MiniTouch 2nd Edition: Four Envelopes, Ten World Scales, and $35
The MiniTouch 2: What $35 Can Do With the Right Design Choices
The MiniTouch 2nd edition is a standalone synthesizer built on the Teensy 4.0 — battery powered, with a built-in speaker, 18-note capacitive keyboard, and MIDI in and out. It sells for $35. That last detail grabs attention, but the more interesting story is in the signal chain.
Most small, affordable synths give you two ADSR envelopes at most. The MiniTouch 2 has four.
Why Four Envelopes Changes Everything
An ADSR envelope generator shapes how a parameter changes over time in response to a note: attack defines how quickly it rises, decay how fast it falls to the sustain level, and release how long it takes to fade after the key lifts. Apply that to volume and you have the basic shape of a note. Apply it to a filter cutoff and sounds open and close in ways that feel alive.
The MiniTouch 2 takes this further. Its third envelope controls FM depth — frequency modulation, where one oscillator modulates the pitch of another. FM is the engine behind metallic, glassy, and bell-like tones. Without an envelope on FM depth, those sounds stay static. With one, the character of the FM effect can evolve across the note: a percussive hit that starts harmonically rich and settles to something cleaner, or a pluck with an initial bright bite that falls away. On small synths, FM is usually a fixed knob.
The fourth envelope handles pitch. A brief upward pitch transient at the start of a note is what makes plucked strings and struck percussion feel physically real. The difference between a piano sample with and without a slight pitch drop in the attack is audible even to untrained ears. Having a dedicated envelope for this — its own attack, decay, sustain, and release — puts a lot of timbral territory in reach without touching presets at all.
Combined with two oscillators, a noise generator, and two separate filters, this is a more complete synthesis architecture than many commercial instruments costing several times more.
The 18-Note Capacitive Touch Keyboard
No mechanical keys. Capacitive touch pads detect the change in electrical field when a finger approaches a conductive surface — the same principle behind a phone screen. Chips like the MPR121 handle sensing and thresholding over I2C, leaving the Teensy’s processor free for audio work.
The practical trade-off is velocity. Capacitive pads don’t measure how hard you pressed; they register contact. Some firmware estimates velocity from the speed of capacitance change, but it remains an approximation. The MiniTouch doesn’t advertise velocity sensitivity, which is honest. For workshops, live sketch work, and melodic improvisation, 18 touch-responsive notes in whatever scale you’ve selected is perfectly adequate. No mechanical wear, no key travel to recalibrate, no moving parts to fail in a bag.
Ten Scales Across World Traditions
This is a detail that gets overlooked in the feature list. Ten selectable scales covering European, African, Asian, Eastern European, and Middle Eastern musical traditions is not just a checkbox — it changes what the instrument sounds like in use.
Western music theory tends toward the chromatic scale and its modes. But the world’s musical traditions include intervals and scale structures that don’t map cleanly onto a 12-semitone framework. Middle Eastern maqam uses microtonal intervals. Sub-Saharan African music uses pentatonic structures that differ from Western major pentatonic in both pitch content and melodic function. East Asian scales carry different harmonic weights and implied progressions.
On an 18-key instrument where pads are fixed to specific scale degrees, choosing a scale at the hardware level is the only way to make those traditions genuinely playable. A beginner in a workshop can pick an African or Middle Eastern scale and immediately play something that sounds culturally coherent — without knowing a note name. That’s a significant pedagogical decision embedded in what looks like a simple menu option.
The Ctrlr Control Panel
Sixteen physical pots with a shift layer gives you 32 editable parameters directly on the hardware. That works for real-time sound design. It’s slow for building and comparing presets, which is where the companion app comes in.
Emmanuel built the control panel in Ctrlr, an open-source MIDI editor and panel builder. Ctrlr panels are XML files with optional Lua scripting, and the tool can export panels as VST or AU plugins — meaning the same editor can run inside a DAW. It works on Windows, macOS, and Linux. The choice avoids writing a custom editor application from scratch, which is a significant time investment, and it hands the panel format off to an existing open ecosystem where other builders can adapt it.
The Lua scripting is worth noting for anyone building similar devices. You can attach logic to any control — automatic preset comparison, MIDI learn, conditional parameter locking — without writing MIDI protocol code by hand. Ctrlr handles the transport layer.
Connectivity and Portability
MIDI IN and OUT over DIN connectors. Not USB-only — actual 5-pin DIN, which matters for hardware sequencers, vintage gear, and any setup where a USB host isn’t available. Line out and headphone out are separate from the internal speaker, so recording doesn’t require flipping a switch or pulling a plug.
Battery power is standard on the MiniTouch 2. Combined with the built-in speaker, this is genuinely portable — not “portable with a power bank and a mixer” portable, but carry-in-a-bag-and-play-anywhere portable. For workshop use and outdoor demos, that distinction is real.
On the Closed Source
The firmware is not public. The reasoning is practical: synthesizer code written for a specific hardware layout — particular pin assignments, a particular pot map, a specific capacitive pad arrangement — is hard to adapt without significant effort. Sharing it would generate more confusion than clarity.
What’s on offer instead is direct explanation. Emmanuel has invited questions in the thread and offered to share code chunks illustrating how specific features work. For anyone curious about how the FM envelope is implemented, how the scale quantizer maps touch input to MIDI notes, or how presets are stored and recalled on the Teensy 4.0, asking directly is the way to get a real answer.