What I'm listening to today: "Mixtur Trautonium (exercise #4)" LudoWic
The Trautonium is an early electronic instrument from the 1930s. Instead of a "keyboard" like a post-1965 synthesizer would use players make contact between a resistive wire and a metal plate, allowing fine control more akin to a violin than a piano. In this piece, the musician works the plate (and the pedals?) for a complex and stunning tremolo effect, like a guitar pedal under direct human control.