Every musical pitch is really a stack of pure sine waves — a fundamental frequency plus a ladder of overtones (integer multiples of it) called the harmonic series. Spectral composers such as Gérard Grisey and Tristan Murail treated this spectrum itself as compositional material, analysing the overtones of a single instrumental sound and orchestrating them individually to "compose" timbre the way a painter mixes colour.
Grisey's landmark cycle Les Espaces Acoustiques (1974–85) grew an entire orchestral work out of the measured overtone spectrum of a low trombone E — spectral analysis became the seed of the score itself.
A 3D harmonic-series rack of glowing overtone bars plus a live waveform ribbon showing how adding, removing and detuning individual partials reshapes a sound's timbre — the raw material spectral composers work with directly.
Each bar is one partial in the harmonic series; its amplitude and detuning combine into the ribbon waveform in front, exactly as additive synthesis builds a complex tone from simple sine waves.
Set the fundamental, how many overtones are active, the spectral tilt (brightness) and inharmonicity (stretch), then press Play tone to hear the additive-synthesis chord you built.
Spectral composers like Grisey and Murail analysed real instrument spectra with sonograms and orchestrated the overtones themselves — turning acoustic analysis into a compositional method.