LG OLED C2 Optical and ARC Sound Drops: Isolate the Shared Fault

Quick Answer

When an LG C2 produces the same brief sound dip through optical and HDMI ARC, do not conclude that both output ports failed. Optical S/PDIF and ARC are different transports, but they can receive the same audio after the same source app, decoder and TV processing stages. First test the C2 speakers with the exact scene. Then compare a simple stereo PCM source through optical and ARC separately, using direct cables and one audio device. A dropout that occurs at the same timestamp on TV speakers, optical and ARC points upstream to the source, app, stream or common TV audio processing. A fault that follows only one cable or transport belongs to that branch.

Do not enable eARC to “improve” an optical connection; eARC has no role in S/PDIF. Do not replace both cables, reset the television and change every codec option simultaneously. The useful evidence is where the interruption first appears.

Symptoms to Record

Sound falls for a fraction of a second at a regular or repeatable interval.

The same title dips through optical and ARC, but another app is stable.

TV speakers also interrupt at the same timestamp.

Optical drops while ARC and TV speakers remain clean, or the reverse.

Stereo PCM is stable but Dolby Digital from the same source is not.

The DAC loses its input-lock indicator during an optical interruption.

An AVR display changes format when ARC audio vanishes.

Video continues normally, or video blacks out as well.

Record whether the test uses an internal webOS app or an HDMI source, the selected track, LG Digital Sound Output, receiver/DAC display and whether the event follows a pause, advertisement, chapter or format change. Community reports establish that C2 owners see dips on both routes; they do not prove one universal cause.

Causes: Shared Stage or Separate Transport?

Source, app or stream before either output

An internal streaming app can deliver a damaged segment, switch between stereo menus and Dolby playback, or suffer a network interruption. An HDMI player may momentarily stop its audio clock. The C2 then sends that interruption to whichever output is selected. If TV speakers reproduce it, optical jitter is not the root cause.

TV decode or conversion

The television may decode a source to PCM or package a supported compressed format for output. Both optical and ARC can therefore expose a problem associated with the selected codec or conversion state. “PCM stable, Auto unstable” is evidence about format handling, not proof that PCM is the best permanent surround configuration.

Optical-specific receiver lock

S/PDIF is a one-way optical link without HDMI capability negotiation. A marginal connector, tight cable bend, damaged transmitter/receiver or a DAC with poor tolerance for the incoming clock can cause its lock to drop. ARC success during the same test isolates that optical branch. Optical also cannot carry lossless Dolby TrueHD/Atmos or multichannel uncompressed PCM; expecting those formats is a capability mistake, not a dropout.

ARC-specific control and handshake

ARC shares HDMI with CEC/Simplink control. Port selection, CEC state, an AVR input change or cable fault can interrupt ARC while optical remains stable. ARC and eARC are not synonyms: ordinary ARC generally carries stereo PCM and compatible compressed formats, while eARC adds a higher-capacity return path and enhanced capability discovery.

Downstream audio device

If one soundbar, DAC or extractor fails on both feeds but another device does not, its input stage, firmware or power state is implicated. An optical-to-ARC extractor adds another conversion and is not a clean independent comparison.

Step-by-Step Safe Diagnosis

1. Build a repeatable source test

Choose a locally available clip or a streaming scene that has already failed, then note the exact time. Also prepare a known stereo PCM file. Avoid random online “Atmos samples” with uncertain encoding. Disable volume leveling and AI Sound temporarily so fewer processors change during the comparison.

2. Listen through C2 speakers

Select TV Speaker and replay both samples. If the dip remains, compare a second internal app and a separate HDMI source. A single app/title failure belongs with the provider or network path. Multiple independent sources failing at the speaker stage justify LG's Sound Self-Diagnosis and support path.

3. Test optical alone

Disconnect HDMI from the sound system so CEC cannot change its input. Use one direct optical cable, remove protective caps, seat both ends fully and select the audio device's optical input. On the 2022 C2 menu, choose the wired optical output and begin with stereo PCM. Observe whether the receiver's optical-lock indicator disappears.

If moving the cable triggers a loss, replace it with a short known-good optical lead and avoid sharp bends. A red glow only proves that light is present, not that the digital stream is error-free.

4. Test ARC as a fresh branch

Remove optical. Connect the C2 HDMI port physically labeled ARC/eARC to the audio product's ARC/eARC port. Enable Simplink and select HDMI ARC as Sound Out. For a basic ARC comparison, start with eARC Support off and stereo PCM, then test a supported compressed track. If basic ARC is stable, enable eARC only when the audio device supports it and the desired format requires it.

Do not leave optical and HDMI connected during this isolation; some soundbars automatically switch or prioritize one input.

5. Interpret the matrix

If speakers, optical and ARC fail together, move upstream: source, app, network, TV firmware or decode path. If only optical fails, inspect optical cable, DAC lock and supported S/PDIF format. If only ARC fails, inspect HDMI port, Simplink, cable, standby state and receiver firmware. If both external outputs fail but speakers remain stable, test a second audio device before assigning blame to the C2 outputs.

6. Introduce formats one at a time

After stereo PCM is stable, test Dolby Digital, then Dolby Digital Plus over a transport that supports the intended result. Confirm the receiver display. Optical is not the baseline for lossless or high-channel-count audio. A format transition dropout at an app menu boundary differs from recurring silence during a steady soundtrack.

7. Update and reproduce after standby

Record C2 and audio-device firmware, install stable public updates, then perform one complete power restart. Recheck cold start and standby wake separately. If a restart helps only temporarily, report that pattern; it is evidence of state/firmware behavior, not a satisfactory daily fix.

webOS 22 groups output under Sound Out and wired-speaker choices; wording can move after firmware updates. Follow the on-screen description rather than a C1 menu screenshot. Digital Sound Output Auto, PCM and Pass Through change conversion behavior. Pass Through cannot make an unsupported codec compatible, and PCM may reduce channel count depending on the route.

An external HDMI streamer connected directly to an AVR bypasses the TV return path but may sacrifice 4K120, VRR or Dolby Vision if the AVR cannot pass them. Test video capabilities before adopting that wiring permanently.

Cautions

Do not enter the service menu, disable OLED protection, run Pixel Cleaning or change picture calibration. None affects digital audio continuity. Avoid factory reset until the speaker/optical/ARC matrix is complete; a reset erases useful configuration while leaving a bad source or DAC untouched. Do not assume “both outputs” means a failed mainboard until independent sources and receivers reproduce it.