Thereminist robot (via Kyoto University)
Robots have been playing music for a while now on their own, but getting them to play in tune with humans is a feat in itself. The newest robotic member of the band plays one of the weirdest instruments on the planet: the Theremin. The electrical instrument is played using no physical contact and uses oscillators that control frequency based on how close/far the user’s hands are in relation to the instruments antenna. Actually, this music machine is probably the most appropriate instrument for the ‘Thereminist robot’ developed by Takeshi Mizumoto from Kyoto University for playing alongside human musicians.
The problem with playing that instrument is that when someone invades the airspace around the Theremin it changes tune (because of the electric field produced around the antenna). To overcome this problem when playing with a group Takeshi developed a "special algorithm" that uses ‘parametric and non-parametric’ pitch models that allow the HRP-2 robot (from Kwanda Industries) to remain ‘in tune’ while playing with its human band-mates. To accomplish this, the robot first adjusts the pitch model using the Levenberg-Marquardt algorithm (LMA), which uses a ‘numerical solution’ to minimize the robots adjustment function while calibrating or adjusting the pitch for the instrument. The robot then moves its hand(s) coarsely to find the pitch model desired using ‘feedforward’ control.
Once the robot finds the desired pitch using its hand it then adjusts its body-position to fine-tune the feedback control. These adjustments are done relatively quickly in order to maintain harmony when playing with others. This is because the robot doesn’t listen to the Theremin sounds but rather uses the (software) pitch model instead. To put it plainly; the robot maintains the pitch control (or the note) when an object interferes in the electromagnetic field produced by the Theremin until the object is removed whereby it then goes back to playing the original melody (if you can call it that). While the Theremin is defiantly one of the most unusual musical instruments ever to be devised, it certainly is a good choice to match with our mechanical friends.
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