Simple and Compound Intervals

Interval Octave Interval Number Register

Once the distance between two notes exceeds an octave, the naming changes method. Anything within an octave is a simple interval; anything wider is a compound interval.

How compound intervals are read

A compound name is the simple name plus the number of octaves:

Actual interval	Read as	Also read as
C up to D	major ninth	major second + an octave
C up to E	major tenth	major third + an octave
C up to G	perfect twelfth	perfect fifth + an octave

The arithmetic is reversible: subtract 7 from a compound degree and you are back to a simple interval (major ninth → major second; perfect twelfth → perfect fifth). So compound intervals add no new listening category — they lift something you already know by an octave.

Why the terminology is needed

Because in writing, "a leap of a ninth" and "a leap of a second" are two different acts:

Simple intervals shape the melodic outline — step or leap;
Compound intervals set the space between voices — written close together or spread far apart.

Take the same material and raise the upper voice by an octave: every interval gains 7, the melody still reads as the same melody, but the sense of distance between the parts changes completely. That belongs to register and orchestration.

Diagram: subtract 7 and the simple interval returns

Listen: lifted by an octave

The same interval before and after an octave lift reads as "the same thing", yet the sense of space differs.

Common misconceptions

"A compound interval is a separate category." It is a simple interval lifted an octave; the quality (major, minor, perfect, augmented, diminished) never changes.
"Ninths are much harder to hear than seconds." It is a second plus an octave. Identify the simple interval first, then hear the octave.
"Compound intervals stop at two octaves." They do not; the name simply keeps adding. Performance limits are the instrument's range, not notation.
"One degree number always means one distance." A ninth can be major or minor; the simple layer decides.

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Listen in the library

Piano Sonata No. 14 in C-Sharp Minor, Op. 27 No. 2 "Moonlight": I. Adagio sostenutoC16:10The first movement of the Moonlight Sonata — a single arpeggio figure spans more than two octaves, textbook compound-interval materialDetailsInvention 08C11:06Bach's eighth two-part invention — the voices often stretch beyond an octave, so simple and compound alternate inside one phraseDetailsScales, Arpeggios, and CadencesC13:22Scale and arpeggio exercises cross the octave boundary repeatedly — the line between simple and compoundDetails

All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).

Sources

单音程（八度以内）与复音程（超出八度）的划分，属乐理通则
复音程"减 7 得单音程"的换算方法为通行表述，本文行文为原创

Used for fact-checking only; all prose is original.

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