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Optical Digital Audio
- Cable and Connection Explained

Updated: March 08, 2021

Optical digital audio connections are a popular way to send high-quality audio between devices. They are also known as TOSLINK connections.

You might have several different choices when it comes to the audio for your system, and optical is always a good choice.

So what are they exactly, and what are the advantages and disadvantages?

Also, is optical audio better than a coaxial connection? And, can you convert optical to coaxial? Or into stereo analog audio?

Read on to find the answers to these questions and more.

What Does the Optical Connector Look Like?

An optical digital audio connection on your device will look something like this:

Optical audio connection on the rear of a media player

 Clue - it's on the right, hiding above the word optical!

In this example, there is an optical output, and a coaxial connection above it - as well as other connections that we're not interested in right now.

When connecting two devices, one device will have an optical outputThis is the device sending the sound. Like your TV, for example.

The other will have an optical inputThis is the device receiving the sound. Like your amplifier.

In the picture above, the optical port has a protective 'door' which will move out of the way when you push the cable in.

Some optical ports have a protective cap over the hole which needs to be removed before you can plug in the cable. As is the case in the picture here with this optical digital audio out:

Optical audio connection with protective cap

When you remove the cap you will be able to see the bright red light from inside the device.

What Does the Optical Audio Cable Look Like?

Optical Audio Cable

An optical audio cable looks like this.

When you insert the optical cable, it should click into place. It is designed to fit one way only; one side is squared-off while the opposite is angled on the corners.

If you look carefully you will see that this matches the shape of the port on your device.

Optical cables used for digital audio come in a wide range of lengths, colors - and prices!

You may be tempted to buy the most expensive optical cable on the market because... well, it's going to sound better, right?

Well, not in my opinion, no. You won't get any extra special audio by spending an extortionate amount on a cable. I would just buy a good value, well-made brand. Note the emphasis on well-made.

So, where can we go and buy an optical audio cable?

There are many choices available on Amazon, so I would just check the reviews and buy one there.

The AmazonBasics digital optical audio cable should do the job just fine - however, there are other good value brands there too like this BlueRigger digital optical audio cable:

BlueRigger Digital Optical Audio CableBlueRigger Digital Optical Audio Cable
Image Credit: BlueRigger
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Just make sure you double-check the length of the cable you are buying and get the right size for your needs. There's nothing more annoying than buying a cable and then finding out it's too short.

Been there. Done that.

What Does an Optical Digital Audio Connection Do?

An optical digital audio connection sends digital audio between devices.

An everyday use for this type of connection is the digital audio output on the back of your TV.

By connecting this output to an amplifier, you can quickly improve the sound of your television.

Does an Optical Audio Cable Send Video?

No, the optical connection on your AV device is for digital audio only.

What Audio Formats Are Supported by an Optical Connection?

Optical audio connections support the following audio formats:

  • Lossless 2.0 (stereo) PCM audio
  • Compressed Dolby Digital 2.0/5.1 and Dolby Digital EX
  • Compressed DTS Digital Surround, DTS-ES Matrix 6.1 and DTS-ES Discrete 6.1

Due to bandwidth restrictions, optical outputs do not support multichannel LPCM, Dolby Digital Plus, Dolby Atmos and DTS:X - or high-definition audio such as Dolby TrueHD and DTS-HD Master Audio.

Discrete 7.1 soundtracks are not supported as they are only encoded in higher resolution audio formats.

Due to copyright restrictions, optical connections also do not support SACD audio and DVD-Audio.

If you try to play unsupported formats on your player via an optical output, the player will usually downmix to stereo or play a lower resolution version of the audio.

The manual for your player will tell you how it will handle the unsupported audio formats.

Check out my home theater glossary if you don't know what these types of audio are.

When Should I Use an Optical Connection?

A common question that gets asked is, "Do I need optical audio if I have HDMI?"

If your AV equipment has an HDMI port, then in most cases it would be best to transfer the audio signals via HDMI. This is because HDMI supports all types of audio signals and you can send all the video and audio signals via one cable.

However, if you don't have HDMI as an option, then an optical audio cable is a good way to transfer the audio between devices.

