The Hornbostel-Sachs classification system is a system, devised in 1914, for the classification of musical instruments based on the sound produced by the vibrating material. The five major categories are: idiophones (self-sounding instruments); membranophones (instruments producing sound by means of a stretched skin or membrane; aerophones (wind instruments with the sound caused by vibrating air); chordophones (string instruments); electrophones (instruments using electronic circuits).