Ostinato

A melodic phrase repeated persistently in the same voice and at the same pitch. (Repetition at a different pitch is called sequence). The ostinato principle is the chief characteristic of chaconne and passacaglia. The stepwise semitonic descent from the tonic to the dominant in a minor key forms a special kind of ostinato which is associated with operatic lament (the lament aria in Cavalli's Ormindo in B minor; Dido's lament in Purcell's Dido and Aeneas in G minor; Crucifixus in Bach's Mass in B minor; Mourn, all ye muses in Handel's Acis and Galatea in F minor). This chromatic fourth was also used in instrumental music as the ostinato in Biber's Passacaglia in G minor.