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The trombone is a musical instrument in the brass family. Like all brass instruments, it is a lip-reed aerophone; sound is produced when the player’s buzzing lips (embouchure) cause the air column inside the instrument to vibrate. The trombone is usually characterised by a telescopic slide with which the player varies the length of the tube to change pitches, although the less common valve trombone uses three valves similar to those on a trumpet. (wikipedia)