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Zen Flute Is A Teensy Powered Mouth Theremin

May 17, 2025 by 13 Comments

An intriguing mouth-played instrument emerged—and won—at the 2023 Guthman Musical Instrument Contest hosted by Georgia Tech. [Keith Baxter] took notice and reproduced the idea for others to explore. The result is the Zen Flute Mouth Theremin, a hybrid of acoustics, electronics, and expressive performance.

At its core lies a forced Helmholtz resonator, a feedback system built with a simple microphone and speaker setup. The resonator itself? The user’s mouth. The resulting pitch, shaped by subtle jaw and tongue movements, is detected and used to drive a MIDI controller feeding an external synthesizer.

Like a trombone or classic electromagnetic theremin, the Zen Flute doesn’t rely on discrete notes. Instead, the pitch is bent manually to the desired frequency. That’s great for expression, but traditional MIDI quantisation can map those “in-between” notes to unexpected semitones. The solution? MIDI Polyphonic Expression (MPE). This newer MIDI extension allows smooth pitch transitions and nuanced control, giving the Zen Flute its expressive character without the hiccups.

Physically, it’s an elegant build. A flat speaker and microphone sit side-by-side at the mouth end, acoustically isolated with a custom silicone insert. This assembly connects to a length of clear PVC pipe, flared slightly to resemble a wind instrument. Inside, a custom PCB (schematic here) hosts a mic preamp, an audio power amp, and a Teensy 4.1. The Teensy handles everything: sampling the mic input, generating a 90-degree phase shift, and feeding it back to the speaker to maintain resonance. It also detects the resonant frequency and translates it to MPE over USB.  A push-button triggers note onset, while a joystick adjusts timbre and selects modes. Different instrument profiles can be pre-programmed and toggled with a joystick click, each mapped to separate MIDI channels.

Mouth-controlled instruments are a fascinating corner of experimental interfaces. They remind us of this Hackaday Prize entry from 2018, this wind-MIDI hybrid controller, and, of course, a classic final project from the Cornell ECE4760 course, a four-voice theremin controlled by IR sensors.

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Harmonic Table Keyboard Brings Old Idea Back To Life

June 17, 2024 by 11 Comments

If you missed the introduction of the Axis-49 and Axis-64 keyboards by C-Thru Music, you’re definitely not alone. At the time it was a new musical instrument that was based on the harmonic table, but it launched during the Great Recession and due to its nontraditional nature and poor timing, the company went out of business. But the harmonic table layout has a number advantages for musicians over other keyboard layouts, so [Ben] has brought his own version of the unique instrument to life in his latest project.

Called the Midihex, the keyboard has a number of improvements over the version from C-Thru Music, most obviously its much larger 98 playable keys and five function keys. The keys themselves are similar to Cherry MX keys but which use Hall-effect sensors. This style of key allows the device to send continuous key position information to the host computer, and since this is a MIDI instrument, this capability allows it to support a MIDI protocol called MIDI Polyphonic Expression (MPE) which allows each note to be more finely controlled by the musician than a standard MIDI instrument. The PCB is powered by a Teensy 4.1 at the core.

For any musicians that haven’t tried out a harmonic table before, an instrument like this might be worth trying out. The layout provides easier chord and scale patterns, and for beginner musicians it can have a much shallower learning curve than other types of instruments. If you can’t find an original Axis-49 or Axis-64 anywhere to try out, though, we actually posted a teardown of one way back in 2009 when the company was still producing instruments.

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