Every infectious disease in the ICD-11 (International Classification of Diseases, 11th revision, published by the WHO) has been assigned a musical chord drawn from western tonal and modal harmony. The assignment follows a three-layer system: the pathogen type determines the scale family, the transmission route determines the chord quality, and the clinical severity determines the degree of harmonic extension.
The result is an acoustic taxonomy. Diseases that sound stable and resolved tend to be mild and bacterial. Diseases that sound tense, dissonant, or suspended tend to be viral, vector-borne, or fatal. Prion diseases map to the whole-tone scale — no tonal center, no resolution, no cure.
| Dimension | ICD-11 property | Musical result | Reasoning |
|---|---|---|---|
| Scale family | Bacterial | Major scales | Known, structured, usually treatable |
| Viral | Natural minor / Aeolian | Evasive, mutating — unresolved | |
| Fungal | Dorian / Phrygian modes | Opportunistic, ambiguous tonal identity | |
| Parasitic | Harmonic / Double harmonic minor | Complex lifecycles, exotic intervals | |
| Prion | Whole-tone scale | No tonal center. No resolution. No cure. | |
| Chord quality | Airborne | Major | Open, expansive transmission |
| Direct contact | Minor | Close, contained | |
| Vector-borne | Diminished | Unstable — requires intermediary host | |
| Bloodborne | Augmented | Maximum tension interval | |
| Foodborne / waterborne | Suspended sus2/sus4 | Neither major nor minor — pure tension | |
| Extension | Self-limiting / mild | Triad | Complete, no excess |
| Moderate / treatable | 7th chord | Wants resolution but finds it | |
| Severe / hospitalization | 9th chord | Extended, layered tension | |
| Life-threatening | 11th with alterations | Clustered dissonance | |
| Pandemic / no treatment | 13th ♭9 ♯11 ♭13 | Maximum tension, no resolution |
Each chord is synthesised in real time using the Web Audio API — two stacked oscillators (sine + triangle wave, 1.4 cents detuned) through a procedurally generated reverb. Notes stagger by 44 ms so the chord opens like a slow arpeggio.
The spectrogram is a rolling frequency-time waterfall (0–1 000 Hz, magma colormap). Guide lines mark each chord tone; triangle waves show odd harmonics at 3×, 5×, 7× each fundamental. The waveform view shows the time-domain signal in phosphor oscilloscope style.