What Is the Optical Audio Port, and When Should I Use It?

Ever wonder what that trapezoidal “optical” audio port is? You’ll find these on the back of computers, HDTVs, media receivers, and more, but hardly anyone uses them. That little oft-neglected port can be a real life saver, though. Let’s look at what it is and how you can take advantage of it.

What Exactly Is Optical Audio?

The vast majority of cabling you use for your media centers, personal computers, and audio/visual equipment uses electrical signals. Be it analog or digital, the signal is sent as an electrical impulse over conductive wire. Every cable, from the speaker wire on your 1970s turntable to the HDMI cable on your new HDTV, contains wires, wires, and more wires inside.

The one standout in home audio/video market is the optical audio cable. Unlike other cabling standards, the optical audio system uses fiber optic cables and laser light to transmit digital audio signals between devices. The standard was introduced way back in 1983 by Toshiba, and was originally intended for use with their fledgling Compact Disc players. (This is why you’ll sometimes hear them referred to as Toshiba-Link, or TOSLINK cables.)

You can check if your devices support TOSLINK audio cabling by looking on the back of the device for the distinct TOSLINK port. The port is typically labeled “optical audio”, “TOSLINK”, “Digital Audio Out (Optical)” or something similar, but you certainly don’t need a label to identify it. The TOSLINK port is distinct among all other ports and looks strikingly like a tiny little doggie door into the bowels of your device. Even more distinctive than shape is the fact that when the device is powered on, you can see a faint glow of red laser light around the port door. (See the photo at the top of this article.)

Although the standard is over thirty years old now, it has been refined quite a bit, and modern TOSLINK connections are as useful as ever. So why is the lonely optical cable so underutilized? While that question could be a historical inquiry unto itself, here’s the short version: when TOSLINK came out, it was overpowered for most people’s needs, and by the time the average consumer was rocking an intense home theater, the TOSLINK cable had been eclipsed by the HDMI cable. (HDMI is not only simpler, since it carries video and audio together, but it also supports newer high resolution audio formats like Dolby TrueHD and DTS HD Master Audio. TOSLINK does not.)

The Many Uses of Optical Audio (Even Today)

If HDMI has mostly replaced TOSLINK, then why should you even care? While it’s absolutely true that the TOSLINK cable has been, for video systems at least, made more or less obsolete by HDMI, that doesn’t mean the TOSLINK cable should be relegated to Museum of Obsolete Ports and Standards.

The TOSLINK system is still capable of carrying up to 7.1 channels of very high-resolution audio. For the majority of consumer setups, there will be absolutely no discernible difference between audio quality when using an HDMI cable or a TOSLINK cable.

Our goal isn’t to convince you to switch from HDMI cables to TOSLINK. If all your devices and everything is functioning just the way you want, then by all means carry on. The point of this article is to highlight how the TOSLINK standard is the unsung hero, the hail-Mary-pass if you will, of the digital audio world. Just when you think you’re out of luck, just when you think there is no way to accomplish the audio-system-wrangling required to achieve your goal, the TOSLINK cable can often save the day.

Let’s look at three common situations where it is beneficial to use TOSLINK over HDMI.

Keeping Older Audio Gear In Service

This is probably the most common and pressing reason people turn to the TOSLINK standard today. You have a wonderful and high-quality older media receiver that has every port under the sun except HDMI inputs.

You don’t have to take your premium paid-$1000-for-it-back-in-the-day receiver and put it on Craigslist for pennies on the dollar. The vast majority of HDTV sets as well as many Blu-ray players, game consoles, and other devices still have TOSLINK out ports. You can pipe the HDMI video from the source (say your cable box) into your TV, then turn right back around and pipe the optical audio out to your receiver and speaker system. Remember, TOSLINK has been on the market since 1983: there is good chance that a premium audio/video receiver manufactured anytime in the last decade or two has a TOSLINK port.

Isolating The Audio

You can separate the audio signal from an HDMI cable but it’s a finicky business that requires decoders, adapters, and a bunch of nonsense bordering on digital black magic. If you have any reason at all to isolate the audio signal from a digital source it is almost always, without a doubt, easiest to do so via TOSLINK cables.

Let’s say, for example, you want to use your Blu-ray player as CD player, but don’t want to have to turn your TV on to listen to those CDs. If the Blu-ray player has a TOSLINK port, you can pipe out the audio through the optical port to your speakers or receiver.

Here’s another example: you have a nice set of speakers hooked up to a quality receiver, but that receiver is old enough that it has no digital connections to speak of–including no TOSLINK port. Put a $10 optical-to-analog converter between your optical audio out and your receiver, and you’re in business: you can break the audio out of its digital cage and pipe it into any analog device you want: your wireless headphones, your old receiver, your 1990s-era whole-house audio system, or any other system that only accepts analog audio.

What if you want to use a pair of analog headphones with your TV, but your spouse wants to use the speakers so they can listen at a different volume? Many television sets and receivers have a plain old headphone jack, but most of them kill the audio to the speakers when a headphone cable is plugged in. In this situation, you can use that same TOSLINK converter to send that audio to whatever you want, without the hassle of HDMI content protection standards.

Eliminating Ground Loop Hum

Ground loops are, from an electrical engineering standpoint, a fairly complex subject. Rather than dive into an arcane description of what a ground loop is (feel free to do some advanced reading on the topic if you’re curious) it’s sufficient to say that a ground loop can occur in your home when there is more than one path for electricity to take to the ground. This, in turn, can cause a “hum” to come from your speakers.

One of the most common causes of a ground loop in home media gear is poorly grounded cable TV equipment. In this situation, your power outlets and the connected media equipment are on one ground (hopefully, if your house is up to code, the main earth-ground spike outside) but the coax cable is grounded to another ground (often a water-pipe ground if there is a water pipe or spigot near where the cable enters the home).

This disparity between the placement, capacity, and total potential energy of the two different grounding locations causes, in a manner of speaking, congestion in the electrical system. At best, this ground conflict does nothing and you never even notice. Sometimes, though, it can cause humming over your speakers and even potentially damage your equipment. In a perfect world, we would all hunt down the source of the ground loop and fix it, but sometimes you’re at the mercy of your environment (good luck finding the source of the bad ground if you live in a big apartment complex).

In such cases, you can often completely eliminate annoying ground loop humming from your audio system by isolating the offending device with a TOSLINK cable. Remember, TOSLINK cables are fiber optic, and because the cables are either entirely plastic or plastic and glass, there is no electrical conductivity to transfer the ground loop noise.


Although HDMI has superseded TOSLINK as the all-in-one, higher-bandwidth solution for most consumers, the humble TOSLINK cable still has a place in the modern media center–if for no other reason than those rare moments it saves the day.

Image Credits: Hustvedt, Michael Gaida.

Jason Fitzpatrick is a warranty-voiding DIYer who spends his days cracking opening cases and wrestling with code so you don't have to. If it can be modded, optimized, repurposed, or torn apart for fun he's interested (and probably already at the workbench taking it apart). You can follow him on if you'd like.