star topology A network in which there is an individual