The Yamaha DX7 and the Moment Mathematics Beat the Wires

In the autumn of 1967 a young music instructor named John Chowning sat at night in Stanford University’s artificial intelligence laboratory making a big Burroughs computer sing. He punched the program for it onto punch cards, the computer took a long time to calculate the sound, and Chowning was experimenting with vibrato: how would a note sound if its pitch wobbled quickly up and down. He sped the wobble up more and more, and at some point the vibrato stopped being vibrato. The wobble disappeared, and in its place a new timbre appeared, ringing, metallic, something between a bell and brass. “I realized that I was probably the first person in the world to hear these sounds,” he recalled later.

It works like this. If you swing the pitch of one simple tone with another simple tone, slowly, you get ordinary vibrato. If you speed the swing up to hundreds and thousands of times a second, the ear stops hearing the swing and starts hearing new overtones that were in neither of the two original tones. By changing the ratio of the frequencies and the depth of the swing, you can get a bell out of two sine waves, an electric piano, a brass instrument, a hissing hit. Before, to build a rich timbre, sine waves were added one by one, and each needed its own oscillator. Frequency modulation, or simply FM, gave the same richness almost for free, with two or three oscillators.