Paul Hindemith wrote several short trios for three Trautoniums with three different tunings: bass, middle, and high voice. His student, Harald Genzmer, wrote two concertos with orchestra, one for the monophonic Trautonium and, later, one for Sala's "Mixtur-Trautonium". One of the first additions of Sala was to add a switch for changing the static tuning. Later he added a noise generator and an envelope generator (so called 'Schlagwerk'), formant filter (several bandpass filters) and the subharmonic oscillators. These oscillators generate a main pitch and several harmonics, which are not multiples of the fundamental tone, but fractions of it. For any of the now two manuals, four of these waves can be mixed and the player can switch through these predefined settings. Thus, it was called the "Mixtur-Trautonium". Oskar Sala composed music for industrial films, but the most famous was the bird noises for Alfred Hitchcock's The Birds.