Teenage Engineering OP-XY Auxiliary Mode Guide: Brain, Punch-In FX, Tape, and FX Tracks

If you've spent any time with the OP-XY (or read through my beginner's guide to get familiar with the layout), you've probably noticed those 8 track buttons light up red instead of white every once in a while. That's Auxiliary mode, and honestly, it took me a minute to wrap my head around it the first time I poked around in there. It's not another set of instrument tracks, it's more like a toolbox sitting behind your song that handles transposition, performance effects, external gear, and your FX sends all in one place.

I'm covering all 8 aux tracks here since they share a home button, but each one does something completely different once you're inside it.

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Getting Into Auxiliary Mode

Press the Auxiliary button and you're in. Press it again and you'll bounce back to your instrument tracks, but the 8 track buttons themselves work as a toggle too, red means you're editing an aux track and white means you're back on an instrument track. Press 1 through 8 to jump between the aux tracks themselves.

Here's the lineup:

• Track 1: Brain
• Track 2: Punch-in FX
• Track 3: External MIDI
• Track 4: External CV
• Track 5: External Audio
• Track 6: Tape
• Track 7: FX I
• Track 8: FX II

Every aux track still uses the same M1 through M4 module buttons you're used to from Instrument mode, but what they control changes depending on which of the 8 you're standing on.

Brain (Track 1)

Brain is one of those features that sounds like marketing fluff until you actually use it, then it becomes one of the more genuinely useful things on the whole device. It listens to your song and figures out the key and scale on its own, or you can just tell it the key if you already know it. Once it knows the key, you can play the musical keyboard to transpose any tracks you've routed into it, live, without breaking anything.

Press M1 to see the key and scale settings:

• Dark Gray knob switches between manual key entry and automatic detection
• Mid gray knob picks the key
• Light gray knob picks the scale
• White knob links an instrument track to Brain so you can riff over your song while it transposes underneath you

Press M2 to route tracks into Brain. Click any encoder to flip between tracks 1 through 4 and 5 through 8, then turn the encoders to add or pull tracks from the routing. Only routed tracks get transposed, and only routed tracks factor into the automatic key detection, so keep that in mind if your bass track sounds like it's playing in the wrong key all of a sudden.

Punch-in FX (Track 2)

Punch-in FX are little performance effects you trigger by holding a key on the keyboard, and they're genuinely fun to mess around with once you get a feel for them. Hold Shift and press any key while you're on an instrument track and you'll trigger whichever effect lives on that key. The keyboard splits itself into two zones too, the lower octave hits your percussion tracks and the upper octave hits your melodic tracks.

A few of these effects respond to the accelerometer or the pitchbend pad, so if one feels a little flat, try tilting the device or leaning on the pitchbend while you trigger it.

Want to record these into your song instead of just playing them live? Start a recording, hold Shift, and play the keys like normal. Everything gets written straight into the Punch-in FX track. There's also an LFO tucked into M4 here that you can use to modulate parameters within the punch-in effects themselves, so don't sleep on it if you're trying to get more movement out of a performance effect.

External MIDI (Track 3)

This track turns your OP-XY into a sequencer for outboard MIDI gear, connected over USB-C or the multi-out jack. You can play notes on the keyboard to control the external device directly, and sequence those notes the same way you would on any other track.

• M1 controls channel, bank, and program (Dark Gray, Mid gray, and Light gray knobs respectively)
• M2 and M3 hold your MIDI CCs, rotate an encoder to edit a CC value, hold Shift and rotate to turn on or pick a different CC message
• M4 is the LFO, same 4 knob layout you'll see across most other aux tracks (speed, amount, destination, parameter)

External CV (Track 4)

If you're dipping into Eurorack or anything else that speaks control voltage, this is your bridge. The multi-out jack sends CV out the tip and gate out the ring, so grab the right splitter cable and you're off. Play notes on the keyboard to control your connected CV gear, and sequence them just like an instrument track. There aren't any adjustable parameters on this one, it's really just there to play and sequence whatever you've hooked up.

External Audio (Track 5)

This is the track you'll want if you're running the OP-XY's signal through an outboard pedal or bringing in a mic or line source. I think of it as the audio equivalent of the External MIDI track.

M1 handles your input:

• Dark Gray knob picks the input source (mic, headset, audio input, USB audio, or main output), click it to activate whatever you've selected
• Mid gray knob adjusts drive, which is really just gain through the built-in preamps for analog sources
• Light gray knob adjusts the level of that input in your master mix
• White knob blends the routed audio into your main output

M2 handles routing, click an encoder to flip between tracks 1 through 4 and 5 through 8, then dial in how much of each instrument track gets sent into the aux audio path.

M3 is a high-pass/low-pass filter (Dark Gray for the high-pass cutoff, White for the low-pass cutoff), and holding Shift lets you set tape send and FX send levels on the mid and light gray/white knobs.

M4 is the usual LFO layout.

Tape (Track 6)

Tape is where things get weird in a good way. It grabs audio playing inside the OP-XY and lets you chop it up for glitchy, tape-style effects, kind of like a mini sampler for whatever's already happening in your song.

M1 covers the core tape controls:

• Dark Gray knob shifts pitch, this one can get pretty chaotic pretty fast
• Mid gray knob adjusts speed, a more gentle way to control playback than the pitch knob
• Light gray knob changes the loop length
• White knob blends the tape effect with the original audio

M2 routes tracks into Tape the same way as External Audio, M3 gives you the high-pass/low-pass filter plus FX send levels under Shift, and M4 is your LFO.

FX I and FX II (Tracks 7 and 8)

These two hold your send effects, and yes, you can even send FX I into FX II if you want to stack something like a delay into a reverb. Hold Shift and press FX I or FX II to open the effect browser and load something new, everything from chorus and delay to phaser and reverb lives in here. While you're on either track, the keyboard plays back whatever instrument track you last had selected, which makes dialing in an effect while you can actually hear it a lot easier.

• M1 shows the parameters for whatever effect is loaded, 4 knobs, 4 parameters, the specifics depend on the effect
• M2 is routing, same click-to-switch-banks and turn-to-adjust pattern as the other aux tracks
• M3 is the high-pass/low-pass filter, and on FX I specifically, holding Shift while turning the white knob sets how much of FX I bleeds into FX II
• M4 is the LFO

Wrapping Up

Auxiliary mode is one of those areas of the OP-XY that rewards spending an afternoon just poking around in it. None of these 8 tracks are complicated on their own, there's just a lot of them, and they all live behind the same button. Once Brain, Punch-in FX, and the FX tracks click for you, building out a full arrangement (which I'll get into next) starts feeling a lot more natural.

If you want to see how this all fits into the bigger picture of what the OP-XY can do, check out my full review of the OP-XY. And if you're curious what I've actually made with this thing, my music page has a running list.