Quick answer: For channel count and format support, HDMI wins: eARC carries up to 37 Mbit/s and passes TrueHD, DTS-HD Master Audio and object-based Atmos, while TOSLINK carries two channels of PCM at up to 192 kHz or compressed 5.1 at roughly 1.5 Mbit/s and nothing above that. For electrical isolation and hum rejection, optical wins outright, because there is no galvanic connection between the two devices. Choose HDMI when the source has a modern soundtrack to deliver, and optical when the room hums or the run crosses grounded equipment.
The two links solve different problems. HDMI audio is embedded in the video stream, so it inherits the video link’s bandwidth and its EDID negotiation. TOSLINK carries a S/PDIF frame with no negotiation at all: the sender transmits, the receiver locks, and nothing is exchanged. That simplicity is both its strength and the reason it stopped at 5.1.
Two links built for different jobs
HDMI audio rides with video
On a direct connection the audio sits in the blanking interval of the video stream, so the format ceiling is set by the sink’s EDID and the link budget. The audio return channel flips the direction: the TV sends audio back down the same cable to a soundbar or AVR. The original ARC implementation allowed about 1 Mbit/s, enough for Dolby Digital 5.1 but not for lossless. eARC raised that to roughly 37 Mbit/s and added automatic lip sync.
TOSLINK carries one fixed frame
S/PDIF is a one-way stream of 64-bit subframes at the sample rate, giving two channels of up to 24-bit PCM, or a compressed bitstream wrapped inside the same frame. There is no handshake, no capability exchange and no return path, so any device that receives a format it cannot decode produces noise or silence rather than falling back. That is the single biggest practical difference from HDMI.
What each link can actually carry
| Link | PCM ceiling | Compressed | Atmos |
|---|
| HDMI direct | 8 ch, 192 kHz, 24 bit | All, including lossless | Yes |
| HDMI ARC | 2 ch | Dolby Digital 5.1, DTS | No |
| HDMI eARC | 8 ch, 192 kHz, 24 bit | All, up to 37 Mbit/s | Yes |
| TOSLINK | 2 ch, 192 kHz, 24 bit | Dolby Digital 5.1, DTS 5.1 | No |
| Coaxial S/PDIF | 2 ch, 192 kHz, 24 bit | Dolby Digital 5.1, DTS 5.1 | No |
Where optical is the better cable
A ground loop is a difference in earth potential between two devices, and it shows up as mains hum or as a high-pitched whine that changes with the dimmer in the next room. Fiber breaks the electrical path completely, so the loop cannot form. The same property makes optical the safer choice between a TV on one circuit and an amplifier on another, and it removes the risk of a fault in one chassis reaching the other. Distances of 5 to 10 m are cheap in plastic fiber, and there is no EDID to go wrong. The TOSLINK vs coaxial digital comparison covers the copper alternative when isolation is not needed.
There is a second, quieter advantage: an optical link cannot inject radio-frequency noise from a switching supply into the audio ground. In a rack with a media PC, a network switch and a Class D amplifier on the same earth, that noise often appears as a faint hiss at the tweeter rather than as hum. Disconnecting the fiber and hearing the hiss stop is the fastest diagnostic, and it points to the power supply rather than to the cable.
Where HDMI wins
Any soundtrack with more than six channels, or with height objects, needs eARC or a direct HDMI path. CEC also lets the TV remote control the receiver’s volume, which no S/PDIF link can do. If the display supports eARC, keep the AVR on the eARC port and let the TV forward the bitstream; the eARC cable page explains why a High Speed cable is sufficient for that role and where certification starts to matter. The HDMI ARC vs optical breakdown maps the same decision for older TVs that only offer ARC.
Practical scenarios
- Streaming stick into an older soundbar: the stick has no optical output, so use the TV as the switch and send Dolby Digital 5.1 back over ARC; expect no Atmos because ARC cannot carry it.
- Turntable preamp in a room with dimmers: run TOSLINK from the preamp to the amplifier. The hum disappears because the ground loop is broken, even though the format ceiling drops to two channels.
- Console plus Atmos soundbar: connect the console directly to the soundbar’s HDMI input for object audio, then pass video to the TV, so the bitstream never depends on an ARC link.
- Long run to a second room: optical is cheaper than a long HDMI cable and immune to electrical noise, but it is limited to 5.1 compressed, which is fine for a second zone.
FAQ
Is optical audio lower quality than HDMI?
Not in itself. Both carry digital samples, and two-channel PCM is bit-identical on either link. The difference is format support: optical cannot carry lossless multichannel or object audio, so a high bitrate track has to be downmixed before it fits. If you only listen in stereo, the two links are equivalent.
Does HDMI audio have more jitter than optical?
The clock is recovered from the incoming stream on both links, and a competent receiver buffers and re-clocks either one. Measured differences are well below audibility in normal rooms. Ground loops and level mismatches cause far more audible problems than jitter on a working link.
Can I use both at once?
Yes, but the source usually sends to one output at a time, and running both often forces the lower common format. Pick one path per zone: HDMI to the AVR for main listening, optical to a second amplifier or a hearing-assist transmitter, with the source set to output simultaneously if it supports that.
