Digital Optical Cables: Decoding Audio Connections

Digital optical audio cable

Cables aren’t the most glamorous components of the audio-visual world, but they’re certainly one of the most important. 

One essential yet often overlooked cable is the digital optical audio cable, designed by Toshiba in 1983 – long before the fiber-optic connectivity we’re familiar with today became mainstream. 

Many AV devices, such as Blu-ray players, soundbars, PCs, and even some game consoles like the Xbox One, feature a “digital audio out” connection, also sometimes called “S/PDIF,” “optical out,” or “TOSLINK.” 

In this article, we’ll explore the digital optical cable in-depth, including its functionality, limitations, and when to consider using it. 

Table of Contents

What is an Optical Digital Audio Cable?

An optical digital cable transmits digital audio signals between devices via light. 

In essence, optical digital cables are a variation of fiber-optic technology, using light to transmit signals through the cable. There are no metal wires involved in signal transmission whatsoever. 

The light carried by an optical cable is created by LEDs (light-emitting diodes). LEDs convert the electrical audio signals into light pulses at the transmitting end. 

At the receiving end, another LED or photodiode converts these light pulses back into electrical signals that your audio device can process.

Are Optical Digital Audio Cables TOSLINK Cables?

TOSLINK, an acronym for “Toshiba Link,” was initially developed by Toshiba back in 1983 as a way to connect their CD players to receivers. 

While optical digital audio cables are interchangeably known as TOSLINK cables, TOSLINK more strictly refers to the connector system – Toshiba standardized optical digital audio connectors in the late 80s and 90s.

Construction

The main component of an optical digital audio cable is its fiber-optic core. In budget-friendly cables, the core is usually made of a type of plastic called PMMA.

This is the same material that’s often used in ‘Plexiglass’ or clear acrylic sheets. 

Higher-end optical digital audio cables often have cores made from glass fibers, which offer superior signal transmission at a heftier price tag.

Compatibility

Optical digital audio cables have established themselves as versatile cables that are compatible with a wide range of high-definition audio devices. 

Whether you have an HDTV, a soundbar, a gaming console, a Blu-ray player, or an AV receiver, the odds are high that one or more of these devices will have a port labeled “Digital Audio Out” explicitly designed for an optical digital audio cable.

This connection may also be labeled “S/PDIF,” “optical out,” or “TOSLINK” on older devices. 

Digital optical cable connection diagram

How Do Optical Digital Audio Cables Work?

Fundamentally, optical digital audio cables transmit digital signals using light via the S/PDIF connection standard.

Optical cables are a form of fiber-optic cables – there are no copper wires. S/PDIF signals can carry two channels of uncompressed audio or compressed 5.1 surround sound, which includes Dolby codecs such as DTS 5.1 and Dolby Digital. 

It’s worth mentioning that these cables can’t correctly handle Dolby’s newest codecs, such as Dolby Atmos or Dolby TrueHD.

The process of transmitting audio via optical digital audio cables can be broken down into distinct phases: encoding, transmission, and decoding.

Let’s take a closer look:

1: Encoding

Source devices with digital audio outs, such as Blu-ray players, are equipped with an LED at the transmitting end. That LED converts the electrical digital audio signal into light pulses. 

The encoding process starts with the source device converting audio data into a stream of digital signals. 

This digital stream then triggers the LED to emit a sequence of light pulses, each corresponding to a specific piece of audio information.

2: Transmission

Once the digital audio signal is encoded into light pulses, it’s sent down the fiber-optic core of the cable. 

Herein lies one of the key advantages of optical cables – light is immune to electromagnetic interference. 

Conversely, traditional copper-based audio cables can be susceptible to interference from various electrical and magnetic sources. 

3: Decoding

The light pulses eventually reach their destination, often an AV receiver, a soundbar, or a similar device equipped with an optical digital audio input.

At this receiving end, another LED (or sometimes a photodiode) is tasked with converting these light pulses into an electrical digital audio signal.

This signal isn’t yet audible – it’s still in its digital form. The receiving device processes this digital data into an analog audio signal through a digital-to-analog converter (DAC).

The DAC transforms the electrical signal into audio waves that are amplified and sent to speakers, completing the transformation from light pulses to sound.

Common Questions & Misconceptions

Does Length Matter?

You’ve got your gear set up across the room, and you wonder if that long optical cable run will degrade your audio.

Generally speaking, you’re unlikely to notice any drop in audio quality for runs less than 30 feet (about 9 meters). 

Toshiba designed the TOSLINK standard with a technical limit of 32.8 feet (10 meters).

However, modern optical digital audio cables can generally support cable lengths of up to 50 feet (15 meters), though that’s seldom necessary. 

Optical cables length

Can I Use It for Video?

Optical digital audio cables are for audio only. They cannot transmit video signals. The light pulses these cables use are coded to represent audio data. 

Video data, being far more complex and demanding in terms of bandwidth, is not something these cables are designed to handle. 

