Optical to Coaxial Converter: Converting the Medium, Not the Signal
Quick answer / TL;DR: Short answer: use an optical to coaxial converter when a source has only an optical output and the destination has only a coaxial input, or the reverse. The data is unchanged, so the converter cannot improve sound quality. It needs power, and it should support the formats you use, including compressed 5.1. Because coaxial introduces a ground connection, a source that was previously isolated may develop hum, which is the one audible side effect.
Three coaxial families: BNC for CCTV, F-type for TV, N for RF – each with its impedance.TOSLINK and coaxial digital audio carry the same S/PDIF bitstream on different media. Converting between them does not change the data, so there is no question of one sounding better than the other.
What a converter changes is which physical connection is available, which solves a compatibility problem rather than an audio one. It also introduces a powered device and, in some designs, a ground connection that did not exist before.
What Changes and What Does Not
The bitstream is identical, so the conversion is a matter of physical compatibility and, occasionally, of grounding.
| Aspect | Effect of conversion | Note |
|---|
| Data | unchanged | same S/PDIF stream | Sound quality | unchanged | no improvement possible | Grounding | coaxial introduces a ground path | optical was isolated | Format support | depends on the converter | check compressed 5.1 | Power | required | adds a supply | Latency | negligible | no buffering in most units |
The grounding row is the practical one. A system connected entirely by optical is isolated, and inserting a coaxial link can create a hum path that was previously absent.
When a Converter Solves a Real Problem
The use cases are compatibility problems, and each has a straightforward alternative if the converter is not available.
- Soundbar has coaxial input, television has optical only
- AV receiver has optical inputs, source has coaxial only
- Long run where coaxial is preferred after an optical source
- Legacy equipment with a single digital input
- Where a single converter replaces a cable change
Real-World Applications
Television optical to a coaxial-only amplifier
The converter sits at the amplifier and takes a short optical cable from the television. Set the television to bitstream if the amplifier can decode it, or PCM if it cannot.
Coaxial source to an optical-only soundbar
The reverse direction, using the same class of product. Confirm the converter supports the direction, because some units are one-way.
Long run from an optical source
Copper coaxial tolerates longer runs than plastic optical fibre. A converter at the source, then coaxial for the distance, is a legitimate design.
Where a converter is unnecessary
When the equipment offers both connections. Choosing the right cable is cheaper than adding a powered device and a ground path.
Related reading: Digital coaxial cable requirements — blogs/news/digital-coaxial-rca-cable
Related reading: Optical against coaxial in practice — blogs/news/coax-vs-optical-audio
Standards and Verification
S/PDIF is specified in IEC 60958, which defines both the optical and coaxial variants of the same interface. That shared definition is why a converter is a medium change rather than a protocol change.
Verify by testing with content that carries the formats you need. A converter that passes stereo may fail on compressed 5.1, and the failure appears as silence rather than as degraded audio.
If hum appears after adding the converter, the coaxial link has introduced a ground path. A ground loop isolator in the coaxial path, or reverting to optical, resolves it.
Confirm directionality before buying. Some converters handle only optical to coaxial or only coaxial to optical, and the listing may not make it obvious.
Frequently Asked Questions
Does optical to coaxial conversion change sound quality?
No. The data is identical. The converter changes the physical medium only.
Which direction does the converter work?
Some are one-way. Check the listing, because bidirectional units are less common.
Can it carry surround sound?
Yes if it supports the bitstream. The conversion is format-agnostic when done properly.
Why does hum appear now?
Coaxial introduces a ground connection that optical did not have. A ground loop isolator resolves it.
Is coaxial better for long runs?
Yes. Copper coaxial carries further than plastic optical fibre without excessive attenuation.
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