The Ondes Martenot (or Ondes-Martenot or Ondes martenot or Ondium Martenot or Martenot or ondes musicale) is an early electronic musical instrument with a keyboard and slide invented in 1928 by Maurice Martenot[?], and originally very similar in sound to the Theremin. The sonic capabilities of the instrument were subsequently expanded by the addition of filter banks and switchable loudspeakers.
The instrument has been used by many composers, most notably Olivier Messiaen. He used it in many of his works, such as the Turangalīla Symphony[?] and the Trois Petites Liturgies de la Presence Divine.