S/PDIF is a data link layer protocol and a set of physical layer specifications for carrying digital audio signals between devices and components over either optical or electrical cable. The name stands for Sony/Philips Digital Interconnect Format (more commonly known as Sony Philips Digital Interface), Sony and Philips being the primary designers of S/PDIF. S/PDIF is standardized in IEC 60958 as IEC 60958 type II (IEC 958 before 1998). S/PDIF is essentially a minor modification of the original AES3 standard for consumer use, providing small differences in the protocol and requiring less-expensive hardware.
A common use for the S/PDIF interface is to carry compressed digital audio as defined by the standard IEC 61937. This mode is used to connect the output of a DVD player to a home-theater receiver that supports Dolby Digital or DTS surround sound. Another common use is to carry uncompressed digital audio from a CD player to a receiver. This specification also allows for the coupling of personal computer digital sound (if equipped) via optical or coax to Dolby or DTS capable receivers. This only supports stereo sound, unless the personal computer supports Dolby Digital Live or DTS Connect
S/PDIF was developed at the same time as the main standard, AES3, used to interconnect professional audio equipment in the professional audio field. This resulted from the desire of the various standards committees to have at least sufficient similarities between the two interfaces to allow the use of the same, or very similar, designs for interfacing ICs. S/PDIF remained almost identical at the protocol level (consumer S/PDIF provides for copy protection, whereas professional interfaces do not), but changed the physical connectors from XLR to either electrical coaxial cable (with RCA connectors) or optical fibre (TOSLINK; i.e., F05 or EIAJ Optical), both of which cost less. The RCA connectors are typically color-coded orange to differentiate from other RCA connector uses such as composite video. The cable was also changed from 110 Ω balanced twisted pair to the already far more common (and therefore compatible and inexpensive) 75 Ω coaxial cable, using RCA jacks instead of the BNC connector, which is more common in commercial applications. S/PDIF is a consumer version of the AES3 format.
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