undertonal

Undertonal is an adjective used in acoustics and music theory to describe phenomena, concepts, or systems centered on undertones or subharmonics — pitches produced by dividing a vibrating frequency rather than multiplying it. In this usage, undertones are considered the counterpart to the more familiar overtones that form the harmonic series.

In acoustics, subharmonics are frequencies at integers divided into the fundamental, f/n, yielding pitches lower than the base frequency. The undertone series is thus the set of these subharmonics (often discussed in relation to the octave-equivalent pitch space) and is contrasted with the overtone or harmonic series f, 2f, 3f, etc. Subharmonics can occur in nonlinear systems and can be generated in laboratories or via electronic synthesis.

In music theory and composition, undertonal concepts have been explored as a framework for alternative tonal centers and harmony. Undertonal systems attempt to organize pitches around subharmonic relationships, producing interval structures that differ from conventional equal-tempered or just intonation frameworks. Such approaches are encountered in microtonal and experimental music, and they are discussed primarily in theoretical literature rather than as mainstream practice.

Notational and analytical approaches to undertonal music vary. Some writers treat subharmonic pitches as members of an octave-reducing set, using numbering schemes f/n to indicate subharmonics. Performance often relies on electronic sound generation or specialized techniques, as producing stable subharmonics on standard instruments is technically challenging.

See also: overtone, subharmonic, subharmonics, undertone singing, microtonal music, non-western tuning systems.