"The French horn (since the 1930s known simply as the horn in professional music circles) is a brass instrument made of tubing wrapped into a coil ...
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with a flared bell. The double horn in F/B♭ (technically a variety of German horn) is the horn most often used by players in professional orchestras and bands. A musician who plays a horn is known as a horn player or hornist.
Pitch is controlled through the combination of the following factors: speed of air through the instrument (controlled by the player´s lungs and thoracic diaphragm); diameter and tension of lip aperture (by the player´s lip muscles—the embouchure) in the mouthpiece; plus, in a modern horn, the operation of valves by the left hand, which route the air into extra sections of tubing. 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. The key of a natural horn can be changed by adding different crooks of different lengths." - (en.wikipedia.org 07.01.2022)