Macmonium is a native macOS prototype that turns a Mac keyboard into a small harmonium. Keys trigger notes, a virtual air reservoir modulates the sound in real time, and fallback bellows controls let the prototype remain playable even when lid motion data is not available on the current Mac.

Macmonium takes direct inspiration from Hingemonium by Vedaant Rajeshirke / rocktopus101, especially its keyboard-as-instrument concept and its lid-velocity bellows model.

The lid sensor integration approach also builds on the original LidAngleSensor work by Sam Gold, which Hingemonium adapted into a musical interface.

• SwiftUI single-window instrument UI with an Apple-leaning minimal presentation
• Realtime air-pressure model with decay and smoothing
• Keyboard note mapping with polyphony
• Scale switching for chromatic, major, minor, and pentatonic play
• Octave shift, drone toggle, volume, release, air decay, and sensitivity controls
• Custom AVAudioEngine source-node synth shaped to feel closer to a harmonium than a plain sine tone
• Fallback bellows controls using the space bar or vertical drag gestures in the resonance area

The source tree includes a dedicated lid-motion provider seam at:

• Sources/HingeHarmonium/BellowsInput.swift

The current implementation attempts the same internal HID sensor path used by Hingemonium. Compatibility is still machine-dependent, so the app also includes fallback bellows controls using the space bar and on-screen gestures when lid input is unavailable or unreliable.

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