Modulation
Change of key within a piece.
What it means
Modulation is the term for the change from one key to another within a piece. Decisive is that the new key is confirmed as a new centre, usually through a cadence in it. A merely brief excursion after which the music immediately returns is called a tonicization and does not count as modulation in the full sense.
Musical use
The procedures can be ordered by the type of transition. In diatonic modulation, a sonority common to both keys serves as a pivot: it is reached in the old key and reinterpreted in the new one. This is the smoothest path and usual for closely related keys. In chromatic modulation, a voice changes a note by a semitone and thereby leads into the new context. In enharmonic modulation, a sonority is respelled and continued with a different meaning; ambiguous sonorities such as the diminished seventh chord or the augmented sixth chord are especially suited to this and make possible the path into remote keys.
Modulation is a load-bearing element of form. In sonata form, the second theme stands in a different key from the first, in major pieces usually in the dominant, in minor pieces in the relative major; the development wanders through further keys, and the recapitulation returns.
Modulation is to be distinguished from the sudden shift, an abrupt change of key without a mediating transition, and from the secondary dominant, which only briefly emphasizes another degree without leaving the key.
Several procedures are distinguished: diatonic modulation uses a chord common to both keys; chromatic modulation changes one note; enharmonic modulation reinterprets a chord, for instance the diminished seventh chord. To be distinguished from modulation is the tonicization, which leads only briefly into another key.
Performance practice
Determine the pivot point of a modulation and mark it — there the frame of reference changes, even if the fingers notice nothing of it. Shape the arrival in the new key audibly. And with variable intonation, take care that the role of the notes changes with the key.