Music boxes, amps, iPods, and stereos are all types of audio equipment used to play music. Music boxes are mechanical devices that use a set of pins on a revolving cylinder or disc to pluck the tuned teeth of a steel comb. Amps, short for amplifiers, are electronic devices used to increase the volume of an audio signal. iPods are portable digital media players developed by Apple Inc. Stereos, short for stereophonic sound, are audio systems that create a three-dimensional sound experience.