S/PDIF format

December 2016

S/PDIF format

The S/PDIF standard ("Sony/Philips Digital Interface", or SPDIF for short) is a digital audio data transfer format. It is an international standard known as "IEC-958 type II", which defines both hardware specifications (physical connection characteristics) and a data transfer protocol (16-bit to 24-bit encoding). The S/PDIF standard can be considered the consumer version of the professional interface AES/EBU, to which it adds some power-saving measures.

S/PDIF is used for storing sound digitally on media like DAT (Digital Audio Tape) or manipulating it with audio-manipulation devices. The primary advantage of S/PDIF lies in its ability to transfer sound between two digital audio devices without using an analog connection, which by necessity would reduce some of the quality.

An S/PDIF-encoded audio signal, however, suffers no attenuation or distortion and may be transferred losslessly.

Characteristics

S/PDIF is used for encoding stereo or multichannel sound data (AC3, DTS, MPEG2, etc.).

The S/PDIF standard supports the following sampling rates:

  • 44.1kHz from a CD
  • 48 kHz from a DAT tape
  • 32 kHz from DSR

Connectors

The S/PDIF standard allows for the following connection methods:

  • Asymmetrical coaxial cable with 75 Ohms resistance and RCA connectors. Recommended maximum distance for wiring is about fifteen metres.
  • Fibre-optic cable (1mm plastic fibre) with a Toslink connection (TOShiba LINK by Toshiba). The data is transmitted by the same format, but with visible light signals emitted by a red LED. Taking into account the deterioration of the optical signal, the optic cable cannot exceed 10m in length.
  • Fibre-optic cable with 3.5 mm minijack (or miniplug). The minijack connector is identical to a normal mono-audio jack (3.5 mm in diameter), except that its tip contains a lens, which allows it to transmit data over a fibre-optic cable.

In practice, most devices (like sound cards, CD and DVD players, 5.1 amplifiers etc.) usually come with an RCA jack (CINCH).


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