Optical vs HDMI ARC Optical (TOSLINK) vs HDMI ARC vs HDMI eARC for TV-to-Soundbar Audio

What each connection carries

The three connections differ by bandwidth, and bandwidth decides which audio formats survive the trip. Samsung's soundbar connection guide lays it out as a support table. Dolby Digital and Dolby Digital 5.1 work on HDMI-eARC, HDMI, optical, and Bluetooth. Dolby Digital Plus, including compressed Dolby Atmos, works on eARC and HDMI but not optical. Dolby TrueHD, including uncompressed Atmos, works only on eARC. A Sonos community answer says the same about the Arc Ultra: over its optical adapter, Dolby Atmos will not play.

How the three links work

Optical is S/PDIF as light. Wikipedia lists its payload at 3.1 Mbit/s for 48 kHz PCM, and plastic fiber is effective to 5 to 10 m. It carries two-channel PCM or compressed 5.1 (see TOSLINK).

ARC reuses the same S/PDIF signaling inside the HDMI cable. A DPL Labs technical write-up derives ARC from IEC 60958, puts its data rate at approximately 3 Mbps, and says that is sufficient for up to 5.1 channels of encoded sound: Dolby Digital, DTS, and MPEG-2 AAC, with no Dolby TrueHD or DTS-HD Master Audio. ARC and optical sit at similar bandwidth, but the formats differ: per Samsung's table, ARC-class HDMI passes Dolby Digital Plus and a TV's optical output does not.

eARC is a different link. HDMI.org gives a maximum audio bandwidth of 37 Mbit/s and support for up to 192 kHz sampling at 24-bit, with DTS-HD Master Audio, DTS:X, Dolby TrueHD, and Dolby Atmos, plus uncompressed 5.1, 7.1, and 32-channel audio. That is roughly 12 times optical's 3.1 Mbit/s (37 / 3.1). HDMI.org also says either a Premium High Speed cable (up to 18 Gbps) or an Ultra High Speed cable (up to 48 Gbps) delivers strong audio, so eARC does not force a cable upgrade for audio alone.

The bandwidth arithmetic

The numbers explain the format limits. Uncompressed 5.1 PCM at 24-bit and 48 kHz is 6 channels x 24 bits x 48,000 = 6.9 Mbit/s, more than double the 3.1 Mbit/s an S/PDIF link carries, so multichannel PCM cannot go over optical or ARC. Eight channels of 24-bit audio at 192 kHz is 8 x 24 x 192,000 = 36.9 Mbit/s, which is where eARC's 37 Mbit/s figure comes from (my arithmetic, and it matches DPL Labs' description of eight-channel, 192 kHz, 24-bit uncompressed audio). A Dolby Digital 5.1 stream is capped at 640 kbit/s, about a fifth of the optical payload, so it fits easily, and so does Dolby Digital Plus in principle. The limit on DD+ over optical is what devices implement, not raw capacity: Wikipedia says S/PDIF has bandwidth for DD+ at 3.0 Mbit/s but that manufacturer adoption has been lacking.

Optical vs ARC vs eARC: the decision

Pick by the source, not the connector. Streaming Atmos from a TV's own apps typically arrives as Dolby Digital Plus, with Atmos carried as metadata inside it. That fits through ARC and does not fit through a TV's optical output, which Samsung's table marks as unsupported for Dolby Digital Plus. See DD+ JOC for why streaming Atmos is lossy DD+ and not TrueHD. So for Atmos from TV apps, ARC is enough; optical drops the Atmos layer.

A disc player is the other case. A 4K Blu-ray with a TrueHD Atmos or DTS-HD Master Audio track can only reach a soundbar losslessly if the player's HDMI goes to the TV and the TV returns it over eARC, or if the player goes straight to an AVR and bypasses the TV. Through plain ARC or optical the TV must re-encode or downmix. If you own a receiver, the cleaner design is source to receiver by HDMI and receiver to TV by HDMI, and then ARC or eARC only carries the TV's own apps back. The tradeoffs are covered in eARC vs ARC.

Lip sync is the quieter difference. A DPL Labs article says eARC provides automatic lip-sync compensation through metadata exchange: the sink reports its video latency and the source adjusts audio delay. That removes a manual delay setting from many setups, and HDMI 2.2's Latency Indication Protocol extends the idea to multi-hop chains.

Where each connection lives

LG's customer care answer for the 2025 C5 OLED lists one optical digital audio out and HDMI eARC on HDMI port 2, and says eARC can carry Dolby Atmos. A Sonos community answer says the Sonos Arc Ultra has no optical port of its own and reaches an optical TV output only through the Sonos Optical Audio Adapter, which gives up Atmos. In both cases eARC is the route that keeps the format intact. Check both ends, because an eARC port talking to an ARC-only device is an ARC link. The wiring angle is in the apartment soundbar guide and the HDMI cable guide.

Common confusions

An Atmos badge on the soundbar does not prove lossless audio. Over ARC the badge is DD+ Atmos. Lossless Atmos needs TrueHD over eARC. Another trap is eARC fallback: an eARC port on a TV talking to an ARC-only soundbar is just an ARC link, and the lossless formats are unavailable until both ends are eARC (see ARC and eARC).

Finally, optical is not "worse sound" for stereo music. For two-channel PCM, optical carries the same bits. Measured jitter differences between cables are small and, where they exist, depend on the receiving DAC (the evidence is in the TOSLINK entry). The limit is format, not fidelity: optical cannot carry what eARC can, and for plain stereo and Dolby Digital 5.1 it does the job.