The French horn is the most common variation,[citation needed] and is often known simply as the "horn". The double horn in F/B♭ is the version most used by professional bands and orchestras. The main tubing on an F Horn is about 12–13 ft (3.7–4.0 m) long and that associated with the valves adds additional length to achieve up to about 17 ft (5.2 m) of tubing overall.[citation needed] A musician who plays the French horn is called a horn player (or less frequently, a hornist). Pitch is controlled through the adjustment of lip tension in the mouthpiece and the operation of valves by the left hand, which route the air into extra tubing.[6] Most horns have lever-operated rotary valves, but some, especially older horns, use piston valves (similar to a trumpet's) and the Vienna horn uses double-piston valves, or pumpenvalves. The backward-facing orientation of the bell relates to the perceived desirability to create a subdued sound, in concert situations, in contrast to the more-piercing quality of the trumpet. A horn without valves is known as a natural horn, changing pitch along the natural harmonics of the instrument (similar to a bugle). Pitch may also be controlled by the position of the hand in the bell, in effect reducing the bell's diameter. The pitch of any note can easily be raised or lowered by adjusting the hand position in the bell.[7]
Three valves control the flow of air in the single horn, which is tuned to F or less commonly B♭. The more common double horn has a fourth valve, usually operated by the thumb, which routes the air to one set of tubing tuned to F or another tuned to B♭. Triple horns with five valves are also made, tuned in F, B♭, and a descant E♭ or F. Also common are descant doubles, which typically provide B♭ and Alto F branches. This configuration provides a high-range horn while avoiding the additional complexity and weight of a triple.
A crucial element in playing the horn deals with the mouthpiece. Most of the time, the mouthpiece is placed in the exact center of the lips, but, because of differences in the formation of the lips and teeth of different players, some tend to play with the mouthpiece slightly off center.[8] Although the exact side-to-side placement of the mouthpiece varies for most horn players, the up-and-down placement of the mouthpiece is generally two-thirds on the upper lip and one-third on the lower lip.[8] Usually, in order to play higher octave notes, the pressure exerted on the lips from the mouthpiece is increased. But, although some pressure is needed, excessive pressure is not desirable. Playing with excessive pressure makes the playing of the horn sound forced and harsh as well as decreases endurance of the player by about half.[9]