The trombone is a deep brass instrument, which is one of the trumpet instruments because of its largely cylindrical bore (narrow scale). As with all brass instruments, the sound is created by the vibration of the player's lips on the mouthpiece. Thanks to its length, the notes of the trombone sound harder than those of the instruments of the horn family, which have a softer sound volume. The scale length also affects the sound energy. For example, the sound of a trombone is more concentrated than, for example, a tenor horn. The slide trombone usually has seven slide positions, each differing by a semitone. The slide can be shifted steplessly so that the trombone is the only brass instrument that can "slide" from one pitch to another (real glissando).