'Mikrophonie' calls for 6 percussionists playing a single instrument a giant 60 tam-tam. Three musicians activate the instrument from either side. One player performs on the tam-tam using a large array of mallets and small objects, a second holds a highly directional microphone and also plays the tam-tam, and the third is a sound designer who sits in the hall and regulates settings for volume, filtration and spatial diffusion of the sounds. The result is an extraordinary and theatrical sound world. In 'Refrain', the three performers produce an array of pure tones from their primary instruments to noisy shouted syllables and tongue clicks. In the most complex passages, the sounds merge nearly completely. 'Schlagtrio' is one of Stockhausen s earliest published pieces. Rather than articulating the differences between piano and percussion, he is interested in creating a continuum between the two.