The trombone is a musical instrument in the brass family. As with all brass instruments, sound is produced when the player's vibrating lips (embouchure) cause the air column inside the instrument to vibrate. Unlike most other brass instruments, which have valves that, when pressed, alter the pitch of the instrument, trombones instead have a telescoping slide mechanism that varies the length of the instrument to change the pitch. However, many modern trombone models also have a valve attachment which lowers the pitch of the instrument. Variants such as the valve trombone and superbone have three valves similar to those on the trumpet.