Dennis HilkLinux Fix LabDE

Audio, ALSA & PipeWire

S/PDIF stays silent or passthrough fails

Separate ordinary stereo PCM on S/PDIF from compressed passthrough, and check the digital profile, mixer switch and receiver capabilities before enabling codecs.

Editorial source review: Start with the evidenceShare this guide
On this page
  1. Symptoms & scope
  2. Possible causes
  3. Diagnose safely
  4. Evidence-guided next steps
  5. References & review
  6. Related problems

Symptoms & scope

  • Analog playback works but the digital receiver stays silent.
  • Stereo PCM works while compressed movie audio does not.

Relevant environment

Optical or coaxial IEC958 outputs managed by ALSA and PipeWire/WirePlumber, connected to a compatible DAC or receiver.

Possible causes

These are possible explanations, not a confirmed diagnosis. Several independent faults can coexist.

  • The card may use an analog profile, or its IEC958 playback switch can remain off.
  • Passthrough requires receiver-supported codecs and an appropriate application path; arbitrary multichannel PCM does not fit conventional S/PDIF.

Diagnose safely

Run one command at a time in the relevant session. Read the explanation first. Uppercase placeholders need your own values; tools and privileges vary by distribution. These commands are displayed here and never executed by the website.

Check 1

Read the card and exposed sinks, then identify whether the expected digital endpoint exists.

wpctl status

Interpret the result: A digital sink’s absence can reflect the current profile rather than missing hardware. Sink presence does not confirm receiver lock.

Check 2

Replace card 0 with the ALSA card index from /proc/asound/cards. Read controls, including IEC958 where this hardware exposes it.

amixer -c 0 scontents

Interpret the result: An IEC958 Playback Switch off can explain silence. Not every card uses that control name; do not change a similarly named capture switch.

Evidence-guided next steps

Restore the verified stereo digital path

If the card is on analog output or its verified IEC958 playback switch is off, select the supported digital stereo profile and enable that playback switch in the mixer. Select the receiver’s matching input and first compare ordinary stereo PCM.

Precautions: Record prior controls and keep receiver volume low. An optical light alone does not prove valid audio frames or a compatible sample rate.

Recovery / rollback: Restore the prior profile and IEC958 switch state if digital routing affects other outputs.

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Enable only receiver-supported passthrough

If stereo PCM works and the receiver explicitly supports the movie codec, enable only those supported passthrough codecs in the audio/device settings and the player. If it does not support them, let the player decode to stereo PCM.

Precautions: Do not enable every IEC958 codec from an example list. Receiver and transport limits differ, and encoded data sent as PCM can produce loud noise.

Recovery / rollback: Disable the experimental passthrough codec and restore PCM decoding and the recorded receiver/input settings.

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References & review

This guide was prepared from primary project or distribution sources and reviewed on the date shown. This is an editorial source check, not evidence that a fix was reproduced on your hardware. Diagnostic log examples are synthetic fixtures. Version-dependent details must be checked against your installed release.