The First Phonograph
On the surface of the metal cylinder was inscribed a continuous groove in the shape of a helix. When a sheet of tinfoil was wrapped around the cylinder, the phonograph needle was placed so that it followed the groove underneath the foil. The depth of impression in the tinfoil change with each new sound, this became known as a hill-and-dale recording. Later on he switched the tinfoil to wax as a recording substance. This technique greatly improved the sound quality.