Plugging in: differences between optical and aux audio

If you’ve owned or used a speaker before, you’ll likely have used one of two inputs: optical and auxiliary (aux). Broadly speaking, these are two different ways of moving audio from your device to your speaker. Though they are both commonly used in speakers and transmit audio, the ways they work are entirely different.

This difference comes down, in part, to their connectivity: optical is digital and aux is analogue. But what does this mean, and how exactly do they work? Here, we’ll go into the depths of these two popular formats, weighing up their pros and cons, and thinking about what the future holds for them.

Aux and optical: the differences

In the timeline of these two formats, aux came first, in the 1960s. It’s an analogue medium, meaning it can only transmit sound. In addition to this aux cables are made of copper, and the data transmitted through it do so via the continuous waveform of electrical information.

By contrast, optical audio is a completely different beast. Originally named "Toslink" (short for 'Toshiba Link'), it was developed in the early 1980s as a means to connect Toshiba CD players and receivers. Unlike aux, optical is digital: it uses laser light to transmit digital information in the form of discrete 'bits' of information down a hollow fibre optic cable. It can transmit more types of information than an aux cable can — in fact, it's the exact same technology used in lightning-fast fibre optic broadband.

Pros and cons

How do the two formats fare against each other? In terms of audio quality, aux is more open to line loss and interference. This is because electrical sources, like your mains power, can distort the signal. If you've ever heard your speaker buzz, that's interference. The easiest way to combat this is to route your aux cables as far away from the mains as possible (though that's not to say that you won't have other sources of interference that can mess with your signal). Higher quality aux cables can also help as they’re better shielded.

Optical isn’t foolproof either. Though not prone to interference in the way that aux is, digital can 'lose' data, especially over longer cable runs. This is what happens when some of the binary '1s' or '0s' arrive at the wrong time (or don't make it down the cable at all). This can sometimes result in jittery or blank portions of audio — which is why, especially over long cable runs, well-routed and shielded aux can come out as the winner.

As we’ve already touched on, optical can carry various types of information from a to b. Aux, on the other hand, can’t carry the data required for different types of proprietary digital processing, such as Dolby Surround. So, if you want to achieve surround sound with aux, you'd need to route multiple aux cables to the various speakers — which can be impractical and messy.

In terms of value for money, aux cables are usually cheaper, more versatile, and most commonly found on modern devices than their digital counterpart. You can connect them to anything with an aux in/aux out – which, due to it predating digital, is about half a century worth of audio devices.

Which should you choose?

Most people would probably agree that, all things being equal, you get clearer sound, better channel separation and superior spatial quality from an optical line. However, those same people may also tell you the difference isn't particularly noticeable, as it also depends in part on how good your speakers are, how long your cable is, the source recording that you're listening too, and, ultimately, how good your hearing is. For example, you're more likely to pick out the differences between aux and optical listening to an uncompressed FLAC recording played through a high-end sound system than you are listening to a 128kbps mp3 file played through your phone.

But does this difference really matter? In reality, everyone’s setup is different and, as with most things, nothing beats trying it out for yourself. Why not do a comparison of both formats? If your device supports the two, it's easy — just plug both in and then switch outputs on your device. You may find that you favour one over another, or you may find that it's just not significant enough a difference to worry about.

What does the future have in store for aux and optical?

When it comes to audio, it seems that both aux and optical are on their way out. In fact, it might seem surprising how long the humble aux cable has lasted in an industry that regularly kills off formats every few years. Analogue as a medium for home entertainment was designed to meet the needs of an era that is long behind us. And when it finally goes, it’ll probably take aux with it.

The situation isn’t much better for optical, either. Other digital formats, such as HDMI — and more recently, USB 3.1 — have the ability to do everything that optical can, but with higher rates of data transfer, increased reliability, and smaller form factors. Perhaps ironically, optical isn’t really in decline, it’s just moving away from audio, and into in the broadband space. But does this spell disaster for the two formats? Not yet. It’ll be years until they disappear entirely, and it’s looking like our speakers and computers will have both ports for a while to come.

Ultimately, the differences between aux and optical have arguably very minute impacts on the quality of what you hear. As to which option you choose, it might come down to convenience, or just personal preference. Our Dock E30 speaker offers both, with the addition of more modern technologies like Qi wireless charging, USB 3.1, and Airsound technology. If you’d like to find out more about the revolutionary speaker, head over here.