TOSLINK TOSLINK Optical Digital Audio (optical S/PDIF)

What TOSLINK is

TOSLINK is the optical sibling of the coaxial S/PDIF connection. The data is the same IEC 60958 bitstream, but instead of a voltage on a 75 ohm cable, an LED pulses red light down a plastic fiber. Wikipedia describes the light as red with a peak wavelength of 650 nm, and the standard plug as the rectangular EIAJ/JEITA RC-5720 connector, also catalogued as CP-1201 and JIS C5974-1993 F05. A smaller Mini-TOSLINK plug, close to the size of a 3.5 mm TRS plug, also exists.

Because light carries the signal, the link is galvanically isolated. Wikipedia notes that this makes it immune to ground loops, RF interference, and ESD events. That is the one structural advantage over coax, and it is the reason optical is the usual first fix when a coaxial digital link hums (see ground loop hum).

How TOSLINK works

Wikipedia lists the S/PDIF payload at 3.1 Mbit/s for 48 kHz PCM. The arithmetic is simple: IEC 61937 data runs at 64 times the sample rate, so 48 kHz gives 3.072 Mbit/s, 44.1 kHz gives 2.82 Mbit/s, 96 kHz gives 6.14 Mbit/s, and 192 kHz gives 12.29 Mbit/s (my arithmetic from that 64x figure). The common TORX147 optical receiver is listed at 15 Mbit/s, so 192 kHz stereo fits on paper. In practice many optical ports stop at 24-bit/96 kHz, which is why hi-res sources are better sent over coax or USB. The Audio Stuff glossary advises checking the spec sheets at both ends before relying on optical above 96 kHz.

Length is the other limit. Plastic fiber loses light with distance and tight bends. Wikipedia gives an effective range of 5 to 10 m, with typical cables limited to 5 m and a technical maximum near 10 m. Glass or silica fiber loses less and goes further. A TV and soundbar a few meters apart are well inside the limit.

TOSLINK vs the formats people expect

Optical carries two-channel PCM at up to 24 bits, or compressed surround. Wikipedia's TOSLINK entry says the signal is two-channel PCM stereo or compressed 5.1 surround such as Dolby Digital and DTS. The AC-3 standard allows a maximum coded bit rate of 640 kbit/s, which is why a 5.1 Dolby Digital stream fits comfortably.

Everything above that does not. Wikipedia's TOSLINK entry says it cannot carry uncompressed Dolby TrueHD, DTS-HD Master Audio, or more than two channels of PCM. Samsung's soundbar guidance shows the practical result: Dolby TrueHD (including uncompressed Atmos) is supported only over HDMI-eARC, Dolby Digital Plus (including compressed Atmos) works over HDMI and eARC but not optical, and Dolby Digital works on every connection. Samsung also states that with the TV's optical output set to simultaneous output, the signal is PCM or Dolby Digital. A TV that receives a Dolby Digital Plus Atmos stream from Netflix and has only optical to the soundbar will output PCM or Dolby Digital instead. Wikipedia's Dolby Digital Plus entry describes decoders that convert DD+ to a 640 kbit/s Dolby Digital stream without re-encoding, aimed at legacy S/PDIF connections.

Where TOSLINK lives

Current examples show how the connection is used. LG's customer care answer for the 2025 C5 OLED lists one optical digital audio out alongside HDMI eARC on port 2. Samsung's HW-S60D soundbar spec sheet lists one optical digital audio input beside HDMI eARC. The Denon AVR-X3900H lists two optical and two coaxial digital inputs. A Sonos community member says the Arc Ultra has no optical port of its own and connects through the Sonos Optical Audio Adapter, with the caveat that Dolby Atmos will not play over that connection.

The pattern is that optical sits beside eARC as the compatibility option. LG's answer says eARC can carry high-quality formats including Dolby Atmos, and HDMI.org lists eARC support for up to 192 kHz, 24-bit audio and 32-channel uncompressed audio, against optical's two-channel PCM ceiling. The full decision table is in optical vs HDMI ARC.

Common confusions

The first myth is that expensive optical cables sound better. Archimago measured four cables from cheap to glass-fiber, at 6 ft, plus a 12 ft coupled pair, with the Dunn J-Test jitter signal and concluded that jitter does not appear to be affected by TOSLINK cable quality. The cable is a light pipe; the timing is set by the transmitter and receiver.

The second is that optical has worse jitter than coax. There is real evidence that it can, but it lives in the DAC. In a 2018 test Archimago found that TosLink tends to have higher jitter than coaxial S/PDIF in general, that the TEAC UD-501 rejected it poorly, and that an Oppo and an RME DAC showed no significant difference. His conclusion was that clock fluctuations are primarily a function of the DAC, and that the jitter was low and inaudible. A TV-to-soundbar link is a compressed-surround use case where none of this matters. Where it might matter is a hi-res stereo source into a DAC with a weak clock, and the fix there is coax, which the Audio Stuff glossary says commonly handles 24-bit/192 kHz, not a better optical cable.

The third is "optical is digital so it is lossless for everything." The link is lossless for the PCM or bitstream it carries, but that bitstream tops out at lossy 5.1. If your goal is TrueHD or DTS-HD Master Audio from a disc player, the path has to be HDMI. See bitstream vs PCM.