How do I add more inputs and outputs to my audio interface?


The modern audio interface is a pretty impressive piece of kit. In just a small desktop box, you can record a couple of microphones and/or guitars, set up some direct monitoring for your performer, get those signals converted into a format your computer can understand and get audio back out to a set of monitors; maybe even connect up some outboard effects processors as well. And all for not too much outlay.

Add more inputs and outputs with ADAT

What do you do when you think you’ve outgrown your audio interface though? Is it time to throw it in the bin (obviously not, it should be re-homed, repurposed or otherwise disposed of correctly), or can its usefulness be extended?

Why might you want to expand your interface by adding more inputs and outputs?

Why might you have ‘outgrown’ your audio interface? Depending on the interface you currently use, what you were doing with it when you bought it, and what you need to do with it now, there might be a number of reasons.

Adding more inputs

Maybe you bought an interface like the Focusrite Scarlett 18i8. With its 4 mic preamps it had you covered for recording your duo with two guitars and two vocalists.

Now though, you’ve added bass, fiddle and bodhran and need some more inputs for getting the band recorded in one pass to capture that everyone-playing-together vibe.

Adding more outputs

Maybe you use a Presonus Audiobox 1818 VSL as the centrepiece of your studio, but you want more outputs to mix on an analogue mixer rather than in the DAW; you might want to

How can you expand your interface?

You’ve realised that you need more inputs and/or outputs than you currently have, how do you go about expanding?

Buy another one

Sell your existing interface and buy another one. Easy.

Pros: You end up with (hopefully) one box that has all the features you need.

Cons: You will lose money on your original interface; the single box with all the features you need may not exist or you may have to pay for features you don’t want.

Aggregate devices

If you buy a second interface, you can set your operating system to see two separate interfaces as one audio device; this gives you access to the combined total of inputs and outputs across multiple units.

Pros: You can keep the audio interface you already have; you can choose a second interface that offers the missing functionality, hopefully without paying for more than you need.

Cons: Requires a bit more configuration in the operating system; your operating system may not support it; uses up more ports on your computer; increased latency.

Expand using digital connectivity

There is, however, another way. If your interface has digital connectivity, you can use those to add additional input and output options.


The Sony/Philips Digital Interface can send two channels of audio down a single cable. S/PDIF I/O can either be on an RCA phono type of connection, or an optical one. S/PDIF connections can also be used to transmit compressed multi-channel audio using Dolby or DTS encoding.

While normal analogue audio coaxial cables can be used for short cable runs, digital coaxial cable is recommended for longer runs, generally over 1m or so.

As a two channel protocol, S/PDIF is perfect for roles such as sending a stereo output through a standalone digital to analogue converter (DAC) for higher quality conversion to feed to your monitors. If you want to connect a Bricasti M1 DAC to your Scarlett 6i6, S/PDIF gets the job done easily!


ADAT (Alesis Digital Audio Tape) has become a common method of sending a good few signals down a single optical cable.

Many audio interfaces feature ADAT optical inputs (especially) and outputs as it is an ideal protocol for allowing a lot of connectivity without taking up the whole back panel of the interface.

In its standard format, ADAT is used to send 8 (mono) channels of audio at sample rates of up to 48 kHz. Of course, these days a lot of people want to go beyond that, but fear not: there is a way…

What is SMUX?

I don’t really like this acronym for a couple of reasons. The first is that it’s a little bit contrived, the second is that it stands for sample multiplexing, but what is really going on is the opposite of that.

ADAT usually carries eight 44.1 kHz or 48 kHz audio signals over a single optical cable. However, using devices that support it, two cables can transfer eight channels at 88.2 kHz or 96 kHz, or four channels at up to 192 kHz. If that’s a sample rate you’ve decided you need to work at.

What products are out there to let me take advantage of this wonderful lightpipe?

Let’s take a look at some of the products that let you get expanded…

Behringer ADA 8200 ADAT expander

The Behringer ADA8200

With 8 mic/line inputs with Midas-designed preamps and 8 line outputs for only £159, the Behringer ADA 8200 is perhaps the biggest bargain out there. The ADA 8200 is great for adding an extra 8 microphone preamps for bigger recording sessions, and those line outputs can get more tracks sent outside for processing with external hardware or mixing with a hardware mixer.

The ADA 8200 is limited to 44.1 or 48 kHz 24-bit and the output of the preamps cannot be sent to the line outputs – only to the ADAT outputs- so it can’t be used as a standalone preamp to add microphone inputs to a mixer.

Focusrite Octopre mkII ADAT expander at Red Dog Music

The Focusrite Octopre mkII 

The Octopre mkII features 8 mic/line inputs with Focusrite mic preamps and inputs 1 and 2 offering instrument inputs as well. The inputs offer 10 dB pads and phantom power is switchable in two banks of four.

The 8 line outputs give you the preamp outs, so this can be used as a standalone preamp. Two ADAT outputs let you record at up to 96 kHz, and the unit can be clocked using its wordclock in. As there is no ADAT in, the Octopre mkII cannot be used as a D/A converter.

Focusrite Octopre Dynamic mkII ADAT expander

The Focusrite Octopre mkII Dynamic 

The evolution of the Octopre mkII, the Octopre mkII Dynamic offers the same eight input functionality of its little sibling, but adds a one knob compressor on each input channel (with a more switch), ADAT inputs allowing the unit to be used as an 8 channel DAC and a wordclock output.

Audient ASP880 ADAT expander at Red Dog Music

The Audient ASP880

With the preamps from their highly-respected consoles, the Audient ASP880 is a top-end way of adding 8 inputs to your system.

With the first two channels featuring JFET instrument inputs and pad switches, and all 8 channels offering a choice of three input impedances to get the best of your choice of mic, polarity inversion and a sweepable high-pass filter, the ASP880 is fully featured at the front.

‘Round the back, things are just as well thought out, with 8 Neutrik combo sockets, 8 channels of send and return on DB25 connectors, 2 ADAT outs for 96 kHz SMUX use, a word clock input with switchable 75 Ohm terminator and an additional 9-pin DSUB socket for AES or S/PDIF output.


All in all then, chances are the solution you need to add more inputs and outputs to make your system the way you need it is out there. If you want to record a band with a full kit, get all your synths connected so you don’t have to continually unplug and repatch, add a whole load of outboard gear to your system or mix on an analogue console, there is a way for you to do it.

Red Dog Music is the UK’s friendliest musical instrument and pro-audio dealer. Between our 5000 square foot Edinburgh shop filled with an incredible range of products, and our London showroom in Clapham specialising in high-end instruments, dj and pro-audio, Red Dog Music has you covered from north to south and from performance to playback.

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Fynn Callum

producer, guitarist, engineer & dj
From indie guitarist to deep house producer via Northern Soul dj; mix engineer, producer and gear enthusiast. Jaffa Cake aficionado.

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