In 1807, Joseph Fourier claimed that any periodic signal could be approximated by the arbitrary sum of sine and cosine waves of different frequencies and chosen amplitudes. This webpage demonstrates that claim.
The shape of a sound wave determines a perceptual quality of sound known as timbre. Timbre is what distinguishes the sound of, e.g., a flute from that of a trumpet, even if both instruments have identical pitch and volume. Thanks to Fourier's remarkable discovery, this webpage can simulate an approximation of any imaginable sound.