Coax Input Audio: What the Socket Carries
Quick answer / TL;DR: Short answer: a coaxial digital input expects S/PDIF on a 75-ohm RCA cable, not an antenna feed. Set the source to output PCM or bitstream over coax, and check that the destination decodes that format. For an analogue-only amplifier, use a coax-to-analogue converter rather than an adapter.
Three coaxial families: BNC for CCTV, F-type for TV, N for RF – each with its impedance.A coaxial audio input on a television, soundbar or receiver carries S/PDIF digital audio. It looks like the RF socket next to it and is not the same: one carries a digital bitstream, the other an antenna signal. Confusing them produces silence.
This is the coax-input guide: what the socket expects, the settings that matter, and the converter needed for an analogue-only amplifier.
What the Socket Expects
| The socket | The signal | The cable |
|---|
| Coaxial digital | S/PDIF | 75-ohm RCA |
| RF input | Antenna or cable | Aerial lead |
| Composite video | Analogue video | 75-ohm RCA |
The three sockets accept the same plug family, which is why mis-plugging is common and diagnosis starts with the label.
The Settings
- Source output: coax rather than HDMI
- Format: PCM for stereo, bitstream for surround
- Destination: must decode the chosen format
- Volume: digital outputs ignore the TV's volume on some sets
The settings chain decides more outcomes than the cable, and each link must agree.
Standards and Verification
| The reference | The relevance |
|---|
| IEC 60958 | S/PDIF interface |
| IEC 61169 | Coaxial connectors |
| Field test | Receiver locking to the stream |
Per-device menu names are not provided in the knowledge base. The interface is standard; check the manual for the exact setting.
Practical Notes
If a coax input produces silence, test the same cable on a known-good source before buying a converter. The socket may be an RF input, and no converter will make it accept S/PDIF.
Real-World Applications
The soundbar
A television with coax digital output feeding a soundbar: a 75-ohm cable, the TV set to PCM – sound without an HDMI ARC connection.
The wrong socket
A coax digital cable plugged into the antenna input: no audio. The labels compared – two sockets, two different signals.
Related reading: audio cable — blogs/news/audio-cable
Related reading: coax vs optical audio — blogs/news/coax-vs-optical-audio
Related reading: coax to coax cable — blogs/news/coax-to-coax-cable
Frequently Asked Questions
What does a coax audio input carry?
S/PDIF digital audio.
Is it the same as the antenna socket?
No – the antenna socket carries an RF signal.
What cable do I need?
A 75-ohm RCA cable.
Why is there no sound?
Check the source's output setting and the format.
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