An interval is the distance in pitch between two notes.
There are two parts to an interval name, quality and size.
Interval size is measured by counting the number of lines and spaces (or alphabet letters) between two notes, including both notes.
For example, the size of the interval between F-C is a fifth.
The quality of an interval is determined by the number of half steps contained in the interval.
Intervals with the same size can have different qualities.
For example, the intervals between C-E and E-G are both thirds, but there are four half steps between C-E, versus three half steps between E-G.
The third containing four half steps is called a major third.
The third containing three half steps is called a minor third.
The terms perfect, major, minor, diminished, and augmented are used to describe the quality of an interval.
Perfect is used with unisons, fourths, fifths, and octaves.
Major and minor is used with seconds, thirds, sixths and sevenths.
Diminished and augmented are used with all intervals.
Perfect intervals are labeled with an upper case "P." Major intervals are labeled with an upper case "M." Minor intervals are labeled with a lower case "m." Diminished intervals are labeled "d", "dim." or "deg. or " o." Augmented intervals are labeled "A", "Aug." or "+."
Examples: P1, P4, m2, m6, M3, M7, d3, deg.5, dim. 5, A6, Aug.
6, +6.
To identify the size and quality of an interval using a major scale
for reference, assume the bottom note of the interval is the tonic of
a major scale.
1. If the upper note of the interval belongs to that major scale, then
unisons, 4ths, 5ths and 8ves will be perfect, and 2nds, 3rds, 6ths, and
7ths will be major.
2. If the upper note of the interval does not belong to that major scale,
determine by how many half steps it differs from that scale degree of
the major scale. Based on the half step differential, determine the quality.
Identification
To identify the size and quality of an interval without a key reference
to a major scale, do the following:
1. Find the interval size by counting the lines and spaces between the
two notes (including both notes).
2. Find the interval quality by determining the number of half steps between
the two notes and then use the table of interval sizes to determine the
quality.
Perfect Intervals
Perfect intervals are the unison, fourth, fifth, and octave. Perfect
intervals are formed in the major scale when the lower note is the tonic.
Perfect unison (P1) has 0 half steps
Perfect fourth (P4) has 5 half steps
Perfect fifth (P5) has 7 half steps
Perfect octave (P8) has 12 half steps
Major Intervals
Major intervals are the second, third, sixth, and seventh. Major intervals
are formed in the major scale when the lower note is the tonic.
Major second (M2) has 2 half steps
Major third (M3) has 4 half steps
Major sixth (M6) has 9 half steps
Major seventh (M7) has 11 half steps
Minor Intervals
Minor Intervals are the second, third, sixth, and seventh. minor intervals
are formed in the major scale when the upper note is the tonic.
Minor second (m2) has 1 half steps
Minor third (m3) has 3 half steps
Minor sixth (m6) has 8 half steps
Minor seventh (m7) has 10 half steps
Harmonic/Melodic Intervals
Intervals can appear as harmonic or melodic intervals. In harmonic intervals
the notes are played simultaneously. In melodic intervals the notes are
played separately. Melodic intervals can appear as ascending or descending
intervals.
Altered Perfect Intervals
When a perfect interval is made one half step larger it becomes augmented.
When a perfect interval is made one half step smaller it becomes diminished.
Notice how you can shrink or expand the interval from either the top
or bottom note.
Altered Major/Minor Intervals
A major interval one half step larger becomes augmented. A major interval
one half step smaller becomes minor. A minor interval one half step larger
becomes major. A minor interval one half step smaller becomes diminished.
Altered Diminished/Augmented Intervals
An augmented interval one half step larger becomes doubly augmented.
A diminished interval one half step smaller becomes doubly diminished.
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