Horst Stein adopted this solution in Bayreuth in 1975. In Hamburg, Ludwig and Liebermann used a tape loop of piano sounds, recorded inside the instrument, mixed with bell sounds. In 1976, Maronn and Hecht, of the Studio for Musical Communication in Hamburg, produced a synthesised bell sound based on the analysis of German cathedral bells. This is produced from an initial recording of 14 superimposed sine waves, to which various different harmonics have been added at different volumes to produce a bell-like sound. The mixture is then passed through a magic box which forms a sound with an extremely short attack time followed by a long exponential decay of 3-7 seconds.
Pitch is controlled by adjusting the speed of the tape.
The results are in use at Bayreuth and major European opera houses.