Digital Coaxial S/PDIF to 15-Pin D-sub Adapter Cable. S/PDIF is a digital audio interconnect used in consumer audio equipment over relatively short distances. The signal is transmitted over either a coaxial cable with RCA connectors or a fiber optic cable with TOSLINK connectors. S/PDIF interconnects components in home theaters and other digital high fidelity systems. S/PDIF is based on the professional AES3 interconnect standard.