Microtonality

Microtonality is the use in music of microtones — intervals smaller than a semitone, also called "microintervals". It may also be extended to include any music using intervals not found in the customary Western tuning of twelve equal intervals per octave. In other words, a microtone may be thought of as a note that falls "between the keys" of a piano tuned in equal temperament.

musical tuning system with 19 pitches equally-spaced on a logarithmic scale

musical tuning system with 53 pitches equally-spaced on a logarithmic scale

musical tuning system with 31 pitches equally-spaced on a logarithmic scale