A cable that uses light beams to transmit information rather than electrical signals traveling over metal wires. Fiber-optic cables are used routinely in the telephone industry to send high-quality signals over long distances. This technology has been applied to audio to connect digital audio devices. he fiber-optic cables used in audio (AT&T ST and Toslink) are composed of glass fibers (AT&T) or plastic fibers (Toslink) which can transmit beams of light. The light beams are generated at one end of the cable and received at the other where they are converted from digital signals into analog waveforms for audio reproduction through speakers and amplifiers. This type of cable is often used to connect CD transports, CD players, DVD players and laserdisc players to external digital-to-analog converters (DACs) or digital surround sound processors (for use with Dolby Digital and DTS discrete digital surround sound audio systems). he greatest benefit of using fiber-optic cables in an audio system is their immunity to electromagnetic interference. Traditional metal wires carrying electric signals are subject to distortion from other wires, power supplies, magnetic interference, etc. However, the light pulses traveling through fiber-optic cables are not subject to the same distortions. he AT&T glass cable is the higher quality of the two types of fiber-optic cable frequently used in audio, but the Toslink cable is much more prevalent and less costly. Other forms of digital signal transmission commonly used (using traditional electrical signals and metal wires instead of fiber optics) are AES/EBU and digital coaxial cables.