Sävelluokat

Sävelluokat, or sävelluokka in singular, is a concept in music theory that refers to pitch classes: the set of all pitches that are equivalent under octave transposition. In Western music, there are twelve distinct pitch classes, corresponding to the twelve semitones within an octave. Each pitch class can be named (for example C, C♯/D♭, D, and so on) and represents all pitches that share the same letter and accidental when octave is disregarded.

Mathematically, pitch classes are treated modulo octave, meaning that moving up or down by octaves does not change the class. The standard representation assigns numbers 0–11 to the classes, often with C as 0, C♯/D♭ as 1, D as 2, through B as 11. This framework underpins chromaticism, set theory, and twelve-tone technique, and it is widely used in analysis, composition, and computer-assisted music research.

In analysis and composition, sävelluokat are used to describe intervals, chords, and scales without regard to octave. Two common operations are transposition and inversion: transposition Tn shifts every pitch class by n semitones, while inversion In reflects pitch classes around a chosen axis. For example, the diatonic major scale corresponds to the pitch-class set {0,2,4,5,7,9,11} if C is taken as 0, whereas the chromatic scale uses the full set {0,1,2,3,4,5,6,7,8,9,10,11}.

Historically, sävelluokat gained prominence with 20th-century music theory and the development of twelve-tone technique, but the concept remains a foundational tool in pedagogy and analytical practice. See also pitch class, set theory, and Forte numbers.