Wikipedia
Mikrophonie is the title given by Karlheinz Stockhausen to two of his compositions, written in 1964 and 1965, in which “normally inaudible vibrations . . . are made audible by an active process of sound detection (comparable to the auscultation of a body by a physician); the microphone is used actively as a musical instrument, in contrast to its former passive function of reproducing sounds as faithfully as possible” .
Together with Stockhausen’s immediately preceding work Mixtur, for five orchestra groups, four sine-wave generators, four ring modulators, they form a tryptych of live-electronic works, where electronic transformations are accomplished during the performance (as opposed to studio-produced electronic music on tape). Similar to a group of three of the composer’s works from the previous decade, Gruppen, Zeitmaße, and Gesang der Jünglinge, there is one work each for orchestral, chamber, and vocal forces.