Derived from David Hughes’ experiments in 1878 and telephone transmitters, carbon contact microphones were used by numerous radio stations in the 1920s and ’30s. Amateurs also appreciated their low cost and easy use. These microphones could be plugged directly into the pick-up socket of a radio receiver without additional amplifying lamps. The most high-performance carbon microphones used the ‘transverse-current’ produced by two electrodes, which passes over a very thin coating of carbon granules on a relatively large surface. However, they still lacked fidelity in reproducing the human voice, and were soon superseded by electrodynamic ribbon microphones and the piezoelectric systems that emerged in the 1930s.