Members of the brass family are equipped with either valves, or a slide. Slides and valves on brass instruments provide the player with a different method to change pitch. Both methods change the length of the instrument to change the pitch. The longer the instrument, the lower the pitch; the shorter the instrument, the higher the pitch.
The Slide
A slide is a long, cylindrical tube that extends from the main body of the instrument. On a trombone, the player moves the slide in and out to change the length of the tubing. By varying the length of the tubing, the player can produce a continuous range of pitches between the instrument’s lowest and highest notes. This allows for greater control over pitch and intonation, as well as the ability to create glissandos and other expressive effects.
Valves
On the other hand, brass instruments with valves use a system of three or four valves to alter the length of the tubing. The player presses down on one or more of the valves to route the air through a different set of tubing, which changes the pitch of the instrument. Each valve has a discrete additional length of tubing. When a player presses down several valves, the lengths of the additional tubing for each valve are added to together.
How do valves and the slide relate?
Each set of valve combinations can be equated to a slide position. When no valves are pressed, the instrument is as short as it can be. This is 1st position on the trombone. When the 2nd valve is pressed, it lowers the instrument by 1 semitone. This is 2nd position on the trombone. When the 1st valve is pressed, it lowers the instrument by a tone. This is equivalent to 3rd position on the trombone. And so on.
Unlike the slide, which allows for continuous pitch changes, valves can only produce a discrete set of pitches, by half-steps. This can make it more challenging to achieve accurate intonation, particularly when playing in higher registers.
Conclusion
Both slide and valve systems have their advantages and disadvantages, and different instruments in the brass family use different systems. Trombones use a slide, while most other brass instruments, including the French horn, tuba, and trumpets, use valves. Ultimately, the choice of slide or valves depends on the specific needs of the instrument and the preferences of the player.