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. 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. When playing higher notes, the majority of players exert a small degree of additional pressure on the lips using the mouthpiece. However, this is undesirable from the perspective of both endurance and tone: excessive mouthpiece pressure makes the horn sound forced and harsh and decreases the player's stamina due to the resulting constricted flow of blood to the lips and lip muscles.