You will be able to play uncompressed stereo audio and compressed DTS or Dolby Digital 5.1 surround sound over an optical connection.

Some older devices with HDMI ports don't support the transfer of audio via HDMI. Therefore, this would be another instance where you could utilize this alternative digital interface.

Another common use for this type of connection is for connecting your TV to your hi-fi sound system or soundbar - or for wiring your CD player to an amplifier.

For example, if you get your TV transmissions via an internal tuner or a smart TV app, then you might want to send the audio from your TV into your home theater speaker system.

Most modern TVs have an optical audio output for this purpose. You connect the optical audio output on the rear of your TV to an optical input on your AV receiver or amplifier.

What Is the Maximum Length of an Optical Audio Cable?

A well-made optical audio cable should work well up to 5 meters. You may even find that you will get a good signal at 10 meters or more. However, by the time you get to this length, then you are more likely to run into problems.

It would certainly be worth considering buying a higher-quality digital optical cable for longer runs.

However, bear in mind that your equipment will also have an impact on this. 

The electronics built into your hardware can vary in quality. You may find that some devices will work over a long cable run – while others don’t.

You may just have to try it and see.

Alternatively, you could consider buying a set of optical audio extenders like this:

J-Tech Optical & Coaxial Digital Audio Cat5e/6 ExtendersJ-Tech Optical & Coaxial Digital Audio Cat5e/6 Extenders
Image Credit: J-Tech Digital
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These extenders use Cat5 or Cat6 cable to send the optical audio signal over very long distances.

They work up to a distance of 300 meters and also support coaxial audio connections.

Optical vs HDMI Cable - Which Is Better?

Many people wonder which connection they should use to send audio between their devices - optical or HDMI cables.

Firstly, do they sound different? No, they don't.

If you are sending the same type of audio format, then it will sound the same regardless if you are using optical or HDMI.

The main advantage of HDMI over an optical connection is that HDMI supports more audio formats.

Optical and HDMI both support uncompressed stereo - and 5.1 Dolby Digital and DTS audio.

However, HDMI also supports Dolby Digital Plus, and high-resolution audio like Dolby TrueHD, DTS-HD Master Audio, Dolby Atmos and DTS:X.

Also, HDMI has the advantage of HDMI ARC and HDMI eARC connections. This is where you can send audio from a TV to a soundbar or AV receiver.

This can sometimes save you installing an extra cable in your system.

Here is a handy table comparing the differences between optical and HDMI ARC and HDMI eARC connections:

Toslink Optical, HDMI ARC and HDMI eARC Connection ComparisionOptical, HDMI ARC and HDMI eARC Connection Comparision
Source: HDMI.org

The bottom line? HDMI supports more audio formats and might save you an extra cable if your system supports ARC or eARC.

However, an optical connection will sound just as good as HDMI if you don't need anything more than stereo or compressed 5.1 surround sound.

What Else Can You Tell Me About Optical Audio?

This type of interface is often referred to as a TOSLINK port - and the interconnect a TOSLINK cable. This refers to the developer of this connection type, Toshiba.

In this type of connection, the digital signal is converted into light and transferred via a cable made from optical fiber.

This fiber optic cable can be quite thin, so you need to make sure that you are careful when handling it. You can break the core if you bend it too much.

Optical cables for digital audio are usually constructed with multimode plastic optical fiber (POF).

This is cheaper than alternative options such as glass or silica optical fibers - but is perfectly suited to short runs typical in home audio applications.

Plastic optical fiber is also more flexible which is another benefit when wiring a sound system.

Aside from an HDMI cable, there are two main methods of connecting devices to send digital audio - optical and coaxial digital audio.

Both of these connection types are also known as S/PDIF connections.

S/PDIF is short for Sony/Philips Digital Interface. Sony and Philips were both involved in the initial design of this audio connection.

Regardless of the connection type used, there is no difference in the actual data transferred.

You often find these two connections side-by-side on a device (as in the picture at the top of the page) - or you may get one or the other.

If you have both, the decision of which one to use will usually come down to something simple such as the type of connection you have on the other device.

Which Is Better - Optical or Coaxial Audio Connections?

For the same audio format, they offer the same audio quality. Both send S/PDIF digital audio signals.

