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AP Music Theory

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Unit 2

2.5 Interval Size and Quality

2 min readโ€ขnovember 2, 2020

Caroline Koffke

Mickey Hansen

2.5: Interval Size and Quality

An interval is the distance in pitch between two notes. It is determined by two factors: size and quality. Interval size is the numerical distance between the two pitches if you were simply counting staff lines.

These are all of the intervals within an octave:


Listen to the different intervals in an octave!

If you count the lines and spaces from one note to the other (including the line or space that each note is on), you will find the interval size! Counting lines and spaces can be a bit tedious, so luckily there are some tips you can use to recognize intervals more quickly.

โžก๏ธ Odd-numbered intervals are both on lines or both on spaces

โžก๏ธEven-numbered intervals are on opposites (one line, one space)

Interval quality can be major, minor, perfect, augmented or diminished.

Within the octave there are certain intervals that are perfect and certain intervals that are major or minor. Both of these intervals can also be augmented (raised by a semitone) or diminished (lowered by a semitone).


The four perfect intervals are unison, 4ths, 5ths and octaves (8ths). All of the other intervals (2nds, 3rds, 6ths, 7ths) are major or minor. Again, these intervals can all be augmented or diminished as well.

There are also a few intervals that are referred to by unique names, such as the tritone (diminished 5th/augmented 4th), unison, and the octave.

Here is what a tritone sounds like:


Listen to an example of a Tritone!

This is a unison:


Listen to an example of Unison!

And this is an octave:


Listen to an example of an octave!

Intervals show up in music in two different ways: harmonic intervals and melodic intervals. Harmonic intervals are two notes played at the same time, while melodic intervals are played one after another. In the last few audio examples, we first heard melodic intervals, then harmonic intervals.

You might have heard the terms consonance and dissonance in music before, usually to describe a chord, but it's important to understand where those terms come from. Intervals are also consonant or dissonant depending on how stable they are. Consonant intervals like perfect 5ths are very stable and don't feel the need to resolve or move. While dissonant intervals like the tritone (diminished 5th) have a strong pull to resolve to a more stable interval.

Here is a tritone vs. a perfect 5th:

Listen to the difference between Tritones and Perfect 5ths!

๐Ÿฆœ Polly wants a progress tracker: What is the interval from Ab to D? Or B# to E#? ๐Ÿ˜‰

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Unit 1: Music Fundamentals I: Pitch, Major Scales and Key Signatures, Rhythm, Meter, and Expressive Elements

Unit 3: Music Fundamentals III: Triads and Seventh Chords

Unit 4: Harmony and Voice Leading I: Chord Function, Cadence, and Phrase

Unit 5: Harmony and Voice Leading II: Chord Progressions and Predominant Function