Music Theory

Interval Inversion

The process of flipping an interval so that the lower note moves above the higher; a 2nd inverted becomes a 7th, a 3rd becomes a 6th, etc.

Rule of 9

When an interval is inverted, the two interval numbers always add up to nine (e.g., 2nd ↔ 7th, 3rd ↔ 6th).

Semitone (Half Step)

The smallest standard distance between two pitches in Western music; one semitone equals one half step.

Pitch

A specific musical note perceived as high or low and located on the staff.

Octave Equivalence

The concept that pitches separated by any number of octaves sound functionally identical (e.g., every C belongs to the same pitch class).

Pitch Class

The collection of all notes with the same letter name regardless of octave (e.g., C in any register).

Enharmonic Equivalence

Different spellings that produce the same pitch, such as D♭♭, C, and B♯.

Interval

The measured distance between two pitches, named by quantity (2nd, 3rd, etc.) and quality (major, minor, etc.).

Ottava Sign

Notation indicating octave displacement: 8va directs playing an octave higher; 8vb (or 8va bassa) directs playing an octave lower.

8va

Abbreviation of ‘ottava alta’; instructs the performer to play the passage one octave above written pitch.

8vb

Abbreviation of ‘ottava bassa’; instructs the performer to play the passage one octave below written pitch.