Pitch class

A class of sound contains all the sounds that share certain characteristics with each other. Formally, a class of sound therefore an equivalence relation of tones with respect to a certain characteristic. Accordingly, various divisions of the sounds are in classes of sound possible, depending on which feature one assumes. In the modern 12-part European sound system three types are mainly distinguished from pitch classes:

• Classes of sound with octave equivalence:

• Unchanged naturals: A- H -C -D-E -F -G
• Increased by a half naturals: A # H # -C # -D # - E # -F # -G #
• Two semitones higher naturals: Ax- Hx - Cx Dx Ex Fx - Gx
• Lowered by a half step naturals: From B Cb Db Eb Fb Gb
• Two semitones humbled naturals: Abb- Hbb - Cbb Dbb - Ebb - Gbb Fbb -

• The equal temperament now the most commonly used enables the pitch classes with so-called enharmonic equivalence. It includes all the sounds that can be heard at the same frequency in a class of sound. For example, include the notes d ', cx ' and ebb ' in the same class of sound, because all exactly the same pitch, respectively. However not a part of D'' to the same class of sound, because the pitch is different from the other tones.

• Combining these two Oktaväquivalenz with enharmonic equivalence, we obtain twelve pitch classes:

It makes sense to pitch classes if you want to talk about certain features that can fulfill a sound independent of its pitch (for example, as a leading tone within a key ).