Reaper, Linux, and the Behringer X-Air - Complete Studio Solution, Part 1

 

Building the ChordCaster Stomp: A Peek Inside My New Harmonizer Pedal

Every once in a while, a project grabs you by the collar and refuses to let go. For me, that project has been the ChordCaster Stomp - a compact, musician‑friendly harmonizer pedal built around a Teensy microcontroller, a custom audio front end, and a handful of ideas that have been rattling around in my head for years.

I wanted something that didn’t exist yet: a pedal that could grab a single note, understand the musical context, and generate harmony that feels intentional rather than robotic. Something that could switch between diatonic intelligence and unapologetically synthetic fixed‑interval parallel harmony. Something that guitarists, synth players, and experimentalists could all use without needing a theory textbook.

So I built it.

Here's a very quick & low effort demo of it in action. I plan to put together a full tour at a later date.

The Hardware: A Custom Brain in a Custom Box

The first prototypes ran on a Teensy 4.1 with the standard audio board - great for development, but not something I’d ever want to ship. Once the firmware stabilized, I moved everything over to a Teensy 4.0 and started designing a custom audio board to match the needs of a real pedal.

The stock Teensy audio board is a solid reference, but it’s built for general‑purpose use, not guitar. I needed a proper high‑impedance input buffer so the pedal behaves like a real instrument input, not a line‑level consumer device. I needed a cleaner, more robust line output that plays nicely with amps, interfaces, and other pedals. And I needed a compact layout that fits inside a stompbox enclosure without a rat’s nest of jumper wires.

So I kept the heart of the Teensy audio board - the SGTL5000 codec - and rebuilt everything around it. The digital side stayed almost identical: I²S for audio, I²C for control, clean 3.3V rails, and the usual decoupling. But the analog side is all mine: a JFET input buffer, proper AC coupling, a stable output driver, and ESD protection so the pedal doesn’t fry itself the first time someone plugs in a cable on a static‑heavy stage.

The USB port is panel‑mounted, too. No more dangling micro‑USB connectors waiting to snap off.

Harmony That Feels Musical

The ChordCaster Stomp has one job: turn a single note into something bigger. Hit the footswitch while you are playing a single note - the pedal “grabs” the note you’re playing and holds the harmony until you release. It’s like a freeze pedal, but for harmony. Great for ambient swells, pads, or turning a single note into a chordal drone. That's the basics, but there are many variations available, which is sort of where the fun begins:

Diatonic Mode

This is the “intelligent” mode. You pick a key and a musical mode (major, minor, modal mixture), step on a footswitch, and the pedal chooses the correct harmony interval based on the scale. It’s the kind of harmony that follows you around like a well‑trained bandmate - always in key, always musical, but keyed off only the notes you want it to pay attention to.

Fixed‑Interval Mode

This one is pure attitude.

Instead of following the key, the pedal applies the same interval no matter what you play. Want everything harmonized a major third up? Done. Want parallel fifths like a medieval monk with a distortion pedal? Go for it. Want to stack weird intervals and make synth‑like textures? Absolutely.

This mode ignores theory and just does what you tell it to do.

Arpeggiator Mode

This is the mode I didn’t realize I needed until I built it. Instead of playing all the harmony voices at once, the pedal cycles through them one at a time, turning a single note into a rhythmic, evolving pattern. The tempo is fully adjustable: you can dial it in through the menu or simply tap the second footswitch to set it on the fly. It’s a surprisingly expressive feature - great for ambient pulses, sequencer‑like textures, or adding motion to otherwise static chords. It feels less like a harmonizer and more like a tiny, obedient arpeggiator living under your foot.

Other Features

Beyond that, it features multiple outputs, reverb, FX and lots of other goodies.

The Idea: A Pedal That Understands Musicians

I’ve always loved harmonizers, but most of them fall into two camps:

1. Too simple - fixed intervals only, no musical awareness

2. Too complicated - menus, presets, MIDI, and a learning curve that scares off half the people who might enjoy them

The ChordCaster Stomp sits right in the middle. It’s musical, but not fussy. It’s expressive, but not overwhelming. It’s smart, but not bossy.

You turn the knob, pick your mode, and play. The pedal does the rest.

Where It’s Going Next

Right now, I’m refining the PCB layout, tightening up the analog noise floor, and polishing the UI so it feels natural on stage. The firmware is already solid - the Teensy 4.0 has more than enough horsepower for real‑time harmony, and the 360K of flash I’m using fits comfortably.

Once the hardware is locked in, I’ll start thinking about enclosures, graphics, and maybe even a small production run (but no promises).

For now, I’m just enjoying the process of turning an idea into a real, playable instrument.

If you’ve ever wanted a pedal that understands harmony the way you do - or the way you wish your bandmates did - the ChordCaster Stomp might be exactly what you’ve been missing.

The software is available on my Github, if you want to "check it out" (haha)