Musical interval

A musical interval is the difference in pitch between two notes, described by the distance between them and, in tonal music, by its quality.

Pitch (music): The perceived highness or lowness of a musical sound, related to its fundamental frequency. An interval compares the pitches of two notes.
Interval inversion: The transformation of an interval by moving one of its notes across an octave. Inversion links complementary interval sizes and qualities.
Melody: A sequence of musical pitches perceived as a coherent line. Successive intervals shape a melody’s contour and character.
Consonance and dissonance: The perceived stability or tension of musical combinations of pitches. Interval size alone does not determine whether a sound feels stable or tense.
Diatonic scale: A seven-note scale organized as five whole steps and two half steps within an octave. Diatonic letter names determine an interval’s numbered size.
Compound interval: An interval spanning more than one octave, such as a ninth or a tenth. Compound intervals extend basic interval names beyond a single octave.
Chord: A combination of two or more notes sounded together. The intervals among simultaneous notes determine a chord’s structure.
Frequency ratio: The quotient of the frequencies of two periodic sounds. Ratios describe acoustic distance independently of note spelling.
Semitone: The smallest commonly used interval in Western tonal music, equal to one twelfth of an octave in equal temperament. Counting semitones distinguishes interval sizes that share a letter-name span.
Harmonic interval: An interval formed by two pitches sounding simultaneously. Simultaneous notes make the interval’s acoustic interaction audible.

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