Basso ostinato
A constantly repeated bass figure.
What it means
A basso ostinato — “obstinate bass” — is a short bass figure that sounds again and again unchanged or nearly unchanged, while the upper voices unfold freely above it. The figure usually comprises only a few bars and forms the fixed frame against which the rest of the music stands out.
Musical use
In the music of the seventeenth and early eighteenth centuries the ostinato is a load-bearing formal principle. Two dance forms rest on it: the passacaglia and the chaconne, such as Bach's Passacaglia in C minor, BWV 582 — over a recurring bass model a series of variations arises in which the upper voices take on new shape with each pass, while the bass remains. Well known are models such as the descending fourth (tetrachord), in which the bass steps down from the root to the dominant — diatonic or chromatic. The chromatic form became the epitome of lament and underlies movements such as Purcell's "Dido's Lament" from Dido and Aeneas.
The effect rests on the opposition of persistence and change. The unchanging bass produces cohesion and a peculiar inevitability, and it is precisely against this fixed ground that every change in the upper voices becomes audible. The art lies in letting the phrases of the upper voices occasionally run across the boundaries of the bass figure, so that the repetition does not seem mechanical.
In later and popular music the principle lives on: as a riff in rock and jazz, as a repeated bass line in minimal music, and as a groove pattern in funk and dance music.
The ostinato is to be distinguished from the pedal point, which means a single sustained note, and from the drone, which forms a continuous ground sonority — the ostinato is a moving, melodically shaped figure.
Performance practice
Keep the bass figure even and stable, without letting it become mechanical — it is the frame for everything else. Shape the upper voices across the boundaries of the repetition. And practise the bass figure until it runs without attention; then the ear is free for the ensemble playing.