In the world of consumer electronics, different types of cables and connections are used to transmit audio between components, with varying levels of quality. One such type is the analogue composite RCA cable connection, and another is the digital S/PDIF-standard coaxial audio.
S/PDIF, short for Sony/Philips Digital Interconnect Format, is a digital audio format used to connect digital components, such as a Blu-ray/DVD player, cable/satellite set-top receiver box or HDTV, to a surround-sound stereo receiver. This is a 16-bit protocol for relaying Dolby Digital and DTS multichannel sound and is more commonly associated with optical (TOSLINK) audio cables but can also apply to coaxial audio cables.
Composite RCA is an analogue stereo audio connection with two separate cables to carry the right and left stereo channels. It has been used for audio components from phonographs to cassette players to CD players and for the audio connection for video components, such as VCRs and DVD players. RCA cables are also used for the audio portion of component video/audio cables.
Though coaxial audio cables resemble RCA cables in the shape and size of their connectors and can be interchangeable because they both have 75 ohm impedance and similar bandwidths, coaxial cables are thicker and have the same shielding as coaxial video cables to minimise interference. Because coaxial cables relay digital signals, they can carry 5.1 channel audio within the single cable, something the analogue RCA cables cannot match.