That same year a new electronic keyboard was developed by a French cellist named Maurice Martenot. It was based on the same principles as the theremin. Called the Ondes Martenot (“Martenot Waves”), this was quite a revolutionary keyboard. The principle at work in the Ondes Martenot was the varying of frequency in vacuum tubes.
The Ondes Martenot. The console is played through a variety of speakers or
diffuseurs. The bevel-top speaker contains a gong, the lyre-like speaker contains sympathetic strings and the rectangular speaker is ordinary. The speakers introduce further rather beautiful effects to the already cool sounds. The operator can turn any of the speakers on or off at will in any combination.
The Ondes keyboard is played with one hand since it is monophonic (only one key plays at a time). The left hand operates a control panel that fits in a little drawer. This panel controls various parameters as timbre, vibrato, etc. The large, white, rectangular button on the right is actually a kind of finger pedal. Left untouched, the keyboard is silent. As the button is depressed, the volume goes up. Pressing the button quickly causes a faster attack. The player continually works the button with the left hand while the right hand plays.
The player can also wear a special metal ring which he runs along a metallic ribbon installed in front of the keyboard. There is a metal marker plate under the ribbon marking off notes. The ribbon is a resistor wire. If the player slides his finger along the ribbon and touches the wear plate, the designated note will play because the metal-on-metal contact between resistor wire and ring forms a circuit which determines the amount of resistance in the circuit. He can jiggle his finger on the ribbon and get a vibrato effect. The point of using the ribbon and ring is that one note glides to another enabling microtonal instruments as cellos and violins to be mimicked. Of course, one can get the spacey theremin effects as well. The Ondes is like a contact theremin with the keyboard and ribbon controlling pitch with one hand and the amplitude button controlling volume with the other. The keys are also touch sensitive like modern synths. In fact, the Ondes is still being made in France where they still teach classes on its use. Trent Reznor of Nine Inch Nails also uses one.
An extremely cool demonstration of the Ondes Martenot:
Jean Laurendeau and the Ondes Martenot - YouTube