What an amazing video:

Anyone who’s played a harmonic on the guitar knows that string vibration is a magical, mysterious phenomenon. I’ve heard it compared to a moving passenger train. As the countryside flies by, your teacup is rattling on your saucer: That’s one kind of vibration. But the whole traincar is vibrating too: A second vibration. The traincar is also swaying as it moves: a third vibration. And the entire train is coursing through s-curves in a winding valley: A final, huge vibration.

In the same way, a plucked string has many different layers of vibrations happening simultaneously: The whole string is moving side-to-side, which creates the fundamental tone that our ear is drawn to. But smaller vibrations—the traincar and teacup vibrations—create overtones that are hard to pick out, but without them our plucked guitar strings would sound more like electronic beeps.

What blows me away in this video is how huge those “teacup” vibrations are. I figured they were tiny, humming wiggles, barely perceptible even if we could slow them down. But apparently, our strings wiggle like sidewinders. Incredible.

Incidentally, if you’re interested in trying to hear those subtle overtones in your guitar’s notes, play a harmonic on a string, then pluck the open string. Listen for the sound of the harmonic quietly ringing behind the loud fundamental pitch.