What is S/PDIF?

You can find one on a lot of different studio-related equipment: the S/PDIF connection. But what does this mysterious connector even do and why would you want to use it? In this blog, we’ll tell you what you need to know about S/PDIF, as well as its professional sibling AES/EBU and the cables required to get it all working properly.

What is S/PDIF?

What does S/PDIF stand for?

The term is short for Sony/Philips Digital Interface Format but is also commonly referred to as Sony/Philips Digital Interconnect Format. As you probably guessed, this type of digital audio connection has been designed by Sony and Philips and can often be found on consumer electronics such like CD players, audio amplifiers, televisions and home cinema systems. But S/PDIF is no stranger in the world of pro audio either and can frequently be seen featured on preamps, audio interfaces and modelling systems as well. An S/PDIF connection allows for the possibility to transfer two audio channels (stereo sound) in uncompressed digital form (PCM). What’s more, in compressed form, it’s even possible to get digital surround sound (5.1/7.1 DTS) when plugged into certain devices. A single S/PDIF connector can only serve as either an input or an output and doesn’t function as both the way USB does. A good reason to use a digital connection such as this one is that it doesn’t require any analogue-to-digital conversion or vice versa, meaning you won’t lose any audio quality whatsoever.

What’s AES3 and AES/EBU?

Without diving too deep into the technicalities, it would be wise to clear up a number of things regarding this so-called protocol. An S/PDIF connection is based on the AES3 standard: an ‘agreement’ within the audio industry that determines how digital audio signals are transferred. Having said that, AES/EBU is also based on this AES3 standard and in that regard is very similar to S/PDIF. One of the most important differences between the two is that S/PDIF requires an RCA or Toslink cable, while AES/EBU transfers its signals via a more robust and more importantly, balanced XLR connection as used on the analogue side of audio. While there’s more it, this is primarily the reason AES/EBU is used on professional equipment. Also, AES/EBU is not to be confused with ADAT, which offers the simultaneous transfer of up to eight audio channels.

What’s S/PDIF used for?

Like we said, S/PDIF can be regularly found on consumer electronics but probably just as often on studio gear to hook up AD/DA converters or a load box linked through to an audio interface. If you’re a guitarist playing over a modeller, you might find that your modelling amp has its own S/PDIF output. This means it can be directly connected to your audio interface so you can record the outbound signal in stereo in your DAW or simply monitor in stereo. Most desktop computers are also home to an S/PDIF output that can be used to route the sound coming from the computer to the digital S/PDIF input on a suitable amplifier, to name an example.

What is S/PDIF?

RCA, Toslink and XLR

You’ll often find S/PDIF signals run through RCA cables, since these are what we call ‘coaxial’ cables. This would generally be a 75-Ohm video cable with RCA connector, seeing as these offer higher quality than regular RCA cables equipped with the characteristic red and white plugs. Another option would be Toslink: an optical cable that’s particularly popular in consumer electronics and which shoots out a little red light you probably don’t want to stare into. The technology behind this type of cable has been developed by Toshiba (hence, Toslink) and includes the use of optical fibres or in some cases even fibreglass. One of the big advantages of Toslink cables is that they’re designed to block out signal interference, even though it’s probably difficult to tell if someone is using RCA or Toslink by ear alone. This leaves us with the XLR connector, which within the context of this blog is not used for S/PDIF but only for AES/EBU and more specifically, for pro audio purposes. An XLR connection ensures a balanced signal, resulting in a greatly reduced chance of any interference happening when you’re using long cables. You will however need a special 110-Ohm XLR cable (also suitable for DMX lighting). Some pro-grade equipment even comes with different AES3 connectors lined up next to each other so that you can pick your preferred connection. As a final note, it may also be worth mentioning that ADAT, which we briefly mentioned earlier, is compatible with Toslink but can’t be used with S/PDIF.

Leave a comment below and let us know how you are using S/PDIF in your (home) studio set-up!