All “brass” instruments work in the same way. The player blows through the mouthpiece to make a “buzzing” sound with their lips. This buzzing vibrates the air in the instrument and causes a sound wave to resonate within the length of the tubing to produce a musical note.
The musical notes that can be produced depend on the length of the tubing and the way the player vibrates their lips. In the simplest brass instruments such as the bugle shown here, the length of tubing is fixed but the player can still play lots of different notes by the way they blow.
Higher notes are played by making the air vibrate faster. This is done by tensing the lips more firmly to make a smaller hole, blowing slightly harder and thinking of an “eeee” sound; lower notes are produced by relaxing the lips a little and thinking of an “arhhh” sound.
The bugle is used in military and youth organisations to play a variety of calls such as the Last Post and Reveille. Another simple brass instrument, the post-horn was used to announce the arrival of the post in days past. Have a listen to both, and watch how the bugle is played.
Can you imagine the postie coming down your street, announcing their arrival with a fanfare? Good as they are, instruments like the bugle and post-horn are limited in the notes they can play. They can only play a series of harmonics.
But to make brass instruments suitable for use in all forms of music, they need to be able to play a full chromatic scale (i.e. all notes that can be played on the white and black keys of a piano).
In order to achieve this, it is necessary to alter the length of tubing of the instrument. This is done in one of 2 ways: in the trombone a slide is moved out to extend the length of the instrument and thereby play lower notes. In all other brass instruments, valves are used to open extra lengths of tubing to achieve the same effect.
The trombone slide can be extended through 7 “positions” from 1st position when the slide is fully pulled in, to 7th position when the slide is fully extended. Each time the slide is extended to the next position out, it lowers the pitch of the instrument by one semi-tone (which is the difference between any 2 adjacent keys – black and white – on a piano).
Other brass instruments, such as the cornet shown below, have 3 valves which open extra lengths of tubing. The middle or second valve opens a short length of tubing which lowers the pitch by a semi-tone. The first valve opens a longer length of tubing which lowers the pitch by a tone. The third valve opens an even longer length of tubing which lowers the pitch by a tone and a half. By pressing combinations of valves it is therefore possible to play a descending chromatic scale of semi-tones from open (no valves pressed), valve 2 pressed, valve 1 pressed, valve 1 and 2 together (or valve 3), valves 2 and 3, valves 1 and 3, valves 1, 2 and 3.
Note that the above is a simplification, and some instruments have additional valves, and/or ways to alter the tuning by smaller amounts as the instrument is being played.
The tubing of a brass instrument opens out into a “bell” at the far end. This improves the resonance and helps produce a nicer sounding musical note.
Brass instruments are fitted with “tuning slides” which allow slight changes to the length of the tubing so the instrument can be tuned to a standard pitch, or to the rest of the orchestra or band.
Because air is being blown through the instrument, moisture condenses and collects within the tubing. The instruments are therefore fitted with water keys that allow this water to be expelled.