Type of high-quality glass fiber-optic cable used to transmit digital data between digital audio sources and digital-to-analog converters. The AT&T ST fiber is the highest quality fiber-optic cable used in audio. The Toslink style cable, by comparison, uses clear plastic fibers instead of glass and does not achieve as high a level of data transmission quality as the glass AT&T style fiber. However, the AT&T fiber is used much less frequently than Toslink connections or non-fiber connections due to its cost. Fiber-optic cables send digital data as pulses of light beamed along thin, clear fibers. By using light instead of electronic data transmission, the signal is kept free from electronic distortion.