onharmonisch

Onharmonisch is a Dutch term used in acoustics and musicology to describe sounds or spectra in which the partials do not align with the harmonic series of a fundamental frequency. In such a spectrum, the overtones are not exact integer multiples of the fundamental, giving the sound a different timbre than a perfectly harmonic one.

Etymology and usage: The word comprises the prefix on- meaning not, and harmonisch meaning harmonic. It is commonly used to contrast with harmonic sounds, where partials follow integer multiples of the fundamental. The term appears in analyses of instrument spectra, room acoustics, and electronic sound design.

Causes and typical sources: Inharmonicity arises from physical properties of the sound source. In strings, stiffness causes higher partials to deviate upward from exact multiples as frequency increases. In bells and other percussion, shape and material properties create complex, non-integer overtones. Air-column resonances and instrument construction can also produce inharmonic spectra. The degree of inharmonicity is often described by an inharmonicity coefficient, and varies with instrument design, playing technique, and pitch range.

Implications: Inharmonicity influences timbre, perceived brightness, and tuning practices. For fixed-pitch instruments like pianos, significant inharmonicity leads to stretch tuning, where higher notes are tuned slightly sharper to compensate for the inharmonic spectrum. In electronic synthesis, inharmonic spectra are intentional, used to simulate bells, metal sounds, or other non-harmonic textures.

See also: inharmonicity, overtone, timbre, piano, bells, acoustics.