Sinusoids are the indivisible atoms of all sound and vibration.

Evidence

The sinusoid is the fundamental and indivisible unit, the atom, of signal analysis and also of vibration, sound, and music. The sinusoids, each plain and colorless, together can describe any tone or indeed any sound. — Eric J. Heller, Why You Hear What You Hear- An…, 333

Categorization

• DEFINE: Deploys the ‘atom’ metaphor establishing sinusoids as the primitive building block of signal analysis.
• XREF: Connects to the book’s broader project of explaining pitch perception and sound production mechanics; also resonates with ideas in The Soundscape about decomposing complex auditory scenes.