Why Instruments Sound Different

Play the same note — middle C at 261.6 Hz — on a piano, a violin, and a flute. Each sounds distinct, yet all three vibrate at the same fundamental frequency. The difference is in the overtones: quieter higher frequencies layered on top. A violin is rich in upper overtones; a flute is nearly pure fundamental. That recipe of overtones is what we call timbre.

This is Fourier analysis at work: any periodic sound can be split into a sum of pure sine waves. MP3 compression drops the overtones your ear barely notices, shrinking files dramatically with little audible loss.