What is "stimmung"

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 catalog. It is a tonal, and yet also a serial composition (; ).