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!

  • Aaron Liddell

    I was wondering if anyone could over me some advice.
    I have the soundcraft Si Impact mixing console. The console is a digital mixer.After exhaustive research and back and forth with sales people, and distributors, yada yada.
    Anyway my main thing is that i would like to use some of my analog outboard gear.
    Easy right… I thought it would be but here is the problem.
    The impact has NO LINE LEVEL inputs ( beside a digital source, but the user is not able to choose) and no aux sends or inserts. Well it does have 22 inserts, but you are only allowed to assign a digital source as the return.

    So i have the Si Impact which has a MADI/USB card in one expansion slot, another MADI/USB card (brand new not installed) that could go into the 2nd expansion slot, and i also have the Soundcraft Stage Box mini 16.

    I was trying to figure out how to route things so i can use my outboard gear ( API pres, Distressor, Transient Designer, 1073, Pulteq EQ, some other stuff also).

    I also have another computer i could use, if say i had a 2 DAW set up sort of like a Mastering set up (at least what my very limited knowledge vaguely envisions it to be).
    I just want to be able to use my gear in some way.

    I imagine an audio interface and maybe a small mixer could somehow solve this problem ( maybe the multi-digital card for the 2nd expansion slot of the Si Impact). I would like to somehow be able to interface the Impact and say another device that could essentially act as the expansion that now allows me to put an outboard processor on an insert, or have a line level input source. But my gut tells me that they wouldn’t be able to work that way – that is data exchange between the digital mixer and say a motu interface (just an example).

    The other crazy thought is do you think there could be a way to Mod the Impact? Of course there is a way but is it remotely probable? Looking at the schematic there is a Line level path that bypasses the pre amp/gain stage. Also regarding a mod i have enough channels that i would be good with dedicating 8-10 I/O’s to this fate permanently without them having the ability to interchange Mic level and Line level. They could be dedicated permanently to support this need.

    I am not sure if this is just too outside the box for anyone to have any advice, but no one has even tried to answer me anywhere else. I was hoping someone here might be up for the challenge.



    Si Impact Manual

    Stage Box Manual

    —- Oh yeah and i use Reaper which only will recognize 1 audio interface at a time

    • Sorry man. I don’t know that Impact at all. It sounds like if you wanted to use a lot of outboard gear the Impact wasn’t a great choice for you. 🙂
      You can always use the outboard gear on the way IN while recording, then use plugins for your processing while mixing.

      • Aaron Liddell

        Yeah i definitely should have chosen a different mixer. I am a long time musician but complete newbie to sound engineering side of things. I researched a ton b4 purchase. TBH i was focusing on Live Sound when i purchased ( about 8 months ago) but since then have also decided to build a studio.
        Also the manual is very misleading as it continually refers to selecting Line or Mic input.

        Using it on the way in is actually what I want to do, or at least my priority regarding the outboard gear. But with no line level inputs it is hard to get into the console. If i use a pre amp signal comes in sooo hot – i have been able to gain stage accordingly with most pre’s but the pulteq eq is just way to hot to use.

        I read a ton yesterday and i am looking at a few Motu devices. I have an AES output as well as a ether link out. The thing ii am trying to figure out is if any type of digital send/return will communicate with the Impact (i.e. use a thunderbolt or fire-wire connection to connect the motu and the Impact). My instinct says that isn’t possible, but im not so sure. Thunderbolt connection on the Motu says you can Daisy chain any thunderbolt devices. I just dont know about the functionality if that is done, and i dont want to spend a GRAND to find out.

        But i could get a multi digital card and have ADAT optical and S/PDIF fire wire, thunderbolt. So if there is a way to set the devices up so that they could communicate that would be a preferred option.

        I should bite the bullet and sell the board but i really cant afford to go that route at this time.

        I Appreciate the reply though!

        • I just think it’s really not worth it to be able to route ONE track through ONE piece of gear, y’know? It’s a lot of work for something that you may not end up using all that much. I’ve tried routing out through analog hardware, and the sonic benefits aren’t so great that it makes it worth all the time to bounce everything in realtime, and take pictures of settings, etc.

  • Ronnie Wilde

    Great post Joe , really learned a lot !
    I’m setting up a studio with Focusrite Saffire 56 being the central unit.
    This is what I have:
    Saffire 56
    Octopre mk 2 dynamic
    ISA 430 producer pack
    Line 6POD pro (older rack version)
    Line 6POD pro Bass ( older rack version)

    What would be the best way to set it up?
    Adat from the octopre to the 56 for an additional 8 channels , that one I got , but what about the rest ?
    Line6 has SPDIF out and the ISA 430 has both SPDIF and ADAT.
    Of course they have all the analog I/O as well, but I’m just confused.
    Why does the ISA have adat ?
    Would love it if you could shed some lift on this .

    • Honestly I would just plug analog out of the others into the focusrite. The more digital connections you have the more problems you will have. Analog never has sync issues. 🙂

      • Ronnie Wilde

        Ha ha.true that.:)
        I was just curious.
        Thanks !

  • Hans Fieggen

    High Joe,

    I have a home studio where I mainly record voice-overs and audiobooks. My setup is a Neumann TLM102 into a Focusrite ISA430 Mk2 which connects to a RME Babyface Pro and onto an iMac with Hindenburg Journalist Pro as my recording software. Despite this rather high quality equipment I am not satisfied with the quality of my recordings. Allthough my voice booth is small it is acoustically sound I think (made by a professional studio builder). And after a lot of time tweaking with both the EQ on the Focusrite and on the RME it keeps giving a bit of hollowness and an “indirect” sound. Not really an echo but rather to much of a frequency which I can’t seem to filter out which makes it sound a little like I am talking through a pipe, a kind of metallic sound.

