ical instrument. Source input format. Used in MPEG, and not to be confused with the Common Intermediate Format (CIF) used in the ITU-T's H.32X family of videoconferencing standards. Glossary of Terms signal-to-noise A ratio used to describe the clarity or degradation of a circuit. Signal-to-noise is measured in decibels. An acceptable signal-to-noise ratio is generally 200:1 or 46 See Session Initiation Protocol. simplex A circuit capable of transmissions in only one direction. sine wave The smooth, symmetrical curve that is created by natural vibrations that occur in the universe. single mode fiber Optical fiber with a central core of such small dimension that only a single mode of transmission is possible. Light travels straight down the middle of the fiber without zigzagging from side to side. Single mode fibers transmit high bit rates over long distances. slow-scan Television or video scanning system in which a frame rate lower than normal is used to reduce the bandwidth required for transmission. Often associated with the transmission of video frames over the public switched telephone network. SMATV Satellite Master Antenna Television. A distribution system that feeds satellite signals to hotels, apartments, etc. Often associated with pay-per-view. Switched Multimegabit Digital Service. A public networking service based on the IEEE's 802.6 specification. smear The undesirable blurring of edges in a compressed image, often caused by the DCT that tends to eliminate the high-frequency portions of an image that represent sharp edges. SMPTE Society of Motion Picture and Television Engineers, the authors of the SMPTE time code used in video film and A/V production. SMPTE Time Code An 80-bit time code used in video editing. Developed by the SMPTE. Random noise or interference appearing in a video picture as white specs. Video Communication: the Whole Picture software The programs, procedures, rules and routines used to extend the capabilities of computers. SONET Synchronous Optical Network. sound waves Naturally oc