You're probably familiar with a sound wave, where a hertz is one cycle of a wave's oscillation. The more cycles of the sound wave per second, the higher the perceived pitch to the ear because of the spiral of the cochlea. Every musical note corresponds to a specific frequency.

Sound can manifest shape in many more interesting ways. For example, the geometric shapes of frequenciesis revealed through cymatics. Below are notes from the Solfège scale.

Some musicians have hidden images embedded in their songs that are only revealed through a spectrograph. Nine Inch Nail's album Year Zero features a spectorgaph-made alien hand coming down as the album cover. The song The Warning features this alien hand sound at the end of the song.