The identical RCA connector used for analog audio signals is also used for connecting digital audio components following the SPDIF (Sony–Philips Digital Interface Format) standard. A coaxial jack can carry either a stereo (CD format) or multichannel (Dolby Digital/DTS) digital audio signal and will be labeled as an input or an output. Jacks of either type are usually color-coded orange or black. Though any cable with RCA plugs at the ends can be used to make a digital audio connection, you should use a cable that’s specifically designed for digital audio to ensure the best possible signal transfer. In other words, use a cable that’s rated for 75 ohms impedance in which both the conductors and the plugs are coaxial.

Toslink optical ports pass the very same SPDIF-format digital audio data as coaxial RCA jacks, but they use pulsating light, instead of fluctuating electrical current, to carry the data. Toslink connections use special fiber-optic cables as the medium. The red light you see coming from an active Toslink output isn’t laser light and isn’t harmful. Dirt and dust can impede the optical link, so avoid handling cable ends, and keep dust caps in place over unused ports. Also avoid kinking Toslink cables, which can render them permanently useless.

The digital audio signal format adopted by the Audio Engineering Society (AES) and the European Broadcasting Union (EBU) uses the same XLR “microphone” jacks and plugs as for balanced-line analog audio. Connections for it are found widely on pro-audio gear but on only a few ultra-high-end audio and home theater components.