Helmut Lachenmann is a German composer that is born 1955. He is associated with what is called musique concrète instrumentale. The most striking aspect of his music is the fact that many times he simply removes pitch as a musical parameter and uses a lot of unusual playing techniques. That result in music where other musical parameters such as timbre is more prominent.
Lachenmann has written three string quartets. The first one is Gran Torso from 1971. It is for the most parts very quiet. The unusual playing techniques is also very skillfully used and combined. A bit like different sounds that is combined in musique concrete to form new sounds that are distanced and not associated with the original sounds.
Another early piece is Guero. It is one of several study pieces that Lachenmann wrote to explore the possibilities of individual instruments. Other pieces include Pression for solo cello. Guero is written for piano but its very far from a traditional piano piece. There you can also hear very clear what happens when you remove pitch and somewhat replace it with timbre.
Schwankungen am Rand is a piece from 1974-1975 written for brass, electric guitars, pianos, thunder sheets, and strings. It is a fascinating piece on several levels. One thing is the skillful treatment of sounds, that I already mentioned. Another aspect is the “speed” of the piece. Lachenmann stops the development several times and repeats, with slight variation, the same pattern for an extended period of time.
Accanto, music for solo clarinet and orchestra, from 1975-1976. It is based on the last clarinet concerto by Mozart. The idea is to let fragments of the concerto emerge to the surface. It is only in a brief passage near the end that the original concerto is heard. One very nice passage is in the first half of the piece where there are pulses of different textures and timbres that come in and out.