Impur is an album by English guitarist, composer and improvisor Fred Frith. It was composed in 1996 by Frith "for 100 musicians, large building and mobile audience" and was performed on 30 May 1996 by students and teachers from L’Ecole Nationale de Musique, Villeurbanne, France. Frith directed the performance but did perform himself.

Impur is the first of two performances commissioned by L’Ecole Nationale de Musique while Frith was resident music professor at the institution. The second was Impur II (2009).

Between 1994 and 1996, Frith was Composer-in-Residence at L’Ecole Nationale de Musique in Villeurbanne, France. At the end of the two-year residency, Frith organised a musical event at the school involving as many students as possible. He grouped them according to their music disciplines and placed them in all the rooms of a music building. Each group of musicians then played music Frith had prepared for them or, when required, improvised. Using synchronized stopwatches, all the groups, who could not hear each other, played strictly according to a 55-minute time-score that Frith had written. During the concert the public was invited to wander from room to room, or sit in the courtyard and listen to the sounds from the open windows. The whole performance was recorded on four ADAT recorders and later mixed.

Downtown Music Gallery wrote of this album:

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