Coaxial Digital cable to RCA
Toslink optical cable and RCA digital cable are both used to carry digital audio signals. Using digital rather than analog allows for better quality audio and surround sound that is determined by the audio creator, such as a movie studio producing a DVD, rather than through audio equipment simulating and creating the surround effects. The two cabling systems have some practical differences, and there is some debate about which is best.
Toslink is the name of a system for connecting two devices and transmitting a digital audio signal through an optical fiber cable. The name comes from Toshiba, which originally developed the system and trademarked the term TOSLINK, short for "Toshiba link." Today the term is used as a generic term for optical audio cabling. RCA refers to a specific type of connector that uses a standard size and design of a circular pin in a jack. RCA can carry many different types of audio and video information, including digital audio. Though strictly speaking it is factually correct, the term "RCA digital cable" is not used as commonly as alternatives such as "digital coaxial" or simply "coaxial." Rather confusingly, people sometimes use just "digital" to distinguish RCA/coaxial cabling, even though Toslink is also a digital system.
Toslink cabling uses a fiber optic cable, meaning it carries audio information as light pulses, in this case red light. Coaxial digital audio carries the information as electrical pulses across coaxial cable in much the same way as most audio and video cabling before the emergence of the HDMI format. While coaxial cable uses the RCA format plug, Toslink cables have a transparent connector that is almost square rather than circular.
In perfect conditions there should be no discernible difference in quality between the two formats. This is because with digital, unlike with analog, each individual instance of audio is either transmitted perfectly or not at all. In practice, however, very lengthy coaxial cabling could be subject to electrical interference or even degraded cabling.
Choosing which format to use is largely a matter of practicalities. For example, one or both devices being connected may only have sockets for one of the two formats. As mentioned above, Toslink may perform better over longer cabling. On the other hand, Toslink is more susceptible to damage from bending or being stood upon by accident because the optical fiber is more fragile than metal wires. Coaxial may therefore be a better choice for shorter cable lengths or for use in tight spaces where the cable is not in a perfectly straight line.