AUGMENTATION (MUSIC)

In music and music theory 'augmentation' is the lengthening or widening of rhythms, melodies, intervals, chords. The opposite is diminution (as in "a diminished triad").
A melody or series of notes is ''augmented'' if the lengths of the notes are prolonged. A melody originally consisting of four quavers (eighth-notes) for example, is augmented if it later appears with four crotchets (quarter-notes) instead. This technique is often used in contrapuntal music. It gives rise to the "canon in augmentation", in which the notes in the following voice are longer than those in the leading. The music of Johann Sebastian Bach provides examples of this application.
An interval is ''augmented'' if it is widened by a chromatic semitone; an augmented chord is one which contains an augmented interval. Thus an augmented fifth, for example, is a chromatic semitone wider than the perfect fifth, and an augmented triad is a major triad whose fifth has been raised a chromatic semitone.
A good example of this can be seen in the left hand part of Chopin's famous E minor prelude. Many of the chord sequences change with the top or bottom note augmenting or diminishing the next chord as the music progresses.