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Q. How can I use multiple audio interfaces together?

Mackie Onyx audio interface.

I’m currently upgrading my project studio, which is based around a Focusrite Saffire LE and is fine when using Cubase or NI’s Traktor. However, I am looking to bring Pro Tools into the equation, and despite some hunting I’m still stumped. Would using an M Box affect the sound drivers for my Saffire, forcing me to disable one piece of hardware and restart my system? Despite all my reading in forums, I am still unsure about the feasibility of adding a second Mackie Onyx 400F to my Windows XP DAW system. I understand Mac OS has the ability to aggregate, but it is not clear to me if Windows XP can handle the two interfaces at once or not. Would the drivers do this for me, and will I effectively end up with a 20-in/20-out interface to use with the bundled Tracktion 2?

SOS contributor Martin Walker replies: When plug-and-play soundcards started appearing in 1998, the need to manually choose such arcana as IRQ numbers and DMA channels disappeared, and since then it’s been comparatively easy to physically install and run more than one audio interface in a computer. Occasionally a particular model of PCI soundcard might refuse to share the interrupt it had been given with that of another expansion card, which might result in you having to shuffle it to a different slot, but over the years I’ve regularly managed to install up to four soundcards in a single computer without things ending in tears. With modern Firewire and USB audio interfaces it’s even easier, since even if you run out of suitable ports on your computer, many Firewire audio interfaces can be daisy–chained, and you can add more USB ports using a (preferably powered) hub.

So, to answer the first question, adding an M Box wouldn’t cause any conflicts with an existing Saffire LE interface, and the two should both run happily when plugged into the same computer. To be compatible with Pro Tools software, an audio interface will either need to be from Digidesign or from M-Audio’s ‘Pro Tools M-Powered’ range, but all such interfaces additionally have both ASIO and Core Audio drivers, so that you can also use them with any other Mac or PC audio application. Therefore you could either replace the Saffire LE with a Pro Tools–compatible interface and use the latter either with Pro Tools or Traktor (but not both at once), or you could simultaneously run Pro Tools with an M Box and Traktor with the Saffire LE.

The second question covers slightly different ground. Combining two or more audio interfaces from the same manufacturer into a single ‘super interface’ with more inputs and outputs requires an ASIO ‘multi-device’ driver. Many audio interface manufacturers offer such drivers (typically supporting up to four devices), so that you can increase your I/O complement easily as your recording and playback requirements become more sophisticated. There’s no increase in latency, and as long as there’s a way to lock the clocks of all the devices together, they should stay locked permanently in sample-accurate sync (follow the manufacturer’s instructions on the best way to do this for your particular interface).

Without multi-device drivers, there’s no way to install and run two or more identical audio interfaces in a computer, since the operating system would have no way to differentiate between the various units. However, in this particular case there’s a happy ending, since from version 3.2.8 onwards Mackie’s Onyx drivers for Windows XP do support several devices, so you can create a single interface with 20 inputs and outputs.

Those with two or more different audio interfaces can try a different approach. On the PC you can try combining their functions using the freeware ASIO4ALL driver (www.asio4all.com), although this can result in increased latency, and on the Mac you can try creating an ‘Aggregate Device’. Once again, this can significantly increase latency.

By the way, MIDI and audio drivers are quite separate, and you can nearly always combine the MIDI ports from several different audio interfaces and use them within a single sequencer application, whichever interface is providing the audio I/O.

Published November 2008