Optical vs Coaxial vs USB Audio: Which Digital Connection Should You Use?

Digital audio connections are often treated as if one cable must “sound better” than another. In practice, the useful differences are compatibility, supported formats, electrical isolation, clocking, cable length, and how each device handles volume or sample-rate conversion.

The short answer

Use optical when you want electrical isolation or need to break a ground loop. Use coaxial S/PDIF when both devices support it and you want a robust two-channel link. Use USB when a computer, phone, streamer, or server needs to send higher-rate PCM or DSD to a compatible DAC. A correctly functioning connection should be chosen for the system—not for cable mythology.

Optical: convenient isolation

TOSLINK carries S/PDIF data as light through plastic or glass fibre. Because there is no conductive path between the source and DAC, optical can prevent hum caused by ground loops. It is common on televisions, streamers, game consoles, soundbars, and DACs.

Optical is normally used for two-channel PCM and may also carry compressed home-theatre formats when both ends support them. The exact PCM limit depends on the transmitter, receiver, cable quality, and firmware. Many products specify up to 24-bit/192 kHz, but a specification on one side does not guarantee the complete chain will run reliably at that rate.

Coaxial S/PDIF: electrical and widely compatible

Coaxial S/PDIF sends the same basic protocol over an electrical 75-ohm connection, usually with RCA sockets. It is often more tolerant of high sample rates than inexpensive optical hardware, but it does not provide galvanic isolation. In systems with poorly managed grounding, connecting two mains-powered components can expose noise that optical avoids.

A proper digital coaxial cable should have controlled 75-ohm impedance. For short domestic runs, a well-made video or digital cable is usually sufficient; price and heavy construction do not guarantee better data integrity.

USB audio: a different architecture

USB Audio is not S/PDIF. The source acts as a USB host and the DAC or streamer acts as a USB audio device. Modern asynchronous USB implementations allow the receiving audio device to control timing while the source supplies packetized data. Depending on both products and their drivers, USB may support PCM beyond 192 kHz, native DSD or DoP, multichannel audio, and device-control functions.

Compatibility is the main catch. A USB port may be intended only for storage, service, power, or audio output. USB-C describes the connector, not the function. Always check whether the port is USB Audio input, USB Audio output, or only a host for drives.

Does one connection sound better?

If the data reaches the DAC intact and the receiving interface is well designed, audible differences should not be assumed. Real differences can still arise from sample-rate conversion, DSP, volume control, grounding, noise leakage, or different input circuitry inside the DAC. Compare at matched volume and verify the signal path before crediting the cable.

Format and control limits

• Optical and coaxial: generally two-channel PCM, with compressed surround only where explicitly supported. They do not normally carry metadata or volume commands.
• USB: potentially higher PCM rates, DSD, multichannel audio, and software volume, but only when host, operating system, driver, cable, and DAC agree.
• TV connections: HDMI ARC is often more practical when television remote control, automatic input switching, or surround formats matter.

A practical selection checklist

1. Confirm the exact function of every port.
2. Check the maximum supported format at both ends.
3. Decide whether electrical isolation is valuable.
4. Check whether volume control and TV integration are required.
5. Use a short, correctly specified cable before buying an exotic one.
6. Verify whether the source resamples all output to one rate.

Bottom line

Optical, coaxial, and USB solve different integration problems. Optical is excellent for isolation, coaxial is a simple and reliable S/PDIF link, and USB is the most flexible computer-to-DAC interface. The best choice is the connection that preserves the features your system actually needs.

Editorial classification: protocol and system-design guide. Product capabilities should always be confirmed in current manufacturer documentation.