What is the X in X-mas?
(French: "musical waves"), electronic musical instrument demonstrated in 1928 in France by the inventor Maurice Martenot. Oscillating radio tubes produce electric pulses at two supersonic sound-wave frequencies. They in turn produce a lower frequency within audible range that is equal to the difference in their rates of vibration and that is amplified and converted into sound by a loudspeaker. Many timbres, or tone colours, can be created by filtering out upper harmonics, or component tones, of the audible notes.