TOSLINK connections were originally designed to run to a maximum of 48 kHz. However, many newer devices increased the supported resolution to 24/96.

This is commonly thought to be the maximum resolution of optical audio - although there is a question of why many devices don't support higher resolutions.

Coaxial connections commonly support 24/192 resolution audio. So this support for higher resolution audio formats may one reason to choose coaxial over optical audio.

A potential benefit of optical connections is that they won't be affected by electromagnetic interference. In theory, coaxial could be.

Another consideration is that the sound quality may vary by device.

Before you hear a digital audio signal it needs to be converted to analog audio. A DAC performs this process.

A poorly-designed device may create audible differences when using the optical or coaxial inputs. In a high-quality device, it shouldn't sound any different.

In the real world, there won't be much difference between the sound quality of optical and coaxial connections.

The one you choose will usually depend on the connections on your other devices. Or, the cables that you have available.

How Do I Convert Digital Optical Audio to RCA Coaxial?

One scenario you may come across is that you have an optical output on your device (a DVD or Blu-ray player, for example), but only a coaxial input on your amplifier.

How annoying is that?

However, there is a simple solution. You can buy an optical to RCA coaxial converter like the one pictured below:

ROOFULL Optical-to-Coaxial or Coax-to-Optical Digital Audio ConverterROOFULL Optical to Coaxial Bi-Directional Digital Audio Converter
Image Credit: ROOFULL
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This will take an optical output - like from your Blu-ray player - and output the audio signal via coaxial.

Terrific!

The one highlighted above is bi-directional. This means that you can also use it to convert a coaxial output to an optical input. Which might prove to be really useful.

The use of converters can solve many potential problems when we need to mix and match different audio types and connections.

You just need to make sure that the converter will pass all the signals that you want. For example, some may only send stereo audio and not multichannel surround sound.

The one above supports both.

Can I Convert Optical Audio to Stereo Analog?

Another solution to the problem of the wrong inputs on your amplifier would be to convert the optical digital audio to analog and connect to your amplifier using our old friend the stereo analog audio connection.

But how can I possibly do this, I hear you cry? Well, buy a digital optical to analog RCA audio converter of course.

You can see an example of one pictured below:

PROZOR 192KHz Digital to Analog Audio ConverterPROZOR 192KHz Digital to Analog Audio Converter
Image Credit: PROZOR
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This device will accept either an optical or coaxial digital audio connection and output the audio as stereo analog.

It even has a 3.5mm jack output for connecting a pair of headphones.

It's like magic I tell you!

How to Convert Analog RCA to Digital Optical Audio

In the previous example, we wanted to convert from digital to analog audio.

However, what if you needed to convert the audio the other way? From analog to digital.

An example might be where you have a device like an old tape deck - and wanted to send the audio to the optical input of an amplifier or soundbar.

You can do that with a converter like this:

Musou RCA Analog to Digital Optical Audio ConverterMusou RCA Analog to Digital Optical Audio Converter
Image Credit: Musou
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The above device also converts to a coaxial output in addition to the optical connection.

Before you buy any converters like these, always make sure you are clear about the format of the audio output and input.

If you get a device that converts the wrong way then it won't work.

What Is an Optical Audio Switch Used For?

Another potential issue you may come across is that you have a limited number of optical inputs on your AV receiver or soundbar.  

In this scenario, if you have two or three devices that you want to connect into your amplifier via an optical connection, then you can buy an optical audio switch, like the one pictured below:

eSynic 3x1 Toslink Optical Digital Audio SwitchereSynic 3x1 Toslink Optical Digital Audio Switcher
Image Credit: eSynic
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This little box of tricks will accept the optical audio outputs of up to three different devices, and then output them into the one input on your amplifier.

The model above comes with a remote control so you can switch between the different audio inputs.

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About Home Cinema Guide

Paul started the Home Cinema Guide to help less-experienced users get the most out of today's audio-visual technology. He has worked as a sound, lighting and audio-visual engineer for around 20 years. At home, he has spent more time than is probably healthy installing, configuring, testing, de-rigging, fixing, tweaking, re-installing again (and sometimes using) various pieces of hi-fi and home cinema equipment.


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