    Now in my setup the signal passes through both the preamp of the Focusrite and that of the RME and I got this idea that maybe that is the problem. Now I could buy an ADC card for the Focusrite and feed the RME through ADAT or S/PDIF (both would be possible) as to bypass the preamp of the RME. In your opinion, could that make a difference at all for the soundquality?

    • Hi Hans. I think you’re overthinking it. The problem won’t be solved with an extra converter card. Without hearing it, I can’t say for sure, but I would guess it’s any number of things. It could be that the TLM102 doesn’t match your voice very well. It could be that you just need to learn to EQ the vocal better to make it sound amazing. It could be that your voice isn’t as good as the professional voices you’re used to hearing. I don’t know.
      But if you want to book a critique session with me and send me a clip to listen to and give some feedback, I’m happy to. Details here:

      • Hans Fieggen

        Hi Joe, thanks for your input. I think for now I will economize on new hardware 🙂 allthough I have doubts myself about the TLM102. As for the quality of my voice: of course that is rather subjective but I’ve done voice recordings in other studio’s and I just can’t seem to match the sound in my own studio with those. A matter of being a voice rather then a sound engineer I guess.

        I will send you a clip to comment on in a couple of days! Thnx!

  • sushant sonawale

    I have Msi GL627QF laptop,it has Headphone-out (SPDIF,Focusrite Saffire Pro 24 DSP which also has SPDIF/Stereo in/out….hence technically i should be able to connect these 2 an dhave sound on speakers without any other cable attached,right?

  • David Commey

    so then can i hook up a mixer through s/pdif to my Fast Track and get additional left and right channels?

  • Mick

    Hi, I’m thinking of getting rme raydat pci ex card (I have a really good deal on it so it’s hard to pass) and wondering how will I be able to get sound out of it? do I need an amplifier with adat/spdif input? I don’t have any interface atm due to gear shifting.

    • Doesn’t sound like a great deal if you don’t know how to get audio out of it….
      But I don’t know that particular device so you’ll have to do your homework, read the manual, etc.

      • Mick

        Thanks Joe. Homework done – I didn’t think it was so obvious.

  • Erik Himbert

    thanks for the info! i’m sort of a newbie as well, have never figured out the adat or spdif. i’m running a Focusrite Saffire Pro 40. it is firewire only (other than adat and spdif). i recently upgraded my laptop, and no firewire port. i bought apple’s firewire to thunderbolt adapter, and it didn’t work. can i bypass firewire, and just use the adat? how would i connect the adat out to my computer?

    thanks in advance for the input!!

  • Victor Logidasan

    hi i have zed 16fx mixer and fast track pro ,and mac system,and logic pro 9 &logic pro x
    pls do suggest what else i need to record a band with drum mics

  • George Wiegand

    I have a Alexis I/o26 8 channel interface. And I would like to know if I can connect it to my Tascam dp-01 8 track multi track recorder? Basically I wanna know if I can use the 8 inputs on the Alexis as 8 individual tracks on the tascam? And record using the tascam. Cause I record drums usually using 4 to 6 mics. But the tascam only has 2, 1/4″ inputs and no phantom power for condenser mics. If anyone knows anything about what I’m talking about and if its possible let me know please.

  • David Cordero

    I just stumbled up on this post, it was REALLY helpful! thanks alot!

  • Ralph

    By the way, The Fostex also has a midi in and out. Why isn’t this ADAT to USB a staple?

  • Ralph

    I have two old Fostex 8 Channel digital mixers with ADAT outs. I simply need at least one inexpensive ADAT to USB converter. Sounds simple right? My left testicle for a $30-$40 device. A damn shame. I wouldn’t even need an interface.

  • Mark Emery

    I have a Yamaha i88x which has ADAT optical In/Out. My interface is a Tascam US2000 which has S/PDIF Digital in (RCA type jack) (no ADAT In) can i link them together to give me a further 8 tracks?

    • Sorry Mark, I don’t know. Never used either one. Check the manual?

  • Jose H López

    May be dumb question. So can I use 18 actual mics on my Audiobox 1818? 8 from the Audiobox, 8 from a digimax and 2 more via S/PDIF?

  • Jorge Antonio Cárdenas Venegas

    I actually have an adat, a alesis adathd24. Could I use an interface with it, if it has an adat input? Or at least transfer the sound files that I have on the adat to my laptop? The manual, like the machine, is pretty old. And not updated to newer systems and computers. Tried with the adats Ethernet output to try to transfer the audio files to my computer. But I can not figure out how that actually works. And there’s really not much info on the web.

    • dj shadow

      Yes, you can do this. I use my old Alesis ADAT machine to bring in 8 separate audio tracks (I use the 8 tracks for 8 separate outputs of my 808 drum machine). I use the Alesis’ optical out to connect to the optical in in the Focusrite. You have to set your MixControl’s sync source to ADAT, and sample rate at 48kHz. You are right that there is not much information about how to do this on the web! I had to do a lot of trial and error to get it right.

      Oops – I forgot to mention that I use a Focusrite audio interface with the Saffire MixControl software to make these settings. If you use a different audio interface, there might be something similar for you.