The French horn, referred to by professional musicians as just 'the horn,' is a highly expressive brass instrument that produces sounds that are often described as rich, haunting, distant and romantic. It consists of an intricately coiled metal tube four meters or more in length that has a large, backward-facing flared bell at its end. Sound is produced by blowing into the mouthpiece while buzzing the lips together, and pitch is controlled by altering the pressure of the lips and selectively pressing the three rotary valves to change the effective length of the tubing. The horn's range is lower than those of trumpets and trombones, but higher than that of the tuba. Muting can be accomplished by inserting the right hand into the bell, which also raises the pitch approximately a semitone but for which the player can compensate. It is widely said that the horn is one of the most beautiful of instruments, both in sound and appearance, but one of the most difficult to master. The horn is a standard component of orchestras, in which it is usually employed in two pairs, as well as in wind bands and marching bands.