What is SPDIF

S/PDIF stands for Sony/Philips Digital Interconnect Format and it is used to transfer the digital audio signals between the devices and the stereo components. It specifies a Data Link Layer protocol and the choice of the Physical Layer for transferring the signals. S/PDIF uses 'bi-phase mark code' for modulation in which a logical 1 is resembled by two zero-crossings of the signal and one zero-crossing of the signal means a logical 0. It also uses inexpensive 75ohm coaxial cable or optical cable along with TOSLINK, BNC or RCA connectors. The signal level found in the Sony/Philips Digital Interconnect Format ranges from 0.

5 to 1 volt and the sub-code information is provided via SCMS. In each block, 384 bits of the channel status and the sub-code information are transmitted. These sub-code bits are used by manufacturers at their will. In addition to this, S/PDIF has no defined data rate and the most common transfer frequency for Digital Audio Tape is 48 kHz and 44.

1 kHz for CD quality audio. The maximum resolution offered by S/PDIF is of 20 bits only. In order to transmit sources having sample accuracy of less than 20 bits, the superfluous bits are set to zero. It can also be used to transport 24-bit samples by using four extra bits but this is not supported by all the equipments as some equipment ignore the extra bits. DVD Players, computer sound cards, receivers and CD players are some of the common devices that take advantage of the Sony/Philips Digital Interconnect Format (S/PDIF).

Sarah Parker writes on topics such as SPDIF, AES EBU and I2S for The Tech FAQ.