Tubas belong to a class of instruments known as brass wind instruments. The sounds that these instruments make are produced by the buzzing of the musicians lips against the mouthpiece. This causes the column of air inside the instrument to vibrate. As it exits the instrument through the bell, audible sound is created. The tone that is heard is directly related to the length of tubing through which the air traveled. By engaging a valve, the tubing is shortened or lengthened and the tone is changed. In an orchestra, the tuba is used to produce the lowest notes. Depending on the type of tuba it can reach notes as low as bottom D of the piano. It is often used to play quick staccato solos but can also play sustained melodies.