The instrument made in France, Ondes Martenot (Martenot Waves), originally called Ondes Musicales ("musical waves"), was designed by musician Maurice Martenot (1898–1980). He wanted to invent an electronic musical instrument that could join traditional symphonic instruments and be the subject of the work of leading composers. To achieve this, he had to face two major hurdles that prevented Theremin from gaining wider acceptance by musicians and composers. First, the Theremin did not look like a musical instrument, but more like a radio; second, most people had difficulty mastering the spatially controlled instrument. Martenot borrowed Theremin's principles of generating musical sounds, but proposed a completely different instrument design that was pleasing to the eye and looked good in an orchestra. It was the size of a small, upright keyboard instrument like a clavichord. The elegant wooden cabinet and matching loudspeakers were designed fashionably with an art deco motif.
The Martenot Waves were more than a Theremin hidden in a fancy cupboard. Although it used the same beat frequency technology as Theremin, Martenot designed it specifically for playing voices that could be transcribed onto a keyboard. The instrument was monophonic, so it was limited to playing melodies, but it released sounds in such a way that the musician could relate them to the chromatic scale. The original instrument that Martenot played at its Paris premiere controlled the pitch by moving a ring attached to a metal wire. The ring was moved with the index finger of the right hand. This in turn regulated a variable capacitor on the tape that varied the frequency of the tone over a range of seven octaves. By moving the ring to the left, he played the lower notes, moving it to the right, he played the higher notes. The tape was brilliantly applied to the image with the piano keyboard, and the movements of the ring corresponded to the notes of the scale and the distances between them.
By 1932, Martenot had made several improvements to the Martenot Waves and introduced the instrument that is best known now. The most important of these changes was the addition of an organ keyboard, which he used in early versions from 1929. The instrument could be played with a keyboard or a ring slider - which now used a metal ribbon instead of a wire and was placed in front of the keyboard - but not with both at the same time. Five and seven octave versions were available. An intriguing feature of the keyboard was that each key could be moved side to side to produce slight pitch fluctuations in order to achieve a vibrato effect. These effects can also be achieved with the ribbon controlled model by slightly sliding your finger back and forth. The slider worked parallel to the keyboard, allowing the musician to relate the position of the ring to the notes on the keyboard. The sliding surface was also marked with small metal ridges corresponding to the notes on the scale. The volume was controlled with the left hand by a pressure-sensitive key. The special thing about this was that there was no sound when the key was fully released. As the player gradually pressed it down, the volume rose. A knee lever was also mounted to adjust the volume key. Using the knee lever to adjust the volume freed the left hand so it could control a small set of expression keys to filter the sound colors. Finally, there was also a pedal volume control with a unique pressure-sensitive mechanism.
Martenot carefully developed several ways to project the sound of his invention. Four basic loudspeakers or "diffusers" have been proposed. The first, called the haut-parleur ("speaker"), was the standard speaker and was the loudest of the four variants. Resonance was an exceptional speaker for creating reverberation. It had a vertical rectangular wooden enclosure and, in addition to a conventional speaker cone, could transmit electric sound through a vertical curtain of transparent plastic strips resembling louvers. This was creating poignant, resonant tonalities that sounded surprisingly fresh at the time. The layout of the third loudspeaker, known as the métallique, was shorter and reproduced the sound with a metal gong. The audio signals were passed through the transducer directly into the gong, using the vibrations of the metal body to resonate the audible tone. The chime's resonance properties additionally modulated the sound and produced an effective, metallic ringing resembling ring modulation. The fourth loudspeaker, called the hand, had a resonance body resembling an inverted cello. Twelve strings were stretched across the front and rear of the speaker. The audible electrical signals were processed by the transducer and played directly by the strings themselves, which vibrated to recreate the pitch. The combination of vibrating strings and a resonating cello-like body produced amazing sounds that sounded like being played by string instruments.
The musician used the keys on the left hand controller to select the speaker to play. Combined with the filter controls, the four types of speakers gave the musician and composer a remarkable range of sound effects. The ability to mute the Ondes Martenot sound by releasing the volume key allowed the performer to suppress the glissando sounds created by moving the ribbon from note to note, thus eliminating one of the major challenges of playing Theremin. The volume control allowed the use of glissandos when required, as well as manual shaping of the sound envelope. Moreover, since the version of the Ondes Martenot with the ring-shaped fader control for the finger could reproduce the twelve notes of the chromatic scale and everything in between, it was possible to use the instrument to perform microtone music. The image of the traditional piano keyboard could then be replaced with another one modeled on quarter tones or other scale division desired by the composer.