SOUND PRODUCTON

Sound is produced when the player blows through the mouthpiece and the air in the tube vibrates. To create low notes, the player's lips must be relaxed or slackened. For high notes, the lips must be tensed or tight.

Valves are used in all the brass instruments except for the trombone, which uses the slide. Players change the pitch of the notes by pressing on the valves or (for the case of the trombone) pulling the slide in and out. This alters the length of the tubing. Before the valves were invented in 1815, only lip pressure was available for controlling pitches.