Coaxial vs Optical: Picking the Better Digital Jack
Quick answer / TL;DR: Coaxial and optical carry the same S/PDIF formats, so neither sounds better by design: two-channel PCM, Dolby Digital 5.1 and DTS 5.1 pass on both. Optical is electrically isolated, which kills ground loop hum and ignores electrical interference; coaxial shares a ground with the equipment but takes heavier plugs and survives long indoor runs with cheap 75-ohm cable. Choose optical for consoles, wall-mounted televisions and hum-prone racks, coaxial for long dressed runs and tight budget installs.
Coaxial and optical are the two sockets that carry the same digital audio standard, and the argument between them is older than most of the equipment now using them. One sends S/PDIF as voltage down a 75-ohm copper cable with an RCA plug; the other sends the identical data as red light down a plastic fiber. Both carry two-channel PCM, Dolby Digital 5.1 and DTS 5.1. Neither carries Dolby Digital Plus, TrueHD, Atmos or DTS:X.
This is the buyer's view: what genuinely differs, what only looks like a difference, and a scenario table for the pick that suits the room.
The Same Formats, Two Wires
Start with what does not differ. Both interfaces carry the S/PDIF protocol, frame for frame, including the same channel status bits and the same 5.1 compressed streams. A receiver decoding Dolby Digital from a coaxial socket and the same receiver decoding it from an optical socket produce the same six channels. The difference is the physical layer: a 75-ohm copper pair terminated in an RCA plug, or a 1.0 mm PMMA fiber with an LED at one end and a photodiode at the other. Neither physical layer has any say in the format.
That symmetry is why the choice is usually made by the room rather than the specification. The socket already on the television, the length of the run behind the cabinet, the presence of a turntable or a dimmer on the same circuit – those decide it. A buyer comparing bit depth figures on a product page is comparing the wrong column.
Isolation Against Ground
The real difference is electrical. An optical link has no conductor between the two chassis, so no current can flow along the cable and no ground potential difference can turn into noise. Coaxial joins the grounds of the television and the amplifier through the shield of its cable, and if those two devices sit on different circuits with a voltage between them, that voltage finds the shield. The audible result is a hum at mains frequency, or a ticking that follows a dimmer.
The hum that only appears with coax
Ground loop hum is intermittent and easy to misdiagnose. It appears when a new device joins the rack, disappears when a cable is unplugged, and follows the volume control. Swapping the coaxial lead for an optical one removes the path entirely, which is why optical is the standard answer in racks fed from more than one outlet. The hum is not the cable's fault; the cable is simply the wire that completed the circuit.
Jitter, Measured Against the Noise Floor
Timing jitter is the technical argument usually raised for coaxial. In theory a copper link carries the clock with less conversion than an LED and photodiode pair, and measurements in a laboratory can show a lower jitter figure for coaxial. In practice the receiving chip buffers and reclocks the stream, and the residual jitter sits far below the distortion of the speakers and the room. A living room with a rug, a sofa and two children is not a measurement bench.
What the numbers mean in a living room
The honest summary is that both are transparent for 5.1 at these lengths, and any difference is smaller than the difference between two speaker placements. Where a real difference does appear, it comes from a bad cable rather than the interface: a coaxial lead with the wrong impedance, or an optical fiber bent past its minimum radius, will drop data. Buy a specified cable of either kind and the jitter conversation stops mattering.
| Scenario | Pick | Why |
|---|---|---|
| Console to a soundbar, short run | Optical | Isolated, and the console expects TOSLINK |
| Wall-mounted TV, cable behind drywall | Optical | No ground path, no hum through the stud |
| Run over 5 m along a skirting | Coaxial | 75-ohm copper holds level; fiber is lossy and fragile |
| Rack fed from two circuits | Optical | Breaks the ground loop that causes hum |
| Tight budget, single short link | Coaxial | The cheaper plug and cable, same formats |
| Old receiver with one input free | Either | Match the free socket, assign it in the menu |
Runs, Plugs and Handling
- Coaxial: 75-ohm RCA, firm friction fit, tolerant of a 10 m indoor run
- Optical: square TOSLINK, latched, best kept under 5 m
- Coaxial: a crushed or kinked cable still passes signal, degraded
- Optical: a bend tighter than the core allows loses light at once
- Coaxial: the shield can pick up hum from a dimmer or a fridge
- Optical: no shield, no hum, no pickup of any kind
Handling separates them as much as physics does. An RCA plug pushes on and pulls off, survives being stood on, and a long coiled length costs little. A TOSLINK plug is latched, its fiber does not like a bend radius under about 25 mm, and a cable that has been trapped behind a cabinet door will lose light before it breaks visibly. For a run that is dressed once and never touched, either is fine; for a run that gets moved, coaxial forgives more.
The Practical Pick
The short answer for most rooms: optical when a console, a wall-mounted television or a multi-outlet rack is involved, because isolation solves a problem that actually occurs. Coaxial when the run is long, the budget is tight, or the receiver has a free coaxial socket and no optical one. Both deliver identical 5.1, so the deciding factors are hum, length and connectors. The comparison that matters is not copper against light; it is which of the two the room will let you install without a compromise.
One further check before buying: many receivers carry both socket types on different source groups, and the menu assigns each by name. A free optical socket on the wrong group is less useful than a free coaxial socket on the right one, so read the assignable input list on the unit rather than the label on the cable you already own. The socket you can assign is the one that will actually get used.
Coaxial S/PDIF cables are stocked in 75-ohm RCA form and optical cables in the square TOSLINK form, both carrying the same Dolby Digital and DTS streams; the catalog lists the lengths, the plug bodies and the jacket per part number.
Related reading: The fiber side in full, from plug to core: the TOSLINK cable — toslink-cable
Related reading: The specific differences, argued in depth: S/PDIF versus optical — spdif-vs-optical
Frequently Asked Questions
Does coaxial sound better than optical?
Not in any way you can hear in a normal room. Both carry the same S/PDIF data, and both are transparent for two-channel PCM and 5.1 at domestic lengths. Coaxial can measure lower jitter in a laboratory, but the receiving chip reclocks the stream and the residual sits below the distortion of the speakers. Cable quality matters more than the interface.
Which is better for a long cable run?
Coaxial, generally. A 75-ohm copper lead holds its signal over 10 m of indoor routing and tolerates being clipped along a skirting. Optical fiber is lossy past about 5 m, dislikes tight bends, and a kink loses light before the cable looks damaged. For a run around a large room, coaxial is the more forgiving choice.
Why does optical remove hum?
Because there is no conductor between the two devices. A coaxial cable joins the grounds of the television and the amplifier through its shield, and any voltage between those grounds flows along it as hum. The optical link has an LED at one end and a photodiode at the other, with a plastic fiber between them, so no circuit exists for the current to travel.
Can I use both at once on one receiver?
Yes, if the receiver has both sockets and assigns them to different sources. Each input is switched by name, so the coaxial socket can serve a disc player while the optical socket serves the television. Both carry the same formats, so the only limit is the number of inputs and the length of cable each device needs.
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