Modern trumpets have three (or, infrequently, four) piston valves, each of which increases the length of tubing when engaged, thereby lowering the pitch. The first valve lowers the instrument's pitch by a whole step (two semitones), the second valve by a half step (one semitone), and the third valve by one and a half steps (three semitones). When a fourth valve is present, as with some piccolo trumpets, it usually lowers the pitch a perfect fourth (five semitones). Used singly and in combination these valves make the instrument fully chromatic, i.e., able to play all twelve pitches of classical music. For more information about the different types of valves, see Brass instrument valves.