The theremin, named for its inventor Louis Théremin, is the only instrument that is played without the performer touching any part of it. It uses two ultrasonic oscillators, one of fixed pitch and the other variable. The variable frequency oscillator is attached to an antenna. Audible pitch results from the heterodyne interaction of the two oscillators. That is, what we hear are the beats between two ultrasonic pitches, the difference tones. The frequency of the pitch results from how close or how far away the performers right hand is to the antenna. The performer’s left hand similarly controls the volume by moving in relation to a metal loop on the instrument. With some difficulty and practice, performers can play melodies. They can make weird sound effects much more easily. Slonimsky notes that is very effective for killing cockroaches.