Unmeasured prelude

Unmeasured or non-measured prelude is a prelude in which the duration of each note is left to the performer. Typically the term is used for 17th century harpsichord compositions that are written without rhythm or metre indications, although various composers of the Classical music era were composing small preludes for woodwind instruments using non-measured notation well into the 19th century. The form resurfaced in the aleatory music of the 20th century, where various other aspects of performance are also left to free interpretation.