PreSonus Blog

So…What’s the Deal with Aux Channels?


Hardware is making a comeback. Real-time, improvisation-based drum machines and synths are gaining popularity, and you can find occasional bargains for used synths that were top of the line only a few years ago. So, it makes sense that Studio One would want to simplify integrating external hardware synths (similarly to how Pipeline integrates external hardware effects).

When Version 5 introduced the Aux Channel, comments ranged from “So great—I’ve been wanting this for years!” to “why not just feed the instrument into audio tracks?” Well, they’re both right—Aux Channels are about workflow with external hardware synthesizers. But Aux Channels can streamline workflow and simplify setup, compared to assigning the instrument outs into audio tracks, which then route to the mixer.

Aux Channels monitor external audio interface inputs directly, not the outputs from recorded tracks, in the mixer. These external inputs can be any audio. For example, when mixing, you might want to listen to a well-mixed CD for comparison. You don’t need to record this as a track, just monitor the inputs it’s feeding as needed.

Aux Channel Benefits

My favorite feature is that you can add a hardware synthesizer to the External Instruments folder (located in the Browser’s Instruments tab), and drag and drop the hardware synth into the arrange view—just like a virtual instrument. This automatically creates the Aux Channel, and sets up the Instrument track as you saved it. Set up the external synth once, then use it any time you want.

Also, the external instrument needs only the Note data track in the Arrange view—audio tracks are unnecessary because you’re just going to mix them in the console anyway. This is consistent with Studio One’s design philosophy of dedicating the Arrange view to arranging, not mixing. Of course, you can show/hide audio tracks in the Arrange view, but it’s more convenient to have those audio tracks show up directly in the console, like your other audio sources.

How to Create an Aux Channel

First, your hardware sound generator needs to be set up as an external Instrument in the Options (Windows) or Preferences (Mac) window. Then, in the Console, click on External toward the lower left. Click the downward arrow for the desired External Device, and choose Edit. (Note that if it’s a workstation that combines a sound generator with a keyboard, you should have two entries—one for the Keyboard, and one for the Instrument. Choose the instrument.)

When the control mapping window appears, click on the Outputs button (the one with the right arrow; see fig. 1), and choose Add Aux Channel.

Figure 1: How to add an Aux Channel for an external device.

After the Aux Channel appears, assign its input to the audio input(s) being fed by the hardware synth. For example, if the synth’s audio is going to stereo input 3+4, then choose that stereo input. (If your existing Song Setup I/O doesn’t include an easily identifiable name for the inputs being used for the Aux track, considering doing some renaming.)

Next, save these default settings. If needed, click on Outputs again to bring up the controller mapping window, and click on Save Default. Saving it is what allows the hardware instrument to show up in the Browser.

All Ready!

In the Browser’s Instruments tab, look under External Instruments (toward the top, just under Multi Instruments). Drag your instrument into the Arrange view, and start playing. If you don’t hear anything, the likely causes are either that the keyboard being assigned to the synth isn’t the default keyboard (specify All Inputs for MIDI in, and it should work), or the Aux Channel input hasn’t been assigned to the correct audio interface inputs.

Also note that with workstations whose keyboard drives the sound generator, turn off the Local Control parameter (usually in the instrument’s MIDI setup menu). Otherwise, you’ll be playing the sound generator from the keyboard, and Studio One will also be feeding it notes. The result is note double-triggering.


To preserve what the Instrument track plays as an audio track, choose a track’s Transform to Audio Track option, or select the Event and bounce to a new track (fig. 2).

Figure 2: The bounce menu for hardware instruments.

When bouncing, make sure that the Record Input is assigned to the Aux Channel where the Instrument’s audio appears. Finally, Studio One knows that because the bounce involves external hardware, the bounce must be done in real-time (faster than real-time bouncing is possible only with virtual instruments that live inside the computer). Happy hardware, everyone!

  • Nick Cent

    Appreciate the feedback!

  • Gregor Beyerle

    Hey @nickcent:disqus , Gregor here! Here’s the video that Craig referred to – Hope you’ll find it inspiring. 🙂

  • Craig Anderton

    Glad you found it helpful! Gregor has also done some videos on how to separate the mixing and arranging process. I don’t recall the titles offhand, but maybe he can point to them.

  • Nick Cent

    Excellent! thank you for clarifying everything. I love the idea of separating mixing from arranging. I have always been keen on mixing a stupid repeating pattern because I dedicated too little to arranging. I guess I love mixing a bit more. Thanks Craig!