A brass instrument is a musical instrument that produces sound by the sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player's lips. Brass instruments are also called labrosones, literally meaning "lip-vibrated instruments". There are several factors involved in producing different pitches on a brass instrument: One is alteration of the player's lip tension and another is air flow. Also, slides or valves are used to change the length of the tubing, thus changing the harmonic series presented by the instrument to the player.