Intervals
An interval is the distance between two musical notes. All melodies and chords are made up of a series of intervals. Intervals are measured in numbers, and are calculated by counting the number of letter names (A B C D E) between and in cluding the notes being measured. Within an octave, intervals are: Unison (two notes of the same pitch played or sung together or consecutively), 2nd, 3rd, 4th, 5th, 6th, 7th and Octave (two notes an octave apart). Thus A to B is a 2nd interval, as is B to C, C to D etc. A to C is a 3rd interval, A to D is a 4th, A to E is a 5th, A to F is a 6th, A to G is a 7th and A to the next A is an octave.
Intervals may be melodic (two notes played consecutively) or harmonic (two notes played at the same time). Hence two people singing at the same time are said to be singing in harmony.
Interval Qualities
Different intervals have different qualities:
Interval qualities can be best explained with the aid of a chromatic scale. If you look at the one below, it is easy to see that since intervals are measured in semitones, they may begin or end on a sharp or flat rather than a natural note.
Perfect intervals are 4ths, 5ths and octaves. If you widen a perfect interval by a semitone it becomes augmented (added to). E.g. if you add a semitone to the perfect 4th interval C to F, it becomes the augmented 4th interval C to F#. Notice that the letter names remain the same - F# is not referred to as Gb
If you narrow a perfect interval by a semitone it becomes diminished (lessened). E.g. if you lessen the perfect 5th interval D to A by a semitone, it becomes the diminished 5th interval D to Ab. Again, the letter name remains the same - Ab is not referred to as D to G#.
Major intervals (2nds, 3rds, 6ths and 7ths) become minor if narrowed by a semitone and minor intervals become major if widened by a semitone. A diminished interval can be created by narrowing a perfect or minor interval by a semitone. An augmented interval can be created by widening a perfect or major interval by a semitone.
Interval Distances
To summarize, here is a list of the distances of all common intervals up to an octave, measured in semitones. Each new interval is one semitone further apart than the previous one. Notice that the interval of an octave is exactly twelve semitones. This is because there are twelve different notes in the chromatic scale. Notice also that the interval which has a distance of six semitones can be called either an augmented 4th or a diminished 5th. This interval is also often called a tritone (because 6 semitones = 3 tones).
Minor 2nd - One semitone
Major 2nd - Two semitones
Minor 3rd - Three semitones
Major 3rd - Four semitonesM
Perfect 4th - Five semitones
Augmented 4th or Diminished 5th - Six semitones
Perfect 5th - Seven semitones
Minor 6th - Eight semitones
Major 6th - Nine semitones
Minor 7th - Ten semitones
Major 7th - Eleven semitones
Perfect Octave - Twelve semitones
Below are the same intervals ascending within one octave, starting and ending on the note C.
