Stimmung, for six vocalists and six microphones, is a piece by Karlheinz Stockhausen, written in 1968 and commissioned by the City of Cologne for the Collegium Vocale Köln. Its average length is seventy-four minutes, and it bears the work number 24 in the composer's catalogue. It is a tonal, and yet also a serial composition ). It is "the first major Western composition to be based entirely on the production of vocal harmonics", the first "to use overtones as a primary element". An additional innovation is "the unique kind of rhythmic polyphony which arises from the gradual transformation/assimilation of rhythmic models".