crossoctave

Crossoctave is a term encountered in discussions of music theory and digital audio to describe phenomena or techniques that relate notes, signals, or musical materials across octaves. The exact meaning varies by context, but the core idea is the interaction of pitch content that spans more than a single octave or leverages octave relationships as a structural or perceptual element.

In music theory, cross-octave concepts arise from octave equivalence—the perceptual phenomenon that pitches separated by octaves are often treated as belonging to the same pitch class. Crossoctave in this sense may refer to constructions where motives or harmonies reuse pitch classes across octaves to generate cohesion, or to analysis methods that collapse or compare content across octaves using modular arithmetic.

In audio processing and synthesis, cross-octave techniques map or modulate signals across octave boundaries. Examples include octave-shifting or cross-octave filtering, where a signal is combined with its octave-shifted counterparts to create thickened or harmonically rich textures, or where modulation sources maintain octave-relative relationships to produce musically coherent results.

Notation and terminology are not standardized, and "crossoctave" can be used differently in academic writing, software documentation, and musical practice. As a result, definitions should be clarified by the author when encountered in a text or project.

See also: octave, octave equivalence, pitch class, frequency doubling, cross-synthesis.