 Long thought to have been lost, the tape of the "Etude" was, according to one source, rediscovered by Rudolf Frisius ; according to another, it was found by the composer himself, "in a pile of old tapes" .Even after its rediscovery, Stockhausen did not permit the work to be published until 1992 .There are references to another, earlier and possibly unrealised "musique concrète" project, "Studie über einen Ton" (Study on One Sound), in two parts .