Coaxial Digital Inputs: TV, Receiver and Soundbar Ports Explained
A coaxial digital input is the orange RCA socket on a receiver, soundbar or TV that accepts S/PDIF over 75 ohm coax. Most devices ship with two digital inputs – ‘coaxial’ and ‘optical’ – and the manual rarely explains which to prefer or what to set after plugging in. This guide covers what devices can feed a coaxial digital input, how coax compares to optical, the exact wiring and menu steps, and the troubleshooting order that resolves most no-signal cases in minutes.
Quick Answer
Connect a 75 ohm digital coax cable (orange RCA plugs) from the source’s ‘Digital Out Coaxial’ port to the component’s ‘Digital In Coaxial’ port, select that input on the receiving unit, and choose PCM or bitstream in the source’s audio menu: bitstream lets the receiver decode Dolby Digital/DTS 5.1, PCM sends already-decoded stereo. A coaxial digital input accepts PCM up to 24-bit/192 kHz and compressed 5.1 at 48 kHz – the same ceiling as optical, delivered through a more robust connection.
What Can Feed a Coaxial Digital Input
Any device with an S/PDIF coaxial output can feed the input: Blu-ray and DVD players, TV set-top boxes, game consoles (where the port exists), PCs and sound cards, streaming boxes, network audio players, and the digital out of another receiver in a multi-zone chain. The input carries one audio program – stereo PCM or a compressed 5.1 stream – so each input serves one source at a time. Devices without a coax out (most modern consoles, many soundbars) can only feed the input through an active optical-to-coax converter.
Source devices that expose coax out
Check the back panel for an orange RCA socket labeled ‘Digital Out Coaxial’, ‘Coax Out’ or ‘S/PDIF Out’. TVs, AV receivers and set-top boxes most often carry one; some add a 3.5 mm digital out that is electrically the same S/PDIF on a different plug. If the source has both coax and optical outs, either may feed the input – pick based on cable route and length.
Coaxial vs Optical Input: Same Spec, Different Physics
Both ports implement S/PDIF with identical audio ceilings, so the choice is physical, not sonic. Optical sends light through a fragile plastic fiber; the plug is keyed and the core cracks if pinched. Coax sends electrical bits over a 75 ohm line; the RCA connection is mechanically robust, tolerates longer runs, and costs less per meter. The trade-offs: optical isolates the ground between devices (no ground-loop hum), while coax can inherit ground offsets in multi-device racks. In a clean install either is fine; in a noisy or long-run install coax usually wins.
Why coax survives longer runs
Optical fiber has no electrical length problem, but its practical limit is the source’s laser output and the fiber’s bending loss – most consumer optical cables are sold to 5 m for a reason. Coax’s electrical limit is about 15 m with a good build. For a run across a room or through a wall chase, coax is the lower-risk choice.
Wiring a Coaxial Digital Input Correctly
Step one: identify the input – the orange RCA socket, usually paired with a clear optical socket. Step two: use a 75 ohm S/PDIF cable with RCA plugs, long enough to drape without tension. Step three: plug into the source’s coaxial out and the destination’s coaxial in – direction matters, the input only receives. Step four: select ‘coaxial’ or ‘digital coax’ as the active input on the destination. Step five: set the source output to bitstream or PCM and verify with a known surround track. For the source-side details, see our digital audio out coaxial guide, and the full cable spec in audio digital cables.
Troubleshooting a Coaxial Digital Input
No signal indicator at all: confirm the source has a coax out (not just optical), confirm the cable is 75 ohm digital coax, and try the optical input to isolate which side is at fault. Signal appears then drops: loose RCA, marginal cable, or the source sending a rate the input rejects – lock the source to 48 kHz. Crackling: reseat or swap the cable; a failing crimp is the usual cause. Only stereo when 5.1 is expected: the source is set to PCM, or the content is not encoded 5.1. After any change, power-cycle the receiving unit – format detection often happens at boot.
Digital Input Port Comparison
| Port | Signal | Max PCM | Max compressed | Cable |
|---|---|---|---|---|
| Coaxial in | S/PDIF electrical, 75 ohm | 24-bit/192 kHz | 5.1 at 48 kHz | Digital coax, RCA |
| Optical in | S/PDIF optical | 24-bit/192 kHz | 5.1 at 48 kHz | TOSLINK fiber |
| HDMI in | TMDS multi-channel | 32 ch / 384 kHz | DD+ / TrueHD / DTS-HD 7.1 | HDMI A or C |
| Analog RCA in (contrast) | Line-level analog | n/a | n/a | Stereo RCA |
Real-World Applications
Coaxial digital inputs anchor specific real-world setups: a multi-source home theater where a Blu-ray player, set-top box and streaming box each occupy a coax input on the AV receiver; a bedroom TV feeding a wall-mount soundbar’s coax in for music and apps; an AV processor front end in a commercial space, where every source standardizes on S/PDIF coax; a zone-2 output from a main receiver into a kitchen amp’s digital input; a car audio chain where a head unit’s coax out feeds a processor; and a test bench, where the coax input gives a clean, ground-reference-free signal to measure. Because the spec is identical in every region and every decade of equipment, a coaxial input remains usable for twenty years of gear.
Related Guides
Frequently Asked Questions
Can I plug an antenna cable into a coaxial digital input?
Do not. An RF antenna line carries a modulated carrier, not S/PDIF; the input will show no signal, and the impedance mismatch can degrade the antenna feed. Use a 75 ohm cable specified for digital audio.
Do I need to set anything after plugging in a coaxial digital cable?
Yes: select the coaxial input on the receiving device and set the source’s digital output to PCM or bitstream, with the sample rate matched to what the input accepts. Many ‘no sound’ cases are pure menu state.
Why does my soundbar show ‘no signal’ on the coax input?
Three causes cover almost all cases: the source is outputting on optical instead of coax, the cable is not a proper 75 ohm S/PDIF build, or the source is locked to a rate the soundbar rejects (96/192 kHz). Check in that order.
Is a coaxial digital input better than an optical input?
Audio ceiling is identical. Coax is mechanically more robust and better for longer runs; optical isolates grounds and is better when hum appears between devices. Choose by the install, not by sound.