If you need to transmit video signals, you’ll need HDMI, DisplayPort, or older technologies like component or composite video cables.

Are Optical Cables Obsolete?

Given HDMI’s dominance in the AV world, many question whether optical cables have been rendered obsolete. 

While it’s true that newer connections like HDMI and DisplayPort can handle both audio and video, optical cables still hold a place in many audio-centric setups. 

One possibility is that you have an older vintage or classic receiver or other setup that doesn’t handle HDMI. There are other use cases for the optical cable, too, such as isolating audio from video to use devices such as Blu-ray players as CD players via soundbars without HDMI. 

Moreover, HDMI Arc for soundbars can be tricky and suffers from compatibility issues, making the humble optical cable an excellent backup.

Finally, digital-to-analog converters that accept optical cables are cheap – about $15 – and would enable you to connect any optical cable-enabled device to old-school audio gear. 

Are Coaxial Cables Better than Optical Digital Cables?

Coaxial cables, another type of audio-only cable, directly compete with optical digital audio cables.

Some report that coaxial cables have higher bandwidth than optical digital cables, which means they offer better quality by default, but this isn’t necessarily true.

Bandwidth capabilities of both coaxial and optical digital audio cables can vary depending on the cable’s quality and the connected equipment’s specifications.

However, for most digital audio applications, both types can handle as much bandwidth as needed.

For instance, while uncompressed FLAC (Free Lossless Audio Codec) files vary in bit rate, both optical and coaxial cables will handle even a high-quality FLAC file.

With that said, most optical audio cables won’t cope with 24-bit/192kHz files.

Ultimately, it’s best to try both connections and use your ears to gauge which sounds best for your particular setup.

Advantages and Disadvantages of Digital Optical Audio Cables

Let’s break down and distill some of the advantages and disadvantages of digital optical audio cables. 

Advantages

High-Quality Audio

The main draw of optical digital audio cables is their ability to deliver high-quality, uncompressed audio or surround sound through multi-channel formats such as:

  • PCM 2.0
  • Dolby Digital 2.0 to 5.1
  • Dolby Digital EX 6.
  • DTS Digital Surround (DTS 5.1)
  • DTS-ES Matrix 6.1
  • DTS-ES Discrete 6.1
  • DTS 96/24 (96kHz/24bit audio)

The fiber-optic core insulates the signal from electromagnetic interference, ensuring the audio remains clear and pure from source to receiver. 

If you can’t seem to avoid interference creeping into your AV setups, try switching to an optical cable. 

Ease of Setup

Optical digital audio cables require no drivers to install, no complex settings to fiddle with, and no special tools. 

It’s as easy as inserting the cable into your device’s corresponding port. You may need to select the appropriate audio input on the receiving device or the output settings on the output device. For example, you might have to select both ‘optical’ out and ‘PCM’ on a TV display device or Blu-ray player.

Affordability

With a wide range of pricing options, finding an optical digital audio cable that fits your budget is generally straightforward. 

Given that even budget-friendly options deliver excellent audio quality, optical audio cables offer fantastic value. Moreover, since these cables are often bundled with TVs, AV receivers, and soundbars, they’re one of the quickest ways to get high-quality audio up and running. 

You can also up your budget to include higher-quality glass optical cables, though most report the difference in quality as relatively minor. 

Disadvantages

Limited Distance

Although optical digital audio cables are ideal for short to moderate runs, audio quality can drop at distances exceeding 30 – 40 feet (9 – 12 meters). 

Beyond this range, the signal may suffer from attenuation and dispersion, resulting in a loss of audio quality. This has become less of an issue with modern optical cables. 

Fragility

Fiber-optic cables, especially those with a glass core, can be delicate. They’re not suited for environments where they might be bent, twisted, or stepped on. 

Even slight kinks or bends can break the fiber-optic core, rendering the cable useless. 

Audio-Only Capability

Optical digital audio cables are single-purpose cables designed to handle audio data only.

Conclusion

Optical digital audio cables are a stalwart in the AV cable world, delivering high-quality audio to various devices since the 80s. 

While they have their limitations, they remain an excellent choice for a clutter-free, simple, yet effective audio connection. 

Since they use light for signal transmission, which is immune to electromagnetic interference, they’re worth trying if you’re experiencing a lot of interference through your audio system.  

Plus, if you love to mix and match new and old-school AV gear, you’ll likely need something other than HDMI cables in your arsenal. 

If you have further questions, our dedicated forum community is here to help! 

Dive into the world of home theater technology by joining our discussions, and feel free to check out other relevant articles here on HomeTheaterForum.com.

Sam Jeans Bio Photo

Sam Jeans is a freelance writer who has worked with prestigious clients such as the Royal Mint, The Independent, DailyAI, and top tech companies like Lenovo and Toshiba. With an MSc in International Development and Social Anthropology and a BA in Audio and Music Production, Sam brings a unique perspective to his writing, blending cultural knowledge with insights into audio engineering and the latest tech gadgets and trends.

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