Under the familiar feel of an Axiom 25 keyboard lives a very different instrument: a dedicated mono synth brain purpose-built for hands-on sound design and expressive performance.
Black Pill Synth by Craig Barnes takes the original BP Synth engine and turns it into a self-contained hardware instrument, with the core synth logic running on an STM32F411 processor and a hardware editor driven by a Teensy 4.0 microcontroller inside the Axiom chassis. You get velocity-sensitive keys, monophonic aftertouch, pitch bend and mod wheels, plus a front panel of buttons and pots that mirror the original software GUI via MCP23017 controller chips. Every physical control sends MIDI CC, so the unit doubles as a versatile USB and DIN MIDI controller with MIDI in, out, thru and side-mounted stereo audio outputs.
The synth engine itself is a flexible virtual analog design, offering roughly 15 to 16 waveforms including sawtooth, square, sine, triangle and noise, with options for up to three sawtooth oscillators, oscillator sync and pulse width modulation. A full subtractive path follows, with resonant low-pass and high-pass filter modes, cutoff, resonance, envelope depth, key tracking and velocity control, plus standard ADSR envelopes for the VCA and a dedicated pitch envelope with positive or negative modulation. Two LFOs with six waveforms each handle movement, while the highly assignable mod wheel can drive vibrato, tremolo or filter LFO speed. Onboard echo and phaser effects with adjustable rate, feedback and wet/dry mix complete the signal chain, giving this compact prototype the character and polish of a finished electronic instrument.
