A digital coaxial cable is a type of cable used to transfer digital audio signals between compatible audio components. It is commonly used to connect devices such as CD players, network streamers and televisions to DACs, amplifiers and AV receivers.
Digital coaxial connections commonly use the S/PDIF digital audio standard. Unlike an analogue RCA connection, which carries an analogue audio signal, a digital coaxial connection transfers audio as digital data that must be converted into analogue audio before it can ultimately be amplified and reproduced by loudspeakers.
The cable normally uses an RCA connector at each end, making it look similar to a conventional analogue RCA cable. However, a digital coaxial cable is designed with a characteristic impedance of 75 ohms for transmitting the digital signal reliably.
Inside the cable, a central conductor carries the signal while an outer shield helps protect it from electromagnetic and radio-frequency interference. The coaxial construction gives the cable its name because the inner conductor and surrounding shield share the same central axis.
When a source such as a CD player sends audio through its digital coaxial output, the digital signal travels along the cable to the receiving component. A DAC then converts the digital audio information into an analogue electrical signal that can be passed to an amplifier and eventually reproduced through loudspeakers.
Digital coaxial connections can carry two-channel PCM audio and can also transport certain compressed multichannel audio formats. The exact formats and sample rates supported depend on the equipment connected at either end.
Digital coaxial and optical TOSLINK connections can both use S/PDIF to transfer digital audio, but they use different transmission methods. Coaxial cables transmit the signal electrically through a conductor, whereas TOSLINK cables convert the signal into pulses of light and transmit them through an optical fibre.
One advantage of TOSLINK is electrical isolation between connected components, while digital coaxial connections are often capable of reliable transmission over suitable cable lengths. In either case, the capabilities of the source and receiving equipment are more important than simply choosing one connection type over the other.
Although a standard RCA analogue cable may sometimes appear to work for a digital coaxial connection, a properly specified 75-ohm digital coaxial cable is the appropriate choice. It provides a straightforward and widely supported way of transferring digital audio between components in a hi-fi system.