The other primary type of digital audio connection is the optical connection. Unlike the digital coaxial connection, which transmits the digital signal electrically through copper wire, the digital optical connection (also called a S/PDIF connection, for Sony/Philips Digital Interface) transmits the digital signal across a fiber optic cable (see Figure 2). The result is the cleanest form of signal transfer currently available.
You see, as good as digital coax is, there are some inherent problems with the physical format, chiefly due to the limitations of the electrical signal. Electrical signals degrade over long distances, and are prone to interference from other electrical devices—even when shielded, as with coaxial cable.
Fiber optic cable has none of these drawbacks. A fiber optic cable is simply several small strands of polished plastic specifically designed to transfer light. The digital audio signals are transmitted through the cable as pulses of light. They're immune to electrical interference, and the signal holds up better over longer distances. The only drawback is that the signal can sometimes be affected by extreme bends in the cable; you can't get light to turn corners!
Because you don't need to shield an optical signal, digital optical cables are thinner than digital coaxial cables. They're still expensive, however, because of the fiber optics; you'll typically pay a 50% premium over a digital coax cable of similar length.
The connectors at either end of the digital optical cable are called Toslink (or EIA-J) connectors. Toslink connections are found on some CD and DVD players (and satellite/cable boxes), but not all. Since Toslink jacks are a bit more expensive than RCA jacks, some lower-priced equipment features digital coaxial connections only. Most higher-end equipment will have both digital coaxial and digital optical connections.
Figure 2 Digital optical cables.
Some portable CD and audio players feature digital optical connections with a slightly different jack, called a mini-optical jack. To connect one of these players to your home A/V receiver, you'll need a special Toslink–to–mini-optical cable.
As with digital coaxial cables, a single digital optical cable carries all available audio channels—left/right stereo and 5.1-channel surround sound.