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What is the difference between a S/PDIF connector and a TOSLINK connector?

When I look at the relevant Wikipedia articles, it shows identical photographs on the S/PDIF page and the TOSLINK page.

From those articles, the only difference I can tell is that S/PDIF is apparently only round connectors, whereas TOSLINK can be round or rectangular connectors.

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    TOSLINK specifies the physical connector for optical cable at the physical layer. S/PDIF specifies the protocol at the data link layer. You can also transmit S/PDIF over copper wire (e.g. the other digital audio port using a RCA jack). The relationship is similar to Ethernet RJ45 and TCP/IP. End-users often misuse the signal or protocol name for the proper connector name.
    – sawdust
    Jun 27, 2015 at 3:28
  • @sawdust Thank you! kazoni provided a similar answer below, to which I requested a clarification. You might be able to help with that clarification as well. Jun 27, 2015 at 3:48

2 Answers 2

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S/PDIF isn't a connector type but a communication standard. It stands for Sony/Philips Digital Interface Format. There are two cables/connectors it uses: a fiber optic cable with TOSLINK terminations, or a coaxial cable with RCA terminations.

Wiki S/PDIF
Wiki TOSLINK
Wiki RCA

As far as the actual signal, they are identical, however the TOSLINK has higher jitter. See here for the in-depth discussion on it.

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  • Thank you! The part that confused me is that the Wikipedia S/PDIF article states "S/PDIF is a data link layer protocol and a set of physical layer specifications for carrying digital audio signals". The "physical layer" part made me think it's referring to the connector itself as well as the communications protocol. Does it mean something else, or is it just wrong? Jun 27, 2015 at 3:47
  • I think it's probably right. They were wanting something similar but cheaper so they could use similar chips from pro audio equipment.
    – kazoni
    Jun 27, 2015 at 5:45
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    I'm feeling dense. Of what does the S/PDIF "physical layer" consist? Jun 27, 2015 at 10:07
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The Sony/Philips Digital Interface (S/PDIF) is a consumer standard, modeled after the professional Audio Engineering Society standard AES3, that includes both Layer 1 physical interfaces and a Layer 2 data link layer protocol.

The S/PDIF digital PROTOCOL aspect expects a stream of 1s and 0s in a certain order, not caring whether the information is sent across its optional Layer 1 Toslink fiber using light or its alternative option Layer 1 orange RCA terminated coaxial cable using electricity.

The physical interface or Layer One (1), at the bottom of the commonly referenced ISO stack, is what you see on the back of a computer, stereo, and set top cable and satellite boxes

  • RJ45 Cat 5e and 6a ethernet LAN 8-wire (4-twisted pair) cables and ports
  • USB
  • Apple Thunderbolt & Lightning
  • RS-232 serial DB9 connectors & cables
  • RCA, BNC and F-type connectors & coaxial cable
  • XLR microphone & and Neutrik Speakon loudspeaker professional audio connectors
  • Antennas, Transmitters, Receivers (Bluetooth, WiFi, cellular, AM/FM, CB)
  • Fiber optic connectors & cables: SC, ST, single mode (SM), multi-mode (MM), Toshiba Link (TosLink)
  • VGA | RGBHV Component | S-video | Composite (yellow) | DVI | DisplayPort | HDMI | HDBaseT video

Layer 1 is the electromagnetic methodology for transmitting AND receiving communications signals amongst components and subsystems using light, electricity, or radio waves.

ISO 7-Layer Stack

The ISO stack is a way of breaking up the complexity of software, firmware, and hardware into understandable chunks for geeks, nerds, dweebs and the socially challenged. The rest of you just wouldn't understand.

Indeed, in most militaries around the world, the guys (and now gals) that fly airplanes, drive tanks, and sail ships simply use the acronym “BFM”, as in Black F’n Magic.

Whereas Layer 1 is something you can touch and see (radio with a receiver) Layer 2 is a protocol, not a physical interface, that defines what each block of 1s and 0s means, does error detection and how to synchronize time between the sender and receiver.

Layer 1 modulates and demodulates (FM, AM, FSK, ASK, PSK, QAM, BPSK), nowadays using Digital Signal Processors (DSPs), analog to digital converters (ADCs) and digital to analog converters (DACs) so the upper layers of the stack can make sense of what would otherwise be gibberish. Layer 1 outputs a stream of 1s and 0s to the conceptual Layer 2 Data Link Layer. In the case of S/PDIF this is a bi-phase-mark encoded data stream of 192-frames per block with error detection and timing to prevent jitter.

As an aside, the nice thing about light is it won't shock or electrocute you, nor does it pick up 60Hz hum from the flourescent lights or miswiring that causes undesirable ground loops in unbalanced circuits. This is the nice thing about Toslink optical plastic fiber optic cable.

In both cases you'll either have two channels (left & right) of analog pulse code modulated (PCM) into digital signal or 5.1 channels for surround sound.

Orange was randomly chosen to signify a digital signal input/output rather than a red right analog audio, white left analog audio, yellow analog composite video and colors used in RGB sync on green or VGA RGBHV analog component video signals.

High definition audio such as Dolby TrueHD, Dolby Atmos, DTS-HD Master Audio, and DTS:X won't run across S/PDIF. You'll need to use a device with the newer HDMI 1.3 standard and an HDMI cable instead of Toslink optical or RCA coax.

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