Mantra is a piece for two pianos and Electronics written in 1070 by Karlheinz Stockhausen. It is a highly structured piece that is based on a thirteen note theme, the “mantra”. Each note is assigned characteristic (like periodic repetition at the beginning), duration and dynamic. Stockhausen then make 13 parts, one for each note. Resulting in a piece that is about 70 minutes long.
For the electronics Stockhausen had a device built, “Module 69 B”, that picked up the sound of the piano and transformed it. The central transformation performed is a ring modulation with the pitch from note for the currently playing part.