Coaxial vs Optical - Which Digital Audio Connection Should You Use?

The Short Answer

Coaxial and optical carry the same digital audio signal. Both are versions of the same standard, called S/PDIF. A Dolby Digital 5.1 track reaches your receiver as the same data over either cable.

Pick coaxial for runs longer than about 5 meters (16 ft). Pick it also if your source puts out 24-bit/192 kHz audio and your receiver accepts it.

Pick optical if you hear hum in the system. Optical also wins when your gear sits on different outlets, or when a cable TV feed is part of the chain.

For a TV and soundbar playing normal surround sound, both cables sound the same. The real question is which ports your two devices actually have.

What Is a Coaxial Digital Audio Connection?

A coaxial digital connection sends the audio data as an electrical signal. It runs over one shielded 75-ohm cable with RCA plugs at each end.

The port is a round RCA socket. Look for a label like Digital Coax Out or S/PDIF. It is often orange, which separates it from the red and white analog jacks beside it.

You will find coaxial outputs on AV receivers, amplifiers, DACs, CD players, and some cable boxes. TVs are a different story. On US models sold today, the digital audio output is almost always optical.

What Is an Optical (TOSLINK) Connection?

An optical digital connection sends the same data as pulses of light. The light travels down a thin fiber. The plug is called TOSLINK, and it clicks into a square port with a small dust flap.

Light carries no electricity. That keeps the two devices electrically separate, so no hum or electrical noise can cross the cable.

Most cheap optical cables use plastic fiber. Plastic loses signal strength faster than glass over long runs. Optical outputs are still common on TVs, soundbars, set-top boxes, and older consoles. New consoles dropped them: the PlayStation 5 and Xbox Series X/S have no optical port and send audio over HDMI instead.

Can You Use a Regular RCA Cable for Coaxial Digital Audio?

A plain analog RCA cable fits the same socket. It will often work. It is not built to 75 ohms, though, and that is the number the digital signal expects.

When the number is wrong, part of the signal bounces back down the cable. Those echoes blur the shape of the data. The receiver then struggles to tell where each bit starts.

On a 1-meter run into decent gear, you will not notice. Either the link works, or it drops out, and it works. Past 3 meters, the odds change. You may get dropouts, clicks between tracks, or a signal that keeps cutting in and out.

Buy a cable sold as 75-ohm digital coaxial or S/PDIF coaxial. Analog cables list no impedance at all. That is the easiest way to tell them apart in a store listing.

Coaxial vs Optical Side-by-Side Comparison

Four things separate the two connections: how the signal travels, how far it goes, what happens to electrical noise, and how much data each end can handle.

Which Audio Formats Each Connection Supports

Both cables carry the same three formats. Two-channel LPCM up to 24-bit. Dolby Digital up to 5.1. DTS up to 5.1. Nothing above that fits in the S/PDIF standard.

Neither one carries Dolby TrueHD, DTS-HD Master Audio, Dolby Atmos, or DTS:X. These formats need more bandwidth than S/PDIF was built for. The limit comes from the standard itself, so copper and fiber fail here equally.

Neither one carries multichannel uncompressed PCM either. Set a Blu-ray player to 5.1 LPCM over S/PDIF, and it will fold the sound down to stereo or switch to a compressed track. People often blame optical for this. Coaxial has the same limit.

What this means in practice: a 4K Blu-ray player or a streaming box will hand your receiver a compressed 5.1 track over either cable. The full soundtrack needs HDMI.

Does Coaxial Actually Sound Better Than Optical?

On the same content, both cables deliver identical data. A 640 kbps Dolby Digital stream keeps every bit intact over coaxial and over optical. So any difference you hear comes from timing, not from the audio data.

Timing errors are called jitter. Jitter means the receiver reads each bit a fraction too early or too late. Optical adds two extra steps here, since the signal turns into light and back again. Cheap TOSLINK parts are slow at those steps, which widens the timing window. Coaxial skips the conversion but picks up electrical noise from the shared ground.

Most DACs and receivers from the last ten years fix this anyway. They store the incoming signal and re-time it with their own clock. On that gear, both inputs measure the same and sound the same.

Where the 96 kHz limit actually comes from

The 96 kHz limit people quote for optical belongs to the parts at each end, not to the fiber. A 24-bit/96 kHz stereo stream runs at about 12.3 Mbit/s. At 192 kHz it doubles to about 24.6 Mbit/s. Older optical transmitters were rated below that higher figure, and the limit stuck.

Newer optical parts handle 192 kHz without trouble. Plenty of current DACs accept it on the TOSLINK input. Check the spec sheet of your own gear instead of judging by the port.

Where coaxial genuinely loses

Coaxial ties the grounds of two devices together. That link can create a ground loop, which you hear as a steady low hum. It shows up most often when devices use different outlets, or when a cable TV feed enters the system. No cable upgrade fixes it. Optical breaks the loop by design, and this is the one case where the choice really matters.

When to Choose Coaxial and When to Choose Optical

Match the cable to the problem in front of you.

Choose coaxial if:

• the run is longer than about 5 meters (16 ft)
• your source outputs 24-bit/192 kHz and your DAC accepts it on the coax input
• the cable has to bend tightly behind a media cabinet, where fiber can crack
• you are connecting a CD transport or a standalone DAC, where the coax input is often the better one

Choose optical if:

• you hear hum after connecting the two devices
• a cable TV or antenna feed is part of the system
• source and receiver plug into different outlets or different circuits
• the cable runs near power leads, dimmers, or a network switch
• your TV has no coaxial output, which covers most current models

If both devices have both ports and none of these apply, use the cable you already own. You will not hear a difference.

When Neither Connection Is Enough

Both cables stop at compressed 5.1. Dolby Atmos, DTS:X, Dolby TrueHD and DTS-HD Master Audio will not pass through either one. No cable upgrade changes that.

Those formats need HDMI. HDMI ARC carries Dolby Atmos inside Dolby Digital Plus. HDMI eARC adds enough bandwidth for lossless TrueHD and DTS-HD Master Audio, including full Atmos.

Coaxial and optical still earn their place elsewhere. They work well for a CD player, a DAC, a stereo amplifier or an older set-top box, where the source only puts out two channels anyway.

Key Takeaways

• Coaxial and optical send the same S/PDIF data and sound the same on the same content.
• Coaxial handles higher sample rates on more gear and runs further, up to 10 meters and beyond.
• Optical keeps the two devices electrically separate, which is the only sure fix for ground loop hum.
• Neither cable carries Dolby Atmos, DTS:X, Dolby TrueHD, DTS-HD Master Audio or multichannel uncompressed PCM.
• The 96 kHz limit tied to optical comes from older parts at each end, and current hardware often handles 192 kHz.
• For lossless or object-based surround, use HDMI eARC and treat both S/PDIF cables as stereo and compressed 5.1 links.