Brass instruments are instruments that were originally made from brass but which may today be made from other metals. Some instruments which were once made of wood but are now made of metal, like the flute, are not considered brass instruments, nor are metal instruments that have a reed, like the saxophone. Brass instruments usually consist of a tube that flairs out at the end on one end like a bell, and a cup-shaped mouth piece which is pressed agains the player’s lips. When the player blows into the mouth piece, their lips vibrate, which is what produces the sound. The shape of the mouthpiece effects the tone of the the instrument with a longer, funnel shaped, mouthpiece producing a smoother tone, like on the horn, and a shorter, cup-shaped, mouth piece producing a brighter, more brilliant, tone, as on the trumpet. The shape of the tube and bell also effects the sound of the instrument.
Originally, brass instruments could only play a small number of notes (the notes of the harmonic series above their fundamental or bottom note, which is determined by the length of the tube), but eventually a system of valves were introduced to allow the instrument to instantly change its fundamental note, and so produce a greater number of playable notes. The trombone, however, has always formed a class of its own since it has a sliding mechanism which allows the player the change the tube’s length, without the need for valves.
Read about specific brass instruments by following the links below.