Toslink vs Coaxial Digital: Same Data, Different Medium
Quick answer / TL;DR: Short answer: Toslink and coaxial digital both carry S/PDIF and produce identical data when both work correctly, so neither is inherently better sounding. Toslink is immune to electrical interference and breaks ground loops, but plastic fibre limits bandwidth and the connectors are fragile. Coaxial uses a 75 ohm RCA or BNC connection, has more bandwidth headroom for high sample rates and is mechanically robust. Choose Toslink where a ground loop or electrical noise exists, and coaxial where the run is long, the connectors get handled, or higher sample rates are needed.
Light carries the signal: no ground, no hum, and no tolerance for tight bends.Toslink and coaxial digital carry the same S/PDIF bitstream. The framing, the sample rates and the channel status are identical, which means the choice between them is about the physical medium rather than about sound quality in any inherent sense.
That said, the medium does have consequences: optical is immune to electrical interference and cannot create a ground loop, while coaxial has more bandwidth headroom and more robust connectors.
What Each Medium Does Well
The protocol is the same; the physics are not. Optical transmission converts electrical pulses to light and back, which removes any conductive path between the two devices.
| Property | Toslink | Coaxial digital |
|---|
| Protocol | S/PDIF | S/PDIF |
| Medium | optical fibre, usually plastic | 75 ohm coaxial |
| Galvanic isolation | inherent | none |
| Immunity to EMI | high | depends on shielding |
| Typical bandwidth limit | about 6 MHz with plastic fibre | higher with good cable |
| Connector | square optical, friction fit | RCA or BNC |
| Bend sensitivity | high, minimum radius applies | moderate |
The bandwidth row explains most practical failures. Plastic fibre has a limited bandwidth-length product, so a long or sharply bent Toslink cable can fail at higher sample rates while working at 48 kHz.
Ground Loops and Noise
A ground loop occurs when two devices connect to earth through different paths, and the resulting current appears as hum or as digital errors. Coaxial digital creates a conductive path between devices, so it can complete a loop; Toslink cannot.
This is the strongest argument for optical in a system with a television, a computer and an amplifier on different outlets. If a hum disappears when the coaxial cable is unplugged, the loop is real and optical is the fix.
Where Each Is the Better Choice
| Situation | Preferred | Reason |
|---|
| Devices on different mains circuits with hum | Toslink | breaks the ground path |
| Short run between adjacent devices | either | no practical difference |
| Run over 5 m | coaxial | optical loss and bandwidth limits |
| Equipment handled frequently | coaxial | robust connectors |
| High sample rate, 192 kHz | coaxial | more bandwidth headroom |
| Tight bend around a corner | coaxial | optical minimum bend radius |
Real-World Applications
Television to soundbar
Most soundbars accept both. Use optical if there is any hum, and coaxial if the soundbar's optical port is recessed and the cable has to bend sharply behind a wall-mounted television.
Desktop DAC on a computer
A short coaxial cable is usually the simpler choice, and the computer's optical output, where present, is often a combination jack that needs an adapter. Both work; choose by connector availability.
Multi-room distribution
Long runs favour coaxial because the cable can be terminated and tested like any 75 ohm line. Optical runs beyond a few metres need better fibre than the typical plastic patch lead, which is an easy specification to get wrong.
Standards and Verification
The protocol is standardised, which is why converters and cables interoperate across brands.
- IEC 60958-1 and 60958-3: the S/PDIF interface, framing and channel status bits
- IEC 60958-4: the professional AES3 variant, for context on the consumer differences
- EIAJ CP-340: the original optical interface specification
- IEC 61196 series: coaxial cable test methods relevant to the 75 ohm link
- TOSLINK connector specifications: the JIS F05 optical connector used on consumer equipment
Verification is a listening test plus a format check, not a cable measurement. Confirm that the receiving device reports the expected sample rate and channel count, then test with a known high-sample-rate source if you intend to use one. A cable that works at 48 kHz and fails at 96 kHz is a bandwidth problem, and the fix is a shorter or better cable rather than a different type.
Related reading: Toslink cable: optical digital audio in practice — blogs/news/toslink-cable
Related reading: Coaxial cable guide: impedance and construction — blogs/news/coax-cable
Related reading: Audio cable guide: analogue and digital families — blogs/news/audio-cable
Frequently Asked Questions
Is Toslink better than coaxial digital?
Neither is inherently better sounding: both carry the same S/PDIF data. Toslink provides galvanic isolation, which helps with ground loops, while coaxial has more bandwidth headroom and sturdier connectors.
Why does my optical cable fail at high sample rates?
Plastic optical fibre has a limited bandwidth-length product. A long or sharply bent cable can pass 48 kHz and fail at 96 or 192 kHz. Use a shorter cable or a better fibre type.
Can I use a coaxial digital cable for analogue audio?
It will pass analogue audio, because it is a 75 ohm shielded cable, but a dedicated analogue interconnect is the correct part. The reverse also works electrically but is not good practice.
Does optical cable remove hum?
Yes, if the hum is caused by a ground loop. Optical transmission has no conductive path between devices, which is why it is the standard fix for hum in mixed systems.
How long can a Toslink cable be?
Practical plastic-fibre cables are reliable to about 5 metres, less if bent tightly. Longer runs should use coaxial digital or a fibre design intended for the distance.
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