In my last blog post, I posted about revisiting the acoustic guitar again, and I posted a song there called "The Fisherman". Normally when I record guitar, I use two inputs - the inbuilt guitar pickup/preamp, as well as a microphone somewhere near the soundhole.

For THIS particular recording though, I wanted to try something different. I wanted to try up to 4 different recording inputs! The problem though, was that I only had an audio interface with 2 input channels. I am using an Apogee Duet, which as its name suggests, is a two input, two output device.

How then would I get 4 inputs? Well, I recently purchased a Steinberg UR22 (once again, a 2 input, 2 output audio interface) for my son. The Apogee Duet has a Firewire interface, whereas the Steinberg has a USB interface. I thought that I might use BOTH on my ageing 2009 17" MacBook Pro.

Plugging in the Steinberg was a piece of cake. I had to download the latest OS X driver from the Steinberg site, and the device was recognised immediately on my system. Great.

The main problem came up when I fired up Logic X. I discovered that Logic will only recognise ONE input device, and ONE input device only. I could only choose between the Duet, or the UR22 as my input, giving me only 2 input channels in total at any one time.

The solution - was actually pretty easy, and took less time than plugging in and setting up the UR22 in the first place!

The secret is - Aggregated Audio Devices. OS X has a nifty feature which allows you to combine two or more hardware (or software) devices into a single virtual device.

Under your 'Applications' folder on your Mac, there is a folder called 'Utilities'. In there, is an app called 'Audio MIDI Setup'. Fire it up, and you will see a screen with all your hardware (and software) audio devices.

Click the little '+' button on the lower left corner, and you will be able to set up a new aggregated device. I ticked the Duet and the UR22 so I could use both devices together. I set up the Duet as the master clock device for the MIDI clock, and I nominated that I wanted to use Input 1 and 2 on the Apogee, as well as Input 1 and 2 on the Steinberg (see image below).

I called my Aggregate Device the 'Dueberg', which was my amalgamation of the words 'Duet' and 'Steinberg' :)

Note that I had KRK Rokit 5 monitors already plugged into my Duet, and nothing plugged into the output ports of the UR22, so I ticked ONLY the 2 output channels on the Duet in my aggregate device. This effectively gave me a 4 input, 2 output device.

Sure enough, when I went back to Logic X, I could choose the 'Dueberg' as my input device, and was able to set up 4 tracks with Inputs 1, 2, 3 and 4 across the two audio interfaces recording simultaneously.

For those that are curious, I set up the inputs as follows:

Apogee Duet Input 1 - Direct from Guitar pickup/preamp
Apogee Duet Input 2 - Rode NT-1A
Steinberg UR22 Input 1 - AKG C5
Steinberg UR22 Input 2 - AKG D40

The NT-1A was placed about 12 inches from the soundhole. The C5 was placed near the lower bout and pointed at a 45 degree angle at the bridge of the guitar, about 10 inches away. The D40 was placed directly over the 12th fret, pointing straight at it from around 6 inches away.

I am not sure if the sound was any better than my older recordings, but I felt I had more scope to play with the frequencies and tone shaping this way, including panning each mic left and right to create more 'space' in the end recording.

In the end, this was an easy and cheap way to get 4 inputs working in short order. I was actually considering getting a Focusrite audio interface with 4 or 8 inputs on it, but this proved to be a far cheaper solution.

Hope it proves useful to others out there.