Here’s a question I get fairly often. Do you have digital connections on your interface? Not sure? You may have more inputs and outputs available than you realized.

Josh wrote:

Hey Joe,

I hope you had an awesome new year. I have a question about using S/PDIF inputs. I have S/PDIF I/O on my fast track pro and I was wondering if  could use these to add more recording channels for drums. I have heard they function similar to ADAT ports but I wasn’t totally sure. If you could explain to me or refer me to an article about how i could use these to expand my input channels that would be great. Maybe I have bad info and the S/PDIf have a totally different purpose but any help would be awesome.

Thanks for all your help I’ve learned so much from your posts and my acoustic guitar no longer sounds muddy thanks to your help with basic EQ.


Great question, Josh.

Here’s the “skinny.” Everything you record into your computer at some point gets converted from an analog audio signal to a digital one.

If you’re just starting out with recording, that conversion probably happens inside your audio interface. In other words, you plug your microphone or guitar directly into the interface, set the gain, and record.

But what if you had a piece of gear that converted the signal FOR you? Something like a preamp with digital outputs. What do you do with that?

That’s where digital inputs come in handy.

Most audio interfaces have some sort of digital i/o. The majority of these are one of two connections – a coaxial S/PDIF connector and an optical connector.


If you see what looks like an RCA connector on the back of your interface, chances are it’s a digital S/PDIF connection. (See picture above.)

What’s S/PDIF? It’s simply a 2-channel digital format. What does that mean? It means a single S/PDIF cable carries two channels of audio.

In Josh’s rig, he has an M-Audio Fast Track Pro. The FTP has two analog mic inputs on the front, and that’s it. What if Josh wants to use more mics? Is he stuck with two inputs? Does he have to buy a new interface if he wants more channels? No.

The Fast Track Pro has a S/PDIF input. That means Josh can buy a 2-channel preamp with a stereo S/PDIF output and record FOUR channels of audio! [*Disclaimer: I didn’t check the Fast Track Pro manual to make sure it supports 4 channels of simultaneous audio, but that’s typically how this works.]

Josh can get something like the the ART Digital MPA II. It’s a stereo preamp with S/PDIF outputs. Go look at the picture at Sweetwater’s website. You’ll see it’s got a S/PDIF output.

Josh can take a S/PDIF cable (which looks like an RCA cable) and run that from the ART to the Fast Track Pro, and BAM! he’s got 2 more mic inputs.

Optical Inputs


If you take a second look at that ART preamp. You’ll see there are also optical outputs. You may recognize these from other places. Sometimes they’re called fiber-optical connections or “lightpipe.”

Optical connections are normally one of two things – S/PDIF or ADAT. While S/PDIF is normally on a coaxial (RCA) connector, it CAN be on an optical connector. It will almost always be labeled.

If the optical connection is an ADAT signal, it can carry not two but eightchannels of audio (at 44.1 kHz or 48 kHz).

If your interface has an ADAT optical input, you can add an additional eight channels of inputs into your system (with something like a Presonus Digimax). Pretty awesome.

Mix it All Together

Now, let’s put all of this together. If you’ve got something like a 003 interface, you may think you can only record 8 inputs, since it only has 4 mic inputs and 4 line inputs.

Nope! You’ll notice it also has S/PDIF AND ADAT inputs on the back, meaning it can record 8 (analog) + 8 (ADAT) + 2 (S/PDIF) = 18 channels of audio.

This may not be new for some of you, but for those of you who don’t know about ADAT and S/PDIF, this is AWESOME stuff to know.


What digital inputs do you have on your interface? Do you even know? Take a look, leave a comment, and let us know.

What ways could you expand your input count digitally?

Big thanks to @StianSylta and @scherbi for the pics!