biography of the inventor, Theremin: Ether Music and Espionage, Albert Glinsky suggested he had fled to escape crushing personal debts, and was then caught up in Stalin's political purges. In any case, Theremin did not return to the United States until 1991. After a flurry of interest in America following the end of the Second World War, the theremin soon fell into disuse with serious musicians, mainly because newer electronic instruments were introduced that were easier to play. However, a niche interest in the theremin persisted, mostly among electronics enthusiasts and kit-building hobbyists. One of these electronics enthusiasts, Robert Moog, began building theremins in the 1950s, while he was a high-school student. Moog subsequently published a number of articles about building theremins, and sold theremin kits that were intended to be assembled by the customer. Moog credited what he learned from the experience as leading directly to his groundbreaking synthesizer, the Moog. (Around 1955, a colleague of Moog's, electronic music pioneer Raymond Scott, purchased one of Moog's theremin subassemblies to incorporate into a new invention, the Clavivox, which was intended to be an easy-to-use keyboard theremin.) Since the release of the film Theremin: An Electronic Odyssey in 1993, the instrument has enjoyed a resurgence in interest and has become more widely used by contemporary musicians. Even though many theremin sounds can be approximated on many modern synthesizers, some musicians continue to appreciate the expressiveness, novelty, and uniqueness of using an actual theremin. The film itself has received positive reviews. Both theremin instruments and kits are available. The Open Theremin, an open hardware and open software project, was developed by Swiss microengineer Urz Gaudenz, using the original heterodyne oscillator architecture for a good playing experience, combined with Arduino. Using a few extra components, a MIDI interface can be added to the Open Theremin, enabling a player to use their Theremin to control different instrument sounds. Some inexpensive theremins may only have a pitch control and may be harder to play accurately because of a relatively non-linear relationship between the distance of the hand and resultant pitch, as well as a relatively short span of hand-to-antenna distance for producing the available range of pitch. Operating principles The theremin is distinguished among musical instruments in that it is played without physical contact. The thereminist stands in front of the instrument and moves their hands in the proximity of two metal antennas. The distance